Collecting acoustics. Simple homemade speakers

Before a detailed consideration of the problem, let's outline the range of tasks, knowing the ultimate goal, it will be easier to choose the right direction. Making speaker systems with your own hands is an infrequent case. It is practiced by pros, novice musicians, when store options are not satisfactory. There is a task of embedding in furniture or high-quality listening to existing media. These are typical examples that are solved by a set of generally accepted methods. We will take a look at it. We do not recommend flipping the speaker device diagonally, delve into it!

Speaker system device

There is no chance of making a speaker system yourself without understanding the theory. Music lovers should be aware that the biological species Homo Sapiens hears sound vibrations of frequencies from 16-20000 Hz with the inner ear. When it comes to classic masterpieces, the spread is high. The bottom edge is 40 Hz, the top edge is 20,000 Hz (20 kHz). The physical meaning of this fact is that not all speakers are able to reproduce the full spectrum at once. Relatively slow frequencies work better with massive subwoofers, and beeping at the lower border is reproduced by smaller loudspeakers. It is clear that for most people this means nothing. And even if part of the signal is lost, will not be reproduced, no one will notice it.

We believe that those who have set themselves the goal of making an acoustic system on their own should critically evaluate the sound. It will be useful to know that a suitable speaker has two or more speakers in order to be able to reflect the sound of a wide band of the audible spectrum. But the subwoofer, even in complex systems, is one. This is due to the fact that low frequencies make the environment vibrate, penetrating even through walls. It becomes unclear where exactly the basses are coming from. Therefore, there is only one bass speaker - a subwoofer. But as for other things, the person will confidently say from which direction this or that special effect came (the ultrasound beam is blocked by the palm of your hand).

In connection with the above, we will divide the acoustic systems:

The sound in Mono format is unpopular, so we avoid touching on historical digressions.
Stereo sound is provided by two channels. Both contain low and high frequencies. Equal columns equipped with a pair of speakers (bass and squeak) are better suited.
Surround Sound is distinguished by the presence of a larger number of channels, creating a surround sound effect. We avoid getting carried away with subtleties, traditionally 5 speakers plus a subwoofer convey the gamut to music lovers. The structure is varied. Research is still ongoing to improve the quality of acoustic transmission. The traditional arrangement is as follows: at the four corners of the room (roughly speaking) along the column, the subwoofer is on the floor to the left or in the center, the front speaker is placed under the TV. The latter in any case is supplied with two speakers or more.

It is important to create the right enclosure for each speaker. Low frequencies will require a wooden resonator, for the upper end of the range it does not matter. In the first case, the sides of the box serve as additional emitters. You will find a video demonstrating the overall dimensions corresponding to the wavelengths of low frequencies in science, it practically remains to copy finished designs, the topic is devoid of practical literature.

The scope of tasks is outlined, readers understand that a home-made acoustic system is built with the following elements:

a set of frequency speakers according to the number of channels;
plywood, veneer, hull boards;
decorative elements, paint, varnish, stain.

Acoustic design

Initially, we select the number of columns, type, location. Obviously, to produce in a larger number than the home theater has channels is an unreasonable tactical move. A cassette recorder needs two speakers. At least six cases will be released for the home theater (there will be more speakers). According to the needs, accessories are built into furniture, the quality of bass reproduction is lame. Now the question of choosing speakers: in the publication of the authorship of Naidenko, Karpov, the nomenclature is given:

Bass - CA21RE (H397) 8" fit.
Medium range - 5" MP14RCY/P (H522) head.
Treble - head 27TDC (H1149) 27 mm.

They gave the basic principles for designing acoustic systems, proposed an electrical circuit for a filter that cuts the stream into two parts (a list of three subranges is given above), and gave the name of purchased speakers that solve the problem of creating two stereo speakers. We avoid repeating ourselves, readers can take the trouble to look through the section, find specific titles.

The next question is the filter. We believe that National Semiconductor will not be offended if we scan the drawing of the Ridiko translation amplifier. The figure shows an active filter powered by +15, -15 volts, 5 of the same type of microcircuits (op-amps), the cutoff frequency of the subranges is calculated by the formula shown in the image (duplicated by text):

P - Pi known to schoolchildren (3.14); R, C - ratings of the resistor, capacitance. In the figure, R \u003d 24 kOhm, C - is hushed up.

Active filter powered by electric current

Given the capabilities of the selected speakers, the reader will be able to choose a parameter. The characteristics of the column playback band are taken, the overlap junction between them is found, and the cutoff frequency is placed there. Thanks to the formula, we calculate the value of the capacitance. Avoid touching the resistance value, reason: it can (disputed fact) set the operating point of the amplifier, the transfer coefficient. On the frequency response given in the translation, which we omit, the boundary is 1 kHz. Let's calculate the capacity of the specified case:

C \u003d 1 / 2P Rf \u003d 1/2 x 3.14 x 24000 x 1000 \u003d 6.6 pF.

Not so hot what a large capacity is selected from the condition of the maximum allowable voltage. In a circuit with +15 and -15 V sources, it is unlikely that the nominal value exceeds the total level (30 volts), take a breakdown voltage (the reference book will help) of at least 50 volts. Don't try to put in DC electrolytic capacitors, the circuit has a chance of blowing up. There is no point in looking for the original circuit of the LM833 chip because of Sisyphean labor. Some readers will find a replacement chip that is different ... we hope for understanding.

As for the relatively small capacitance of capacitors (retail and total), the description of the filter says: due to the low impedance of the heads without active components, the ratings would have to be increased. Naturally causing the appearance of distortion due to the presence of electrolytic capacitors, coils with a ferromagnetic core. Feel free to move the range division boundary, the total bandwidth remains the same.

Passive filters will assemble with their own hands each trained in soldering, a school physics course. In an extreme case, enlist the help of Gonorovsky, there is nowhere better to describe the intricacies of the passage of signals through radio-electronic lines with nonlinear properties. The presented material interested the authors in low and high frequency filters. Those who want to divide the signal into three parts should read the works that reveal the basis of bandpass filters. The maximum allowable (or breakdown) voltage will be scanty, the value will become significant. To match the mentioned electrolytic capacitors with a nominal value of tens of microfarads (three orders of magnitude higher than those used by an active filter).

Beginners are concerned about the issue of obtaining a voltage of +15, -15 V powering speakers. Wind the transformer (an example was given, PC program Trans50Hz), supply a full-wave rectifier (diode bridge), filter, enjoy. Finally, buy an active or passive filter. This thing is called a crossover, carefully select the speakers, more accurately correlate the ranges with the filter parameters.

For passive speaker crossovers, you will find many calculators on the Internet (http://ccs.exl.info/calc_cr.html). The initial figures of the calculation program takes the input impedance of the speakers, the division frequency. Enter the data, the robot will quickly supply the capacitance and inductance values. On the given page, set the filter type (Bessel, Butterworth, Linkwitz-Riley). In our opinion, a task for the pros. The active stage shown above is formed by 2nd order Butterworth filters (frequency response reduction rate of 12 dB per octave). It concerns the frequency response (frequency response) of the system, it is clear only to professionals. When in doubt, choose the golden mean. In the literal sense, check the box on the third circle (Bessel).

Acoustics of computer speakers

I happened to watch a video on YouTube: the young man announced that he would make a speaker system with his own hands. The youth is talented: he ruined the speakers of a personal computer - well, none at all - brought into the world God's amplifier with a regulator, placed it in a matchbox (acoustic system case). Computer speakers are notorious for poor bass reproduction. The devices themselves are small, light, and secondly, the bourgeois save materials. Where does bass come from in an acoustic system? The young man took ... read on!

The most expensive component of the music center. Hi-end class acoustics bypasses a cheap apartment in cost. Repair, assembly of speakers is a good business.

The low-frequency amplifier of the speaker system will assemble an advanced radio amateur, no Kulibins are needed. A volume knob sticks out of a matchbox, input on one side, output on the other. The speakers of the old speaker system are small. The young man got hold of an old loudspeaker not of fabulous size, but solid. From a Soviet-era speaker system.

So that the sound would not disturb the air with a squeak, the clever boy knocked together inch boards in a box. The speaker of an old acoustic system was placed in the size of a mailbox, shifted, as is done by manufacturers of modern home theater subwoofers. I was too lazy to finish the speaker from the inside with a sound insulator. Those who wish can use batting or other similar material for the speaker system. Small speakers are placed inside oblong boxes, just containing the end of the loudspeaker. The proud lad connected one channel of the speaker system to two small speakers, the second to one large one. Works.

The young man is a fabulous fellow, does not drink in the alley, becoming like his peers, does not spoil future brides in his free time, is busy with business. As one acquaintance said: “The young generation is forgiven for the lack of knowledge and experience, not for the excess of arrogance reinforced by indifference.”

Improvements

We decided to improve the technique, frankly we hope that the addition will help make the speaker system a little better on its own. Problem? The concept was invented by radio engineers, the creators of acoustic systems - frequency. The vibration of the universe has a frequency. They say that even the human aura is inherent. It is not for nothing that each good speaker can accommodate several speakers. Large ones are for low frequencies, bass; others - for medium and high. Not only the size, but also the device they have is different. We have already discussed this issue and we refer those who are interested to the written reviews, where the classification of acoustic systems is given, the principles of operation of the most popular ones are revealed.

Computer scientists know the BIOS interrupt system buzzer, which seems to be capable of producing a single sound, but talented programmers have written fanciful melodies on it, even with an attempt at digital synthesis and voice reproduction. However, if desired, such a tweeter cannot produce bass.

Why this conversation ... A large speaker should not just be adapted to one of the channels, but bass specialization should be awarded. As you know, most modern compositions (we don’t take Sound Around) are designed for two channels (stereo playback). It turns out that two identical speakers (small ones) play the same notes, there is little point in this. At the same time, bass is lost from the same channel, and high frequencies die on a large speaker. How to be? We propose to introduce passive band-pass filters into the circuit, which will help to split the stream into two parts. We take the scheme of a foreign edition for the simple reason that it was the first to catch our eye. Here is a link to the original site chegdomyn.narod.ru. The radio amateur re-shot from the book, we apologize to the author for not indicating the source. This happens for the simple reason that it is not known to us.

So, picture. The words Woofer and Tweeter are immediately evident. As you might guess, this is, respectively, a subwoofer for low frequencies, and a speaker for high frequencies. The range of musical works is covered from 50-20000 Hz, and the subwoofer accounts for the low-frequency band. Radio amateurs themselves can calculate the bandwidths using well-known formulas, for comparison, for the first octave, as you know, is 440 Hz. We believe that such a division is suitable for our case. I would just like to find two large speakers, one for each channel. Let's see the diagram...

Not quite a musical scheme. In the position occupied by the system, the voice is being filtered. Range 300-3000 Hz. The switch is signed Narrow, translated as a stripe. To get Wide (wide) playback, omit the terminals. Music fans can throw away the Narrow bandpass filter, Skype surfers are advised to avoid a hasty decision. The circuit will completely exclude the microphone loop effect, known everywhere: a shrill buzz due to overamplification (positive feedback). A valuable effect, even the military knows the difficulties of using a speakerphone. The owner of the laptop is aware...

To eliminate the feedback effect, study the question, find at what frequency the system resonates, cut off the excess with a filter. Very comfortably. Regarding popular music, we turn off the microphone, take it away from the speakers (the case of karaoke), and start singing. We will leave the high and low pass filters unchanged, the products were calculated by unknown Western friends. For those who have difficulty reading foreign drawings, we explain, the diagram depicts (the Narrow band-pass filter is discarded):

Capacitance 4 uF.
Non-inductive resistances R1, R2 with a nominal value of 2.4 ohms, 20 ohms.
Inductance (coil) 0.27 mH.
Resistance R3 8 Ohm.
Capacitor C4 17 uF.

Speakers must match. Suggestions for this site. The subwoofer will be MSM 1853, the tweeter (the word was not written off) will be PE 270-175. You can calculate the bandwidth yourself. The capital letter Ω means komas - it's okay, change the denomination. Remember, the capacitances of capacitors connected in parallel add up like series-connected resistors. In case it is difficult to get suitable denominations. It is unlikely that it will be possible to make speakers with your own hands, it is realistic to dial small resistance values. Do not use coils, we cut out plates of nichrome, similar alloys. After manufacturing, the resistor is varnished, no high current is planned, the element should not be protected.

It is easier to wind inductors yourself. It is logical to use the online calculator, by setting the capacitance, we will get the parameters: number of turns, diameter, core material, core thickness. Let's give an example, avoiding being unfounded. We visit Yandex, we type something like "online inductance calculator". We get a number of issuance responses. We choose the site you like, we start thinking about how to wind the inductance of the speaker system with a nominal value of 0.27 mH. We liked the site coil32.narod.ru, let's get started.

Initial information: inductance 0.27 mH, frame diameter 15 mm, PEL wire 0.2, winding length 40 millimeters.

The question immediately arises, seeing the calculator, where to get the nominal diameter of the insulated wire ... We worked hard, found on the site servomotors.ru a table taken from the reference book, which is given in the review, consider it to your health. The diameter of copper is 0.2 mm, the insulated core is 0.225 mm. We boldly feed the values \u200b\u200bof the calculator, calculating the required values.

It turned out a two-layer coil, the number of turns is 226. The length of the wire was 10.88 meters with a resistance of about 6 ohms. The main parameters are found, we begin to wind. A home-made speaker system is made in a hand-made case, there is a place to fit the filter. We connect a tweeter to one output, a subwoofer to the other. A few words about amplification. It may be that the amplifier stage will not pull four speakers. Each scheme is characterized by a certain load capacity, you cannot jump higher. The loudspeaker design is designed with a fixed headroom to match the load, often using an emitter follower. The cascade that makes the circuit work, full return on any speaker.

Parting words to novice designers

We believe they helped readers understand how to properly design a speaker system. Passive elements (capacitors, resistors, inductors) can be obtained and made by everyone. It remains to assemble the speaker cabinet with your own hands. And for this, we believe, it will not. It is important to understand that music is shaped by a range of frequencies cut off by improper device manufacturing. If you are going to make a speaker system, think about it, look for components. It is important to convey the splendor of the melody, there will be firm confidence: the work was not in vain. The acoustic system will last a long time, it will give joy.

We believe that readers will enjoy making speaker systems with their own hands. The coming time is unique. Believe me, at the beginning of the 20th century it was impossible to draw tons of information every day. Training resulted in hard painstaking work. I had to rummage through the dusty shelves of the libraries. Rejoice in the internet. Stradivari impregnated the wood of violins with a unique composition. Violinists of today continue to choose Italian specimens. Think about it, 30 years have passed, the cart is left behind.

The current generation knows the brands of adhesives, the names of materials. Necessary is sold by shops. The USSR deprived people of abundance, providing them with relative stability. Today, the advantage is described by the possibility of inventing unique ways to earn money. A self-taught professional cuts down cabbages everywhere.

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 of listeners about the feeling of a piano flying around the room and other wonders of virtual spaces.

Contraperture

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

Minuses: The acoustic space differs noticeably from the sound stage conceived when recording a phonogram.

Other...

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

Nautilus from Bowers & Wilkins is one of the most unusual, expensive and authoritative speakers in terms of sound. Type of design - loading pipes

Such 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.

Many users are wondering: how to make computer speakers with your own hands? And this is not at all surprising, since only do-it-yourself work will not raise any doubts about the quality of the finished system. To create speakers for your computer at home, you will need the ability to handle a soldering iron and an understanding of basic electrical circuits. Yes, even without these skills and knowledge, you can try to create your own invention, but be prepared to face difficulties. If you are on fire to make speakers for your computer, we recommend that you familiarize yourself with each step of creating this useful device. In order to understand the following material, you will need a basic knowledge of school physics and a little perseverance.

We make a "bun"

Obviously, this popular component will not work without a box. The movement of air inside the structure causes the cone to move, which creates the sound volume.

Apparently, you will have to make a closed box with only one hole - for air circulation. Since you're building music hardware on a PC, there's no need for hefty speakers. The best option is factory car acoustics.

Important! This option will not provide you with a lot of air pressure, but it will be enough for a room with a computer.

Important! Do not look for incomprehensible low-pass filters on a large number of amplifiers. A passive filter, which is easily assembled from resistors and capacitors, is quite enough for you.

We make the case

The body needs very strong wood. Well suited for such purposes: chipboard and fiberboard. The thickness of the sheets should not exceed five millimeters, so that the whole structure is light in weight.

Important! If an old TV in a wooden case is lying around in the garage, then you can use this to create a quality box.

Use a jigsaw to cut out all the necessary elements. When creating the case, do not spare glue, self-tapping screws and other elements that provide fixation. Also focus on the front part in which the speaker will be installed.

Important! To achieve the desired rigidity, you should use wood slats that have a triangular shape. Pay attention to all small holes and gaps - they must be glued.

On the “back” do not forget to drill a hole for the cable, and make a connector on the outside in order to connect to the amp. It will be extremely convenient if any external blocks are not present in the design.

BP

How to make speakers for PC? The system must be powered by energy, so a little attention should be paid to the power supply.

Important! Do not use for the design those chips that have a bipolar supply, as it will be extremely difficult to get the right current for optimal performance.

Give preference to the design that will require a unipolar power supply with a voltage in the region of 12-24 V. Such measures in the future will have a positive effect on repairs, because it will be much easier to carry it out in the event of a breakdown.

What else needs to be considered? Pay attention to the following tips:

The output power of the transformer must significantly exceed the total power consumption of energy.
It is best to create one PSU for all components at once.
In order to achieve the greatest efficiency, place the power supply and filter with an amplifier only for the “roll”. It is better to mount ULF near the main speakers and tweeters. Such measures will help to ensure the least number of wires and the greatest economy.

Important! Do not forget that the sub is experiencing a lot of vibration, so all soldering should be done very high quality. All elements in the subwoofer must be firmly fixed.

Amplifier and power supply

It is better to fill the hole with a good sealant, and only after that mount the front panel. Her masters also recommend putting it on a sealant, and after drying, plant it on self-tapping screws.

After the entire box has completely dried, it is necessary to select the appropriate material and fit it. For a PSU, you can use one transformer, a rectifier bridge and about two or three electrolytic capacitors. Such a device will reproduce sound clearly and not create unnecessary interference.

Important! If you observe a small buzz, you should increase the value of the capacity of the electrolytes. If elements with a large capacity cannot be found, then you can simply stick several components parallel to each other.

Main columns

Here, for the case, you can take even wood, even plastic. Of course, it is better to choose the first material, since using it will help to achieve the best sound.

Important! If you are too lazy to process wood, then you can simply cheat and take the old devices from the radio and put them without changes.

As mentioned above, the amplifier and PSU will be in the box, so the finished speakers are simply connected to the desired outputs. If you want to do everything in the best possible way, it is recommended to resort to the following algorithm:

Create two enclosures for the main speakers. As an instruction, use the tips for making the box.
Use the material to fit the structure. Such measures will help to achieve a good sound.
Install two speakers in each cabinet.

Hello Datagor readers! I want to tell you about creating a speaker system using 3D printing technology. With the help of a 3D printer, I was able to build an unusual speaker system in the shape of a ball, as well as solve a number of additional problems that arise in the manufacture of acoustics.
I want to note that I do not at all advocate the use of plastic as the main material for building speakers.

Ever since my student days, I had a dream - to make columns in the form of balls. But the methods available to me in those days for creating a non-standard shaped case did not inspire me in any way. And now, after many years, I got a 3D printer.

Now here is my translation of Troels Gravesen's article about "the world's worst Philips AD 0160 dome tweeter". I think, Soviet, and many modern tweeters did not come across to him.
Most likely, few people will find this particular tweeter (tweeter, not to be confused with Twitter), but Troels' research will be useful for home-made people to assess the quality and proper use of tweeters.

Best regards, Sergei

I will show you with a real example what can be done with old speakers, namely with their speakers, in order to get an improved sound.

Speaker or speaker?
Acoustics and electronics
What is hifi
Speakers
Acoustics

Making loudspeakers with your own hands - this is where many begin their passion for a difficult, but very interesting thing - the technique of sound reproduction. Economic considerations often become the initial motivation: the prices for branded electroacoustics are overstated, not excessively, but outrageously impudent. If the sworn audiophiles, who do not skimp on rare tubes for amplifiers and flat silver wire for winding audio transformers, complain on the forums that the prices for acoustics and speakers for it are systematically inflated, then the problem is really serious. Do you want speakers for the house for 1 million rubles. pair? Please, there are more expensive ones. So The materials in this article are designed primarily for the very, very beginners: they need to quickly, simply and inexpensively make sure that the creation of their own hands, for which everything took dozens of times less money than for a “cool” brand, can “sing” no worse, or at least comparable. But probably, some of the foregoing will be a revelation for the masters of amateur electroacoustics- if it is honored by reading them.

Speaker or speaker?

Sound column (KZ, sound column) is one of the types of acoustic design of electrodynamic loudspeaker heads (GG, speakers), designed for technical and information sounding of large public spaces. In general, the acoustic system (AS) consists of a primary sound emitter (FROM) and its acoustic design, which provides the required sound quality. Home speakers are for the most part similar in appearance to loudspeakers, which is why they are nicknamed. Electroacoustic systems (EAS) also include an electrical part: wires, terminals, crossover filters, built-in audio frequency power amplifiers (UMZCH, in active speakers), computing devices (in speakers with digital channel filtering), etc. Acoustic design of household speakers is usually located in the body, which is why they look like more or less elongated columns.

Acoustics and electronics

The acoustics of an ideal speaker is excited over the entire audible frequency range of 20-20,000 Hz with one broadband primary IZ. Electroacoustics is slowly but surely moving towards the ideal, however, the best results are still shown by speakers with frequency separation into channels (bands) of LF (20-300 Hz, low frequencies, bass), MF (300-5000 Hz, medium) and HF (5000 -20,000 Hz, treble, treble) or LF-MF and HF. The first, of course, are called 3-way, and the second - 2-way. It is best to start mastering electroacoustics with 2-way speakers: they allow you to get sound quality up to high Hi-Fi (see below) inclusive at home without unnecessary costs and difficulties. The sound signal from the UMZCH or, in active speakers, low-power from the primary source (player, computer sound card, tuner, etc.) is distributed over the frequency channels by crossover filters; this is called channel defiltering, like crossover filters themselves.

The remainder of the article focuses primarily on how to make speakers that provide good acoustics. The electronic part of electroacoustics is a subject of special serious discussion, and not just one. Here it should only be noted that, firstly, at first it is not necessary to take on digital filtering that is close to ideal, but complex and expensive, but to apply passive filtering on inductive-capacitive filters. For a 2-way speaker, you need only one plug of low-pass/high-pass crossover filters (LPF/HPF).

There are special programs for the calculation of separation ladder filters AC, for example. JBL Speaker Shop. However, at home, the individual tuning of each plug for a specific instance of the speakers, firstly, does not affect production costs in mass production. Secondly, the replacement of the GG in the AU is required only in exceptional cases. This means that the filtering of the AC frequency channels can be approached unconventionally:

The frequency of the section LF-MF m HF is taken not lower than 6 kHz, otherwise you will not get a sufficiently uniform amplitude-frequency characteristic (AFC) of the entire speaker in the midrange region, which is very bad, see below. In addition, at a high crossover frequency, the filter is inexpensive and compact;
The prototypes for calculating the filter are links and half links of filters of type K, because their phase-frequency characteristics (PFC) are absolutely linear. Without observing this condition, the frequency response in the region of the crossover frequency will turn out to be significantly uneven and overtones will appear in the sound;
To obtain the initial data for the calculation, it is necessary to measure the impedance (impedance) of the LF-MF and HF GG at the crossover frequency. The GG 4 or 8 Ohms indicated in the passport are their active resistance at direct current, and the impedance at the crossover frequency will be greater. The impedance is measured quite simply: the GG is connected to an audio frequency generator (GZCH), tuned to the crossover frequency, with an output of at least 10 V to a load of 600 Ohms through a resistor of obviously high resistance, for example. 1 kOhm You can use low-power GZCH and UMZCH high fidelity. The impedance is determined by the ratio of the audio frequency (AF) voltages across the resistor and GG;
The impedance of the LF-MF link (GG, heads) is taken as the characteristic impedance? n of the low-pass filter (LPF), and the impedance of the HF head is taken as the characteristic impedance of the high-pass filter (HPF). The fact that they are different - well, the fool is with them, the output impedance of the UMZCH, "rocking" the speakers, is negligible compared to this and that;
From the side of the UMZCH, reflective-type low-pass and high-pass filters are installed so as not to overload the amplifier and not take power from the associated speaker channel. To GG, on the contrary, they turn to absorbing links, that the return from the filter did not give overtones. Thus, low-pass and high-pass speakers will have at least a link with a half link;

When joining electroacoustics, you need to know the following about how speakers are arranged and work in acoustic systems. The exciter of the speaker is a thin coil of wire oscillating in the annular gap of the magnetic system under the influence of an audio frequency current. The coil is rigidly connected to the sound emitter itself into space - a diffuser (for bass, midrange, sometimes for high frequencies) or a thin, very light and rigid dome diaphragm (for high frequencies, rarely - for midrange). The efficiency of sound emission strongly depends on the diameter of the IZ; more precisely, it depends on its relation to the wavelength of the emitted frequency, but at the same time, with an increase in the diameter of the IZ, the probability of occurrence of non-linear distortions (NI) of the sound due to the elasticity of the IZ material also increases; more precisely - not its infinite rigidity. They fight against NI in IZ by making radiating surfaces from sound-absorbing (anti-acoustic) materials.

The diameter of the cone is larger than the diameter of the coil, and in diffuser GGs, it and the coil are attached to the speaker housing with separate flexible suspensions. The diffuser configuration is a thin-walled hollow cone with its apex facing the coil. The suspension of the coil simultaneously holds the top of the diffuser, i.e. its suspension is double. The generatrix of a cone can be rectilinear, parabolic, exponential and hyperbolic. The steeper the cone of the diffuser converges to the top, the higher the return and the lower the NI dynamics, but at the same time its frequency range narrows and the radiation directivity increases (the radiation pattern narrows). The narrowing of the DN also narrows the area of the stereo effect and moves it away from the frontal plane of the speaker pair. The diameter of the diaphragm is equal to the diameter of the coil and there is no separate suspension for it. This drastically reduces the SOI GG, because. the diffuser suspension is a very noticeable source of NI sound, and the material for the diaphragm can be taken very hard. However, the diaphragm is capable of emitting sound well only at sufficiently high frequencies.

The coil and the diffuser or diaphragm, together with the suspensions, make up the mobile system (PS) of the GG. The PS has a frequency of its own mechanical resonance Fp, at which the mobility of the PS increases sharply, and a quality factor Q. If Q> 1, then the speaker without a properly selected and executed acoustic design (see below) at Fp will wheeze at a power less than the nominal one, not that peak, this is the so-called. blocking GG. Locking does not apply to distortions, because is a design and manufacturing defect. If 0.7

The efficiency of transferring the energy of an electrical signal from the energy to sound waves in the air is determined by the instantaneous acceleration of the diffuser / diaphragm (who is familiar with mathematical analysis - the second derivative of its displacement with respect to time), since air is highly compressible and highly fluid. The instantaneous acceleration of the coil pushing/pulling the diffuser/diaphragm must be somewhat greater, otherwise it will not "shake" the OUT. A few, but not much. Otherwise, the coil will bend and cause the emitter to vibrate, which will lead to the appearance of NI. This is the so-called membrane effect, in which longitudinal elastic waves propagate in the diffuser/diaphragm material. Simply put, the diffuser / diaphragm should “slow down” the coil a little. And here again there is a contradiction - the stronger the emitter “slows down”, the stronger it radiates. In practice, the "braking" of the emitter is done in such a way that its NI in the entire frequency and power range fit into the norm for a given Hi-Fi class.

Note, output: do not try to "squeeze" out of the speakers what they cannot. For example, speakers on 10GDSh-1 can be built with a frequency response unevenness at the midrange of 2 dB, but in terms of SOI and dynamics, it still pulls on Hi-Fi no higher than the initial one.

At frequencies up to Fp, the membrane effect never manifests itself, this is the so-called. piston mode of operation of the GG - the diffuser / diaphragm just go back and forth. Higher in frequency, the heavy diffuser is no longer able to keep up with the coil, the membrane radiation starts and gets stronger. At a certain frequency, the speaker begins to radiate only as a flexible membrane: at the junction with the suspension, its diffuser is already motionless. At 0.7

The membrane effect dramatically improves the return of GG, tk. the instantaneous accelerations of the vibrating sections of the IZ surface turn out to be very large. This circumstance is widely used by designers of HF and partially MF GG, the distortion spectrum of which immediately goes into ultrasound, as well as when designing GG not for Hi-Fi. SOI GG with a membrane effect and the evenness of the frequency response of speakers with them strongly depend on the mode of the membrane. In the zero mode, when the entire surface of the FM trembles as if in time with itself, Hi-Fi up to the middle inclusive can be achieved at low frequencies, see below.

Note: the frequency at which the HG switches from the “piston to the membrane”, as well as the change in the membrane mode (not growth, it is always integer) significantly depend on the diffuser diameter. The larger it is, the lower in frequency and stronger the speaker begins to “membrane”.

Woofers

High-quality piston woofers GG (simply - “piston”; in English woofers, barking) are made with a relatively small, thick, heavy and hard anti-acoustic cone on a very soft latex suspension, see pos. 1 in fig. Then Fr is below 40 Hz or even below 30-20 Hz, and Q

The periods of low-frequency waves are long, all this time the diffuser in the piston mode must move with acceleration, and therefore the diffuser stroke becomes long. Low frequencies without acoustic design are not reproduced, but it is always closed to one degree or another, isolated from free space. Therefore, the diffuser has to work with a large mass of so-called. of the attached air, for the “buildup” of which a significant effort is required (which is why piston GGs are sometimes called compression), as well as for the accelerated movement of a heavy diffuser with a low quality factor. For these reasons, the magnetic system of the piston GG has to be made very powerful.

Despite all the tricks, the return of the piston GG is small, because. it is impossible for a low-frequency diffuser to develop a large acceleration at long waves: the elasticity of the air is not enough to accept the energy given off. It will spread to the sides, and the speaker will go into locking. In order to increase the return and smoothness of the motion of the moving system (to reduce SOI at high power levels), designers go all out - they use differential magnetic systems, with half-scattering, and other exotics. THD is further reduced by filling the magnetic gap with a non-drying rheological fluid. As a result, the best modern pistons reach a dynamic range of 92-95 dB, and the THD at nominal power does not exceed 0.25%, and at peak power - 1%. All this is very good, but the prices - mom, don't worry! $1000 for a pair with differential magnets and refilling for home acoustics, matched in terms of output, resonant frequency and flexibility of the moving system, is not the limit.

Note: LF GG with rheological filling of the magnetic gap are suitable only for LF links of 3-way speakers, because completely incapable of working in the membrane mode.

Piston GGs have another serious flaw: without strong acoustic damping, they can mechanically collapse. Again, simply: behind the piston speaker there should be a kind of air cushion loosely connected to the free space. Otherwise, the diffuser at the peak will break off the suspension and it will fly out along with the coil. Therefore, you can not put the "piston" in any acoustic design, see below. In addition, piston GGs do not tolerate forced braking of the PS: the coil burns out immediately. But this is already a rare case, the speaker cones are usually not held by hand and matches are not inserted into the magnetic gap.

Craftsmen take note

There is a known “folk” way to increase the return of piston GGs: from the rear, without altering anything in dynamics, an additional annular magnet is firmly attached to the standard magnetic system with the repelling side. It is repulsive, otherwise, when a signal is applied, the coil will immediately be torn off from the diffuser. In principle, it is possible to rewind the speaker, but it is very difficult. And nowhere else has a rewinding speaker become better or at least remain the same as it was.

But it's not really about that. Enthusiasts of this refinement claim that the field of the external magnet concentrates the field of the standard one near the coil, which increases the acceleration of the PS and the return. This is true, but Hi-Fi GG is a very finely balanced system. Recoil is actually a little higher. But here the SOI at its peak immediately "jumps" so that sound distortions become well audible even to inexperienced listeners. At nominal, the sound can become even cleaner, but without Hi-Fi speakers it’s already high-fi.

Leading

So in English (managers) are called SC GG, because. it is the midrange that accounts for the vast majority of the semantic load of the musical opus. The requirements for the midrange GG for Hi-Fi are much softer, so most of them are made of a traditional design with a large cone, cast from cellulose mass along with the suspension, pos. 2. Reviews about the midrange of the dome and with metal diffusers are contradictory. The tone prevails, they say, the sound is harsh. Fans of the classics complain that the bowed speakers squeal from the "non-paper" speakers. Almost everyone recognizes the sound of the midrange GG with plastic diffusers as dull and at the same time hard.

The course of the diffuser of the midrange GG is made short, because. its diameter is comparable to the wavelengths of the MF and the transfer of energy into the air is not difficult. To increase the attenuation of elastic waves in the diffuser and, accordingly, reduce NI, along with expanding the dynamic range, finely chopped silk fibers are added to the mass for casting the Hi-Fi cone midrange GG, then the speaker operates in a piston mode in almost the entire midrange range. As a result of the application of these measures, the dynamics of modern midrange GG of the average price level turns out to be no worse than 70 dB, and THD at a nominal value of no more than 1.5%, which is quite enough for high Hi-Fi in a city apartment.

Note: silk is added to the cone material of almost all good speakers, it is a universal way to reduce THD.

Tweeters

In our opinion - squeakers. As you may have guessed, these are tweeters, HF YY. Spelled with a single t, it's not a gossip social media name. It would be generally easy to make a good “tweeter” from modern materials (the NI spectrum immediately goes into ultrasound), if not for one circumstance - the diameter of the emitter in almost the entire HF range turns out to be of the same order or less than the wavelength. Because of this, interference is possible on the emitter itself due to the propagation of elastic waves in it. In order not to give them a “hook” for radiation into the air at random, the diffuser / dome of the HF GG should be as smooth as possible, for this purpose the domes are made of metallized plastic (it absorbs elastic waves better), and the metal domes are polished.

The selection criterion for the HF GG is indicated above: dome ones are universal, and for fans of the classics who require necessarily “singing” soft tops, diffuser ones are more suitable. It is better to take these elliptical ones and put them in the speakers, orienting their long axis vertically. Then the dynamics of the dynamics in the horizontal plane will be wider, and the stereo zone will be larger. Still on sale there is a HF GG with a built-in horn. Their power can be taken as 0.15-0.2 of the power of the low-frequency link. As for technical quality indicators, any HF GG is suitable for Hi-Fi of any level, as long as it is suitable in terms of power.

Widths

This is a colloquial nickname for broadband GGs (GGSh) that do not require defiltering of AC frequency channels. The emitter of a simple GGSh with a common excitation consists of an LF-MF diffuser and a HF cone rigidly connected to it, pos. 3. This is the so-called. a coaxial radiator, which is why the GGSh is also called coaxial speakers or simply coaxes.

The idea of the GGSh is to give the membrane mode to the HF cone, where it does not particularly harm, and let the cone at the bass and at the bottom of the midrange work “on the piston”, for which the low-midrange cone is corrugated across. This is how broadband GGs are made for initial, sometimes average Hi-Fi, for example. mentioned 10GD-36K (10GDSH-1).

The first HF cone GGS went on sale in the early 50s, but they never achieved a dominant position in the market. The reason is the tendency to transient distortion and the delay in the attack of the sound because the cone dangles and sloshes from the shocks of the cone. Listening to Miguel Ramos playing the Hammond electric organ through a coax with a cone is unbearably painful.

Coaxial GGSh with separate excitation of LF-MF and HF emitters, pos. 4, this shortcoming is devoid of. In them, the RF link is driven by a separate coil from its own magnetic system. The sleeve of the HF coil passes through the LF-MF coil. PS and magnetic systems are located coaxially, i.e. along one axis.

GGSh with separate excitation at low frequencies in all technical parameters and subjective sound assessments are not inferior to piston GGs. On modern coaxial speakers, you can build very compact speakers. The disadvantage is the price. A coaxial for high Hi-Fi is usually more expensive than a LF-MF + HF set, although it is cheaper than LF, MF and HF for a 3-way speaker.

Auto

Car speakers formally also belong to coaxial speakers, but in reality they are 2-3 separate speakers in one case. HF (sometimes midrange) GG are suspended in front of the diffuser LF GG on the bracket, see on the right in fig. at the beginning. Filtering is always built-in, i.e. There are only 2 terminals on the case for connecting wires.

The task of auto speakers is specific: first of all, to “shout out” the noise in the car, so their designers don’t really struggle with the membrane effect. But for the same reason, auto-speakers need a wide dynamic range, at least 70 dB, and their diffusers are necessarily made with silk or use other measures to suppress higher membrane modes - the speaker should not wheeze even in a car on the move.

As a result, auto speakers are in principle suitable for Hi-Fi up to medium inclusive, if you choose the right acoustic design for them. In all the speakers described below, you can put auto-speakers of a suitable size and power, then there will be no need for a cutout for the HF GG and filtering. One condition: the standard terminals with clamps must be very carefully removed and replaced with lamellas for wiring. Speakers made from modern car speakers allow you to listen to good jazz, rock, even individual pieces of symphonic music and many chamber music. Of course, they won't pull Mozart's violin quartets, but very few people listen to such dynamic and meaningful opuses. A pair of auto speakers will cost several times, up to 5 times, cheaper than 2 sets of GG with filter components for a 2-way speaker.

frisky

Friskers, from frisky, this is how American radio amateurs called small-sized low-power GGs with a very thin and light cone, firstly, for their high output - a pair of “frisky” 2-3 W each sounds a room of 20 square meters. m. Secondly - for the hard sound: "frisky" work only in the membrane mode.

Manufacturers and sellers do not single out “frisky” in a special class, because. they are, in theory, not Hi-Fi. The speaker is like a speaker in any Chinese radio or cheap computer speakers like that. However, on the "frisky" one can make good speakers for the computer, providing Hi-Fi up to and including the average in the vicinity of the desktop.

The fact is that the "frisky" ones are able to reproduce the entire sound range, you only need to reduce their SOI and smooth out the frequency response. The first is achieved by adding silk to the diffuser, here you need to navigate by the manufacturer and his (not trade!) Specifications. For example, all GGs of the Canadian company Edifier with silk. By the way, Edifier is a French word and is read "edifier" and not "idifier" in the English manner.

The frequency response of the "frisky" is leveled in two ways. Small bursts / dips are already removed by silk, and larger bumps and troughs are eliminated by acoustic design with free exit to the atmosphere and a damping pre-chamber, see fig.; see an example of such an AS below.

Acoustics

Why do you need acoustic design at all? At low frequencies, the dimensions of the sound emitter are very small compared to the length of the sound wave. If you just put the speaker on the table, the waves from the front and rear surfaces of the diffuser will immediately converge in antiphase, cancel each other out, and you won’t hear bass at all. This is called an acoustic short circuit. You can’t just muffle the speaker from the rear to the bass: the cone will have to strongly compress a small volume of air, which is why the resonance frequency of the PS will “jump” so high that the speaker simply cannot reproduce the bass. From here follows the main task of any acoustic design: either to extinguish the radiation from the rear side of the GG, or to turn it over by 180 degrees and re-emit it in phase from the front of the speaker, while at the same time preventing the expenditure of the energy of the diffuser movement on thermodynamics, i.e. on compression-expansion of air in the AC case. An additional task is, if possible, to form a spherical sound wave at the output of the speaker, because in this case, the stereo effect zone is the widest and deepest, and the effect of room acoustics on the sound of the speakers is the least.

Note, an important corollary: for each speaker cabinet of a specific volume with a specific acoustic design, there is an optimal excitation power range. If the output power is low, it will not swing the acoustics, the sound will be dull, distorted, especially at low frequencies. An excessively powerful GG will go into thermodynamics, which will cause blocking.

The purpose of the speaker cabinet with acoustic design is to provide the best reproduction of low frequencies. Durability, stability, appearance - by itself. Acoustically, home speakers are designed in the form of a shield (speakers built into furniture and building structures), an open box, an open box with an acoustic impedance panel (PAS), a closed box of normal or reduced volume (small-sized acoustic systems, MAC), a phase inverter (FI), passive radiator (PI), direct and reverse horns, quarter-wave (HF) and half-wave (HF) labyrinths.

Built-in acoustics is a subject of special discussion. Open boxes from the era of tube radios, it is unrealistic to get an acceptable stereo from them in an apartment. Of the others, it is best for a beginner for his first AS to opt for a PV labyrinth:

Unlike others, except FI and PI, PV labyrinth allows you to improve bass at frequencies below the natural resonant frequency of the woofer.
Compared to the FI PV, the labyrinth is structurally and easy to set up.
Compared to PI PV, the labyrinth does not require expensive purchased additional components.
The cranked PV labyrinth (see below) creates a sufficient acoustic load for the GG, while at the same time having a free connection with the atmosphere, which makes it possible to use low-frequency GG with both long and short diffuser strokes. Up to replacement in already built speakers. Of course, only a couple. The radiated wave in this case will be almost spherical.
Unlike all, except for the closed box and the HF labyrinth, the acoustic column with the PV labyrinth is able to smooth out the frequency response of the LF GG.
Speakers with a PV labyrinth are structurally easily pulled into a tall thin column, which facilitates their placement in small rooms.

As for the penultimate point - are you surprised if experienced? Consider this one of the promised revelations. And see below.

PV maze

Labyrinths are often considered acoustic design such as a deep slot (Deep Slot, a type of HF labyrinth), pos. 1 in Fig., and convolutional reverse horn (pos. 2). We will touch on the horns, but as for the deep slot, this is actually a PAS, an acoustic shutter that provides free communication with the atmosphere, but does not let sound out: the depth of the slot is a quarter of the wavelength of its tuning frequency. It is easy to verify this by measuring the sound levels in front of the front of the speaker and in the opening of the slot using a highly directional microphone. Resonance at multiple frequencies is suppressed by lining the gap with a sound absorber. A deep slot speaker also dampens any speakers, but raises their resonant frequency, albeit less than a closed box.

The initial element of the PV labyrinth is an open half-wave pipe, pos. 3. As an acoustic design, it is unsuitable: while the wave from the rear reaches the front, its phase will be reversed by another 180 degrees, and the same acoustic short circuit will turn out. On the frequency response of the PV, the pipe gives a high sharp peak, causing the GG to lock at the tuning frequency Fn. But what is already important - Fn and the natural resonance frequency of the GG f (which is higher - Fp) are theoretically not related to each other, i.e. bass can be expected to improve below f (Fp).

The easiest way to turn a pipe into a maze is to bend it in half, pos. 4. This will not only phase the front with the rear, but also smooth out the resonant peak, because the paths of the waves in the pipe will now be different in length. In this way, in principle, it is possible to smooth the frequency response to any predetermined degree of evenness by increasing the number of knees (it should be odd), but in reality it is very rare to use more than 3 knees - the damping of the wave in the pipe interferes.

In the chamber PV labyrinth (pos. 5), the knees are divided into the so-called. Helmholtz resonators - cavity tapering towards the rear end. This further improves the damping of the HG, smoothes the frequency response, reduces losses in the labyrinth and increases the radiation efficiency, because. the rear exit window (port) of the labyrinth always works with "backwater" from the last chamber. Having partitioned the chambers on intermediate resonators, pos. 6, it is possible to achieve a frequency response with a diffuser GG that almost satisfies the requirements of absolute Hi-Fi, but setting up each of a pair of such speakers requires somewhere from six months (!) of the work of an experienced specialist. Once upon a time, in a certain narrow circle, the labyrinth-chamber speaker with chamber separation was called Cremona, with a hint of the unique violins of Italian masters.

In fact, to obtain a frequency response for high Hi-Fi, it turns out that just a pair of cameras on the knee is enough. Drawings of speakers of this design are given in Fig; on the left - Russian development, on the right - Spanish. Both are very good outdoor acoustics. “For complete happiness”, it would not hurt the Russian woman to borrow the Spanish stiffness ties that support the partition (beech sticks with a diameter of 10 mm), and in return to give a smoothing of the pipe bend.

In both of these speakers, one more useful property of the chamber labyrinth is manifested: its acoustic length is greater than the geometric one, because the sound lingers somewhat in each chamber before passing on. Geometrically, these labyrinths are tuned to somewhere around 85 Hz, but measurements show 63 Hz. In reality, the lower limit of the frequency range is 37-45 Hz, depending on the type of LF GG. When the S-30B's filtered speakers are rearranged into such enclosures, the sound changes amazingly. For the better.

The excitation power range for these speakers is 20-80 W peak. Sound-absorbing lining here and there - synthetic winterizer 5-10 mm. Tuning is not always necessary and easy: if the bass is deaf, the port is covered symmetrically on both sides with pieces of foam until the optimal sound is obtained. This should be done slowly, each time listening to the same segment of the phonogram for 10-15 minutes. It must have strong mids with a sharp attack (mids control!), For example, a violin.

jet flow

The chamber labyrinth is successfully combined with the usual tortuous one. An example is the desktop acoustic system Jet Flow (jet stream) developed by American radio amateurs, which made a splash in the 70s, see fig. on right. Case width on the inside - 150-250 mm for speakers 120-220 mm, incl. "frisky" and autodynamics. Body material - pine, spruce, MDF. Sound-absorbing lining and adjustment are not required. Excitation power range - 5-30 W peak.

Note: there is confusion with Jet Flow now - jet sound emitters are sold under the same brand.

For high-spirited and computer

It is also possible to smooth out the frequency response of auto-speakers and “frisky” ones in an ordinary convoluted labyrinth by arranging a compression damping (not resonating!) prechamber in front of its entrance, indicated by K in fig. below.

This mini speaker is designed for PC instead of the old cheap one. The speakers used are the same, but how they start to sound is simply amazing. If the diffuser is with silk, otherwise it makes no sense to fence the garden. An additional advantage is a cylindrical body, on which the midrange interference is close to the minimum, it is less only on a spherical body. Working position - with an inclination forward-up (AC - sound projector). Excitation power - 0.6-3 W nominal. Assembly is carried out in the following. order (glue - PVA):

For children 9 glue a dust filter (you can use scraps of nylon tights);
Det. 8 and 9 are pasted over with synthetic winterizer (indicated in yellow in the figure);
Assemble a package of partitions on the screed and spacers;
Glue the padding rings marked in green;
The package is wrapped, gluing, with whatman paper to a wall thickness of 8 mm;
The body is cut to size and the prechamber is pasted over (highlighted in red);
Paste children. 3;
After complete drying, they sand, paint, attach a stand, mount the speaker. Wires to it pass along the bends of the labyrinth.

About horns

Horn speakers have a high return (remember why he just does it, a mouthpiece). The old 10GDSH-1 yells through a horn so that the ears wither, and the neighbors “I can’t be happy at all”, which is why many are addicted to horns. In home speakers, convoluted horns are used as less bulky. The reverse horn is excited by the rear radiation of the GG and is similar to the PV labyrinth in that it rotates the phase of the wave by 180 degrees. But otherwise:

Structurally and technologically much more complicated, see fig. below.
It does not improve, but on the contrary, spoils the frequency response of the speakers, because The frequency response of any horn is uneven and the horn is not a resonating system, i.e. it is impossible to correct its frequency response in principle.
The radiation from the horn port is significantly directed, and its wave is rather flat than spherical, so a good stereo effect cannot be expected.
It does not create a significant acoustic load of the GG and at the same time requires significant power for excitation (we also remember whether they whisper into a speakerphone). The dynamic range of horn speakers can be extended at best to basic Hi-Fi, and for piston speakers with a very soft suspension (and therefore good and expensive ones), the cone breaks out very often when the GG is installed in the horn.
Gives overtones more than any other type of acoustic design.

Frame

The speaker cabinet is best assembled on beech dowels and PVA glue, its film retains its damping properties for many years. For assembly, one of the sidewalls is placed on the floor, the bottom, lid, front and rear walls, partitions are placed, see fig. on the right, and cover with the other sidewall. If the outer surfaces are to be finished, steel fasteners can be used, but always with gluing and sealing (plasticine, silicone) of non-glue seams.

Much more important for sound quality is the choice of body material. The ideal option is a musical spruce without knots (they are a source of overtones), but it is unrealistic to find its large boards for speakers, because Christmas trees are very knotty trees. As for the plastic cases of the speakers, they sound good only in industrial production, solid-cast, and amateur home-made products made of transparent polycarbonate, etc., are a means of self-expression, not acoustics. They will tell you that this sounds good - ask to turn it on, listen and believe your ears.

In general, it is difficult with natural wood materials for speakers: completely straight-grained pine without defects is expensive, and other available building and furniture species give overtones. It is best to use MDF. The Edifier mentioned above has long since completely switched to it. The suitability of any other tree for AS can be determined as follows. way:

The test is carried out in a quiet room, in which you yourself must first stay in silence for half an hour;
Piece of board approx. 0.5 m is placed on prisms from segments of a steel corner, laid at a distance of 40-45 cm from each other;
The knuckle of a bent finger knocks approx. 10 cm from any of the prisms;
Repeat tapping exactly in the center of the board.

If in both cases the slightest ringing is not heard, the material is suitable. The better, the softer, duller and shorter the sound. According to the results of such a test, you can make good speakers even from chipboard or laminate, see the video below:

Video: do-it-yourself simple laminate speaker for your phone

spikes

Floorstanding and desktop speakers are installed on special legs - acoustic spikes - which exclude the exchange of vibrations between the speakers and the floor or tabletop. Acoustic spikes are on sale, but the prices - you know, a special product. So, weights for building and carpentry plumb lines have exactly the same configuration (cylinder turning into a cone with a rounded nose) and material properties. Price - you know. Feel free to put any speakers on spikes made of weights for plumb lines, they will cope with an unusual task for them perfectly.