Sound-absorbing materials for acoustics. What sound-absorbing and sound-proofing materials to choose. What are we doing

This is a new series of articles dedicated to acoustic systems. Due to the fact that the topic is extremely extensive, we decided to create a series of publications that reflect the selection criteria for buying speakers. This article focuses on the acoustic properties of cabinet materials and acoustic design. The post will be especially helpful for those who are in the middle of choosing speakers, and will also provide information for people who want to create their own speakers in the course of their DIY experiments.

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

Material: from plastic to granite and glass

Plastic - cheap, cheerful, but resonant

Plastic is often used in the production of budget speakers. The plastic case is light, greatly 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, while it is in demand for professional samples, where low weight and mobility of the device are important.

(for most plastics, the sound absorption coefficient is 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 performance and an attractive price: Bookshelf acoustics

Tree - from felling to golden ears

Due to its good absorbing properties, wood is considered one of the best speaker materials.

(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 for speaker production are used relatively rarely and, as a rule, are in demand in the HI-End segment. Gradually, wooden speakers disappear from the market due to low manufacturability, material instability and prohibitively high cost.

Interestingly, in order to create truly high-quality speakers of this type that meet the requirements of the most sophisticated listeners, technologists must select the 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, ending with the humidity level of the room where it was stored, the temperature and duration of drying et cetera. The latter circumstance makes it difficult for DIY development, in the absence of special knowledge, an amateur creating a wooden speaker is doomed to proceed by trial and error.

How things really are, and whether the described conditions are observed, the manufacturers of such acoustics do not report, and, accordingly, any wooden system requires careful listening before buying. 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 to units, their cost is astronomical. Everything that your obedient servant has ever heard sounds excellent. However, in my subjective-pragmatic view, it is disproportionate to the cost. Sometimes, well-designed cases made of plywood and MDF have no less musicality, but for many audiophiles “not wood” = “not true hi-end”, and for someone “not wood” the status simply does not allow or the interior design spoils.

One of the best wooden systems in our catalog is this one:
Floor acoustics (corresponding price)

Chipboard - thickness, density, humidity

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

Sound absorption in chipboard is non-uniform, and in some cases, low- and medium-frequency resonances may occur, although the probability of their occurrence is lower than that of plastic. Plates with a thickness of more than 16 mm, which reach 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 moisture content of the material, since different chipboard plates differ in these parameters. Not infrequently, thick, dense particle boards are used to create studio monitors, which indicates the demand for the material in the production of professional equipment.

Note that chipboard with a density of at least 650 - 820 kg / m³ (with a plate thickness of 16 - 18 mm) and a moisture content of no more than 6-7% is well suited for comrades from the DIY fraternity to create speakers. Failure to comply with these conditions will significantly affect the sound quality and reliability of the speakers.

Among worthy chipboard options for home speakers, our experts distinguish:

MDF: from furniture to acoustics

Today, MDF (Medium Density Fiberboard, 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 corresponds to the parameters necessary to create HI-FI acoustics.

Visual difference between MDF and chipboard

Among the MDF acoustics, there are a lot of wonderful systems, the following are optimal in terms of price / quality ratio:

Acoustic design - boxes, tubes and horns

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

Phase inverter - the main thing is the length of the pipe

The phase inverter 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 case, to obtain a high efficiency, an optimal ratio of frequencies, and to amplify low frequencies. The essence of the phase inverter principle is that a hole with a pipe is placed on the back of the case, which allows you to create low-frequency oscillations in phase with the waves created by the front side of the diffuser. Most often, the phase inverter type is used when creating 2.0 and 4.0 systems.

To facilitate calculations when creating your own speakers, it is convenient to use special calculators, I give one of the convenient ones by reference.

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

“Enemy No. 1 is, of course, non-linear amplifying elements in the audio path (further on, everyone, to the best of education, understands which elements are more linear and which are less). Enemy number 2 is a phase inverter. the phase inverter is designed to splurge, it should allow a small cheap speaker to record 50 ... 40 ... 30 in the passport, and even 20 Hz is trifling at a level of -3dB! But the lower frequency range of the phase inverter ceases to be relevant to music, or rather, the phase inverter itself is a pipe singing its own melody.

A closed box is a coffin for extra low

The classic option for many manufacturers is an ordinary closed box, with speaker cones brought to the surface. This type of acoustics is quite simple for calculations, while the efficiency of such devices does not shine. Also, boxes are not recommended for lovers of characteristically pronounced low frequencies, since in a closed system without additional elements that can enhance the low end (phase inverter, resonator), the frequency spectrum from 20 to 350 Hz is weakly expressed.

Many music lovers prefer the closed type, as 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 has become widespread in the creation of subwoofers. In this type of acoustic design, the emitter is hidden inside the case, while the inside of the box is connected to the external environment by phase inverter pipes. The task of the radiator is to excite low-frequency oscillations, the amplitude of which increases many times thanks to the phase inverter pipes.

Open housing - no extra walls

A relatively rare type of acoustic design today, in which the back wall of the cabinet is repeatedly perforated or completely absent. This type of construction is used in order to reduce the number of cabinet elements that affect the frequency response of the speaker.

In an open box, the front wall has the most significant effect on the sound, which reduces the likelihood of distortion introduced by the rest of the cabinet. The contribution of the side walls (if any are present in the design), with their small width, is minimal and does not exceed 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 radiators), however, there are also 100% original horn designs.

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

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

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

The most popular horn systems have become precisely among audiophiles who are in search of a "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...

All connoisseurs of high-quality sound sooner or later have to face the difficult problem of choosing an acoustic system - speakers. In order to purchase a device that is ideal in terms of price-quality ratio, it is necessary to pay attention not only to the technical characteristics declared by the manufacturer, but also to the material from which the speakers are made. Firstly, because the material affects the sound itself, and secondly, half the cost of the speaker system is the cost of the case. So what sounds better: acoustics made of wood, plastic or metal?

What material should the acoustic system be made of?

Types of acoustic systems

The acoustic system is the most important component of a wide variety of audio equipment. Its purpose is to convert the electrical impulse into a sound signal as efficiently as possible. Depending on the connection with the amplifier, acoustics are usually divided into active (amplifier built into the system) and passive (external amplifier). According to their dimensions, acoustic systems (AC) are shelf and floor. In turn, they are also divided into price categories - budget, Hi-Fi and Hi-End classes.

All-weather systems stand out in a special range, capable of operating in the most extreme conditions: outdoors, in the rain, at high and low temperatures, as well as acoustics of the Lifestyle category, focused on a combination of exclusive design and high-quality sound.

The less distortion, the better.

Despite all the divisions and gradations, the requirements for different acoustic systems are almost identical. If the speakers are used when watching video materials, then their main task is the reliable transmission of the voices of the characters, the music of the movie and all the audio effects. The most stringent requirements are imposed on devices designed for listening to music: the less distortion, the better.

Ideally, speakers should be powerful enough to guarantee a minimum of sonic errors, reproduce the audio frequency band available to the human ear (from 20 Hz to 20,000 Hz), accurately reproduce the sound stage - both when listening to stereo and multi-channel sound - and fit the size room by acoustic pressure, often referred to as loudness. Finally, acoustics must satisfy the emotional and aesthetic needs of the buyer, both in terms of sound and appearance.

hard case

What affects the sound quality of a speaker system the most? Of course, speakers and filters are one of the most important components. However, without a case made of high-quality material in compliance with all technological standards and parameters, it is difficult to imagine high-class equipment. The "body" of the speaker must be rigid enough to provide a good combination of absorption / reflection of sound waves of a certain frequency and power.

Speaker manufacturers use a wide variety of materials to create them. For example, the glass cabinet speakers offered by Waterfall (Waterfall Angel, Waterfall Atabasca, Waterfall Victoria models) create the visual effect of a waterfall, while Henrik Mortinsen's original open-back Jamo R909 speakers have no cabinet at all. However, the main materials for production are still plastic, wood, and metal.

Plastic

Used for quite some time. The ability to produce speakers of various shapes and low cost have made this material the most commonly used in the production of budget category equipment, especially in the segment serving personal computers. However, such speakers have a number of disadvantages: numerous flaws in the sound, rattling at medium and high volumes, mid-frequency resonances.

At the same time, large manufacturers of sound systems offer consumers high-quality acoustics with plastic cases. For example, the DM602 S3 and DM601 S3 models from B&W, the Q 8S model from KEF, and the German company Bell-Audio have patented the technology for manufacturing cases from two-layer monolithic plastic, which is not inferior in its properties to twenty layers of Karelian birch: models Bell V2.300 and Bell C2-200. Therefore, when choosing speakers, you need to pay attention to the quality of the plastic from which the case is made, but do not put an equal sign between the plastic "body" and bad sound.

Tree

This material is considered the best for the production of acoustic systems. However, solid wood is used quite rarely and only in the elite segments. This is due to the complexity of processing processes. Ideally, raw materials should be selected at the cutting stage, kept for a long time, dry naturally, without artificial acceleration. Many operations are done manually. Therefore, it is not necessary to talk about the availability of this material.

Bösendorfer, for example, makes not only its famous grand pianos, but also its loudspeaker panels (Series 1, Series 2, Series 7) from solid wood. The firm's cabinetmakers carefully select and hand-finish the finishing materials for each speaker. And the Sonus faber company positions its acoustics as a musical instrument, so the Guarneri Memento series, dedicated to the memory of the great musical master, is made of solid maple, dried naturally for several years. But still, plywood, chipboard (chipboard) and MDF (medium density fiberboard) are most often used in the production of wooden cases.

Plywood. High-quality plywood, as a rule, is multi-layered - 12 layers or more. It has good absorbing properties, is lighter than chipboard and MDF, and is less prone to delamination. Such plywood is used by Outline in the Victor subwoofer series and in the SM 18 model presented in the BEAT series. However, plywood is an expensive material, which makes it unavailable for mass production.

Acoustic system made of plastic

Chipboard. Much cheaper than solid wood and plywood. But this is not its only advantage. Plates with a thickness of more than 16 mm have a high density, which helps to reduce cabinet resonances. Due to its structure, chipboard does not introduce its own overtones. The problem of delamination and moisture absorption, which is subject to fibreboard, is successfully solved with the help of special coloring or cladding with various materials. Given the availability and good acoustic characteristics, it is used by many manufacturers. In particular, Gemme Audio uses chipboard to produce high quality loudspeakers such as the AN-S/L and AN-K/LX models.

MDF. The most common material. Appeared as a result of improved technologies that were used in the production of chipboard. MDF is made from dried wood fibers treated with synthetic binders and shaped into a carpet followed by hot pressing, veneered with natural or synthetic veneer. Despite the simple technology of obtaining and processing, medium-density slabs can surpass wood in terms of resistance to mechanical damage and moisture resistance.

The main advantages of MDF are good absorption of sound vibrations and ensuring the mechanical rigidity of the speaker cabinet. This explains the frequency of use in the production of columns of various price categories. An example of the use of this material is the following speaker models: ABS530T from BBK, subwoofer ASW855 from B&W and XQ Series from KEF.

Metal

Most often it is aluminum. As a rule, its alloys are used. They provide good mechanical qualities: stiffness, density and lightness. According to some experts, aluminum can reduce resonance and improve the transmission of high frequencies of the sound spectrum. In addition, in air, the "volatile metal" is covered with a thin colorless film that protects it from oxidation. All these qualities contribute to the growth of interest in aluminum on the part of manufacturing companies. It is especially attractive for the manufacture of all-weather systems.

Its characteristics allow to realize the latest design solutions. For example, the American company American Acoustic Development LLC, in its Lifestyle series, manufactures speaker cabinets that provide high sound standards. However, many audiophiles and professionals note the unusual "metal" sound of such systems as a disadvantage.

Listen for yourself, decide for yourself

We can say that none of the types of materials used in the manufacture of acoustic systems, in itself, provides high-quality sound. A huge role here is played by the observance of all technological parameters in the production and assembly of the case, tuning and fine-tuning of the electronic components of the acoustic system. The popularity of the brand does not always guarantee that this speaker is right for you.

As a rule, when buying speakers, the consumer does not have access to sophisticated equipment that allows measurements and an objective assessment of sound quality. Therefore, when choosing, it is necessary to focus primarily on personal emotional perception. Feel whether you can merge with this speaker system into a single whole, whether it can move you into the magical world of sounds, you can also consult with an expert and try to listen to the voice of one or another speaker with him, and good luck with your choice!

The sound quality that is acceptable and desirable to the ear depends almost entirely on what the listener is used to.

Very few people with trained ears can judge sound quality with reasonable accuracy and in objective terms.

The weakest link in the sound path is most often the acoustic system. And this is no coincidence. Designing it is a technically very difficult task associated with many physical limitations. The main problem is usually the reproduction of the lowest frequencies of the audio range. At these frequencies, the loudspeaker must emit sound waves of sufficiently long length. If at a frequency of 300 Hz the length of a sound wave is a little over a meter, then at a frequency of 30 Hz it is already 11 meters. The loudspeaker cone, moving forward, creates a compression wave. But at the same time, a rarefaction wave occurs on the rear side of the diffuser, and if the speed of the diffuser is low, then the air simply flows from the front side of the diffuser to the back, without creating a sound wave in the surrounding space. A so-called acoustic short circuit occurs.

The easiest way to improve bass reproduction is to place the speaker driver on top of an acoustic baffle, a large shield. The screen is effective as long as the distance from the front side of the diffuser to the back, measured around the edge of the screen, is more than half the length of the sound wave, i.e. for the frequency of 30 Hz we mentioned, a screen with a side size of 5.5 meters is needed. Of course, if you really want to really reproduce this frequency, you can drill a hole in the wall separating two adjacent rooms, insert a loudspeaker head into this hole. Well, seriously? Let's try to bend the edges of the screen. You get a box without a back wall. You can make the box bigger, and those low frequencies that are still poorly reproduced, "raise" in the audio frequency amplifier. So, at one time, they did it in order to lower the reproducible frequency range to 70 - 60 Hz.

Modern acoustic systems are made with a closed back wall and treated inside with sound-absorbing material. This eliminates the acoustic short circuit at low frequencies and improves the quality of reproduction at medium frequencies. However, low efficiency. loudspeaker head, which, as you know, is even lower than that of a steam locomotive, is halved when using a closed box. Designers have to solve a number of problems associated with increasing the output of loudspeaker heads.

This is why high-quality speaker systems are so complex and expensive.

The speaker system, at first glance, looks deceptively simple. Two or more loudspeaker heads are mounted in a wooden box and wired to an amplifier. However, it is a deep misconception that several heads installed in a box can act as an acoustic system for high-quality sound reproduction.

A loudspeaker head installed in a box that plays the role of acoustic design is called a loudspeaker. An acoustic system is a loudspeaker containing one or more heads that emit sound in different areas of the audio frequency range. Loudspeaker heads are divided into low-frequency, mid-frequency, high-frequency and wide-range.

Depending on the type of electroacoustic converter of an electrical signal into vibrations of the air surrounding the head, the heads are electrostatic, electromagnetic, piezoelectric, plasma and electrodynamic. The most widespread are electrodynamic loudspeaker heads.

The moving-coil electrodynamic loudspeaker was first invented and patented in 1925 by General Electric and has not changed fundamentally since.

Any electrodynamic head of the moving system, magnetic system and diffuser holder. In turn, the moving system consists of a diffuser, an external suspension, a centering washer and a voice coil.

Diffuser is the main element of the mobile system. The cones of the woofers are always cone-shaped. Mid-range and high-frequency drivers can have diffusers both in the form of a cone (cone heads) and in the form of a sphere (dome heads). Diffusers of cone heads are made by casting from paper pulp with various additives (wool, cotton, etc.) introduced to obtain the necessary physical and mechanical properties, on which the sound quality largely depends. Recently, in the production of heads, diffusers made of synthetic materials, in particular, polypropylene, have been widely used. Some companies use metal alloys for the manufacture of cone head diffusers, and also use layered structures consisting of several layers made of materials with different physical and mechanical properties. Such complex designs are used to improve the sound quality of loudspeakers. For this purpose, paper diffusers are impregnated with special compounds during the production process.

There are diffusers with rectilinear and curvilinear generatrix of the cone. Cones with a rectilinear generatrix are easier to manufacture and were used in loudspeaker heads in the early years after their invention. In modern heads, diffusers are used exclusively with a curvilinear generatrix due to the absence of so-called parametric resonances in such cones, which cause extraneous overtones in the sound. To combat parametric cone resonances, many manufacturers apply a series of concentric grooves to the surface of the cone.

Diffusers of dome heads are made by pressing from natural and synthetic fabrics, followed by impregnation with special compounds, as well as from synthetic films and metal foil. The second element of the movable system of the electrodynamic loudspeaker head is an external suspension, which is necessary for the translational movement of the diffuser during the operation of the loudspeaker head. The suspension can be made as a single unit with the diffuser in the form of a two- or multi-link corrugation, as well as in the form of a ring made of rubber, rubber, polyurethane and other materials glued to the diffuser. Very stringent requirements are imposed on the suspension in terms of its elastic properties. The suspension must have sufficient flexibility and maintain the linearity of elastic properties over the entire range of displacements of the moving system of the loudspeaker head. The fulfillment of the first condition is necessary to obtain a low frequency of the main (natural) resonance of the moving system of the loudspeaker head, which is very important for a good reproduction of the lowest frequencies. The second condition must be met to ensure low non-linear distortion. The fulfillment of the above conditions is achieved by using appropriate materials for the manufacture of the suspension and choosing its appropriate shape (shape and number of grooves, their height, etc.). In modern loudspeaker heads, suspensions are used that have an S-shaped, toroidal shape in cross section.

Centering washer is the third element of the moving system that affects the quality of the loudspeaker head. Its purpose is to ensure the correct position of the voice coil in the air gap of the head's magnetic system. To do this, the centering washer must have a minimum of flexibility in the radial direction and the maximum possible flexibility in the axial direction. The fulfillment of the first condition is necessary to ensure the mechanical reliability of the head (no contact of the voice coil with the walls of the gap of the magnetic system), the second - to ensure the low frequency of its main resonance. In addition, the centering washer must maintain the linearity of the elastic characteristics over the entire range of movement of the moving system of the loudspeaker head. The amount of non-linear distortion of the signal reproduced by the head depends on this. Centering washers can be made of textolite, cardboard, paper or fabric. Washers made of textolite, paper and cardboard, which became widespread in the 30-40s, are now completely replaced by corrugated washers of the so-called box-type, made of cotton or silk fabric impregnated with bakelite varnish. In appearance, such centering washers resemble a cylindrical box with a corrugated bottom and a cylindrical edge flared into a flat ring. The last element of the moving system of the electrodynamic loudspeaker head is the voice coil. The voice coil is wound with copper or aluminum wire in enamel insulation on a paper or metal frame and impregnated with varnish to prevent coils from slipping. When current flows through the voice coil, an electromagnetic field is created around it, when interacting with the magnetic field created by the magnetic system of the head, a Lorentz force arises, which moves the voice coil and the diffuser attached to it in the axial direction. Thus, sound is emitted by the head.

Magnetic system is the most important structural unit of the electrodynamic head, which largely determines its electroacoustic parameters. Back in the late 1940s and early 1950s, heads with electrical excitation were used, in whose magnetic systems an electric coil, called an excitation winding, served to create a constant magnetic field. To supply the excitation winding with direct current, it was necessary to have special rectifiers with very good filtering of the rectified voltage in the equipment. The excitation winding consumed significant power from the power supply and generated a lot of heat during head operation. These and other shortcomings have led to the rapid replacement of heads with electromagnetic excitation by heads with permanent magnet excitation. Without exception, all modern electrodynamic heads have a magnetic system with a permanent magnet. Magnets are core and ring. The material for the manufacture of core magnets are cobalt alloys and various grades of ferrites. Ring magnets are only ferrite. Most modern electrodynamic heads have ring ferrite magnets. Recently, special alloys with very good magnetic properties containing rare earth metals have been used for the manufacture of magnets. This made it possible to significantly increase the sensitivity of the heads without increasing their overall dimensions and weight. The design of the magnetic system is determined by the shape of the magnet used. If the magnet has the shape of a ring, then the magnetic system consists of two annular flanges and a cylindrical core.

The core diameter is smaller than the diameter of the hole in the upper flange. Thus, an air gap is formed in which the voice coil moves. When using a core magnet in the form of a solid or hollow cone, the magnetic system is a closed or semi-open magnetic circuit. The closed magnetic circuit consists of a steel cup, in the center of the bottom of which there is a magnet with a pole tip and an annular upper flange. The hole in the top flange and the pole piece form an air gap that houses the voice coil. In a semi-open magnetic circuit, a metal bracket is used instead of a glass, and the upper flange has a rectangular shape. For the manufacture of core, pole pieces and flanges, special grades of steel are used, the magnetic properties of which are subject to very stringent specific requirements. The shape of the pole pieces and the core has a significant effect on the magnitude of the magnetic induction in the air gap of the magnetic system of the head and the uniformity of the distribution of the magnetic flux in it. The sensitivity and the level of non-linear distortion of the head depend on this. The degree of heating, and hence the thermal stability of the voice coil, depends on the size of the core and pole pieces, as well as on the size of the air gap. Therefore, in powerful low-frequency heads, pole pieces and large-diameter cores are used, and they also strive to increase the air gap as much as possible (as the gap increases, the sensitivity of the head decreases and a more powerful magnet is required to maintain it). Recently, in order to improve the cooling of the voice coil, some companies began to produce heads with filling the air gap of the magnetic system with a special ferromagnetic fluid.

The diffuser holder connects the movable and magnetic systems of the electrodynamic loudspeaker head into a single mechanically strong structure. The diffuser holder has windows for the exit of air enclosed between it and the diffuser. In the absence of windows, air will act on the moving system as an additional acoustic load, reducing the return of the head and worsening its frequency response in the low-frequency region. Diffuser holders are made by stamping from special structural steel, cast by precision casting from light alloys, and also pressed from plastic.

Dynamic loudspeaker drivers are generally not used without the acoustic design necessary to obtain satisfactory results. The reason for this is that when the diffuser oscillates without clearance, the air condensation formed by one side of it is neutralized by the vacuums generated by the other side. The use of any acoustic design lengthens the path of air vibrations between the front and rear sides of the diffuser and complete neutralization of vibrations does not occur. This is especially important at low frequencies, where the dimensions of the diffuser are small compared to the wavelength of the acoustic radiation.

Frame speaker system in addition to performing its main function - the formation of its amplitude-frequency characteristic (AFC) in the low-frequency region, it introduces significant distortions into the reproduced signal due to the vibration of the walls and the vibrations of the air in it. With a decrease in wall thickness, the sound pressure value at low frequencies decreases, the frequency response unevenness in the medium frequency region increases, the level of nonlinear distortion and the duration of transients increase. These factors cause the so-called "box" overtones, which degrade the sound quality. Therefore, the design of cabinets in the practice of developing high-quality acoustic systems is given the most serious attention. There are two sources of vibrations that cause sound radiation from the walls of the speaker cabinet:

• excitation of oscillations of the air in the housing by the rear side of the diffuser of the loudspeaker head installed in it and transmission of vibrations through the air to the walls of the housing;
• direct transmission of vibrations from the diffuser holder of the head to the front wall of the housing, and from it to the side and rear walls.

To reduce wall vibrations, constructors acoustic systems apply various methods of sound and sound absorption, as well as vibration isolation and vibration absorption. One of the widely used sound absorption methods is to fill the internal volume of the body with mineral wool, special synthetic fiber, wool, super-thin fiberglass and other materials. The effectiveness of sound-absorbing materials is evaluated by the sound absorption coefficient A, equal to the ratio of the absorbed energy Wab to the value of the incident energy Wpad. The value of this coefficient depends on the frequency, thickness and density of the material. To increase the value of the sound absorption coefficient at low frequencies, the thickness of the sound absorber is increased, as well as the density of filling the acoustic system case with it. However, the presence of an excessive amount of sound-absorbing material in the case leads to a decrease in the sound pressure value at lower frequencies and the reproduction of a "dry", inexpressive bass.

The sound insulation of a speaker cabinet is determined both by the amount and physical properties of the sound-absorbing material inside it, and by the sound-insulating properties of its walls. The challenge for loudspeaker designers is to maximize the soundproofing of the enclosure by judicious selection of enclosure design and wall material. One of the common methods for increasing sound insulation is to increase the rigidity and mass of the walls of the enclosure. Therefore, some companies use marble, foam concrete and even brick for the manufacture of speaker cabinets. Such enclosures provide good sound insulation (up to 30 dB), but they are too heavy. More practical cases are the walls of which are made of two layers of plywood or chipboard with filling the gap between them with sand, shot or sound-absorbing material. To reduce the vibration amplitude of the housing walls, vibration-absorbing coatings are used in the form of sheet rubber, hard plastic, bituminous mastics, etc., applied to its internal surfaces.

To combat the direct transmission of vibrations from the diffuser holder of the head to the front wall, and from it and to other walls of the housing, solid rubber gaskets are used that are installed between the diffuser holder and the front wall, local support vibration isolators for mounting screws, shock-absorbing pads between the front and side walls of the housing, decoupling the diffuser holder from the front wall by resting it on the bottom of the case and other methods. The sound quality is also affected by the external configuration of the case (its shape, the presence of sound-reflecting protrusions and depressions, the value of the radius of rounding corners, etc.), which determines the degree of manifestation of diffraction effects that cause a violation of the timbre coloration and the stereophonic sound picture. Numerous experimental studies have shown that the transition from rectangular cases with sharp corners to cases of a smooth shape (for example, in the form of a sphere) can significantly reduce the unevenness of the frequency response of sound pressure in the region of medium and higher frequencies. Therefore, many manufacturers of high-quality acoustic systems install mid- and high-frequency loudspeaker heads in streamlined blocks in the form of spheres, cylinders, cuboids with rounded corners, isolated from the acoustic design of low-frequency heads.

To reduce the unevenness of the frequency response of the low-frequency loudspeaker, the front wall of the rectangular enclosure of the acoustic systems is made as narrow as possible (as far as the dimensions of the low-frequency head allow). In this case, the frequencies of diffraction peaks and dips in its frequency response are, as a rule, higher than the crossover filter cutoff frequency. Reducing the width of the front wall of the case also contributes to the expansion of the speaker pattern. The depth of the cabinet significantly affects the amount of "delayed" resonances, which, apparently, are the reason for the long-established empirical fact that loudspeakers with a flat cabinet sound subjectively worse compared to loudspeakers with a fairly deep cabinet.

The main feature of acoustic materials is high porosity (up to 98%). Their structure is cellular, granular, fibrous, lamellar or mixed. The pore size varies widely and usually does not exceed 3-5 mm. Porosity can be adjusted within certain limits by changing the influence of technological factors during production, thus it is possible to obtain materials with desired properties: average density and thermal conductivity.

High porosity is obtained by the following methods: gas formation, high water incorporation, mechanical dispersion, creation of a fibrous skeleton, swelling of mineral and organic raw materials, burnable additives and chemical processing.

The classification of acoustic materials is based on the principle of the functional purpose of these materials. According to this principle, they are divided into:

- sound-absorbing , intended for use in the construction of sound-absorbing linings of interior spaces and for individual sound absorbers to reduce sound pressure in the premises of industrial and public buildings;

- soundproof used as gaskets (interlayers) in multilayer building envelopes to improve the insulation of fences from shock and air sounds;

- vibration-absorbing , designed to attenuate bending vibrations propagating through rigid structures (mainly thin ones) to reduce the sound emitted by them.

Sound-absorbing materials in accordance with the current standard are classified according to the following main features: efficiency, shape, stiffness (relative compression value), structure and flammability.

According to the form, sound-absorbing materials and products are divided into:

On piece (blocks, plates);

Rolled (mats, strip pads, canvases);

Loose and loose (mineral and glass wool, expanded clay, expanded perlite and other porous granular materials).

By hardness these materials and products are divided into soft, semi-rigid, rigid and hard.

According to structural features, sound-absorbing materials and products are divided into into porous-fibrous, porous-cellular (from cellular concrete and perlite) and porous-spongy (polystyrene, rubber).

In terms of flammability, like all building materials, acoustic materials and products are divided into three groups: fireproof, slow-burning and combustible.

Comparing the classification features of sound-absorbing, as well as heat-insulating materials and products, one can see their commonality, which once again emphasizes the identity of the tasks in the production of these materials. However, it should be noted that in order to impart high functional properties to the materials and products under consideration, it is necessary to apply various technological methods that make it possible to form the porous structure necessary for a particular case.

According to their effectiveness, sound-absorbing materials and products are divided into three classes:

1st class - over 0.8;

2nd class - from 0.8 to 0.4;

3rd class - from 0.4 to 0.2.

Soundproof materials are divided into piece (tape, strip and piece gaskets, mats, plates) and loose (expanded clay, blast-furnace slag, sand).

According to the structure, soundproof products (materials) are divided into:

Porous-fibrous made from mineral and glass wool in the form of soft, semi-rigid and rigid gasket products with an average density of 75 to 175 kg / m 3 and a dynamic modulus of elasticity not more than E (w) \u003d 0.5 MPa at a load of 0.002 MPa;

Porous-spongy, made from foam plastics and porous rubber and characterized by E (w) from 1.0 to 5.0 MPa.

The dynamic modulus of elasticity of granular fillings should not exceed E (w) = 15 MPa.

Dynamic modulus of elasticity E (w) . Modulus, defined as the ratio of the stress to that part of the strain that is in phase with the stress. Matches expression

E (w) \u003d E n - (E n - E p) / (1 + (w t2),

Thus, sound-absorbing and sound-insulating materials must have an increased ability to absorb and scatter sound waves.

In addition, sound-absorbing and sound-proof materials and products must have stable physical, mechanical and acoustic properties throughout the entire period of operation, be bio- and moisture resistant, and not emit harmful substances into the environment.

Sound-absorbing products, as a rule, must have high decorative properties, since they are simultaneously used for finishing the internal surfaces of building fences.

Soundproof cushioning materials and products of a porous-fibrous structure made of various soft, semi-rigid and rigid types of wool with E not more than 0.5 MPa or 5 10 5 N / m 2 have a load on the sound-proof layer of 0.002 MPa (2 10 3 N / m 2).

Soundproofing materials are used:

In ceilings - in the form of continuous loaded or unloaded (carrying only their own mass) gaskets, piece loaded and strip loaded gaskets;

In partitions and walls - in the form of a continuous unloaded gasket at the joints of structures.

Vibration absorbing materials. Vibration-absorbing materials are designed to absorb vibration and noise caused by the operation of engineering and sanitary equipment.

Vibration-absorbing materials are some types of rubber and mastics, folgoizol, sheet plastics. Vibration-absorbing materials are applied to thin metal surfaces, creating an effective vibration-absorbing structure with high frictional energy.

Floating floor structures are used to eliminate impact sound transmission.

Elastic pads are placed between the bearing floor slab and the clean floor. It is also necessary to separate the floor structure from the walls along the perimeter of the room with elastic gaskets. Types and properties of some soundproof gaskets are presented in Table. 3.

Effective soundproofing materials are semi-rigid mineral and glass wool boards and mats with a synthetic binder, as well as stitched glass wool mats, wood-fiber boards, porous rubber, polyvinyl chloride and polyurethane foams. They produce tape and strip gaskets with a length of 1000 to 3000 mm and a width of 100, 150, 200 mm, piece gaskets - with a length and width of 100, 150, 200 mm. Products made of fibrous materials are used only in a sheath made of waterproof paper, film, foil.

acoustic panels . Structurally, acoustic panels are arranged in the same way as conventional wall panels, except that one of the panel facings is perforated.

Fig.12.1 Acoustic sandwich panel

Perforation of metal facings in acoustic sandwich panels improves the sound-absorbing properties of the panels, and also gives the panels an additional decorative effect. The percentage of perforation and the diameter of the holes in perforated sheets meet the requirements of GOST 23499-79 “Sound-absorbing and sound-proof building materials and products. Classification and general technical requirements”.

Perforation percentage, not less than - 20; hole diameter, mm. - 4.

Application of acoustic sandwich panels:

For the construction of enclosing structures, ceilings, internal walls and partitions in industrial buildings and structures where protection from the effects of industrial noise is required;

For the construction of soundproof screens (including mobile ones) on the territory of residential development in order to reduce noise pollution of the environment;

For the construction of noise barriers on highways and railways in the city, near settlements and protected areas;

Noise protection for diesel generators, soundproofing of chiller plants, soundproofing of transformer substations.

Soundproofing and soundproofing of the common wall . Street noise can pass through a common wall of adjacent houses, the sound insulation of a common wall can be improved, but the effectiveness will depend on the design of the wall, the presence of a fireplace and the electrical equipment located on it.

Photo. 12.1 Mineral wool and plasterboard

The second method of soundproofing a common wall involves cladding with acoustical mineral wool and cladding with double plasterboard on metal slats.

With this method, the sound does not pass directly, but is scattered.

Initially, a crate is arranged, for which 50x50 mm purlins are attached vertically to the wall, with a distance between them a little less than 600 mm, so that 50 mm thick mineral wool rolled sound insulation. tightly adhered to the purlins and to the wall.

Further, at a distance of 100 mm from the floor, elastic strips are fastened across the lathing in a horizontal position across the lathing, the distance between the strips is from 400 to 600 mm, the last strip is fastened at a distance of 50 mm from the ceiling.

The wall is clad with 19 mm thick acoustic plasterboard, for fastening the panels to the planks, screws 32 mm long are used, they must pass through the plank, but do not touch the wall or purlins.

It is necessary to leave a gap around the perimeter of the room from 3 to 5 mm. A second layer 12.5 mm thick is attached on top of the first layer of drywall, the joints must be shifted in relation to the first layer.

With the help of sound-absorbing sealant, the gaps are closed and the baseboard is installed.

Photo. 12 .2 General view of the sound and noise insulation of a brick wall

Choice of sound-absorbing material. Decorative and finishing sound-absorbing materials and structures are tools that allow you to effectively adjust the acoustics of a room. At the same time, soundproofing materials must perform two main functions - to prevent vibrations of an obstacle by a sound wave (for example, an interior partition), and also, if possible, to absorb and scatter a sound wave. In principle, all of the listed materials are recommended for use as soundproofing of office premises. But I would like to dwell on some nuances. More recently, cork has been widely used as a sound insulator. However, according to experts, in fact, cork is effective only against the so-called "impact noise" (resulting from mechanical impact on elements of building structures), and does not have universal soundproofing characteristics. The same applies to various synthetic foam materials. They are quite attractive in terms of ease of use, but for the most part they do not meet modern requirements for soundproofing public buildings, and in addition, they often do not meet fire safety requirements. Therefore, at present, universal soundproofing materials based on natural raw materials, for example, products based on stone wool, are coming to the fore. Their excellent soundproofing properties are determined by a specific structure - chaotically directed finest fibers, when rubbing against each other, turn the energy of sound vibrations into heat. The use of such heaters significantly reduces the risk of vertical sound waves between the wall surfaces, reducing the reverberation time, and thus reducing the sound level in neighboring rooms.

Fig.12.2. Thermal and sound insulation of entrance doors

WITH ROCKWOOL has developed a new product specifically to provide acoustic comfort in your own home, in public places, in the workplace - ACOUSTIC BATTS sound-absorbing stone wool slabs.

In the form of plates of various thicknesses, they are used for soundproofing rooms of all types. Among them are universal materials to increase the sound insulation of walls, floors and ceilings. For example, ROCKWOOL ACOUSTIC BATTS with a density of 40 kg / m 3; constructions using which provide a sound insulation index of up to 60 dB.

Rice. 12.3. Plates ACOUSTIC BATTS

1. Gypsum board; 2. Ceiling profile; 3. Profile guide; 4. Suspension straight; 5. Sealing tape; 6. Dowel; 7. Self-tapping screw; 8. Self-tapping screw; 9. Acoustic Butts

Plates placed between the rack profiles of the frame of plasterboard walls significantly increase the sound insulation index of interior partitions in an office or apartment.

They are also used when creating a floor on reinforced concrete or beam floors. For soundproofing the ceiling, the material can be mounted directly on the ceiling under the surface of suspended or stretch ceilings.

Flame retardant stone fiber material able to withstand, without melting, temperatures above 1000 ° C. While the binder vaporizes at 250°C, the fibers remain intact, bonded together, retaining their strength and providing fire protection. ROCKWOOL products are non-combustible (KMO fire class). This property allows them to prevent the spread of flame during fires, as well as to delay the process of destruction of the supporting structures of buildings for a certain time.

D additional insulation from airborne noise of interfloor ceilings on a reinforced concrete slab.

Deformation resistance. This is, first of all, the absence of shrinkage throughout the entire life of the material. If the material is not able to maintain the required thickness under mechanical stress, its insulating properties are lost. Part of the fibers of our material is located vertically, as a result of which the overall structure does not have a certain direction, which ensures high rigidity of the heat-insulating material.

Fig.12.4. Acoustic plates

stacked between the lags on the slab

floors

Soundproofing. Due to its structure - open porous structure - stone wool has excellent acoustic properties: it improves the air sound insulation of the room, the sound-absorbing properties of the structure, reduces the reverberation time, and thus reduces the sound level of noise in neighboring rooms.

Water repellency and vapor permeability . Stone wool has excellent water-repellent properties, which, together with excellent vapor permeability, allows you to easily and effectively remove vapors from rooms and structures to the outside. These properties allow you to create a favorable indoor climate, as well as the entire structure in general and thermal insulation in particular, to work in a dry state. After all, as you know, moisture is a good conductor of heat. Getting into the heat-insulating material, it fills the air pores. In this case, the heat-shielding properties of the wet material deteriorate noticeably. And the moisture that has fallen on the surface of the material does not penetrate into its thickness, so that it remains dry and retains its high heat-shielding properties.

P suspended, acoustic ceilings.

1. drywall sheet

2. ceiling profile

4. Acoustic plates

Acoustic panels are installed in the space between the suspended ceiling and the floor slab. The slabs are laid behind the suspended ceiling, or mounted to the floor slabs using fixing dowels.

Rice. 12.5. Plates Acoustic

mounted above the suspension

ceiling

Plates "Akminit" and "Akmigran" - acoustic materials made on the basis of granulated mineral wool and starch binder compositions with additives. Plates are produced with a size of 300x300x20 mm, a density of 350 ... 400 kg / m 3 and a bending strength of 0.7 ... 1.0 MPa, with a high sound absorption coefficient - up to 0.8. These boards are designed for sound-absorbing finishing of ceilings and upper walls of premises, public and administrative buildings operated with relative air humidity not exceeding 70%. The front surface of the slabs has a texture in the form of directed cracks (caverns), similar to the surface texture of weathered limestone. The plates are fastened to the ceiling using metal profiles, they can also be glued with special mastics directly to a hard surface.

A peculiar texture and a wide range of colors bring variety to the interiors of the premises with the massive use of decorative acoustic plates "Silakpor" and plates made of gas silicates.

Plates "Silakpore" are made from lightweight aerated concrete of a special structure with a density of 300 ... 350 kg / m 3. The front surface of the slabs can have longitudinal slotted perforation, which gives it not only a better appearance, but also an increased ability to absorb noise. The sound absorption coefficient of Silakpore boards in the frequency range from 200 to 4000 Hz is 0.3 - 0.8.

Slabs of gas silicate have good operational and architectural and construction properties and represent a special group of sound-absorbing materials, including those with a macroporous structure. Plates with a size of 750x350x25 mm are made from gas silicate, with a density of 500 ... ...0.3, and for macroporous 0.6...0.9. The technological process for the production of boards consists of mixing raw materials - lime, sand and dye; pouring the prepared solution into molds and autoclaving, after which the products are milled and calibrated. Acoustic perforated dry plaster boards and gypsum perforated boards with mineral wool sound absorber have good appearance, sufficient fire resistance and high sound absorbing properties. They are widely used for interior decoration of walls and ceilings in cultural and public buildings.

Previously, the speakers were ordinary horn loudspeakers and did not have a housing as such. That all changed when paper cone speakers appeared in the 1920s.

Manufacturers began to make large cases that contained all the electronics. However, until the 50s, many manufacturers of audio equipment 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 job of a speaker cabinet is to control the acoustic environment and contain the speakers and other system components. Even then, it was noticed that the cabinet is able to have a serious impact on the sound of the loudspeaker. Since the front and rear of the speaker emit sound with different phases, there was an amplifying or attenuating interference, resulting in degraded sound and a comb filtering effect.

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

Waves reflected from the inner surface of the speaker cabinet walls 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 manufacturing cabinets in large factories, all decisions regarding the choice of shape and thickness of materials are made on the basis of calculations and tests, however, Yuri Fomin, sound engineer and acoustic system 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% of success,” says Yuri Fomin.

When creating a speaker system case, it should be remembered that, ideally, sound should only come from the speakers and special technological holes in the case (phase inverter, transmission line) - care must be taken that it does not penetrate through the walls of the speakers. For this, it is recommended to make them from dense materials with a high level of internal sound absorption. Here are a few examples of what a speaker enclosure can be made from.

Chipboard (chipboard)

These are boards made from compressed wood shavings and glue. The material has a smooth surface and a loose loose core. Chipboard dampens vibrations well, but passes sound through itself. The boards are easily held together with wood glue or construction adhesive, however, their edges tend to crumble, making the material a little more difficult to work with. He is also afraid of moisture - in case of violation of production processes, it easily absorbs and swells.

The stores sell boards of different thicknesses: 10, 12, 16, 19, 22 mm and so on. For small cabinets (less than 10 liters), 16 mm thick chipboard is suitable, and for larger cabinets, boards with a thickness of 19 mm should be chosen. Chipboard can be veneered: pasted over with a film or cloth, 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 and do not color the sound even at high volumes.

Lined chipboard

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

Blockboard

A popular building material made of slats, bars or other fillers, which are pasted over on both sides with veneer or plywood. The advantages of blockboard: relatively low weight and ease of processing edges.

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 yellow and brown mosaic. The surface of the material itself is uneven, but it can be sanded and varnished, as the texture of the wood gives this material an unusual look. Such a plate 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 experience the sound of loudspeakers in near-ideal conditions. Strips of OSB are attached at a certain distance from each other, thus forming a Shredder panel. The essence of the solution lies in the fact that the strip fixed at certain points under the influence of an acoustic wave of the calculated length begins to radiate in antiphase and extinguishes it.

Medium Density Fibreboard (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 is easy to cut, which simplifies the joining of parts that are fastened together with a mounting adhesive.

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

Leaving the sonic aspects aside when choosing a speaker cabinet material, three defining parameters remain: low cost, ease of processing, ease of gluing. MDF just 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 of pressed and glued thin veneer (about 1 mm). To increase the strength of plywood, layers of veneer are superimposed so that the wood fibers are directed perpendicular to the fibers of the previous sheet. Plywood is the best material for dampening vibrations and keeping sound inside the cabinet. You can glue plywood boards together with ordinary wood glue.

Sanding plywood is more difficult than MDF, so you need to cut out the details as accurately as possible. Among the advantages of plywood, it is worth highlighting its lightness. For this reason, cases for musical instruments are often made from it, because it’s quite a shame to cancel a concert due to the fact that a musician has broken his back.

It is this material that is used by Penaudio for the production of floor 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 case a unique look. This is what the company uses: the transverse layers of plywood have become a kind of “visiting card” of Penaudio.

Stone

The most commonly used marble, granite and slate. Slate is the most suitable material for making cases: it is easy to work with due to its structure, and it effectively absorbs vibrations. 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 cases seriously improve the sound quality, but their cost can be "unbearable".

Speakers from a single piece of stone are made by the guys from Audiomasons. The hulls 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.

Plexiglas/glass

You can make the speaker case 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 acoustic hi-end equipment made of glass is Crystal Cable Arabesque. Cases of Crystal Cable equipment are made in Germany from 19 mm thick glass strips with ground edges. The parts are bonded together with an invisible glue in a vacuum setting to avoid the appearance of air bubbles.

At CES 2010 in Las Vegas, the redesigned Arabesque won all three Innovation Awards. “Until now, no manufacturer of equipment has been able to achieve true hi-end sound from acoustics made from such a complex material. critics wrote. "Crystal Cable has proven it's possible."

Glued wood/wood

Good hulls are made from wood, but an important point must be taken into account 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, stress is created in it, which can lead to cracking of the wood. In this case, the cabinet will lose its acoustic properties.

Metal

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

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

Source: www.geektimes.ru