What sound-absorbing and sound-proofing materials to choose. DIY bass trap (low frequency absorber) Sound absorbing material for speakers

In soundproofing noise with a pronounced low-frequency component (thumping drums, special effects when watching a movie), which can be heard on all adjacent walls, it is necessary to use a “room-in-room” design. The term implies the installation of a “floating” floor on a sound-absorbing substrate and cladding of walls and ceilings on a vibration-decoupled frame. For example, the most effective and at the same time cost-effective way to combat impact noise from a neighbor above (sounds of footsteps, moving furniture, etc.) is an acoustic “floating” floor in an upper-level room. It is much easier to control noise where it occurs than to carry out expensive measures to soundproof all structures along which it is distributed.

In soundproofing low-frequency sound, what is more important is not the number of dense layers in the wall cladding, but the distance between the wall and the dense layers - the greater the distance from the wall, the less low frequencies will penetrate into the room.

Soundproofing a single element of the building envelope (floor, ceiling or one wall) will not always solve the problem of soundproofing an apartment. The effectiveness of this measure will depend on how pronounced the indirect transmission of noise through the enclosing structures is. For example, if it is heard only on the wall adjacent to the neighbor and does not re-radiate to others, then soundproofing cladding of one wall with soundproofing material will most likely solve the problem. If noise can also be heard on adjacent walls, then sound insulation of one wall will be ineffective. It is advisable to draw a plan of the apartment indicating the thickness of the walls and partitions and the places where you hear the sound when listening to them. This will help you get a clear picture of areas of high sound emission and choose an adequate sound insulation solution.

Fighting sound at the source

This is the most effective, but, unfortunately, not always feasible method of sound insulation. For example, the most effective and at the same time cost-effective way to combat impact sound from a neighbor above (sounds of footsteps, moving furniture, etc.) is an acoustic “floating” floor in an upper-level room. It is much easier to control sound at the point of origin than to carry out expensive measures to soundproof all structures through which it spreads.

Considering the fact that almost all new buildings are being rented today without interior finishing, with inter-apartment fences that do not comply with current sound insulation standards, answer the question: who besides you will invest in your comfort?.

There is no such method of sound insulation as covering the room with some thin material. The materials offered on the market are used only as part of soundproofing structures. For example, high material density " Texound» increases the weight of structures, taking up virtually no space. This means that it is possible to achieve high sound insulation rates due to the minimum thickness and is used as a damping (anti-resonance) gasket between layers of plasterboard, and together with a soft layer of sound-absorbing material, better results can be achieved. In thin partitions and acoustic ceilings, this property of the material allows you to achieve an effect that can be compared to creating an additional concrete wall 20 cm thick. This will be enough to reduce disturbing noise to a level that will never bother you and your family members. Pasting the walls or ceiling directly with Texound material will not affect the acoustic properties of the room in any way.

What not to do

When faced with the problem of sound insulation, you have probably already received many recommendations from friends and store consultants. The list of recommended materials usually comes down to a short list: polystyrene foam, cork, polyethylene foam, egg trays. The listed materials do not belong to soundproofing materials and are not used as part of soundproofing structures.

Some craftsmen use polystyrene foam, cork, and polyethylene foam as part of floating floor structures. The effectiveness of designs incorporating these materials in reducing percussion sound not high.

Taking advantage of widespread myths about the “soundproofing” properties of the mentioned materials, their manufacturers and sellers persistently exaggerate and support these myths, without going into the subtleties of physical processes or particularly terminology.

Sound absorption index of the mentioned materials (the ratio of unreflected sound wave energy to radiated energy) does not exceed 0.3, while materials with a sound absorption index of 0.7 - 1 are considered sound absorbing.

Fact: cladding a wall with polystyrene foam (expanded polystyrene) followed by plastering is practically not will reduce apartment sound insulation index. In other words, if you plan to use polystyrene foam, cork, polyethylene foam as a sound-absorbing material, it’s time to abandon this idea.

Also, do not waste your time and money on “sound insulation” with carpets, mattresses, straw, reeds, “special” wallpaper and paints, cellulose plasters - some of the listed materials, although they have insignificant sound-absorbing properties, but this is not the point: The task is to prevent the penetration of extraneous noise into the room, and not to absorb noise that has already penetrated.

Filling the voids of the frame with sound-absorbing material

The free space inside the frame is filled in order to reduce resonance phenomena in the partition.

Acoustic mineral wool with a density of 30-50 kg/m3 is an effective sound-absorbing material. Fill spaces to at least half the total volume of the space.

In protection against low-frequency noise, an important role is played by the increase in the surface mass of the sheathing and the distance between the wall and the reflective layer of the structure - the further the dense layers are from the wall, the higher the sound-insulating ability of the structure at low frequencies. The installation of independent frames for partitions will reduce the indirect transmission of noise through the frame elements.

The use of Tecsound plastic membranes between layers of frame sheathing:

For three-layer sheathing, the spacer should be placed between the outer and middle layers.
The frame covering should be flexible and massive, so you should not try to increase the rigidity of the frame.
Shift the holes for sockets, electrical outlets, and switches relative to each other for each of the partition skins (the holes in the partition should not be through).

Instructions for installation of soundproofing partitions and wall cladding

Depending on the height of the plasterboard partition being erected, the expected load, and the desired level of sound insulation, profiles with a width of 50, 75 or 100 mm are used.

To limit the re-radiation of vibration (noise) from the enclosing structures to the frame, and as a result, to its cladding, a sound-proof profile with built-in vibration isolation units is used.
Spread the backing under the guide profile, extending it 25 mm from the installation side of the plasterboard sheet.
Lay the profile on the substrate, drill holes with a hammer drill for anchor fastening through the vibration isolation unit and secure the profile.
After installing the guide profile on the floor and ceiling, insert the rack profile into it in increments of 600, 400 or 300 mm.
If the cantilever load on the partition is large (for example, you need to hang a TV, bookshelves, etc.), then the rigidity of the partition frame can be increased by using wooden inserts and reducing the distance between the posts.
Fill the space between the profiles with acoustic mineral wool with a density of 50-60 kg/m3.
Recommendations for constructing the frame:
The installation of a double frame for a partition with a distance between them of 5 mm will increase the soundproofing properties of the structure. For example, the installation of two independent frames using a 50 mm profile, instead of one with a 100 mm profile.
The construction of independent partition frames will reduce the indirect transmission of vibration through the frame elements.

A little about common installation mistakes

Let's consider two aspects of sound insulation of such a design.

Airborne sound insulation(sound waves propagating in an elastic medium of air).

A loud music center, and even a normal conversation behind the wall, causes the fence to vibrate - this is one way for an unwanted sound wave to penetrate the room.

Craftsmen often connect the structure frame to the wall in order to ensure high “reliability” of the structure.

These rigid connections transmit the vibration of the wall with virtually no loss to the frame and cladding, which, as a result, vibrates and emits sound in the room. If the space is not filled with sound-absorbing material, then the air (as a spring) enhances the noise emission at the natural resonance frequency of the system.

If the space is filled with sound-absorbing material, then it remains unused, since the two reflective layers of the structure are rigidly connected and vibrate almost synchronously.

Therefore, the frame of the wall cladding is either not connected to the protected fence, or is connected with special vibration-decoupling fasteners if a high cantilever load is planned on the wall cladding (kitchen cabinets, bookshelves, etc.).

Soundproofing of structural noise(sound waves propagating along enclosing structures).

In the absence of acoustic decoupling of the frame from the enclosing structures of the room, structural noise conducted by the walls and ceilings will easily be re-radiated onto the structure frame and its cladding. The frame skin, vibrating, emits a sound wave into the room in the form of airborne noise.

A soundproofing partition or wall cladding is a resonant type structure, which from a physics point of view can be considered as an oscillatory system [mass1]-[spring]-[mass2], Where mass1 And mass2- these are reflective layers (sheathing a frame or wall with soundproofing material), and spring- this is a layer of effective sound-absorbing material (in the partition it is between the soundproofing materials, and in the wall it is the first layer, i.e. in front of the soundproofing material).

No need to strive to create structures with more than two reflective layers, and more than one gap between them, as this reduces the efficiency of the design at low frequencies. When installing partitions, it is better to sheathe the frame of the soundproofing structure different number of layers , consisting of materials with different mechanical properties and different thicknesses (for example, gypsum fiber board with a thickness of 10 mm and gypsum board with a thickness of 12.5 mm) - in this case, there is a mismatch in the frequencies of the wave coincidence of the sheathing layers (the critical frequency of the layer), which leads to an increase in additional insulation by 2-3 dB.

Soundproofing structures

The general principle of a soundproofing structure is the alternation of massive (reflective) and porous (sound-absorbing) layers.

The main factors influencing the sound insulation of a structure are:

acoustic decoupling at junctions with the floor, ceiling, and walls;
the relationship of the soundproofing structure to the protected enclosing structure;
the mass of the reflective layer of the structure.

The use of effective sound-absorbing material inside the frame and several layers of its cladding will not provide a potentially possible 15 dB of additional sound insulation if the frame is installed without acoustic isolation from the enclosing structures (floor, ceiling, walls).

Structural noise is easily re-radiated through the so-called “sound bridges” (profile fastening points, its laying on a rigid base) onto the frame and its cladding.

"Floating“consider a floor built on a layer of sound-absorbing material that does not have rigid connections with the floor slab, walls, communications (heating, ventilation pipes) and other building structures.

For this purpose, the floating floor screed must be separated along the contour from the walls, communications and other building structures by gaps at least 1 cm wide containing sound-absorbing material.

The “floating” floor design is the most effective means of noise protection for interfloor ceilings. Its protective ability is “symmetrical”, i.e. it not only prevents the transmission of noise from falling objects, the sound of footsteps, and the movement of furniture from a neighbor above, but also in the opposite direction - it significantly reduces noise from a neighbor below, for example, low-frequency sound from a home theater, etc. The design adds 6-10 dB of airborne sound insulation to the floor . For overlap this is a very high figure.

One of the most important components of an acoustic system is the speakers. Moreover, not only their technical characteristics are of great importance, but also the material from which they are made. The fact is that the material affects the sound quality. In addition, their cost, and therefore the cost of the entire speaker system, directly depends on what the speakers are made of. In this article we will look at the advantages and disadvantages of the different types of material that speakers can be made from.
Acoustic systems - what are they?
The speaker system is the most important component in any audio equipment. Without it, sound is unthinkable at all, since it is responsible for converting an electrical impulse directly into a sound signal. There are different classifications of acoustic systems:

Based on the method of connection to the amplifier, acoustics are divided into active (the amplifier is built into the system) and passive (the amplifier is external).
In terms of size, acoustic systems can be bookshelf or floor-standing.
Based on cost, acoustics are divided into categories: budget, Hi-Fi and Hi-End classes.

Separately, we note all-weather systems, which are distinguished by their ability to work even in the most extreme conditions: outdoors, in the rain, at high and low temperatures.
Another special category is Lifestyle acoustics, which are distinguished by a combination of exclusive design and high-quality sound.
Basic requirements for a high-quality acoustic system
The requirements for an acoustic system largely depend on the purposes for which you plan to use it. In particular, if the speakers are intended for watching videos, their main task is to accurately convey the voices of the characters, music and audio effects. But the most stringent requirements are placed on systems designed for listening to music. In any case, one rule applies: the less distortion, the better.
Ideally, the speaker system should have the following characteristics:

Having sufficient power will be one of the guarantees of minimal sound errors.
Reproduce the audio frequency band accessible to the human ear - from 20 Hz to 20,000 Hz.
Accurately convey the sound stage - both when listening to stereo and multi-channel sound, which is traditionally equipped with most home theaters today.
Correspond to the size of the room in terms of acoustic pressure, more often called volume.

Another important requirement: acoustics must satisfy the emotional and aesthetic needs of the buyer not only with their sound, but also with their appearance.
Why is the acoustic enclosure important?
The sound in the speakers is converted from an electrical impulse into a sound one. In this case, the main load falls on the speakers and filters. But without a quality case, all the hard work these elements do can simply come to naught. Here are the basic requirements for a high-quality acoustic enclosure:

It must be made of high quality material
During the manufacture of the housing, all technological standards and parameters must be observed.
The housing must be rigid enough to provide a good combination of absorption/reflection of sound waves of a certain frequency and power.

Modern speaker manufacturers use a wide variety of materials to create them. For example, there are speakers with glass bodies that create the visual effect of a waterfall. Some open-type speaker systems do not have a cabinet at all.
The main materials for the production of speaker cabinets today are plastic, wood, and metal. Let's take a closer look at them.
Plastic

Plastic speakers are usually the most affordable. This material has been used for quite some time, and its features make it possible to produce speakers of various shapes. Low cost is one of the reasons why budget acoustics are usually equipped with plastic speakers.
Among the shortcomings we note:

numerous shortcomings in sound,
rattling at medium and high volumes,
mid-frequency resonances.

But this does not mean that all plastic speakers transmit low quality sound. Many manufacturers make high-quality acoustics from plastic. For this purpose, special technologies and proprietary developments are used, which, naturally, are not included in the category with the most affordable prices. For example, the German company Bell-Audio has patented a technology for manufacturing cases from two-layer monolithic plastic, whose properties are not inferior to twenty layers of Karelian birch.
Thus, when choosing a speaker system, it is better to pay attention to the quality of the plastic from which the body is made.
Tree

This material is considered the best for the production of speaker systems.
But there are some subtleties here. The best speakers are made from solid wood, but it is used quite rarely and only in elite segments, since it requires rather complex processing. Ideally, raw materials should be selected at the cutting stage, kept for a long time, and dry naturally, without artificial acceleration. Almost all operations must be done manually. Therefore, the elitism and high cost of real wooden speakers is understandable.
Today, in the production of wooden cabinets, plywood, chipboard (chipboard) and MDF (medium density fiberboard) are most often used.
Plywood.
High-quality plywood, as a rule, has many layers - from 12 to more. Pros: good absorption properties, lighter than chipboard and MDF, less susceptible to delamination. But high-quality plywood is an expensive material, so its use in mass production is limited.
Chipboard.
Significantly cheaper than solid wood and plywood. At the same time, it has certain advantages. In particular, slabs with a thickness of more than 16 mm have a high density, and this characteristic helps to reduce cabinet resonances. In addition, due to its structure, chipboard does not introduce its own overtones.
Among the disadvantages: the problem of delamination and moisture absorption, which the fiberboard is susceptible to. It can be solved using special painting or cladding with various materials.
Given its availability and good acoustic characteristics, chipboard is used by many manufacturers.
MDF.
The most common material. It appeared as a result of improvements in the technologies used in the production of chipboards. MDF is made from dried wood fibers, treated with synthetic binders and formed into a carpet, followed by hot pressing, and lined with natural or synthetic veneer.
Despite the simple technology of production and processing, even medium-density boards can surpass wood in resistance to mechanical damage and moisture resistance.
The main advantages of MDF are good absorption of sound vibrations and provision of mechanical rigidity to the speaker body. This explains the frequency of use in the production of speakers of various price categories.
Metal

Typically, aluminum, or rather its alloys, are used to make speaker housings. These materials have good mechanical properties: rigidity, density and lightness. According to many experts, aluminum can reduce resonance and improve the transmission of high frequencies in the sound spectrum. In addition, when exposed to air, this metal is covered with a thin, colorless film, which protects it from oxidation. Therefore, it is often used to make all-weather systems.
Due to their flexibility, aluminum and its alloys are often used to make Lifestyle speakers. But there is also a drawback that experienced “audiophiles” note: the sound of such systems has something “metallic” in it.
Which material should you prefer?
Important note: none of the materials used in the manufacture of speaker systems by themselves provide high-quality sound.
What matters is not what the acoustics are made of, but how exactly this happened. Only by observing all technological parameters during the production and assembly of the cabinet, and then by fine-tuning and fine-tuning the electronic components, can you obtain the ideal sound of the speaker system.
In addition, ideal sound is, in many ways, an individual characteristic. Therefore, when choosing speakers, be sure to focus on your personal emotional perception. After all, even the most expensive speakers may not transmit sound the way you would like to hear it.
We wish you happy shopping!

This new series of articles is dedicated to acoustic systems. Due to the fact that the topic is extremely broad, we decided to create a series of publications reflecting the selection criteria when purchasing speakers. This article focuses on the acoustic properties of cabinet materials and acoustic design. The post will be especially useful for those who are faced with choosing speakers, and will also provide information for people who want to create their own speakers in the process of their DIY experiments.

There is an opinion that one of the decisive factors affecting the sound of speakers is the material of the housing. PULT experts believe that the importance of this factor is often exaggerated, however, it is truly important and cannot be written off. An equally important factor (among many others) that determines the sound of speakers is the acoustic design.

Material: from plastic to granite and glass

Plastic - cheap, cheerful, but resonates

Plastic is often used in the production of budget speakers. The plastic body is lightweight, significantly expands the possibilities of designers; thanks to casting, almost any shape can be realized. Different types of plastics differ greatly in their acoustic properties. In the production of high-quality home acoustics, plastic is not very popular, but it is in demand for professional samples, where low weight and mobility of the device are important.

(for most plastics the sound absorption coefficient ranges from 0.02 - 0.03 at 125 Hz to 0.05 - 0.06 at 4 kHz)

A typical representative of the “plastic brotherhood” in home acoustics with decent characteristics and an attractive price: Bookshelf acoustics

Tree - from felling to golden ears

Due to its good absorption properties, wood is considered one of the best materials for making speakers.

(the sound absorption coefficient of wood, depending on the species, ranges from 0.15 – 0.17 at 125 Hz to 0.09 at 4 kHz)

Solid wood and veneer are used relatively rarely for the production of speakers and, as a rule, are in demand in the HI-End segment. Wooden speakers are gradually disappearing from the market due to low manufacturability, instability of the material and prohibitively high cost.

It is interesting that in order to create truly high-quality speakers of this type that meet the requirements of the most sophisticated listeners, technologists must select material at the cutting stage, as in the production of acoustic musical instruments. The latter is related to the properties of wood, where everything is important, from the area where the tree grew, to the humidity level of the room where it was stored, the temperature and duration of drying et cetera. The latter circumstance complicates DIY development; in the absence of special knowledge, an amateur creating a wooden speaker is doomed to act by trial and error.

Manufacturers of such acoustics do not report how the situation really is and whether the described conditions are met, and accordingly, any wooden system requires careful listening before purchasing. With a high degree of probability, two speakers of the same model from the same breed will sound slightly different, which is especially important for some demanding listeners.

Columns from an array of valuable rocks are available in units, their cost is astronomical. Everything yours truly has heard sounds excellent. However, in my subjectively pragmatic opinion, it is disproportionate to the cost. Sometimes, well-designed enclosures made of plywood and MDF have no less musicality, but for many audiophiles “not wood” = “not true hi-end”, and for some, “not wood” simply does not allow the status or spoils the interior design.

One of the best wooden systems in our catalog is this:
Floor-standing acoustics (price appropriate)

Chipboard – thickness, density, humidity

Chipboard is comparable in cost to plastic, but does not have a number of disadvantages that are inherent in plastic cases. The most significant problem of chipboard is low strength, with a fairly high mass of material.

Sound absorption in chipboard is non-uniform and in some cases low- and mid-frequency resonances may occur, although the likelihood of their occurrence is lower than in plastic. Plates with a thickness of more than 16 mm, which achieve the required density, can effectively dampen resonances. It should be noted that, as in the case of plastic, the properties of a particular chipboard are of great importance. It is important to take into account the density and humidity of the material, since different chipboards differ in these parameters. Thick, dense chipboards are often used to create studio monitors, which indicates the demand for the material in the production of professional equipment.

On a note, for fellow DIY fraternity, chipboard with a density of at least 650 - 820 kg/m³ (with a board thickness of 16 - 18 mm) and a humidity of no more than 6-7% is well suited for creating speakers. Failure to comply with these conditions will significantly affect the sound quality and reliability of the speakers.

Among the worthy chipboard options for home speakers, our experts highlight:

MDF: from furniture to acoustics

Today, MDF (Medium Density Fiberboard) is used everywhere, among other things, MDF is one of the most common modern materials for the production of acoustics.

The reason for the popularity of MDF was the physical properties of the material, namely:

Density 700 - 800 kg/m³
Sound absorption coefficient 0.15 at 125 Hz – 0.09 at 4 kHz
Humidity 1-3%
Mechanical strength and wear resistance

The material is cheap to produce, has acoustic properties comparable to those of wood, while the resistance of the boards to mechanical damage is somewhat higher. MDF has sufficient acoustic rigidity of the speaker cabinet, and sound absorption meets the parameters necessary for creating HI-FI acoustics.

Visual difference between MDF and chipboard

There are a lot of wonderful systems among MDF acoustics; the following are optimal in terms of price/quality ratio:

Acoustic design - boxes, tubes and horns

Acoustic design is no less important for accurate sound transmission in speakers. The most common types (it is natural that certain types can be combined depending on the specific model, for example, the bass-reflex part of the speaker is responsible for the low and mid-frequency range, and a horn is built for the high ones).

Bass reflex - the main thing is the length of the pipe

A bass reflex is one of the most common types of acoustic design. This method allows, with the correct calculation of the length of the pipe, the cross-section of the hole and the volume of the housing, to obtain high efficiency, an optimal frequency ratio, and amplify low frequencies. The essence of the phase inverter principle is that on the back of the body there is a hole with a pipe, which allows you to create low-frequency oscillations in phase with the waves created by the front side of the diffuser. Most often, the bass reflex type is used when creating 2.0 and 4.0 systems.

To make calculations easier when creating your own speaker, it is convenient to use special calculators; one of the convenient ones is provided at the link.

In the HI-END philosophy, there are extremely radical, uncompromising judgments about bass reflex systems; I present one of them without comment:

“Enemy No. 1 is, of course, nonlinear amplification elements in the sound path (then everyone, to the best of their education, understands which elements are more linear and which are less). Enemy No. 2 is the bass reflex. the bass reflex is designed to show off, it should allow a small cheap speaker to record 50... 40... 30 in the passport, and what a trifle even 20 Hz at a level of -3 dB! But the lower frequency range of the bass reflex ceases to be relevant to music; more precisely, the bass reflex itself is a pipe singing its own melody.”

A closed box is a coffin for extra low ones

The classic option for many manufacturers is a regular closed box with speaker diffusers brought to the surface. This type of acoustics is quite simple to calculate, but the efficiency of such devices is not great. Also, the boxes are not recommended for lovers of characteristically pronounced lows, since in a closed system without additional elements that can enhance the lows (bass reflex, resonator), the frequency spectrum from 20 to 350 Hz is poorly expressed.

Many music lovers prefer the closed type, since it is characterized by a relatively flat frequency response and realistic “honest” transmission of the reproduced musical material. Most studio monitors are created in this acoustic design.

Band-Pass (closed resonator box) – the main thing is not to buzz

Band-Pass became widespread in the creation of subwoofers. In this type of acoustic design, the emitter is hidden inside the housing, while the insides of the box are connected to the external environment by bass reflex pipes. The task of the emitter is to excite low-frequency oscillations, the amplitude of which increases many times thanks to the bass reflex pipes.

Open body - no extra walls

A relatively rare type of acoustic design today, in which the rear wall of the housing is repeatedly perforated or completely absent. This type of design is used to reduce the number of housing elements that affect the frequency response of the speakers.

In an open box, the front wall has the most significant influence on the sound, which reduces the likelihood of distortion introduced by other parts of the case. The contribution of the side walls (if any are present in the structure), given their small width, is minimal and amounts to no more than 1-2 dB.

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Horn design - problematic loudness champions

Horn acoustic design is more often used in combination with other types (in particular for the design of high-frequency emitters), however, there are also original 100% horn designs.

The main advantage of horn speakers is their high volume when combined with sensitive speakers.

Most experts, not without reason, are skeptical about horn acoustics, for several reasons:

Structural and technological complexity, and accordingly, high requirements for assembly
It is almost impossible to create a horn speaker with a uniform frequency response (with the exception of devices costing 10 kilobucks and more)
Due to the fact that the horn is not a resonating system, it is impossible to correct the frequency response (a minus for DIYers who intend to copy a Hi-end horn)
Due to the peculiarities of the waveform of horn acoustics, the sound volume is quite low
Overwhelmingly relatively low dynamic range
It produces a large number of characteristic overtones (considered a virtue by some audiophiles).

Horn systems have become the most popular among audiophiles in search of “divine” sound. The tendentious approach allowed the archaic horn design to get a second life, and modern manufacturers were able to find original solutions (effective, but extremely expensive) to common horn problems.

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To be continued...

Acustic systems- devices for sound reproduction.

Acustic systems There are single-band (one broadband emitter, for example, a dynamic head) and multi-band (two or more heads, each of which creates sound pressure in its own frequency band).

When installing acoustics, rooms must meet a number of requirements: fire safety, hygiene, acoustic, etc. Only compliance with all requirements can make the premises safe and functional. In this section, we will focus on systems for creating acoustic comfort. Currently, the list of rooms in which acoustic requirements are extremely important has expanded significantly. In addition to concert halls, cinemas, lecture halls, acoustics are used in swimming pools and restaurants, discos and offices, in “home cinema” premises, etc.

Acustic systems consist of an acoustic design (for example, a “closed box” or a “system with a bass reflex”, etc.) and radiating heads (usually dynamic) built into it.

Single-sideband systems have not become widespread due to the difficulties of creating an emitter that reproduces signals of different frequencies equally well. High intermodulation distortion with a significant stroke of one emitter is caused by the Doppler effect.

Multi-band acoustic systems - the spectrum of human-audible audio frequencies is divided into several overlapping ranges using filters (a combination of resistors, capacitors and inductors, or using a digital crossover). Each range is fed to its own dynamic head, which has the best characteristics in this range. Thus, the highest quality reproduction of human-audible sound frequencies (20-20,000 Hz) is achieved.

For personal computers, acoustics are usually performed in conjunction with an audio amplifier (the so-called “active acoustic systems”) and are connected to the sound card on the computer system unit.

Types of acoustic systems.

By emitter type

Most speaker systems use dynamic drivers to reproduce sound, but there are other, less common drivers, for example:

Isodynamic (orthodynamic, Hale emitters)
Tape
Plasma
Electrostatic.
Piezoceramic

By type of gain

Passive: groups of emitters are mounted in the body of a multi-way speaker, connected through a passive frequency crossover with one common pair of wires to a separate amplifier.
Passive Bi/Tri-wired: groups of emitters are mounted in the body of a multi-way speaker, each of which is connected through a passive crossover with its own pair of wires to its own amplifier.
Active: an amplifier and groups of emitters are mounted in the body of a multi-way speaker, connected to it through a passive crossover.
Active Bi/Tri-amped: an active filter and groups of amplifiers according to the number of passbands, connected to the corresponding groups of emitters, are mounted in the body of a multi-band speaker.

Acoustic materials

They are divided into sound-absorbing materials and sound-proofing gasket materials. Sound-absorbing materials are used mainly in sound-absorbing cladding of industrial premises and technical devices that require noise reduction (industrial workshops, typing offices, ventilation and air conditioning installations, etc.), as well as to create optimal conditions for audibility and improve the acoustic properties of public buildings ( auditoriums, auditoriums, radio studios, etc.).

The sound-absorbing ability of materials is due to their porous structure and the presence of a large number of open interconnected pores, the maximum diameter of which usually does not exceed 2 mm (the total porosity must be at least 75% by volume). The large specific surface area of materials created by the walls of open pores contributes to the active conversion of sound vibration energy into thermal energy due to friction losses. The effectiveness of sound-absorbing materials is assessed by the sound absorption coefficient a, equal to the ratio of the amount of absorbed energy to the total amount of sound wave energy incident on the material.

Sound-absorbing materials

Sound-absorbing materials have a fibrous, granular or cellular structure and can have varying degrees of rigidity (soft, semi-rigid, hard). Soft sound-absorbing materials are made on the basis of mineral wool or fiberglass with minimal consumption of a synthetic binder (up to 3% by weight) or without it. These include mats or rolls with a volumetric mass of up to 70 kg/m3, which are usually used in combination with a perforated sheet screen (made of aluminum, asbestos cement, rigid polyvinyl chloride) or covered with a porous film. The sound absorption coefficient of these materials at medium frequencies (250-1000 Hz) is from 0.7 to 0.85.

Previously, speakers were ordinary horn loudspeakers and did not have a housing as such. Everything changed when speakers with paper cones appeared in the 20s of the 20th century.

Manufacturers began making large cases that housed all the electronics. However, until the 50s, many audio equipment manufacturers did not completely close the speaker cabinets - the back remained open. This was due to the need to cool the electronic components of that time (tube equipment).

The purpose of a speaker enclosure is to control the acoustic environment and contain the speakers and other system components. Even then it was noticed that the housing can have a serious impact on the sound of the loudspeaker. Since the front and rear parts of the speaker emit sound with different phases, amplification or attenuation interference occurred, resulting in deterioration of the sound and the appearance of comb filtering effect.

In this regard, the search began for ways to improve sound quality. To achieve this, many began to explore the natural acoustic properties of various materials suitable for the manufacture of enclosures.

Waves reflected from the inner surface of the walls of the speaker housing are superimposed on the main signal and create distortion, the intensity of which depends on the density of the materials used. In this regard, it often turns out that the case costs much more than the components contained in it.

When producing cabinets in large factories, all decisions regarding the choice of shape and thickness of materials are made on the basis of calculations and tests, but Yuri Fomin, a sound engineer and speaker design engineer, whose developments form the basis of multimedia systems under the Defender, Jetbalance and Arslab brands, does not excludes that even in the absence of special musical knowledge and extensive experience in the audio industry, it is possible to make something close in characteristics to “serious” Hi-Fi.

“We need to take ready-made developments that engineers share online and repeat them. This is 90% success,” notes Yuri Fomin.

When creating a speaker system housing, you should remember that, ideally, sound should come only from the speakers and special technological holes in the housing (bass reflex, transmission line) - you need to take care that it does not penetrate through the walls of the speakers. To do this, it is recommended to make them from dense materials with a high level of internal sound absorption. Here are some examples of what you can use to build a speaker enclosure.

Chipboard (chipboard)

These are boards made from compressed wood chips and glue. The material has a smooth surface and a loose, loose core. Chipboard dampens vibrations well, but transmits sound through itself. The boards are easily held together with wood glue or assembly adhesive, but their edges tend to crumble, which makes working with the material a little more difficult. It is also afraid of moisture - if production processes are disrupted, it easily absorbs it and swells.

Stores sell boards of different thicknesses: 10, 12, 16, 19, 22 mm and so on. For small cases (volume less than 10 liters) chipboard with a thickness of 16 mm is suitable, and for larger cases you should choose boards with a thickness of 19 mm. Chipboard can be covered: covered with film or fabric, puttied and painted.

Chipboard is used to create the Denon DN-304S speaker system (pictured above). The manufacturer chose chipboard because this material is acoustically inert: the speakers do not resonate or color the sound even at high volumes.

Lined with chipboard

This is chipboard, lined with decorative plastics or veneer on one or both sides. Boards with wood cladding are held together with regular wood glue, but for chipboard lined with plastic, you will have to buy special glue. You can use edge tape to process board cuts.

Joiner board

A popular building material made from slats, bars or other fillers, which are covered on both sides with veneer or plywood. The advantages of wood board: relatively light weight and ease of edge processing.

Oriented Strand Board (OSB)

OSB is boards pressed from several layers of thin plywood and glue, the pattern on the surface of which resembles a mosaic of yellow and brown colors. The surface of the material itself is uneven, but it can be sanded and varnished, since the texture of the wood gives this material an unusual appearance. This slab has a high sound absorption coefficient and is resistant to vibrations.

It is also worth noting that, due to its properties, OSB is used to form acoustic screens. Screens are needed to create listening rooms where users can evaluate the sound of loudspeaker systems under near-ideal conditions. OSB strips are attached at a certain distance from each other, thereby forming a Schroeder panel. The essence of the solution is that a strip fixed at certain points, under the influence of an acoustic wave of the calculated length, begins to emit in antiphase and dampens it.

Medium Density Fiberboard (MDF)

Made from wood chips and glue, this material is smoother than OSB. Due to its structure, MDF is well suited for the manufacture of designer cabinets, since it can be easily cut - this simplifies the joining of parts fastened together using mounting adhesive.

MDF can be veneered, puttied and painted. The thickness of the boards varies from 10 to 22 mm: for speaker bodies with a volume of up to 3 liters, a board with a thickness of 10 mm will be sufficient, for up to 10 liters - 16 mm. For large cases, it is better to choose 19 mm.

If, when choosing a material for the manufacture of speaker cabinets, we put aside the sound aspects, then three defining parameters remain: low cost, ease of processing, ease of gluing. MDF has all three. It is the low cost and “pliability” of MDF that make it one of the most popular materials for making speakers.

Plywood

This material is made from compressed and glued thin veneer (about 1 mm). To increase the strength of plywood, veneer layers are applied so that the wood fibers are directed perpendicular to the fibers of the previous sheet. Plywood is the best material for suppressing vibrations and keeping sound inside the cabinet. You can glue plywood boards together with regular wood glue.

Sanding plywood is more difficult than MDF, so you need to cut out the parts as accurately as possible. Among the advantages of plywood, it is worth highlighting its lightness. For this reason, it is often used to make cases for musical instruments, because it is quite a shame to cancel a concert because a musician injured his back.

It is this material that Penaudio uses to produce floor-standing acoustics - it uses Latvian plywood, which is made from birch. Many people like the way treated birch plywood looks, especially after varnishing - it gives the body a unique look. The company takes advantage of this: the transverse layers of plywood have become a kind of “calling card” of Penaudio.

Stone

The most commonly used stones are marble, granite and slate. Slate is the most suitable material for making cabinets: it is easy to work with due to its structure and it absorbs vibrations effectively. The main disadvantage is that special tools and stone processing skills are required. To somehow simplify the work, it may make sense to make only the front panel from stone.

It is worth noting that to install stone speakers on a shelf, you may need a mini-crane, and the shelves themselves must be strong enough: the weight of a stone audio speaker reaches 54 kg (for comparison, an OSB speaker weighs about 6 kilograms). Such enclosures seriously improve sound quality, but their cost can be prohibitive.

The speakers are made from a single piece of stone by the guys from Audiomasons. The bodies are carved from limestone and weigh about 18 kilograms. According to the developers, the sound of their product will appeal to even the most sophisticated music lovers.

Plexiglass/glass

You can make a speaker housing out of transparent material - it's really cool when you can see the "insides" of the speaker. Only here it is important to remember that without proper insulation the sound will be terrible. On the other hand, if you add a layer of sound-absorbing material, the transparent case will no longer be transparent.

A good example of high-end acoustic equipment made from glass is the Crystal Cable Arabesque. Cases of Crystal Cable equipment are made in Germany from strips of glass 19 mm thick with polished edges. The parts are fastened together with invisible glue in a vacuum installation to avoid the appearance of air bubbles.

At CES 2010, held in Las Vegas, the updated Arabesque won all three awards in the field of Innovation. “Until now, no equipment manufacturer has been able to achieve true hi-end sound from acoustics made from such a complex material. – wrote the critics. “Crystal Cable has proven that it can be done.”

Laminated timber/wood

Wood makes good cabinets, but there is an important point to consider here: wood has the ability to “breathe”, that is, it expands if the air is humid and contracts if the air is dry.

Since the wooden block is glued on all sides, tension is created in it, which can lead to cracking of the wood. In this case, the housing will lose its acoustic properties.

Metal

Most often, aluminum is used for these purposes, or more precisely, its alloys. They are light and tough. According to a number of experts, aluminum can reduce resonance and improve the transmission of high frequencies in the sound spectrum. All these qualities contribute to the growing interest in aluminum from audio equipment manufacturers, and it is used for the manufacture of all-weather speaker systems.

There is an opinion that making an all-metal case is not a good idea. However, it is worth trying to make the top and bottom panels, as well as the stiffening partitions, from aluminum.

Based on materials from: geektimes.ru