Sound-absorbing materials and sound-absorbing structures are summarized into five categories and introduced.
1. Porous sound-absorbing materials
(1) Types of porous sound-absorbing materials include: organic fiber materials, linen wool felt, inorganic fiber materials, glass wool, rock wool, mineral Cotton, urea-formaldehyde foam, urethane foam, etc. PVC and polystyrene foam are not porous materials and are suitable for shockproof and heat insulation materials. ;;(2) Structural characteristics: There should be a large number of micropores and gaps inside the material, and these micropores should be as small as possible and evenly distributed inside the material. The micropores inside the material should be interconnected rather than closed. Individual bubbles and closed gaps cannot absorb sound. The micropores are open to the outside, making it easy for sound waves to enter the micropores.
(3) The sound absorption characteristics are mainly high frequency. The factors that affect the sound absorption performance are mainly the flow resistance, pores, structural factors, thickness, bulk density, and background conditions of the material.
a. The influence of material thickness. The sound absorption coefficient of any porous material generally increases its low-frequency sound absorption effect as the thickness increases, but has little effect on high frequencies. However, when the material thickness increases to a certain level, the improvement in sound absorption effect is not obvious, so it is not appropriate to increase the thickness without limit in order to improve the sound absorption performance of the material. The thickness of commonly used porous materials is:
Glass wool, mineral wool 50-150mm
Felt 4---5mm
Foam plastic 25-50mm
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b. The influence of material bulk density
Changing the bulk density of the material can indirectly control the size of the micro-voids inside the material. Generally speaking, an appropriate increase in the bulk density of porous materials means a reduction in micropores, which can improve the low-frequency sound absorption effect, but the high-frequency sound absorption performance may decrease. Reasonable selection of the bulk density of sound-absorbing materials is very important to obtain the best sound absorption effect. Too large or too small bulk density will have an adverse impact on the sound absorption performance of porous materials.
c. The influence of air layer behind
The presence or absence of air layer behind porous materials has an important impact on the sound absorption characteristics. Most fiberboard porous materials are peripherally fixed on the keel and installed 50-150mm away from the wall. The effect of the air layer of the material is equivalent to increasing the thickness of the material, so its sound absorption characteristics increase as the thickness of the air layer increases. When the distance between the material and the wall (that is, the thickness of the air layer) is equal to an odd number of 1/4 wavelength times, the maximum sound absorption coefficient can be obtained; when the thickness of the air layer is equal to an integer multiple of 1/2 the wavelength, the sound absorption coefficient is the smallest.
d. The impact of material surface decoration treatment. Most sound-absorbing materials often require surface decoration treatment when used. Common methods include: drilling and grooving on the surface, painting, using fabrics, and perforated boards. and plastic film, etc. These methods will affect the sound absorption properties of the material.
Semi-perforated mineral wool sound-absorbing panels increase the area of ??the material exposed to sound waves, which not only increases the effective sound-absorbing area, but also improves the sound-absorbing properties of the material.
Painting is equivalent to adding a layer of high flow resistance material on the surface of the material, which will affect the sound absorption characteristics of the material, especially in the high frequency band.
When metal mesh, glass cloth and low flow resistance materials are used as the protective layer, or a perforated plate with a perforation rate greater than 20% is selected as the protective layer, it will have little impact on the sound absorption performance of the material. If the perforation rate is less than 20%, it will have an impact on the sound absorption in the high frequency band, but will have little impact on the low frequency.
2. Perforated board vibration and sound absorption structure
Perforated asbestos cement, gypsum board, hard fiberboard, plywood, steel plate, and aluminum plate can all be used as perforated boards* The vibration sound-absorbing structure has greater absorption near the maximum vibration frequency of the structure. It is suitable for intermediate frequencies. The formula for the maximum vibration frequency of the perforated plate is: ;;C P ;;fo= ——√ —————— HZ ;; Zπ L(T+δ) ;;fo—the maximum vibration frequency of the perforated plate, HZ;;C—sound speed, CM/S;;L—the thickness of the back air layer, CM;; t—Thickness of the plate, CM;; δ—Relaxation amount at the end of the hole, CM;;P—Perforation rate, that is, the ratio of the perforation area to the total area
3. Thin film sound-absorbing structure
Including leather, artificial leather, plastic film and other materials, which are airtight, soft, and elastic when stretched, and absorb incident sound energy near the first vibration frequency, which is usually between 200 and 1000HZ. range, the maximum sound absorption coefficient is about 0.3 to 0.4, and it is generally used as a sound-absorbing material in the mid-frequency range. If porous material is filled in the cavity behind the film, the sound absorption characteristics at this time depend on the type of film and porous material and the installation method of the film
4. Thin plate sound-absorbing structure
< p> Fix the periphery of plywood, hard fiberboard, gypsum board, asbestos cement board and other boards to the frame, together with the closed air layer behind the board, to form a vibration system. Its maximum vibration frequency is mostly 80 to 300HZ, and its sound absorption The coefficient is about 0.2~0.5, which can be used as a low-frequency sound-absorbing structure. The main factors that determine the sound absorption performance of thin plate sound-absorbing structures are:(1) The influence of the thin plate mass m. Increasing the unit area weight of the plate can generally move its maximum vibration frequency to a low frequency. Choosing low-mass, air-impermeable materials such as leather will help the vibration frequency move toward high frequencies.
(2) The influence of the thickness of the air layer behind it. Changing the thickness of the air layer is the same as changing the mass of the board, and the vibration frequency will also change. Filling the air layer with porous materials can improve the sound absorption coefficient near the maximum vibration frequency. ;;(3) The impact of the keel structure behind the panel and the installation method of the panel. Since the thin panel sound-absorbing structure has a certain low-frequency sound absorption ability, but poor sound absorption at mid- and high-frequency, it has strong reflection ability at mid- and high-frequency. Can increase the diffusion of indoor sound energy. By changing the keel structure and different installation methods, various forms of reflective surfaces, diffusion surfaces and sound absorption---diffusion structures are designed.
5. Special sound-absorbing structure
(1) Curtains
Curtains are textiles with breathable properties and have the sound-absorbing properties of porous materials. If it is thin and used as a sound-absorbing material, it will not achieve a large sound-absorbing effect. If it is used as a curtain and installed at a certain distance from the wall or window opening, it will be like an air layer behind the porous material, so it can have a certain sound absorption effect at medium and high frequencies. When it is hung at an odd multiple of 1/4 wavelength from the wall, high sound absorption at the corresponding frequency can be obtained.
(2) Space sound absorber
The sound-absorbing material is made into a spatial cube such as: flat plate, sphere, cone, pyramid or column, so that it can absorb sound waves on multiple sides. When the projected area is the same, it is equivalent to increasing the effective sound absorption area and edge effect. Coupled with the diffraction effect of sound waves, the actual sound absorption effect is greatly improved. Its high-frequency sound absorption coefficient can reach 1.40. In actual During use, various forms of sound absorbers suspended from the ceiling can be designed according to different usage locations and requirements.
6. How to correctly arrange sound-absorbing materials
(1) When installing sound-absorbing materials, such as perforated boards, the lighting and interior decoration should be considered together and combined in blocks to ensure that It is possible to evenly distribute sound-absorbing materials, which is beneficial to the uniformity of the sound field.
(2) To make the sound-absorbing material play its full role, it should be placed on the surface that is most likely to be exposed to sound waves and has the highest number of reflections, such as the ceiling, the intersection between the ceiling and the wall, and the wall between the wall 1/ Space within 4 wavelengths, etc.
(3) On the back wall of the auditorium and at the platform railings, the sound reflected back may cause echo interference. It is often necessary to arrange high-profile speakers on the wall above the dado of the back wall and at the platform railings. Sound absorption coefficient of materials.
(4) The dispersed arrangement of sound-absorbing materials is more conducive to sound field diffusion and improved sound quality than centralized arrangement.
(5) Generally, the total sound absorption of two opposite walls in a room should be as close as possible, which is conducive to the diffusion of the sound field.
(6) Generally, in rooms with lower ceilings, long and narrow rooms For walkways, sound absorption treatment methods are adopted, and materials with large sound absorption coefficients or suspended space sound absorbers are used, which have a good effect on reducing noise interference. ;;1. The relationship between music and architecture;;
At the end of the 19th century and the beginning of the 20th century, W.C. Sabine proposed the reverberation time theory and proposed the following Sabine formula;; T60=KV/ A ;;
T60——Reverberation time S;; K——Constant, usually 0.161;; V——Room volume (cubic meters);; A——Total indoor sound absorption Amount (square meters)
On the basis of Sabin's formula, later generations made some modifications through research, and derived the EYring formula that is commonly used in engineering: ;;T60=KV /-SLN(1-a)+4mV
V——Room volume (cubic meters)
S——Total indoor surface area (square meters)
α---Indoor average sound absorption coefficient
4m--Air absorption coefficient; People have a relatively complete understanding of the sound quality design of hall buildings, starting from determining the optimal reverberation time of the hall, From the determination of the volume of each seat to the body shape, the selection of sound-absorbing materials, from ensuring the clarity of speech and the fullness of music to the acoustic indicators required by various dramas, operas, movies, and different functions, we began to use a relatively complete set of acoustic indicators. Calculation and design based on theory. Most people believe that halls designed according to acoustic theory will have no problems with sound quality.
But looking back at the history of architectural development, we can see that before the advent of the reverberation time theory, a large number of concert halls, opera houses and other performance buildings have been built around the world, but designers did not follow the Indoor acoustic design theory, and the good sound quality environment of these buildings are recognized by predecessors and descendants.
For example, in Vicenza, Italy, the Olympic Theater designed by PALLDIO was built from 1579 to 1584 and has 3,000 seats; another example is the one designed by ALEOTTI in 1618 The Farnese Theater in Parma, Italy, has a capacity of 2,500 spectators.
No significant defects in sound quality were found in the theaters and halls built at this time. ;;Especially the designers at that time had felt that various styles of music required different halls to play. Baroque music and classical music were not written for church performance. It was usually played on the dance floors of nobles. Italian opera is dramatic. When performed in the horseshoe-shaped opera house, the acoustic environment is very harmonious. The Stat-Cassino Concert Hall in Basel, Switzerland, built in 1876, has very beautiful acoustic effects when performing romantic music. ;;Before the 20th century, there was only one hall designed with acoustic intentions and taking acoustic requirements into consideration in some aspects. The Feistspier Hall in Bayreuth, Germany was the only hall designed and built for the performance of Wagner operas. The hall has circular balconies and tiers of seating, thus reducing the sound-absorbing surface and providing a much longer reverberation time than typical theaters in Europe. ;; During this period, the best reflection of the attitude of some designers towards the design of hall sound quality is the words of CHARLES GARNIER, the architect who designed the Paris Opera House. He said: "I must explain that I did not follow anything In principle, my design has no theoretical basis, and our success or failure is left to its own devices.
" ;; Analyzing these hall buildings according to modern indoor acoustic theory, we can find that their indoor volume and reverberation time have not reached the ideal values ??required by modern urban acoustic theory in terms of ensuring speech clarity and music fullness. What is very interesting is that these halls have excellent acoustic effects and very beautiful sound quality when performing certain styles of music and operas. Why is this? ;; In 1954, Kuhl used modern recording technology to perform in some halls that were recognized as having better sound quality. Various musical works were recorded and evaluated in good halls with different volumes and reverberations. The results show that in halls with a volume greater than 2000 to 3000 cubic meters, the optimal reverberation time is not determined by The volume of the room is related to the characteristics and style of the music played;;;This conclusion raises a question for us: while learning a complete set of room acoustics theory, should we strengthen our understanding of the basics of music from a completely new perspective. The field and perspective clarify the relationship between music and architecture to designers, making the design of architectural acoustics more consistent with people's understanding of objective things. At the same time, it strengthens the cultivation of designers' comprehensive qualities regarding hall sound quality design, requiring designers to understand various aspects. To understand the style of music and the relationship between various styles of music and architecture;; For the audience, the following conditions must be met to listen well: ;; 1. The hall should have sufficient loudness and should be higher than the background noise, which is more appropriate. The response is 60 to 70 square meters, which is higher for music than for language;; 2. It must have good clarity. Both language and music require clear sound, but language has higher requirements, and the clarity of various styles of music is very good. It is difficult to express in quantity, so that the audience can clearly distinguish the timbre of each sound, hear each note clearly, and the melody of fast-paced music can be clear;; Clarity is often expressed in terms of syllable clarity:;;Syllabic clarity. Degree = number of syllables correctly heard by the audience/number of total syllables used for measurement Understand 80% of the bytes of each sentence, and the language intelligibility reaches 100%;;3. To have sufficient fullness, the requirements for music are important, and the language is secondary. Its meaning is. : The sound is melodious (or active), solid and full (or cordial), the tone is rich (or warm), and has a good sense of space. Many famous concert halls use a lot of relief decoration to form a diffused sound field. The higher the sense of space. ;; 4. No echo and noise interference, avoid echo, flutter echo and sound focus. Continuous noise, especially low-frequency noise, will mask speech and music. The additional effect of echo is that the sound quality is dyed. And get worse. ;;5. Subjective evaluation of reverberation;; For various performance halls with different functions such as language, opera, chamber music, symphony and chorus, the audience's subjective evaluation of the reverberation is a very complex issue. , it contains many factors, including the musician's evaluation, the audience's evaluation, and the audience's special love for a certain kind of music, which will form many standards for reverberation evaluation. The average musician has performed in many concert halls, and he can use comparative methods to determine what kind of halls various styles of music are more suitable for performance. However, the audience has relatively fewer opportunities for such comparisons. ;;Generally speaking, in halls where language is the main focus, the reverberation is shorter and the low-frequency reverberation is lower to ensure clarity and language intelligibility; for music, in order to mask the noise during the music performance, For example, the bow noise of strings and the airflow noise of flute should have stronger reverberation. Strong enough reverberation affects the integration of musical sounds, but can increase the loudness and fullness of the sounds to increase the continuity of musical boundaries. ;;The delicate changes in the treble part of Baroque music can only be appreciated in a hall with a short reverberation time and a small volume. However, for classical music like Mozart's music, the corresponding hall volume and reverberation time are relatively long. , especially the romantic music "1812 Overture". In order to enhance its fullness and shocking power, this majestic symphony is only played in relatively large halls. The orchestra configuration of Wagner's operas greatly exceeds the configuration of ordinary operas. To appreciate his operas, you must be in a hall with a relatively long reverberation time. Compared with Italian operas, the reverberation time required is relatively short.