1, porous sound-absorbing material
(1) The types of porous sound-absorbing materials include: organic fiber materials, hemp cotton felt, inorganic fiber materials, glass wool, rock wool, mineral wool, urea-formaldehyde foam, polyurethane foam, etc. Polyvinyl chloride (PVC) and polystyrene foam are not porous materials, and are suitable for shock resistance and heat insulation.
; ; (2) Structural features: There should be a large number of micropores and voids in the material, and these micropores should be as small as possible and evenly distributed in the material. The micropores in the material should be interconnected, not closed, and single bubbles and closed gaps have no sound absorption effect. The micropores are open to the outside, so that sound waves can easily enter the micropores.
(3) The sound absorption characteristics are mainly high frequency, and the factors that affect the sound absorption performance are mainly flow resistance, porosity, structural factors, thickness, bulk density and back surface conditions.
A. Influence of material thickness The sound absorption coefficient of any porous material generally increases with the increase of thickness, and its sound absorption effect at low frequencies increases, but it has little effect on high frequencies. However, after the thickness of the material increases to a certain extent, the improvement of sound absorption effect is not obvious, and it is not appropriate to increase the thickness without limit in order to improve the sound absorption performance of the material. The thickness of common porous materials is:
Glass wool and mineral wool 50- 150mm
Felt 4-5mm
Foam 25-50mm
B. Effect of bulk density of materials
Changing the bulk density of the material can indirectly control the internal void size of the material. Generally speaking, increasing the bulk density of porous materials appropriately means reducing micropores, which can improve the low-frequency sound absorption effect, but the high-frequency sound absorption performance may decline. Reasonable selection of packing density of sound-absorbing materials is very important to obtain the best sound-absorbing effect. Too large or too small bulk density will adversely affect the sound absorption performance of porous materials.
C. the influence of the back air layer
Whether there is an air layer behind the porous material has an important influence on the sound absorption characteristics. Most of the porous materials similar to fiberboard are fixed on the peripheral keel and installed at a position 50- 150 mm away from the wall. The function of air layer is equivalent to increasing the thickness of material, so its sound absorption characteristics improve with the increase of air layer thickness. When the distance between the material and the wall (that is, the thickness of the air layer) is equal to an odd multiple of 1/4 wavelength, the maximum sound absorption coefficient can be obtained. When the thickness of the air layer is equal to an integer multiple of 1/2 wavelength, the sound absorption coefficient is the smallest.
D. Influence of surface decoration treatment of materials Most sound-absorbing materials often need surface decoration treatment when they are used. Common methods include: surface drilling and slotting, painting, weaving, perforated plate, plastic film and so on. These methods will affect the sound absorption characteristics of materials.
The semi-perforated mineral wool sound-absorbing board increases the contact area of sound waves, which not only increases the effective sound-absorbing area, but also improves the sound-absorbing characteristics of the material.
Spray painting is equivalent to adding a layer of material with high flow resistance to the surface of the material, which will affect the sound absorption characteristics of the material, especially in high frequency bands.
When metal mesh, glass cloth and low flow resistance materials are used or perforated plates with perforation rate greater than 20% are selected as protective layers, the sound absorption performance of the materials will not be greatly affected. When the perforation rate is less than 20%, the sound absorption will be affected in high frequency band, but it has little effect in low frequency band.
2. Vibration and sound absorption structure of perforated plate
Perforated asbestos cement, gypsum board, hard fiberboard, plywood, steel plate and aluminum plate can all be used as vibration and sound absorption structures of perforated plates, which have great absorption near the vibration frequency of their structures, and are suitable for the formula of vibration frequency of perforated plates, namely:
; ; C P
; ; fo =—√———HZ
; ; Zπ L(T+δ)
; ; Fo-vibration frequency of perforated plate, HZ.
; ; C-speed of sound, cm/s
; ; L—— thickness of rear air layer, cm.
; ; Thickness of t- plate, cm
; ; δ —— the rest point at the end of the orifice, in CM.
; ; P- perforation rate, that is, the ratio of perforation area to total area.
3. Film sound absorption structure
Including leather, artificial leather, plastic film and other materials, it is waterproof, soft and elastic when stretched. , absorbs the incident sound energy near the vibration frequency of * * *, usually in the range of 200 ~ 1000 Hz, and the maximum sound absorption coefficient is about 0.3 ~ 0.4, so it is generally used as a sound absorption material in the intermediate frequency range. If the cavity behind the membrane is filled with porous materials, the sound absorption characteristics at this time depend on the types of membrane and porous materials and the installation method of the membrane.
4. Thin-plate sound absorption structure
The periphery of plywood, hard fiberboard, gypsum board, asbestos cement board and other boards is fixed on the frame, and together with the closed air layer behind the boards, it forms a vibration system. Its vibration frequency is mostly 80 ~ 300 Hz, and its sound absorption coefficient is about 0.2 ~ 0.5, which can be used as a low-frequency sound absorption structure. The main factors that determine the sound absorption performance of thin-plate sound absorption structure are:
(1) The influence of the mass m of the thin plate increases the weight per unit area of the plate, and generally shifts its * * * vibration frequency to low frequency. Choosing low-quality and airtight materials, such as leather, is conducive to the vibration frequency of * * * moving to high frequency.
(2) The influence of the thickness of the back air layer changes the thickness of the air layer as well as the quality of the plate, and the vibration frequency will also change. Filling the air layer with porous materials can improve the sound absorption coefficient near the vibration frequency.
; ; (3) The influence of the keel structure behind the slab and the installation mode of the slab. Because the thin-plate sound-absorbing structure has a certain low-frequency sound-absorbing ability, it has poor sound-absorbing ability at middle and high frequencies, so it has strong reflection ability at middle and high frequencies. The diffusion of indoor acoustic energy can be increased. By changing the keel structure and different installation methods, various forms of reflection surface, diffusion surface and sound absorption-diffusion structure are designed.
5. Special sound absorption structure
(1) curtain
Curtain is a kind of breathable textile with sound absorption characteristics of porous materials. Because it is very thin, it can't get good sound absorption effect when it is used as sound absorption material. If it is used as a curtain, it can be installed at a certain distance from the wall or window, just like setting an air layer behind a porous material, which can play a certain sound absorption effect at medium and high frequencies. When it is hung on the wall at an odd multiple of 1/4 wavelength, it can obtain high sound absorption at the corresponding frequency.
(2) Spatial sound absorber
The sound-absorbing material is made into a spatial cube, such as a flat plate, a sphere, a frustum or a cylinder, which can absorb sound waves in many aspects. Under the same projection area, it is equivalent to increasing the effective sound absorption area and edge effect. Coupled with the diffraction of sound waves, the actual sound absorption effect is greatly improved, and its high-frequency sound absorption coefficient can reach 1.40. In actual use, various forms can be designed according to different use places and requirements.
6. How to correctly arrange sound-absorbing materials
(1) When installing sound-absorbing materials such as sound-absorbing panels, lamps and indoor decoration should be combined to make the sound-absorbing materials distributed evenly as far as possible, which is beneficial to the uniformity of sound field.
(2) In order to give full play to the role of sound-absorbing materials, they should be arranged on the surfaces that are most exposed to sound waves and reflect the most times, such as ceilings, ceilings and walls, and the space where walls meet within the wavelength of 1/4.
(3) At the back wall of the audience hall and the railing of the podium, the reflected sound may cause echo interference, so it is often necessary to arrange materials with high sound absorption coefficient on the wall above the skirt of the back wall and the railing of the podium.
(4) Scattered arrangement of sound absorbing materials is more conducive to sound field diffusion and sound quality improvement than centralized arrangement.
(5) In general, the total sound absorption of two opposite walls in a room should be as close as possible, which is beneficial to the sound field diffusion.
(6) Generally, in rooms with low ceilings and narrow walkways, sound absorption treatment is adopted, and materials with high sound absorption coefficient or suspended space sound absorbers are selected, which has a good effect on reducing noise interference.
; ; First, the relationship between music and architecture
; ;
At the end of 19 and the beginning of the 20th century, Sabin put forward the reverberation time theory and the following Sabin formula.
; ; T60=KV/A
; ;
T60- reverberation time s
; ; K constant, generally 0. 16 1.
; ; V- room volume (m3)
; ; A- total indoor sound absorption (m2)
Later, on the basis of Sabin's formula, later generations made some modifications through research, and deduced Ilya's formula widely used in engineering:
; ; T60 = KV /-SLN( 1 A) +4mV
V- room volume (m3)
S—— total indoor surface area (m2)
α-indoor average sound absorption coefficient
4m―― Air absorption coefficient
; ; People have a complete understanding of the sound quality design of hall buildings. From determining the best reverberation time of the hall, to determining the volume and shape of each hall, selecting sound-absorbing materials, from ensuring the clarity of language and the fullness of music, to the acoustic indicators needed by various dramas, operas and movies, a set of relatively complete acoustic theories are adopted for calculation and design. Most people think that there will be no problem with the sound quality of the hall designed according to acoustic theory.
However, looking back at the history of architectural development, we can see that before the advent of reverberation time theory, a large number of performance buildings such as concert halls and opera houses have been built all over the world. The designer did not follow the design theory of room acoustics, and the good sound quality environment of these buildings was recognized by predecessors and future generations.
For example, in Vicenza, Italy, the Olympic Theater designed by Paldio was built in 1579- 1584, with 3000 seats. Another example is the Farnese Theatre in Palma, Italy, which was designed by Allehaut Di in 16 18 with an audience of 2,500.
The theaters and halls built at this time did not find any obvious sound quality defects.
; ; In particular, designers at that time felt that different styles of music needed different halls to play. Baroque music and classical music are not created for church performances, but are usually played on the dance floor of nobles. Italian opera is full of drama. When performing at the Horseshoe Opera House, the acoustic environment is very harmonious. 1876 Stat-Casino Concert Hall, built in Basel, Switzerland, has a very beautiful sound effect when playing romantic music.
; ; Before the 20th century, only one hall was designed according to the acoustic intent, and the acoustic requirements were considered in some aspects. Shpir Concert Hall in Bayreuth is the only concert hall designed and built to perform Wagner's opera. The hall is equipped with a ring speaker and multi-storey seats, thus reducing the sound absorption surface, and its reverberation time is much longer than that of a typical European theater.
; ; During this period, the words of Charles Canil, the architect who designed the Paris Opera House, can best reflect the attitude of some designers towards the sound quality design of the hall. He said: "I must explain that I have not followed any principles, and my design has no theoretical basis. Our success or failure depends on nature. "
; ; According to modern room acoustics's theory, it can be found that the indoor volume and reverberation time have not reached the ideal values required by modern urban acoustics theory in terms of ensuring language clarity and music fullness. Interestingly, these halls have excellent sound effects and beautiful sound quality when performing certain styles of music and opera. Why?
; ; During the period of 1954, Kuhl recorded and evaluated various music works in some halls with good sound quality and halls with different volume and reverberation. The results show that the best reverberation time in a hall with a volume of 2000 ~ 3000 cubic meters is not determined by the volume of the room, but related to the characteristics and style of playing music.
; ; This conclusion raises a question for us: while studying a whole set of room acoustics theory, should we strengthen our understanding of the basic knowledge of music and explain the relationship between music and architecture to designers from a brand-new field and angle, so as to make the design of architectural acoustics more in line with people's understanding of objective things? At the same time, strengthen the cultivation of designers' comprehensive quality. In the design of hall sound quality, designers are required to understand different styles of music and the relationship between music and architecture.
; ; For the audience, in order to listen well, the following conditions must be met:
; ; 1, the hall should have enough loudness, which is higher than the background noise. The appropriate response is 60 ~ 70 square meters, and music is higher than language.
; ; 2. To have good clarity, both language and music require clear sound, but the language requirement is higher. It is difficult to quantitatively express the clarity of various styles of music. Let the audience clearly distinguish the timbre of each sound and listen to each note clearly. Fast-paced music can also have a clear melody.
; ; Clarity is usually expressed by syllable clarity:
; ; Syllabic clarity = number of syllables correctly heard by the audience/number of all syllables used for measurement X 100%.
; ; When the syllable clarity reaches more than 85%, the listening feeling is excellent.
; ; Adopt language intelligibility. When the audience can understand 80% of the bytes of each sentence, the language intelligibility reaches 100%.
; ; 3. To be full, the requirement for music is very important, and language is secondary. Its meaning includes: melodious lingering sound (or active), solid fullness (or kindness), rich timbre (or enthusiasm) and good sense of space. Many famous concert halls have adopted many relief decorations to form a diffuse sound field. The more diffuse, the higher the sense of space.
; ; 4, no echo and noise interference, avoid echo, trembling echo and sound focusing, continuous noise, especially low-frequency noise, will cover up language and music, and the incidental effect of echo is that the sound quality is dyed and deteriorated.
; ; 5. Subjective evaluation of reverberation
; ; The subjective evaluation of reverberation in halls with different performance functions, such as language, opera, chamber music, symphony and chorus, is a very complicated problem, which contains many factors, including the evaluation of musicians, the evaluation of listeners and their special love for certain music, which will form many standards for reverberation evaluation. The average musician has been to many concert halls, and he can use comparative methods to determine what kind of hall various styles of music are more suitable for playing, while the audience has relatively few opportunities for such comparison.
; ; Generally speaking, language-oriented halls have short reverberation and low low frequency reverberation to ensure clarity and language intelligibility; For music, in order to cover up the noise in the process of music performance, such as the bow noise of strings and the airflow noise of flutes, the reverberation is stronger. Strong enough reverberation affects the fusion of music sound, but it can increase the loudness and fullness of sound, thus increasing the continuity of music boundary.
; ; For baroque music, the subtle changes in the high-pitched part can only be appreciated in the hall with short reverberation time and low volume, while for classical music like Mozart, the corresponding hall volume and reverberation time are longer, especially for romantic music like overture 18 12. In order to strengthen its fullness and shock, this magnificent symphony is only played in a relatively large hall. Wagner's opera, the band configuration greatly exceeds the general opera configuration, so to appreciate his opera needs to be in the hall with relatively long reverberation time, and compared with Italian opera, the reverberation time is relatively short.