Speaker systems with passive radiators. Acoustic design of the fourth order

In this article we will look at how to make a subwoofer with your own hands, without delving into the depths of electroacoustics, without resorting to complex calculations and subtle measurements, although you will still have to do some things. “Without any special difficulties” does not mean “slap on a brick, drive away, grandma, mogarych.” These days, it is possible to simulate very complex acoustic systems (AS) on a home computer; See the end for a link to a description of this process. But working with a finished device on a whim gives something that you cannot get by any reading or viewing - an intuitive understanding of the essence of the process. In science and technology, discoveries at the tip of a pen are rarely made; Most often, a researcher, having gained experience, begins to “gut” understand what’s what, and only then looks for mathematics suitable for describing the phenomenon and deriving design engineering formulas. Many great people recalled their first unsuccessful experiences with humor and pleasure. Alexander Bell, for example, initially tried to wind the coils for his first telephone with bare wire: he, a musician by training, simply did not yet know that live wire needed to be insulated. But Bell still invented the telephone.

About computer calculations

Do not think that JBL SpeakerShop or other acoustics calculation program will give you the only possible, most correct option. Computer programs are written using established, proven algorithms, but non-trivial solutions are impossible only in theology. “Everyone knows that you can’t do this. There is a fool who doesn't know this. He is the one who makes the invention."– Thomas Alva Edison.

SpeakerShop appeared not so long ago, this application was developed very thoroughly and the fact that it is used very actively is an absolute plus for both developers and amateurs. But in some ways the current situation with him is similar to the story with the first photoshops. Who else used Windows 3.11, remember? - back then they just went crazy with image processing. And then it turned out that in order to take a good picture, you still need to know how to take photographs.

What is this and why?

A subwoofer (simply a sub) in its literal translation sounds funny: a burr. In reality, this is a bass (low-frequency, woofer) speaker that reproduces frequencies below approx. 150 Hz, in a special acoustic design, a box (box) of a rather complex device. Subwoofers are also used in everyday life, in high-quality floor-standing speakers and inexpensive desktop ones, built-in and in cars, see fig. If you manage to make a subwoofer that reproduces bass correctly, you can safely take on it, because LF reproduction is perhaps the fattest of the whales on which all electroacoustics stand.

It is much more difficult to make a compact low-frequency section of the speaker system than the mid-range and high-frequency (mid- and high-frequency) parts, firstly, due to an acoustic short circuit, when sound waves from the front and rear radiating surfaces of the speaker (loudspeaker head, GG) cancel each other out: lengths LF waves are meters, and without proper acoustic design of the GG, nothing prevents them from immediately converging in antiphase. Secondly, the spectrum of sound distortion in the low frequencies extends far into the best audible region of the midrange. In essence, any broadband speaker has a low-frequency section into which midrange and high-frequency emitters are built. But from the point of view of ergonomics, an additional requirement is imposed on the subwoofer: a subwoofer for the home should be as compact as possible.

Note: All types of acoustic design of LF GG can be divided into 2 large classes - some dampen the radiation from the rear of the speaker, the second reverse it in phase by 180 degrees (turn the phase) and re-radiate it from the front. A subwoofer, depending on the properties of the GG (see below) and the required type of its amplitude-frequency response (AFC), can be built according to a circuit of one class or another.

People can distinguish the direction of sounds below 150 Hz very poorly, so in an ordinary living room a sub can be placed basically anywhere. MF-HF speakers (satellites) of acoustics with a subwoofer are very compact; their location in the room can be selected optimally for the given room. Modern housing is, to put it mildly, no different in terms of excess space and good acoustics, and it is not always possible to “stuff” at least a couple of good broadband speakers into it correctly. Therefore, making a subwoofer yourself allows you not only to save a very significant amount of money, but also to still get a clear, true sound in this Khrushchev, Brezhnevka or modern new building. A subwoofer is especially effective in full surround sound systems, because... putting 5-7 columns on a full page each is too much even for the most sophisticated users.

Bass

Reproducing bass is not only technically difficult. The generally narrow low-frequency region of the entire spectrum of sound waves is heterogeneous in its psychophysiological effect and is divided into 3 regions. To choose the right bass speaker and make a subwoofer box with your own hands, you need to know their boundaries and meaning:

• Upper bass (UpperBass) – 80-(150…200) Hz.
• Average bass or midbass (MidBass) – 40-80 Hz.
• Deep bass or sub-bass (SubBass) – below 40 Hz.

Top

Middle

For midbass, the main task when creating a subwoofer is to ensure the highest GG output, a given shape of the frequency response and its maximum uniformity (smoothness) in the minimum volume of the box. The frequency response, which is close to rectangular towards lower frequencies, gives a powerful but harsh bass; Frequency response, uniformly falling - clean and transparent, but weaker. The choice of one or the other depends on the nature of what you are listening to: rockers need an “angrier” sound, while classical music needs a gentler sound. In both cases, large dips and spikes in the frequency response spoil the subjective perception with formally identical sound technical parameters.

Depth

Sub-bass in the car

The noise masking effect is especially necessary in a cramped and noisy car interior, so car subwoofers are optimized for sub-bass. Sometimes, for the sake of this, Hi-Fi lovers at high speed give the entire trunk to the subwoofer, placing 15”-18” monster speakers there with 150-250 W of peak power, see fig. However, a quite decent subwoofer can be made for a car without sacrificing useful volume in the body, see below.

Note: The peak power of a speaker is often equated with noise, which is incorrect. At peak power the sound is distorted, but still intelligible, i.e. distinguishable by meaning. Noise power is defined as that at which a speaker can operate for a certain period of time (usually 20 minutes) without burning out or suffering mechanical damage. The sound in this case is most often an incoherent wheezing, which is why such power is called noise. But in some types of acoustic design, the noise power of the speaker may be lower than the peak, see below.

What kind of speaker do you need?

A complete calculation of acoustic design is carried out according to the so-called. Thiel-Small parameters (TSP). Since we decided to spend time and labor on setting up the sub, we will only need the full quality factor of the head at its own resonant frequency Qts, because It is based on this that the optimal acoustic design option is selected. Depending on the Qts value, speakers are divided into 4 groups:

• Qts<0,5 – «безразличные» сверхнизкодобротные. Очень дорогие, очень низкая отдача, но способны воспроизводить подбасы вплоть до 20-15 Гц. Настройка сабвуфера с такими без звукомерной камеры и специальной измерительной техники невозможна, т.к. резонансный пик не выражен.
• 0,5
• 0,7
• Qts>1 – high-quality. High output, low price, harsh sound in suboptimal design. It is difficult to obtain a smooth frequency response. Compact, available in diameters (smaller) up to 6” (155 mm). Optimal for a desktop subwoofer or for a TV (not for a home theater!).

Measurements

In the manufacturer's specifications for speakers, Qts may be designated as Qп or simply Q, but it is not always present there, and public databases like WinISD are full of errors. Therefore, we will most likely have to determine the Qts value at home.

Preparation

First of all, we select and prepare a room for acoustic measurements. It should have as many curtains, curtains, carpets on the floor and walls, and upholstered furniture as possible. Hard horizontal surfaces (tables) need to be covered with something fluffy; It wouldn’t hurt to throw more pillows everywhere. Corners distort the sound field especially strongly, incl. hard furniture with walls, they need to be curtained with something, for example, clothes on hangers. Next, we connect long wires to the speaker and hang them in the geometric center of the ceiling (under the chandelier, if there is one) with the front side of the diffuser down at a height from the floor of 2/3 of the ceiling height.

Now you need to assemble a measurement diagram, as shown at the top in Fig. We will still need the lower circuit to measure the impedance (impedance) of speaker Z. This one differs from the measuring circuit without a transformer usually used by amateurs in quite professional accuracy: in conventional circuits, approx. 1.5 V even with an input resistance of the tester of 10 MOhm. The operation of this circuit is based on the fact that the impedance of the transformer and R2, on the one hand, is much greater than the impedance of the main generator; on the other hand, it is much less than the output impedance of an audio frequency power amplifier, and on the fact that the lousiest digital multitester at a limit of 200 mV has an input impedance of more than 1 MOhm. However, if the measurement signal is supplied from an audio frequency generator (AFG) with a standard 600-ohm output, this circuit is not suitable for measuring Z.

Procedure

From a computer with a GZH emulation program, the measuring signal is supplied from the output of the sound card. You need to “drive” it within the range of 20-100 Hz at first with a discrete (step) of 10 Hz. If the GG resonance is not visible, it is unsuitable for a subwoofer. Or the seller shamelessly deceived you by selling you for 100 rubles. indifferent GG priced from $200.

When the boundaries of the resonant peak are determined, we “pass” it with a discrete of 1 Hz and build the frequency response. If the high- or medium-quality GG is closer to the upper limit of Qts, you will get a graph similar to the one in pos. I fig. In this case:

• According to formula (1) to pos. II find U(F1,F2);
• According to the graph we find F1 and F2;
• Using formula (2), we check whether the calculated natural resonance frequency in free space F’s coincides with the measured Fs. If the discrepancy is more than 2-3 Hz, see below;
• Using formula (3) we find the mechanical quality factor Qms, then using formula (4) the electrical quality factor Qes and, finally, using formula (5) the required total quality factor Qts.

If the quality factor of the GG is closer to low or such, which is generally good, the resonance curve will be noticeably asymmetrical, and its peak will be flat, blurred, pos. III, or the test using formula (2) will not converge even with repeated measurements. In this case, from the graph we determine the points of greatest inclination of the tangents to the concave “wings” of the peak A1 and A2; mathematically, in them the second derivative of the function describing the resonance curve reaches a maximum. For Umax then we take, as before, its value at the top of the peak, and for Umin - calculated from the f-le at pos. III new value U(F1,F2).

System structure

Have you tried it on? Is the speaker suitable? Take your time to choose a design. First you need to choose a block diagram of the entire sound system, because its electronic part may account for as much of the cost as a good bass speaker. A sound system with a subwoofer can be built according to one of the following. diagrams, see fig.

Note: The equalizer and infra-low-pass filter FINCH (rumble filter) in all circuits are turned on before the inputs of stereo channels.

Pos. 1 – system with passive power filtering. Plus – you don’t need a separate bass amplifier; it connects to any UMZCH. Huge disadvantages, first, mutual electrical leakage of channels in the subwoofer along the midrange: for LC filters that reduce it to an acceptable value, you will need a decent case, which in order to purchase their components will first have to be filled by about a third with money (in 100 ruble bills). Secondly, the output resistances of the low-pass filters of the low-pass filter together with the input GG of the speaker form a tee, and each channel of the UMZCH will theoretically spend a quarter of the power on warming its neighbor with its low-pass filter. In reality – more, because on power and losses in filters are significant. However, the power-filtering system is applicable in low-power subwoofers with independent sound emitters, see below.

Pos. 2 – passive filtering to a separate bass UMZCH. There are no power losses, the mutual influence of channels is weaker, because The characteristic resistances of the filters are kilo-ohms and tens of kilo-ohms. Currently, it is practically not used, because Assembling an active filter on microcircuits turns out to be much simpler and cheaper than winding passive coils.

Pos. 3 – active analog filtering. The channel signals are added by a simple resistor adder, sent to an analog active low-pass filter, and from it to the bass UMZF. The interference of channels is negligible and unnoticeable under normal listening conditions, and the costs for components are low. The optimal circuit for a homemade subwoofer for a novice amateur.

Pos. 4 – full digital filtering. Channel signals are fed to a splitter P, which divides each of them into at least 2 equal to the original one. One signal from the pair is fed to the MF-HF UMZF (possibly directly, without a high-pass filter), and the rest are combined in adder C. The fact is that with resistor addition at the lower frequencies of the midbass and sub-bass, electrical interaction of signals in the low-pass filter is possible, several distorting the total bass. In the adder, the signals are added digitally or analoguely, eliminating their mutual influence.

From the adder, the common signal is fed to a digital low-pass filter with built-in analog-to-digital (ADC) and digital-to-analog (DAC) converters, and from it to the bass UMZCH. The sound quality and channel isolation are the highest possible today. The costs of microcircuits for this entire enterprise turn out to be feasible, but working with ICs requires some amateur radio experience, and even more if you do not buy a ready-made set (which is significantly more expensive), but select the system components yourself.

Decor

In Fig. The most common acoustic design schemes for home subwoofers are given. Labyrinths, horns, etc. do not meet the requirements of compactness. Schemes that are preferable for beginners are highlighted in green, schemes that are feasible for them are highlighted in yellow, and unsuitable ones are highlighted in red. Those with more experience may be surprised: is the 6th bandpass for dummies? No problem, this great bass tube speaker can be set up in a weekend. If you know how.

Shield

Designing a subwoofer in the form of an acoustic screen (shield, item 1) at home is feasible if the GGs are built into the wall cladding, because their sizes are comparable to the lengths of sub-bass waves. Hence the advantage - there are no problems with sub-bass, as long as the speakers can handle it. Another thing is that it is extremely compact; the sub does not take up any useful space at all. But there are also serious disadvantages. The first is a large amount of construction work. Secondly, the acoustic screen does not affect the frequency response of the GG in any way. “Humpbacked” will sing just like that, so you can only install expensive, low-quality and indifferent speakers on the shield. The downside, so to speak, is that their recoil is small and the shield is in no way capable of increasing it.

Closed box

The biggest plus of a closed box (item 2) is deep damping of the GG; for inexpensive, high-output, high-quality speakers, this is the only acceptable type of acoustic design. But this plus also entails a minus: with deep damping, the noise power of the GG is often lower than the peak, especially for expensive powerful heads. The coil is already smoking, but no wheezing can be heard. An overload indicator is needed, but the simplest ones without a separate power supply distort the signal.

An equally big plus is the extremely smooth, smoothly falling frequency response and, as a result, the purest and most vibrant sound. For this reason, high-quality powerful high-quality generators are produced specifically for installation in closed boxes or 4th order bandpasses (see below).

Minus - of all speakers of equal volume, a closed box has the highest lowest reproducible frequency, because it increases the resonant frequency of the speaker and is not able to increase its output at frequencies below it. Those. In terms of compactness, a subwoofer in a closed box is a stretch. This drawback can be reduced to some extent by filling the box with synthetic padding: it perfectly absorbs the energy of sound waves. The thermodynamic process in the box then goes from adiabatic to isothermal, which is equivalent to an increase in its volume by 1.4 times.

Another significant disadvantage is that you can only make a passive subwoofer in a closed box, because The electronics in it get very hot even when placed in a fenced off compartment. If you come across old 10MAS-1M speakers, run them at half power for half an hour and touch the body with your hand - it will be warm.

FI

Note: a passive radiator (PI) is equivalent in all respects - instead of a pipe with a port, a bass speaker is installed without a magnetic system and with a weight instead of a coil. There are no “tuning-free” methods for calculating PI, which is why PI is a rare exception in industrial production. If you have a burnt-out bass speaker lying around, you can experiment - the adjustment is made by changing the weight of the load. But keep in mind that it is better not to make an active PI for the same reason as a closed box.

About deep crevices

Acoustics with deep slots (items 4, 6, 8-10) are sometimes identified with FI, sometimes with a labyrinth, but in fact this is an independent type of acoustic design. There are many advantages to a deep slit:

The deep slot has only one drawback, and only for beginners: it is not adjustable after assembly. As it is done, so it will sing.

About anti-acoustics

Bandpasses

BandPass means band pass, which is the name given to speakers without direct radiation of sound into space. This means that bandpass speakers do not emit midrange due to its internal acoustic filtering: the speaker is placed in a partition between resonating cavities that communicate with the atmosphere through pipe ports or deep slots. Bandpass is an acoustic design specific to subwoofers and is not used for completely separate speakers.

Bandpasses are divided by order of magnitude, and the order of a bandpass is equal to the number of its own resonant frequencies. High-quality GGs are placed in 4th-order bandpasses, where it is easy to organize acoustic damping (position 5); low- and medium-quality - in 6th order bandpasses. Contrary to popular belief, there is no noticeable difference in sound quality between the two: already at the 4th order the frequency response at low frequencies is smoothed to 2 dB or less. The difference between them for an amateur is mainly in the difficulty of setting: in order to accurately adjust the 4th bandpass (see below), you will have to move the partition. As for 8th order bandpasses, they obtain 2 more resonant frequencies due to the acoustic interaction of the same 2 resonators. Therefore, 8th bandpasses are sometimes called 6th order class B bandpasses.

Note: idealized frequency response at low frequencies for some types of acoustic design are shown in Fig. red. The green dotted line shows the ideal frequency response from the point of view of the psychophysiology of hearing. It can be seen that there is still enough work in electroacoustics.

Amplitude-frequency characteristics of the same loudspeaker head in different acoustic designs

Car subwoofers

Car subwoofers are usually placed either in the cargo compartment, or under the driver’s seat, or behind the back of the rear seat, pos. 1-3 in Fig. In the first case, the box takes up useful volume, in the second, the sub works in difficult conditions and can be damaged by feet, in the third, not every passenger will be able to tolerate powerful bass right next to their ears.

Recently, car subwoofers are increasingly being made of the stealth type, built into the rear fender niche, pos. 4 and 5. Sufficient sub-bass power is achieved by using special auto speakers with a diameter of 12” with a rigid diffuser, which is little susceptible to the membrane effect, pos. 5. How to make a subwoofer for a car by molding a wing niche, see next. video.

Video: DIY car subwoofer “stealth”

It couldn't be simpler

A very simple subwoofer that does not require a separate bass amplifier can be made using a circuit with independent sound emitters (IS), see fig. In fact, these are two channel LF GGs placed in a common long housing installed horizontally. If the length of the box is comparable to the distance between the satellites or the width of the TV screen, the “blurring” of the stereo is hardly noticeable. If listening is accompanied by viewing, it is completely unnoticeable due to involuntary visual correction of the localization of sound sources.

Using the scheme with independent FMs, you can make an excellent subwoofer for a computer: a box with speakers is placed in the far upper corner under the tabletop. The cavity underneath is a resonator tuned to a very low frequency, and an unexpectedly good sub-bass comes out from the small box.

FI for a subwoofer with independent FIs can be calculated in the speaker shop. In this case, the equivalent volume Vts is taken twice as large as measured, the resonant frequency Fs is 1.4 times lower, and the total quality factor Qts is 1.4 times higher. The material of the box, as elsewhere below, is MDF from 18 mm; for subwoofer power from 50 W – from 24 mm. But it is better to place the speakers in a closed box; in this case, it can be done without calculation: the length inside is taken at the installation site, ranging from 0.5 m (for a computer) to 1.5 m (for a large TV). The internal cross-section of the box is determined based on the diameter of the speaker cone:

• 6” (155 mm) – 200x200 mm.
• 8” (205 mm) – 250x250 mm.
• 10” (255 mm) – 300x300 mm.
• 12” (305 mm) – 350x350 mm.

In the worst case (an under-table computer sub with 6” speakers), the volume of the box will be 20 liters, and the equivalent with filling will be 33-34 liters. With a UMZCH power of up to 25-30 W per channel, this is enough to get decent midbass.

Filters

In this case, it is better to use LC filters of type K. They require more coils, but in amateur conditions this is not essential. K-filters have low attenuation in the stopband, 6 dB/oct per link or 3 dB/oct per half-link, but have an absolutely linear phase response. In addition, when operating from a voltage source (which, with great accuracy, is the UMZCH), the K-filter is little sensitive to changes in load impedance.

At pos. 1 pic. Diagrams of K-filter sections and calculation formulas for them are given. R for the low-frequency GG is taken equal to its impedance Z at the low-pass filter cutoff frequency of 150 Hz, and for the high-pass filter equal to the satellite impedance z at the high-pass filter cutoff frequency of 185 Hz (formula in position 6). Z and z are determined according to the diagram and formula in Fig. above (with measurement diagrams). Working diagrams of filters are given in pos. 2. If you prefer to buy additional capacitors rather than wind coils, exactly the same parameters can be made from P-links and half-links.

Data and circuits for making filters for a simple subwoofer with independent emitters

The attenuation of the low-pass filter in the stopband is 18 dB/oct, and the attenuation of the high-pass filter is 24 dB/oct. This frankly non-trivial ratio is justified by the fact that the satellites are unloaded from the low frequencies and give a cleaner sound, and the remainder of the low frequencies reflected from the high-pass filter is sent to the low-frequency speakers and makes the bass deeper.

Data for calculating filter coils are given at pos. 3. They need to be positioned mutually perpendicular because K-filters operate without magnetic coupling between the coils. When calculating, the dimensions of the coil are specified and the number of turns is determined using the inductance found in the order of calculating the filter. Then, using the laying coefficient, the diameter of the wire in the insulation is found; it should be at least 0.7 mm. It turns out less - increase the size of the coil and recalculate.

Settings

Setting up this subwoofer comes down to equalizing the volumes of the bass and satellite speakers, respectively. cutoff frequencies. To do this, first prepare the room for acoustic measurements, as described above, and a tester with a bridge and transformer. Next you will need a condenser microphone. For a computer one, you will have to make some kind of microphone amplifier (MCA) with bias applied to the capsule, because a regular sound card cannot simultaneously receive a signal and emulate a frequency generator, pos. 4. If you can find a condenser microphone with a built-in MUS, even an old MKE-101, great, its output is connected directly to the primary (smaller) winding of the transformer. The measurement procedure is simple:

1. The microphone is fixed opposite the geometric center of the satellites at a horizontal distance of 1-1.5 m.
2. Disconnect the subwoofer from the UMZCH and apply a 185 Hz signal.
3. Record the voltmeter readings.
4. Without changing anything in the room, they turn off the satellites and connect the sub.
5. A 150 Hz signal is supplied to the UMZCH and the tester readings are recorded.

Now you need to calculate the equalizing resistors. The volumes are equalized by muting the louder links in a series-parallel circuit (item 5), because it is necessary to keep the previously found values ​​of Z and z unchanged modulo. Calculation formulas for resistors are given in pos. 6. Power Rg – not less than 0.03 of the power of the UMZCH; Rd – any from 0.5 W.

It's also simple

Another option for a simple, but real subwoofer is with a paired low-frequency generator. Pairing woofers is a very effective way to enhance their sound quality. The design of a subwoofer based on a pair of old 10GD-30 is shown in Fig. below.

The design is very perfect, 6th order bandpass. Bass amplifier - TDA1562. You can also use other high-quality GGs with a relatively small diffuser stroke, then you may have to make adjustments by selecting the length of the pipes. It is produced at control frequencies of 63 and 100 Hz. way (control frequencies are not resonant of the acoustic system!):

• Prepare the room, microphone and equipment as described above.
• 63 and 100 Hz are supplied to the UMZCH alternately.
• Change the lengths of the pipes, achieving a difference in voltmeter readings of no more than 3 dB (1.4 times). For gourmets - no more than 2 dB (1.26 times).

The tuning of the resonators is interdependent, so the pipes need to be moved according to: pulled out the short one, pushed the long one in by the same amount, in proportion to its original length. Otherwise, you can completely upset the system: the peak of the optimal setting at the 6th bandpass is very sharp.

1. A dip between 63 and 100 Hz – the partition needs to be moved towards the larger resonator.
2. Dips on both sides of 100 Hz - the partition is shifted towards the smaller resonator.
3. The burst is closer to 63 Hz - you need to increase the diameter of the long pipe by 5-10%
4. A burst closer to 100 Hz is the same, but for a short pipe.

After any of the adjustment procedures, the subwoofer is reconfigured. For its convenience, complete assembly with glue is not done at first: the partition is tightly smeared with plasticine, and one of the side walls is placed on double-sided tape. Make sure there are no gaps!

Pipes for resonators

Ready-made elbow pipes for acoustics are sold in music and radio stores. You can make a telescopic acoustic pipe with your own hands from scraps of plastic or cardboard pipes. In both cases, across the inner mouth, you need to firmly glue 2 pieces of fishing line: one with tension, the other with a loop protruding outward, see fig. on right. If the pipe needs to be moved apart, press on the tight line with a pencil, etc. If you shorten it, pull the loop. Tuning a resonator with a pipe is thus speeded up many times.

Powerful 6th order

Drawings of the 6th order bandpass for 12” GG are given in Fig. This is already a solid floor-standing design with a power of up to 100 W. It is configured like the previous one.

Drawings of a 6th order bandpass subwoofer for a 12″ speaker

4th order

Suddenly you have a 12” high-quality GG at your disposal; on it you can make a 4th order bandpass of the same quality, but more compact, see fig; dimensions in cm. However, setting it up will be much more difficult, because Instead of manipulating the pipe of a larger resonator, you will have to immediately move the partition.

6th order bandpass subwoofer for 12″ speaker

Electronics

The bass UMZF for a subwoofer is subject to the same requirement as filters, the requirement of complete linearity of the phase response. It is satisfied by UMZCHs made using a bridge circuit, which also reduces the nonlinear distortions of integral UMZCHs with a non-complementary output by an order of magnitude. UMZCH for a subwoofer with a power of up to 30 W can be assembled according to the diagram in pos. 1 rice; 60-watt according to the circuit on pos. 2. It is convenient to make an active subwoofer on a single chip of a 4-channel UMZCH TDA7385: a couple of channels are sent to the satellites, and the other two are connected via a bridge circuit to the sub, or, if it has independent amplifiers, they are sent to the woofers. The TDA7385 is also convenient because all 4 channels have common inputs for the St-By and Mute functions.

According to the diagram at pos. 3 makes a good active filter for a subwoofer. The gain of its normalizing amplifier is regulated by a variable resistor of 100 kOhm over a wide range, so in most cases the rather tedious procedure of equalizing the volumes of the subwoofer and satellites is eliminated. Satellites in this version are switched on without a high-pass filter, and volume preset potentiometers with slots for a screwdriver are built into the mid-high frequency amplifiers.

You may want to design a slot sub from scratch rather than mess around with reconfiguring prototype subwoofers to fit your speaker. In this case, follow the link: //cxem.net/sound/dinamics/dinamic98.php. The author, we must give him his due, was able to explain at a “for dummies” level how to calculate and make a high-quality subwoofer using modern software. However, in a big deal there are some mistakes, so when studying the source, keep in mind:

And still…

Making a subwoofer yourself is a fascinating task, useful for the development of intelligence and skill, and besides, a good bass speaker costs one and a half times less than a pair of a lower class. However, during control auditions, both seasoned experts and casual listeners “from the street”, all other things being equal, clearly prefer sound systems with full channel separation. So first think about it: won’t you still have to deal with a couple of separate columns on your hands and your wallet?

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What I like about Kicker is its unconventional approach. While everyone is stubborn and wagons are riveting subwoofers in bass reflex housings, these old car audio people simply remember that there are other types of design. A passive radiator (also known as a passive radiator) has much in common with a bass reflex, but is devoid of many of its disadvantages. And nothing new, Harry Olson described its principle in his patent back in 1935...

Design

I won’t get ahead of myself and the first thing I will do is “meet the clothes.” The Kicker CWTB10 is very compact - the body length does not exceed 44 cm. The outer diameter, correspondingly, is the same as that of a typical “ten” - a little less than 28 cm. The series also has an 8-inch model, which is even more compact.

I would especially like to note that the subwoofer is positioned by the manufacturer as universal - it can be used not only in a car, but also, say, in boats, open SUVs or ATVs. The case is made of thick impact-resistant plastic and is completely sealed.

There are threaded holes for mounting the subwoofer, and the kit includes several brackets for horizontal or vertical mounting.

I received a model with a nominal impedance of 2 ohms for testing, but in general the Kicker CWTB10 also has a 4-ohm version. It is better to connect a 2-ohm one to some kind of bass monoblock, but a 4-ohm one can also be used with multi-channel amplifiers, connecting a subwoofer to a pair of channels in a bridge.

Now, actually, to the acoustic design - the passive radiator. The shape of the body does not play the most important role here, but in our case it is made in the form of a pipe, at the ends of which there is a diffuser. The speaker actually only owns one of them. The second is exactly the same diffuser and on exactly the same suspension - this is a passive radiator.

How does a passive radiator work?

It was not for nothing that I mentioned at the very beginning that a passive radiator has much in common with a bass reflex. For those who don’t know how a bass reflex works, I’ll tell you briefly.

When the speaker cone moves back and forth, it alternately compresses and decompresses the air inside the housing. Accordingly, this air will alternately tend to either go out through the port or be sucked back in through it. But the trick is that the air inside the port has a certain inertia, and all these vibrations will “reach” the exit from it with some delay.

At a certain frequency (this is what is called the port tuning frequency), it will turn out that the air exiting the port will oscillate synchronously with the diffuser itself. That is, the radiation from the diffuser and from the port will add up. Actually, this is the effect of acoustic amplification.

A passive radiator works on exactly the same principle. Only instead of a port with an air mass inside it, there is simply a diffuser on a suspension. In essence, a passive radiator is exactly the same speaker, only without a magnetic system. And if the tuning of a conventional bass reflex port can be changed by its proportions and dimensions, then in a passive radiator the tuning is changed by the mass of the diffuser and the elasticity/viscosity/stiffness of its suspension.

What are the advantages of a passive radiator over a conventional bass reflex port?

And you look at the dimensions of the case, and the question will disappear by itself. In the case of the Kicker CWTB10, the internal volume is something like 27 liters. If you try to calculate a regular port for such a case (for example, in JBL Speakershop or BassPort), the program will give it very inconvenient dimensions. Either the cross-section will be too small, or the length will be insane.

And with a passive radiator you can make any size and any setting. Do you think it will be possible to make a regular port of the same cross-section with a low setting? That's what I'm talking about.

How does it work inside?

The speakers are attached through the “legs” of the protective grill. To get to the screws, you just need to remove the plugs from them.

By the way, these are not some kind of self-tapping screws, everything is serious - with cage nuts implanted into the body.

The inside of the body is filled with fluffy synthetic padding. In short, it, firstly, creates the effect of “increasing” the internal volume, and secondly, to some extent dampens the vibrations of the air inside it.

The speaker itself is without unnecessary labels or other decorations. Although the Comp R series indicated on the front side hints at its relationship with the separate Kicker 43CWR104 subwoofer speaker. Most likely, this is it, only in a simplified version - without decorative overlays and with simpler cable connection terminals.

And here's what's on the other side of the case. From the outside it looks like a speaker, but on the inside it doesn't look like a speaker at all. Or rather, it looks like a speaker without a motor.

Where the coil is usually attached to the diffuser, a metal washer is attached - it adjusts the weight of the moving system.

Measurements

Just for fun, I took the impedance curve not only for the entire subwoofer, but also separately for the speaker. Judging by the nature of the curves, the passive radiator is tuned somewhere around 35 Hz, which is very close to the Fs of the speaker itself.

Measured speaker parameters in the Kicker CWTB10 subwoofer:

• Fs (natural resonant frequency) – 35 Hz
• Vas (equivalent volume) – 19.5 l
• Qms (mechanical quality factor) – 8.97
• Qes (electrical quality factor) – 0.51
• Qts (total quality factor) – 0.49
• Mms (effective mass of the moving system) – 159 g
• BL (electromechanical coupling coefficient) – 11.1 T m
• Re (voice coil DC resistance) – 1.8 Ohm
• dBspl (reference sensitivity, 1m, 1W) – 84.2 dB

However, the speaker parameters are just for fun. We have a ready-made subwoofer, so I’ll evaluate its performance when assembled.

To begin with, I take the frequency response of the radiation from the diffuser itself. Pay attention to the dip right in the passive radiator tuning zone - about 35 Hz:

The fact is that when the subwoofer operates at this frequency, the passive radiator enters into resonance and itself begins to compress and decompress the air in the housing, and for the speaker, the air in the housing seems to become more elastic. Which, in turn, limits the stroke of its diffuser.

It turns out that the subwoofer hardly works at these frequencies? Of course not, it’s just that near the tuning frequency of a passive radiator, it is mainly not the speaker that works, but the radiator itself:

And this is how they work together:

Unfortunately, I cannot show the general frequency response, since measurements at lower frequencies are correct only in the near field (it cannot be carried out in the MTUSI anechoic chamber due to one measurement). But even a cursory analysis of the frequency response of the speaker and passive radiator makes it clear that the subwoofer should work very well in the car interior. Which, in fact, has been confirmed in practice.

Test in action and conclusions

A small experiment in the car showed that you should not prematurely judge the capabilities of this subwoofer by its size. A passive radiator when configured correctly (and here it is configured correctly) is a big force. In terms of bass response and depth, the Kicker CWTB10 is certainly not inferior to the average 12-inch subwoofer.

I can say one thing about the character of the bass – it’s a Kicker. Dense, weighty, juicy. For club music it’s generally a godsend. Interestingly, as the volume increases, the bass does not begin to put pressure on the ears, but it begins to be perceived tactilely - the bass rhythm is perceived by blows to the chest as if from a heavy rubber ball. And this is from some ten!

In an open space (and with this design, the Kicker CWTB10 can be safely used even on a boat, even on an open SUV), the bass quite naturally loses in depth, but almost does not lose in pressure. I would even say that it becomes even more dense and collected in its structure. And again, just right for rhythmic club music.

In general, a correctly calculated passive radiator is not some kind of “phasic on a pipe”. This will be more serious.

• Compact, easy to install
• Can be used in open SUVs, boats, ATVs, etc.
• High quality performance
• Unexpectedly high bass response for a 10-inch caliber
• On club music the bass is simply amazing

• Gravitates mainly towards rhythmic music

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Dedicated to the acoustics of a room, we found out that any room is a kind of resonator that dramatically affects the sound character of the system. Now it’s time to talk directly about the sources of this very sound, that is, about speaker systems.

In order to properly understand the processes occurring in a box on the wall of which one or more speakers are mounted, you need to thoughtfully read a couple of books, each of which contains more formulas than the entire school physics course. I won’t go into such depths, so this material is not worth it as a comprehensive analysis or guide to building audiophile speakers. However, I really hope that it will help beginning music lovers (and some chronic ones too) to properly navigate the variety of acoustic solutions, each of which its developers, of course, call the only correct one.

For some time after the invention of the electrodynamic emitter with a conical diffuser (okay, just dynamics) in 1924, its wooden frame served primarily decorative and protective functions. This is understandable - after many years of listening to records through mica membranes and gramophone bells, the sound of the new device, even without any acoustic modifications, seemed simply the apotheosis of euphony.

However, recording technologies quickly improved and it became clear that it was extremely problematic to more or less plausibly reproduce the audible range with a speaker simply mounted on some kind of stand. The fact is that the dynamic head, left to its own devices, is in a state of acoustic short circuit. That is, the waves from the front and rear surfaces of the diffuser, emitted, of course, in antiphase, seamlessly overlap each other, which most sadly affects the efficiency of operation, and primarily on the transmission of bass.

By the way, in the course of this story I will most often talk about low frequencies, since their reproduction is a key point in the operation of any speaker cabinet. Due to the short length of the emitted waves, HF drivers do not need to interact with the internal volume of the speaker at all, and are most often completely isolated from it.

Soul wide open

The easiest way to separate the front radiation of a speaker from the rear is to mount it on a shield as large as possible. From this simple idea, the first acoustic systems were born, which were a box with an open back wall, since for compactness the edges of the shield were simply taken and bent at a right angle. However, in terms of bass reproduction, the success of such designs was not very impressive. In addition to the imperfection of the body, the problem was also in the suspension travel of the diffusers, which was very small by modern standards. To somehow get out of the situation, speakers were used as large as possible, capable of developing acceptable sound pressure with a small vibration amplitude.

Despite the seeming primitiveness of such designs, they also had some advantages, and they were so specific and interesting that adherents of open speakers have not died out to this day.

To begin with, the absence of any obstacles in the path of sound waves is the best way to increase sensitivity. This point is especially valuable for audiophile tube amplifiers, especially single-ended or feedbackless ones. Large-diameter paper diffusers, even at a power of about four to five watts, are capable of creating a rather impressive, and at the same time surprisingly open and free sound.

As for the rear radiation, in order not to introduce distortion into the direct sound, it must arrive to the listener with a noticeable delay (over 12-15 ms) - in this case, its influence is felt as a slight reverberation, only adding air to the sound and expanding the musical space . The subtlety is that to create this very “noticeable delay”, the speakers, of course, must be located at a fair distance from the walls. In addition, the large area of ​​the front panel and the impressive size of the low-frequency drivers have a corresponding impact on the overall dimensions of the speakers. In a word, owners of small and even medium-sized living rooms, please do not worry.

By the way, a special case of open systems is acoustics built on electrostatic emitters. Only due to the almost weightless diaphragm of a large area, in addition to all the advantages described above, electrostats add the ability to delicately transmit even the sharpest dynamic contrasts, and due to the lack of signal separation in the midrange and treble zones, they also have enviable timbral accuracy.

Open design

Pros: High-end open-back speakers are a great way to get a real kick out of listening to purist tube single-ended speakers.

Minuses: It’s better to forget about fat compression bass right away. The entire sound path must be subordinated to the idea of ​​open acoustics, and the speakers themselves will have to be chosen from an extremely limited number of proposals.

Locked in a box

With the increase in power and improvement in amplifier parameters, the ultra-high sensitivity of acoustics has ceased to be the main stumbling block, but the problems of uneven frequency response, and especially the correct reproduction of bass, have become even more pressing.

A giant step towards progress in this direction was made in 1954 by the American engineer Edgar Vilchur. He patented a closed-type speaker system, and it was by no means a gimmick in the style of today's patent trolls.

By that time, the bass reflex had already been invented and, of course, a speaker was also tried on a box with a bottom more than once, but nothing good came of it. Due to the elasticity of the enclosed volume of air, it was necessary either to lose a significant part of the energy of the diffuser, or to make the body prohibitively large in order to reduce the pressure gradient. Vilchur decided to turn evil into good. He greatly reduced the elasticity of the suspension, thus transferring control of the movement of the diffuser to the volume of air - a spring that is much more linear and stable than a corrugation or rubber ring.

In this way, it was possible not only to completely get rid of the acoustic short circuit and increase the output at low frequencies, but also to significantly smooth out the frequency response throughout its entire length. However, a minor point also emerged. It turned out that damping with a closed volume of air leads to an increase in the resonant frequency of the moving system and a sharp deterioration in the reproduction of frequencies below this threshold. To combat this problem, it was necessary to increase the mass of the diffuser, which logically led to a decrease in sensitivity. Plus, the absorption of almost half of the acoustic energy inside the “black box” could not but contribute to the reduction in sound pressure. In a word, the new type of speakers required amplifiers of quite serious power. Fortunately, at that time they already existed.

Today, closed design is used mostly in subwoofers, especially in those that claim serious musical performance. The fact is that for home theaters, energetic development of the lowest bass is often more important than dynamic and phase accuracy throughout the low-frequency range. But by combining a relatively compact closed sub with decent satellites, you can achieve a much more correct sound - albeit not filled with super-deep bass, but extremely fast, collected and clear. All of the above can also be attributed to full-range speakers, “closed” models of which occasionally appear on the market.

Closed box

Pros: Exemplary attack speed and low-frequency resolution. Relatively compact design.

Minuses: A fairly powerful amplifier is required. Ultra-deep bass on the verge of infrasound is very difficult to achieve.

The case is a pipe

Another way to curb anti-phase rear radiation was the phase inverter, in Russian literally “phase reversal”. Most often it is a hollow tube mounted on the front or rear surface of the housing. The principle of operation is clear from the name and is simple: since it is difficult and irrational to get rid of radiation from the back side of the diffuser, it means that it needs to be synchronized in phase with the front waves and used for the benefit of listeners.

In fact, a pipe with air is an independent oscillatory system that receives impulse from the movement of air inside the housing. Possessing a very specific resonance frequency, the bass reflex works more efficiently the closer the diffuser oscillations are to its tuning frequency. Sound waves of higher frequencies simply do not have time to move the air in the pipe, and although lower frequencies do, the lower they are, the more the phase of the bass reflex radiation shifts, and, accordingly, its efficiency. When the phase rotation reaches 180 degrees, the tunnel begins to frankly and very effectively muffle the sound of the bass driver. This is what explains the very steep drop in speaker sound pressure below the bass reflex tuning frequency - 24 dB/oct.

In a closed box, by the way, at frequencies below the resonant frequency response decay is much smoother - 12 dB/oct. However, unlike a blank box, a box with a pipe in the side wall does not force designers to go to any lengths to minimize the resonant frequency of the speaker itself, which is quite troublesome and expensive. Setting up a bass reflex tunnel is much easier - just select its internal volume. This is, however, in theory. In practice, as always, unforeseen difficulties arise, for example, at high volume levels, the air exiting the hole can make a noise almost like the wind in a stove chimney. In addition, the inertia of the system often causes a drop in attack speed and deterioration of articulation in the bass. In a word, the scope for experimentation and optimization before the designers of bass reflex systems is simply incredible.

Bass reflex

Pros: Energetic response to low frequencies, the ability to reproduce the deepest bass, relative simplicity and low cost of production (with considerable complexity of calculation).

Minuses: In most implementations it is inferior to a closed box in terms of attack speed and clarity of articulation.

Let's do without a reel

Attempts to get rid of the genetic problems of the bass reflex, and at the same time save on the volume of the cabinet without compromising the depth of the bass, gave the developers the idea of ​​​​replacing the hollow pipe with a membrane driven by vibrations of the same working volume of air. Simply put, another low-frequency driver was installed in a closed box, only without a magnet and voice coil.

The design was called “passive radiator”, which is often not very correctly translated from English as “passive radiator”. Unlike a subwoofer pipe, a passive diffuser takes up much less space in the case, is not so critical to the location, and besides, like the air inside a closed box, it dampens the leading driver, smoothing its frequency response.

Another plus is that with an increase in the area of ​​the radiating surface, to achieve the desired sound pressure, a smaller amplitude of vibrations is required, which means that the consequences of nonlinear operation of the suspension are reduced. Both diffusers vibrate in phase, and the resonant frequency of the free membrane is adjusted by precise adjustment of the mass - a weight is simply glued to it.

Passive radiator

Pros: Compact design with impressive bass depth. Lack of bass-reflex overtones.

Minuses: An increase in the mass of emitting elements leads to an increase in transient distortions and a slower impulse response.

Exit from the maze

Acoustics, armed with bass reflexes and passive radiators, reproduce deep bass thanks to resonators operating through the mediation of air inside the speakers. However, who said that the volume of the speaker cannot play the role of a low-frequency emitter in itself? Of course it can, and the corresponding design is called an acoustic labyrinth. In essence, it is a waveguide with a length of half or a quarter of the wavelength at which it is planned to achieve resonance of the system. In other words, the design is adjusted to the lower limit of the speaker frequency range. Of course, using a full-wavelength waveguide would be even more efficient, but then for a frequency of, say, 30 Hz, it would have to be made 11 meters long.

In order to fit even a structure twice as compact into a column of reasonable dimensions, partitions are installed in the housing to form the most compact curved waveguide, with a cross section approximately equal to the area of ​​the diffuser.

The labyrinth differs from the bass reflex primarily in its less “resonant” (that is, not accentuated at a certain frequency) sound. The relatively low speed and laminarity of air movement in a wide waveguide prevents the occurrence of turbulence, which, as we remember, generates unwanted overtones. In addition, in this case the driver is free from compression, which increases the resonant frequency, because its rear radiation encounters virtually no obstacles.

There is an opinion that acoustic labyrinths create fewer problems with standing waves in the room. However, with the slightest miscalculations in development or manufacturing, standing waves can arise in the waveguide itself, which, unlike a bass reflex, has a much more complex structure of resonances.

In general, it must be said that competent calculation and fine-tuning of an acoustic labyrinth are very difficult and labor-intensive processes. It is for this reason that this type of case is rarely found, and only in speakers of a very serious price level.

Acoustic labyrinth

Pros: Not only good response, but also high tonal accuracy of the bass.

Minuses: Serious dimensions, very high complexity (read - cost) of creating a properly functioning structure.

Hey, on the ferry!

The horn is the oldest and, perhaps, the most provocative type of acoustic design. It looks cool, if not shocking, it sounds bright, and at times... In old films, characters sometimes shout something into each other's mouthpieces, and the characteristic coloring of such a sound has long become a meme in both the music and film worlds.

Of course, today's acoustics have moved very far from the tin funnel with a handle, but the principle of operation is still the same - the horn increases the air resistance for better coordination with the relatively high mechanical resistance of the moving speaker system. Thus, its efficiency increases, and at the same time a clear directionality of radiation is formed. Unlike all previously described designs, the horn is most often used in high-frequency speaker sections. The reason is simple - its cross-section increases exponentially, and the lower the reproduced frequency, the larger the size of the output hole should be - already at 60 Hz a bell with a diameter of 1.8 m will be required. It is clear that such monstrous designs are more suitable for stadium concerts, where they really can be found periodically.

The main trump card of adherents of horn playback is that acoustic amplification allows, for a given sound output, to reduce the membrane stroke, and therefore increase sensitivity and improve musical resolution. Yes, yes, again a nod to the owners of single-ended tube circuits. In addition, with proper calculation, bells can play the role of acoustic filters, abruptly cutting off sound outside their band and allowing you to limit yourself to the simplest, and therefore introduce minimal distortion, electric crossovers, and sometimes even do without them.

Skeptics never tire of reminding us of the characteristic horn coloring, which is especially noticeable on vocals and gives it a characteristic nasal quality. It’s really not easy to overcome this problem, although judging by the way the best examples of High-End horns play, it’s quite possible.

Horn

Pros: High acoustic efficiency, which means excellent sensitivity and good musical resolution of the system.

Minuses: Characteristic, difficult-to-remove sound coloration, non-childish sizes of mid- and especially low-frequency structures.

Circles on the water

It is with this analogy that it is easiest to describe the nature of the radiation of counter-aperture acoustic systems, first developed in the Soviet Union in the 80s of the last century. The principle of operation is non-trivial: a pair of identical speakers are mounted so that their diffusers are located opposite each other in a horizontal plane and move symmetrically, either compressing or decompressing the air layer. As a result, annular air waves are created that diverge evenly in all directions. Moreover, the characteristics of these waves during their propagation are minimally distorted, and their energy decays slowly - in proportion to the distance, and not its square, as in the case of conventional speakers.

In addition to long-range and omnidirectionality, counter-aperture systems are interesting due to their surprisingly wide vertical dispersion (about 30 degrees versus standard 4-8 degrees), as well as the absence of the Doppler effect. For speakers, it manifests itself in signal beats caused by a constant change in the distance from the sound source to the listener due to vibrations of the diffuser. True, the actual audibility of these distortions still causes a lot of controversy.

The mutual penetration of the concentric sound fields of the right and left speakers creates a very wide and uniform zone of surround perception, that is, in essence, the issue of precise positioning of the speakers relative to the listener becomes irrelevant.

A characteristic feature of counter-aperture is that the sound coming to the listener from virtually all directions, although it creates an impressive presence effect, cannot fully convey information about the sound stage. Hence the stories from listeners about the feeling of a piano flying around the room and other wonders of virtual spaces.

Counterperture

Pros: A wide zone of spectacular volumetric perception, naturalistic timbres thanks to the non-trivial use of wave acoustic effects.

Minuses: The acoustic space is noticeably different from the sound stage conceived when recording the phonogram.

And others...

If you think that this is the end of the list of speaker design options, then you greatly underestimate the design enthusiasm of electroacoustic speakers. I described only the most popular solutions, leaving behind the scenes a close relative of the labyrinth - the transmission line, the bandpass resonator, the housing with the acoustic resistance panel, the load pipes...

This kind of exoticism is quite rare, but sometimes it materializes in a design with a truly unique sound. And sometimes not. The main thing is not to forget that masterpieces, like mediocrity, are found in all designs, no matter what the ideologists of a particular brand say.

Prepared based on materials from the magazine "Stereo & Video", June 2016.

A characteristic feature of counter-aperture is that the sound coming to the listener from virtually all directions, although it creates an impressive presence effect, cannot fully convey information about the sound stage. Hence the stories from listeners about the feeling of a piano flying around the room and other wonders of virtual spaces.

Counterperture

Pros: A wide zone of spectacular volumetric perception, naturalistic timbres thanks to the non-trivial use of wave acoustic effects.

Minuses: The acoustic space is noticeably different from the sound stage conceived when recording the phonogram.

And others...

If you think that this is the end of the list of speaker design options, then you greatly underestimate the design enthusiasm of electroacoustic speakers. I described only the most popular solutions, leaving behind the scenes a close relative of the labyrinth - the transmission line, the bandpass resonator, the housing with the acoustic resistance panel, the load pipes...

This kind of exoticism is quite rare, but sometimes it materializes in a design with a truly unique sound. And sometimes not. The main thing is not to forget that masterpieces, like mediocrity, are found in all designs, no matter what the ideologists of a particular brand say.

16/09/2013 , Posted in

There are a number of principles by which all subwoofers for, or listening rooms, can be classified. Next we list the main ones, in each case indicating the advantages and disadvantages of each type.

Availability of built-in amplifier

Depending on the presence or absence of a built-in amplifier, there are Active And Passive subwoofers.

Active subwoofers are currently the most common and, by and large, are the optimal choice for use in or. Active subwoofers are, simply put, the most flexible and easy to install. However, they don't necessarily sound the best. The simplest active subwoofer carries on board an amplifier, a crossover frequency control (LPF or High Pass Filter), a phase switch and two types of input connections. The presence of a built-in amplifier necessitates a separate power cord from a 220V outlet to the subwoofer. The crossover frequency control allows you to limit from above the range that the subwoofer will reproduce. A phase control (usually a switch) will allow you to better integrate the subwoofer with the rest of the speakers in your system. It is designed to invert or smoothly change the phase of the audio signal entering the subwoofer input. To install it correctly, you will most likely have to listen to how the system plays in both modes (0 and 180), and choose the option with the most pleasant and deep bass. Well, and, of course, the active subwoofer needs to be supplied with a signal from the corresponding line output of your AV receiver or processor.

Active subwoofers LJAudio and SVSound

Advantages of active subwoofers:

• Very easy to use (like AV receivers compared to a set of individual components);
• Easier to install and configure due to the fact that everything you need is already built into them;
• As a rule, they are less expensive (like AV receivers compared to a set of AV processor + multi-channel amplifier).

Disadvantages of active subwoofers:

• The built-in amplifiers on most, though not all, subwoofers are relatively inferior;
• Less convenient in terms of installation, because You always need to pull 2 ​​cables (power and signal);
• If something bad happens to an amplifier, it is not so easy to find a replacement or repair it;
• Manufacturers do not always sell spare parts for older models;
• Some active subwoofers do not turn on automatically if a low-level audio signal is supplied to them (the auto-off/on system does not work well).

Passive subwoofers originally designed for use in conjunction with an external amplifier. The amplifier can be used either dedicated (the best option) or integrated (for example, you can use the free channels of an AV receiver). The important point is that since the subwoofer initially requires more power to reproduce low-frequency sounds, the amplifier must be powerful enough. In addition, unless the subwoofer has a built-in high-pass filter (and typically a passive subwoofer does not), the signal must be filtered on the AV receiver side before it reaches the subwoofer.

Passive subwoofers PRO, RBH and JBL

Advantages of passive subwoofers:

• External amplifiers are usually of higher quality, they have the right massive power supplies, high-quality wiring of signal circuits;
• Capable of handling more power and delivering more dB;
• A multi-channel amplifier can make multiple passive subwoofers play in your ;
• Passive subwoofers are simpler and cheaper to manufacture;
• The internal useful volume of the case is larger with the same dimensions, which allows for a more flexible approach to the placement of the speaker and bass reflex ports;
• If the amplifier starts to act up, it can easily be replaced with any other one;
• Less fire hazard (electrics and wooden casing are separated in space);
• One of the main advantages is greater flexibility during installation. You can install the amplifier in a rack along with the rest of your home’s equipment, and run only one regular speaker wire to the subwoofer. There is no need to pull food towards them!
• Long speaker cables are usually cheaper than dedicated subwoofer cables of the same length;
• Speaker wires (can be made completely flat) are much easier to hide than subwoofer cables.

External subwoofer amplifier

Disadvantages of passive subwoofers:

• Much more difficult to organize and install;
• External amplifiers can be more expensive than built-in amplifiers.

Emitter directivity

Depending on which direction the speaker faces, subwoofers can be divided into:

Radiating down (DownFiring). This type of subwoofer has a speaker installed in the bottom wall of the cabinet and directed towards the floor. Subwoofers of this type look more like some kind of furniture than a speaker system. They don't need a protective grill. They can play even more efficiently than their relatives, so you should avoid installing them in the corners of rooms and in close proximity to walls (applies to the option with one subwoofer in the system). Otherwise the sound may be too boomy.

Down Firing subwoofers Yamaha and Atlantic Tech

Radiating forward (FrontFiring). The speaker of this type of subwoofer is installed on one of the front walls of the housing and is directed parallel to the plane of the floor. Subwoofers of this type require a protective grille to protect the speaker from damage, and are more like a regular speaker system.

Front Firing subwoofers Earthquake and Rhythmic Audio

Type of acoustic design

This classification is the most extensive and is deeply rooted in the section Acoustics of the science of Physics. As a minimum educational program, we’ll tell you a little about the purpose and function of any acoustic design of the speaker. The speaker emits sound not only forward, but also backward. The front and rear sound waves are opposite in phase. In this regard, there is a term “acoustic closure”, in which the waves on both sides of the speaker cone add up and (if they are completely opposite in phase) cancel each other out. In theory, you should not hear any sound from a bare speaker at all, but in practice the sound will be, but very far from the original. The housing (box) of the acoustic system in which the speaker is installed allows this short circuit to be eliminated and the sound waves to be given the required parameters for dynamics and frequency response.

We will skip further theory and try to briefly consider the most common types of acoustic design, not forgetting to talk about the advantages and disadvantages of each of them.

Closed box (ZYa, Closed case,Enclosure). The speaker is installed in a closed, airtight housing. This solution completely isolates the rear sound wave of the speaker from the front one.

Advantages:

• Ease of design and production (only two parameters need to be taken into account: the volume of the box and the quality factor of the speaker);
• Relatively small body volume;
• Excellent impulse characteristics (response to a short-term signal, the ability of the component to accurately reproduce short-term musical events);
• There is no need to use a subsonic filter (LPF), because there is a natural tendency of the cell phone to suppress frequencies below the resonant frequency of the speaker;
• Fast, natural, smooth, bouncy, clear, controlled and warm are some of the subjective characteristics often used to describe the bass produced by a good subwoofer of this type.

Flaws:

• Relatively high lower frequency limit, rarely below 30 Hz (at -3 dB level);
• Lowest efficiency compared to other types of acoustic design.

Bass reflex(FI, Ported, Vented, Bass-Reflex). The speaker is installed in a housing that has a tunnel that extends inward in the form of a pipe, box or slot for a certain length. This tunnel is called the bass reflex port. Due to it, the internal volume of the box communicates with the surrounding space. The length and cross-sectional area of ​​the tunnel are critical parameters for the correct operation of this type of acoustic design. Both the speaker and the bass reflex port work in tandem, forming a second oscillatory system that emits (already in phase with the speaker cone) additional sound energy of the rear wave. The speaker is usually installed in the front wall of the case. The bass reflex port is most often located on the same wall, less often on the perpendicular (in the case of a downward-facing speaker) wall of the housing and tunes the device for maximum output in a certain (rarely wider than 1-2 octaves) frequency range. In this range, the speaker operates with minimal load, vibration, and distortion (the port emits most of the sound), allowing the subwoofer to handle more maximum power. Above the tuning frequency, the tunnel becomes less and less “transparent” for sound vibrations, and the speaker works as if in a closed box. Below the tuning frequency, the opposite happens: the inertia of the port gradually disappears, and at the lowest frequencies the speaker operates practically without load, as if it had been removed from the housing. The amplitude of the oscillations quickly increases, and with it the risk of spitting out the speaker cone or damaging the voice coil from hitting the magnet. This feature necessitates the use of infra-low frequency filters (subsonics) in bass-reflex type subwoofers.

Advantages:

• A lower frequency response limit, quietly located in the region or even below 20 Hz (at a level of -3 dB);
• Allows you to supply more power due to the smaller amplitude of vibrations of the speaker cone, especially in the region and above the tuning frequency;
• More productive, exceeding on average 3 dB in sound pressure level their counterparts in a closed box;
• Deep, powerful, full, loud, inspiring, stunning and earth-shaking - such epithets often accompany the description of the low-frequency effects reproduced by subwoofers of this type.

Flaws:

• Requires a larger case size;
• It is more difficult to obtain the desired result during design and production;
• They require an additional infra-low-pass filter (subsonic) or volume limitation, because there is a high probability of damage to the speaker at frequencies below the tuning frequency;
• The impulse characteristics are worse than the VZ, which affects the subjective perception of bass notes, especially in music;
• The diameter of the port should be relatively large to avoid unwanted sounds of air passing through it. This entails the need to increase the length of the tunnel, which, in turn, entails the need to increase the body itself. The result may be a box of completely obscene dimensions;
• Boomy, stuffy, sluggish, one-note, slow and inaccurate - these are often subjective epithets regarding the bass from unsuccessful subwoofers of this type.

Most subwoofers on the consumer electronics market are bass reflex. Devices of this type allow you to get the deepest and loudest bass, albeit in some places at the expense of the quality of reproduction of particularly delicate and precise musical details.

4th order bandpass loudspeaker (BandpassVented\Sealed, Bandpass, PSU). A 4th order bandpass is characterized by a speaker whose front and rear parts are installed in two separate chambers of a single housing. Moreover, the rear part of the speaker is in a closed box, and the front part is in a box with a port (tunnel) or vice versa. The body of such a subwoofer is created like a closed box, but with the addition of an acoustic filter (port). This filter, working in tandem with the front sound wave of the speaker, limits the bandwidth of the device, simultaneously raising the sound pressure level in this frequency range.

Advantages:

• A fairly low frequency response limit is achievable (at a level of -3 dB), but only due to lower output and a higher level of distortion;
• Extremely high sound pressure levels are achievable, at the cost of higher tuning frequencies and narrower bandwidths;
• Less total speaker travel required, less likely to damage it;

Flaws:

• It's difficult to design everything correctly. The result strongly depends on the accuracy of the obtained volumes of both chambers, as well as on the frequency of adjustment;
• Tends to be a one-note bass, especially if not designed correctly;
• To achieve a wide bandwidth, you will have to come to terms with low sensitivity and the presence of distortion in a certain range;
• Weak impulse characteristics;
• Bandwidth and sensitivity are inversely related.

Bandpass subwoofers Lanzar and Sonance

Most often, subwoofers of this type are found in car installations aimed at participating in car audio competitions in the maximum sound pressure category (SPL).

6th order bandpass loudspeaker (BandpassVented). A 6th order bandpass is characterized by a speaker whose front and rear parts are installed in two separate chambers of a single housing. Moreover, both the rear and front parts of the speaker are located in a box with a port (tunnel). Each camera is tuned to its own design frequency. In theory, the resulting frequency response should be better than all the previously described design options. The Bose company owns the rights to this type of acoustic design and the secrets of the principles of body design. They explain the theory this way: “The woofers are sandwiched between two separate acoustically elastic volumes inside Bose's patented 'Acoustimass' module. When the speaker cone moves, it excites the air in the chambers. The air in the chamber, acting as an acoustic spring, interacts with the air in the tunnel and produces more low-frequency sound with less amplification power. The system is more sensitive and requires a smaller amplitude of vibration of the speaker cone, which, in turn, produces less distortion. Even if distortion was somehow created, thanks to the patented technology, it will remain captive in the acoustic volumes of the cabinet and will never reach your ears.”

Advantages:

• Greater sensitivity;
• Less vibration of the diffuser – minimal level of audible distortion.

Flaws:

• The total volume of the two chambers results in a rather bulky box;
• Difficult to design. The result strongly depends on the accuracy of the implementation of the calculated parameters;
• There are no clear formulas for calculating the volumes and sizes of ports due to a patent owned by Bose;
• A speaker can quite easily fail as a result of constant high pressure, resulting in overheating of its parts;
• Weak impulse characteristics.

EBS (ExtendedBassShelf, Extended Bass Shelf). EBS is a type of bass reflex design for the speaker cabinet. The difference is that the working volume of the housing is deliberately selected to be 25-75% larger than the optimal calculated one, and the port is tuned to a frequency close to the resonant frequency of the speaker. As a result, we get a decent increase in the lower limit frequency of the subwoofer. If you measure the frequency response of such a device, the same “Shelf” becomes visible, located immediately above the tuning frequency.

Advantages:

• Low frequency response limit (at a level of -3 dB), easily reaching values ​​far down beyond 20 Hz;
• Infra-low, earth-shaking bass;
• Increased output at frequencies below 25 Hz at the expense of reduced output above 30 Hz (frequencies depend on internal volume parameters and port tuning frequency).

Flaws:

• Giant body size;
• The speaker can withstand 25-50% less maximum power before it begins to deteriorate;
• Lack of presence, lack of attack - such epithets are found when describing EBS;
• The overall bass effect is significantly softened. Signals at frequencies from 40 to 60 Hz are extremely low in level;
• It’s more difficult to “sell” because... most people are weakly sensitive to sounds at such low frequencies;
• It takes 8 times more power (as well as the volume of air moved) to make a sound at 20 Hz as loud as at 40 Hz.

Infinite screen (Infinite baffle, IB). IB is a type of open speaker design in which the screen separating the front and rear sound waves is presented as an infinite plane. This design involves installing woofers in a very large isolated working volume, the dimensions of which make it possible to neglect the resistance force created by air compression in other types of design. This type of design does not affect changes in the resonant frequency of the speaker, which inevitably occurs in other cases. Often, the room adjacent to the home theater room (basement, attic, cellar, storage room, garage, etc.) is used as an “isolated” volume. Unlike their bass-reflex and closed counterparts, IB subwoofers are distinguished by the absence of extraneous sounds, so often created by the bass-reflex ports and the walls of the housing. As IB proponents say, “Hear The Bass, Not The Box.”

Advantages:

• The lowest frequency response limit (at a level of -3 dB), reaching a value of 5 Hz;
• Extremely low-pitched, earth-shaking, breath-taking bass;
• Absence of extraneous sounds and sound color;
• Saving internal space - there is no need to install large boxes indoors;
• The secrecy of the installation is a godsend for the interior designer.

Flaws:

• Always a complex custom installation project. IBs are not available in industrial versions;
• Availability of an appropriate adjacent room for installing speakers;
• In the adjacent room there will be as much bass as in your cinema (the question of additional sound insulation arises);
• More speakers are required because... their maximum power is reduced by 50% (there is no acoustic air resistance, it is easier to damage the speaker);
• Difficult to calculate and configure, requiring professional calibration equipment and equalizers.

Options for organizing IB subwoofers

You will only find such subwoofers in the homes of advanced home theater enthusiasts, who are rightly called “Bass Head”. These guys don’t know compromises and build subwoofers, dedicating an entire adjacent room for them, installing several pairs of 15-18” speakers, supplying 3-4 kW of amplification power - all in order to achieve that same presence effect. And, apparently, not in vain, because the LFE channel of the soundtrack of a number of films contains low-frequency effects that go down to 5 Hz!

A real example of the frequency response of an IB subwoofer (red graph)

Passive radiator (PI, Passive Radiator, PR). A passive radiator is always used in combination with an active one and serves as a replacement for the bass reflex tunnel. A speaker with a passive radiator is most similar to a speaker with a bass reflex in terms of its acoustic characteristics, however, with increased sensitivity. Passive radiators are often made in the form of a regular speaker, which does not have a magnet and coil, or simply in the form of a flat diaphragm on a suspension. The driver must be larger or at least the same size as the active speaker.

Advantages:

• Lack of overtones and sound color created by the bass reflex port;
• Easy to set up. By simply adding or subtracting small values ​​of the PI mass, the tuning frequency of the housing can be changed to a value from 0.1 to 15 Hz. Fine tuning is easy;
• Possibility of tuning small enclosures to a lower frequency - there are no restrictions on the length of the tunnel;
• There is less risk of speaker failure at infra-low frequencies; there is no need to use subsonic.

Paradigm, Definitive Tech and Mirage passive radiator subwoofers

Flaws:

• Possible distortion due to the “ping-pong” effect (in short, PI fluctuations can cause fluctuations in the main speaker);
• Slightly higher lower limit of the subwoofer frequency response compared to FI;
• The steepest roll-off (36 dB/octave) is below the tuning frequency;
• More expensive to produce (PI is more expensive than the FI plastic pipe).

Transmission line (TL, Labyrinth, Transmission Line, TL). The speaker is installed in a housing, inside of which there is an acoustic labyrinth or a long pipe, which is called the transmission line. The length of such a labyrinth depends on the resonant frequency of the speaker and the material from which the damping composition covering the walls of the entire labyrinth is made. The TL can narrow and expand or remain with a constant cross-sectional area along its entire length, and also have a number of bends and turns to reduce the final dimensions of the speaker body. The length of the transmission line corresponds to 1/4 of the wavelength of the speaker's resonant frequency. The labyrinth is usually filled with various types of damping material, which helps absorb most of the energy from the return sound wave and allows the use of a shorter TL while maintaining the target speaker tuning frequency.

Advantages:

• Excellent impulse characteristics, equal to (and often superior to) closed designs (CL) and significantly superior to bass reflex designs (FI);
• A priori, a more rigid housing design eliminates distortions introduced by its walls;
• Low slope of the frequency response (around 10 dB/octave or less), leading to an increase in output in the deep bass zone;
• Less color in upper bass notes due to reduced impedance peaks;
• Livelier, cleaner and deeper bass.

Transmission Line subwoofers PMC and Earthquake

Flaws:

• Complexity of design and construction;
• Not all speakers will perform well in a labyrinth, and there are no specific recommendations for choosing them;
• There are no clear design methods and calculation formulas for creating TL; by and large, it is always a trial and error method;
• The size of the case can be impressive.

Rarely seen in home theaters. For the most part, labyrinth-based speakers are the lot of Hi-Fi and Hi-End enthusiasts.

Isobaric (Compound, Isobaric) with two speakers. Two speakers are installed together in a housing that has an enclosed space of a certain volume between them. The speakers must work in phase with each other. The volume of space enclosed between the speakers should be as minimal as possible for the unhindered movement of the diffusers. During the modeling process, this type of enclosure takes half the internal volume of the CB, which makes it possible to design any subwoofer in a twice as compact form as compared to any other type of acoustic design.

Advantages:

• Half the size of the housing for any speaker relative to the ZYa is the main advantage;
• Improved response at the lowest frequencies;
• Denser, faster, clearer and more natural are the adjectives used to describe the bass reproduced by an isobaric.

Flaws:

• To operate the internal speaker, additional amplification power of similar magnitude is required, which is wasted;
• The sensitivity of the system is 3 dB lower compared to the ZYa due to the doubled mass of the diffusers and the halved internal volume;
• The sensitivity of the system is 6 dB lower compared to two sound boxes of the same volume and with similar speakers.

Currently, subwoofers of this type are extremely rare and only where there are big problems with space for their installation, and the bass is required to be clear rather than loud.

Pull/Push (Push/Pull) with two speakers. Two speakers are installed in a special way in a closed housing with a single internal volume. The optimal option is when the speakers are installed in the same plane of the body, with one directed outward and the other directed inward. The connection to the amplifier is carried out in antiphase, when in reality the operation of the speaker cones is in phase. Odd harmonics, according to Vance Dickason's theory, cancel themselves. And if you believe the company, M&K, specializing in the production of Push/Pull subwoofers, this approach even allows you to get rid of even-numbered harmonics. One way or another, harmonic distortions generated by anomalies of the speaker and its components are reduced due to similar inverted anomalies of the second speaker. The sound, as supporters of this type of design say, is as natural and natural as possible due to the corrections made by the speakers in relation to each other. Often there is a Push/Pull design option, when both speakers look outward, which looks more aesthetically pleasing and familiar. Although in this case the effect of reducing distortion is weakly expressed, all other advantages of the approach are preserved. The size of the housing should be twice as large as that calculated for one speaker. The system turns out to be more sensitive (by 3 dB) compared to a half-volume PA and one speaker on board with a completely similar frequency response curve. The subwoofer becomes able to withstand twice the power.

Advantages:

• Better sensitivity;
• Doubled maximum power;
• No harmonic distortion;
• Adequate ability to produce high sound pressure levels (SPL).

Flaws:

• A single large subwoofer enclosure that can be both ugly in appearance and difficult to construct and move.
• The frequency response, by and large, corresponds to two separate subwoofers in housings of half the size, however, here you do not have the opportunity to distribute them to different parts of the room when setting up, which is often extremely necessary.

Push/Pull subwoofers from Blue Sky, MK Sound, as well as 3D DIY model

Companies that have mastered the Push/Pull subwoofer industry, such as MK Sound and Ken Kreisel (founder of MK), now offer great looking subwoofers and speakers with unrivaled performance and sound. This is confirmed by the use of their products in leading film studios in Hollywood and recording studios in London. Let us only add that Ken Kreisel is the inventor of subwoofers as such and satellite-subwoofer systems.

Loudspeaker size

Very often, subwoofers are divided into classes according to the size (usually the diameter) of the working surface of the cone of the installed speaker. The speakers (woofers) used in the construction of subwoofers are, as a rule, the largest in size, because they must move large amounts of air to create low-frequency sound waves. To produce the same volume level at a frequency one octave lower (for example, 30 Hz instead of 60 Hz), you will need four times as much power. The lower the resonant frequency of the speaker, the lower frequency sounds the speaker can reproduce with a given level of distortion. The resonant frequency of a speaker (denoted Fs) is determined by a combination of the mass of its moving parts (cone, protective cap, coil and its base) and the flexibility of the suspension. Under normal conditions, we will need a more powerful amplifier to “drive” the subwoofer speaker than a conventional speaker system. However, it is important to remember that although you should have an amplifier with plenty of power to avoid distortion (clipping), the main task is still to match the subwoofer with the main speaker systems. At any volume level, the subwoofer should not stand out and be localized, but only invisibly expand the sound boundary of the system down the frequency response curve.

The most common speaker sizes for use in subwoofers are 8″, 10″, 12″, 15″ or 18″(we are talking about the diameter of the round diffuser). Although an 18″ subwoofer is capable of producing the lowest frequency bass at maximum volume levels, the largest speaker is not always the best choice for optimal reproduction of bass notes. Large woofers are more difficult to control and tune. There are 10″ subwoofers on the market these days that can move as much air as the old 15″ models could. This is made possible by the 10″ speaker's very long-throw cone, designed to maintain linearity throughout its entire travel, and a high-power Class D digital amplifier capable of driving such a woofer in a small cabinet.