【 Weak current College 】 importance of acoustic design

In recent years, there is increasing concern of acoustics, International Journal of all major forums, discussions on acoustic design is becoming more common. When listening and microphone and flat frequency response, when digital recording solution to the problem of noise of analog era, a new era had arrived for audio. Equipment gap shrinking, but the quality of the recording works basically depends on the recording technology and recording studios and final mix room acoustic design. Therefore, from the objective conditions, acoustical design for recording, than any other factors are important.
Ensure that the control room of the frequency response is flat for mixing and monitoring is very important, but a large portion of the control room did not deal with this. Worse, many people know nothing about it, not knowing ways to solve this problem. Listen for the sound produce distortion, in any case will not be able to make high quality recordings of works. The Studio of design and control room is completely different according to the recording studio working on need-the need for sound field accordingly adjusted, not all of the strong sound absorption. In order to meet the various needs of acoustic source recording, so that the effect of early recordings more perfect.
About sound insulation
In daily life, building or per far away from the street noise pollution sources doubled distance can be reduced noise, 6dB community trees can reduce the noise around 4dB.
(A) the noise propagation
Noise propagation can be in two forms: airborne noise, solid contained noise.
1. airborne noise
Sonic's most basic mode of transmission is airborne, and airborne noise is ambient noise which spreads through the air into the room noise. A fabric with small holes thick metal plate, small area of approximately 13% of metal plates, when a voice against the surface, there will be almost 97% of sound through. Sound propagation through the pore is quite amazing, asubtle cracks can destroy an entire seal acoustic system. Therefore, the room is isolated from the strict seal on airborne noise emitted is very necessary.
2. solid noise load
Sound through the vibration propagation in solid of machinery such as wood, metal, concrete, etc. Because the air transmission of inefficient to bring solid vibration, so solid containing the main source of noise is due to the vibration source contact solid media surface, such as underground generator or some electrical appliances. Solid sound transmission loss ratio of air transmission of small, can spread very far in distance but no major loss of energy. Wood, concrete and other longitudinal vibration about 304.8 m loss around 2dB. If the transmission medium for the iron and steel materials, the loss will be reduced to 20 times.
(Ii) sound processing
Acoustic treatment has many methods, Studio due to its strict on this floor noise, so the use of suspension structure. Suspension structure can greatly improve the sound isolation degree, especially for the Studio in the city. Suspension structure can add rooms and other structural separation, it can be suspended wall and the wall between a cavity and in the cavity fill soft acoustic material, acoustic using cavity absorption, so that the air, solid noise reduction to a minimum. But suspended structure to meet the requirements of the load-bearing structures.
Regarding the diffusion and absorption
Many people get plastered walls of sound-absorbing materials, thought this would be enough to eliminate reflections, because they feel when they clap your hands, so there is no echo, but this reflection on the control of low-frequency has no meaning. The brick and concrete walls, the problem is particularly serious. The more rigid wall, the more reflective.
Most people who blindly believe that a good Studio should do to minimize the reflection of sound absorption. But the shaping of sound field in no way merely refers to the uptakeof reflections, but rather on the room for listening and recording of optimization, that is, for the recording of work to do optimal consideration.
(A)
Diffusion and its role
Diffusion on improvement of sound field and listening to interested has an important role, quadratic residue diffusion body because of its good diffusion capacity and convenient installation, now widely used. Quadratic residue diffusion of formula for hn = (λ 0/2 N)? ' Sn, Sn to n-squared divide by N remainder, λ 0 for diffusion center frequency wavelength, n is the number of diffusion of lattice (must be a prime number), h is the height of a lattice, n = 0, 1, 2, 3, 4, 5, 6 ....
Quadratic residue diffusion of diffusion frequency threshold approximately in the center of the lower frequency-doubling, limit depends on the number of squares, can reach the center frequency n-1 times.
Diffusion and smooth reflector, which can effectively avoid sound focus. When the sound wave through a smooth wall reflection, all of the sound energy is reflected along the same direction, its reflection direction fixed, depending on the location of the sound source. When sound waves through the diffusion of reflection, the sound energy is scattered reflection in different directions, and have different phase.
The formation of uniform energy of irregular reflection sound makes one ear subjective produces a sense of space, at the same time use in high frequency will improve the sound of the proliferation of "bright". Its reflection direction roughly a semicircle, sound energy average spread. Diffuser has another effect, when the sound source, the acoustic reflection through the back wall, if the reflector is a smooth wall, a band only fixed reflection path points to the location of the recording. But when the reflector is a diffuser, due to the proliferation of Sonic to semicircle direction, there are countless different band reflection path converges in the recording location, and so on, there are numerous points of convergence of the same nature, which translates into expanded the best listening to tempo.
(2)
Sound-absorbing material (structure) and its role
Sound absorption can be divided into two situations, low frequency and high frequency absorption and absorption. Sound absorption can reduce echo, but also can effectively control the reverberation time, improve listening to tempo frequency response also play a very important role. So, you can create a listen for more clear and more standard mix environment.
1. high frequency absorption
High-frequency absorption is mainly directed against sound field design, early reflection sound wave interference, reverb and ECHO's control. Usually you can use full-band sound-absorbing glassFibreboard for sound absorption and conducted jointly with the diffusion of sound shaping.
2. low frequency absorption (low frequency sound,)
(1) role
The role of low frequency sound, is to avoid low-frequency interference in wave and sound of the low frequency sound distortion. Shows, when za sound impact wall surface, after reflection of sound waves and za continue to issue of Sonic interference effects. Depending on the wavelength, the sound pressure or be strengthened or be offset, and different locations with different frequency response. In an untreated rooms, Sonic mutual effect of reversed phase interference occurs, most will produce 25dB even more.
Many people mistakenly believe that the use of near-field monitor speakers can exclude acoustic defect. In fact, as there will be a standing wave, just listening position to the sound energy is large. Although the human ear close to the speakers when, because of the high-frequency acoustic reflection will gradually decrease the masking effect, but the low-frequency interference still exists.
Another misconception is to use the equalizer to change because of acoustic phase cancellation caused by the change of frequency response. Sonic interference androom structure, is objective and existent, unless you change the direction of sound transmission, otherwise use equilibrium cannot be changed because the sound wave interference induced frequency distortion. And the different locations of the frequency response curve is totally different, so it is not possible to rely on the equalizer to compensate acoustic defect.
Although the use of headphones you can avoid the room acoustic problems caused by, but the headphones sound only direct sound, making it very difficult for us to go to control the volume of some tracks. When we use the headphones, the main play music or song in a very small volume, you can even listen to very clear, so our final mix, lead singer of the level will be slightly lower than the desired level of value. Similarly, reverb and delay also lack accurate judgment.
Without sound, treatment room, some frequencies decay time reached 300ms, this will give other low frequency tone produces a big impact, damage, or even make voice clarity is harmonious.
In General, a room need as many sound depression. Although he may make the room became the "dead", but the rooms can never have too many mixed low frequency. Sound, can be installed in a room corner, walls, floor and ceiling, the greater the processing area, ideal for low-frequency effects.
(3) commonly used in low-frequency sound
A. Hershey Helmholtz resonator
Helmut Helmholtz resonator and a low frequency sound, that is different from the composition of the sound of glass wool, it can absorb more low-frequency component. It has adjustable hollow structure, a band of absorption is very effective. Absorption frequency range and the quality factor Q, Helmut Helmholtz resonator cavity absorption bandwidth formula is: f2-f1 = fr/Q, fr for resonance frequency is the maximum absorption frequency. By adding glass wool or add several openings of different sizes, you can make the absorption band of variable width. Helmut Helmholtz resonator of many species, usually is uses a large box of internal fill glass wool, front end cover a series of different dimensions, different spacing veneer. This design is known as narrow plates resonator. Although the hull Helmholtz resonator can absorb a certain band, but it can absorb a limited range, and the use of multiple resonator frequency absorption of broadening its scope be on sound field of activity, so it must be very careful.
B. Panel sound,
Panel of the sound in a narrow band noise, which can absorb bandwidth for approximately a octaves, it can use a series of a square around the Panel sound, to cover the entire frequency, without having to use a very heavy materials to increase the acoustic range. Because of the low-frequency components are close to four octave, so you can pass a different thickness of the Panel of the sound absorption in a combination of different frequency of low frequency and high frequency components can be its Panel reflection, therefore install multiple Panel sound, nor will it makes sound absorption can be all too silent sound field caused. Front panel can also be other shapes or combination, if placed in the back wall can be up to the required role diffusion.
C. acoustic suspension of sound-absorbing structure
Due to the wide range of low-frequency radiation, energy intensity, so when the low frequency sound wave into suspension system, the suspension of affected with swing (Visual observation), so will its kinetic energy is converted to its kinetic energy and heat. And because the suspension of the angle is different, so the transmission of sound direction also changed, so that the equivalent of a voice of the labyrinth. Acoustic in which constantly crash and be absorbed up to eliminate almost all energy.
Acoustic design to achieve the following four objectives:
1.
Prevent standing wave and wave interference, and ensure the flat frequency response.
2.
Reduction of small resonant frequency of the room, even distribution of the sound field.
3.
Reduce large room reverberation time of low-frequency, the better the reverberation time frequency characteristics.
4.
By absorption or diffusion, prevent echo and improve stereo positioning capabilities.
5.
Sound needs to meet the requirements of control rooms.
Important factors to consider
1, early reflection
Initial delay gap refers to the direct sound and the first indoor reflection i.e. head early reflection of the time difference, as shown in the figure. In subjective listening to interested, initial delay gap will bring the room characteristics of perception. For example, when we are in a closed room darkness, applaud, we can know the approximate size of room. This is due to the perception of auditory system to its initial delay clearance and transmitted to the brain room information. When the initial delay clearance greater than 20ms, the room will have sense and produced open sound about the same 7m 20ms. Large control room of the side wall of the dots in the early reflection at least listening points 3-4 meters, so make sure you are on the side walls of absorbing or diffusion treatment.



Early reflections on listening quality have a critical role, rich early reflection can bring relative active sound field, and the appropriate early reflection to improve the clarity of the sound has a certain role. 50ms listening points within reach of early reflections will enhance the clarity of the sound, but the control room can not be too much to join their roomCharacteristics, so early reflection should try to control their energy. Selection of the diffuser is a good way to spread evenly, allowing early reflection enhance clarity and sound field with a certain sense of space. At the same time help to promote high-reflection, whereas the low frequencies loudness makes sound reflection, so non-roiling should only non-high-frequency components (center frequency is approximately 1kHz), reflection onthe low-frequency should be absorbed.
But early reflection will also bring comb filter, noise interference problems that affect the sound field of positioning and listening spot frequency response. Many people early reflections are very inconsistent, reflections on the direct sound serious interference, can affect the forward sound image orientation, and then it will be very dogmas and all of the reflex points all covered with absorption material, and to top the whole room filled with sound-absorbing materials! this will only be more attenuated sound energy that we in the mix is constantly upgrading and enhancing the reverb loudness.
We are in the control room as well as shrinkage concrete strip processing, you need a standard space environment, the band reverberation time and room of frequency response as straight. At the same time, we want to ensure that the reflection of sound does the formation of mutual interference or influence the comb filter frequency response.
2. room dimensions and shapes
Room structure to listen to the sound effects are:
Parallel walls of stationed in wave resonance problems
Asymmetric structure on the positioning of
(1) in wave and resonance
Standing wave is composed of two columns in the opposite direction, with the frequency of the sound wave overlapping. When parallel wall space is an integer multiple of half-wavelength, that is, standing wave generated axial. At the same time, there is a ramp and tangential standing wave. When standing wave continues, will have resonance. The room of the resonance frequency of the general formula is:



Where c is the speed of sound, lx, ly, lz-room length, width and height, n is 0, 1, 2, 3, 4, ….
When several resonance mode resonance frequency of the same, the phenomenon of resonance frequency degenerate. A degenerate resonance frequency on the same frequency and resonance of sound is greatly enhanced, this could cause serious distortion of frequency. In the low frequency range, this phenomenon is particularly serious.
(2) symmetric structure
Thanks to produce stereo positioning two speakers to the sound of the volume and the time is different, therefore, in order to ensure accurate positioning of the original signal, Binaural accept to room information to maintain a certain balance. That is, when the speaker plays a tone when the test signal, Binaural should accept to almost the same reflection sound signal. If the room is a rectangle, the speaker should call set in a relatively short length of the front end, making listening location away from the back wall, so that it can be avoided in the back wall, near the most complex sound interference. The following figure is a set of comparison chart, on the left is the correct symmetric structures, the right to not ideal layout structure. On the right, the left speaker's high frequency components can be directly reflected to the listening point, while the right side of the left part of the sound through speakers wall reflection, reflection through the back wall part, leading to listen and point on either side of the reflex sound different, resulting in the sound and image positioning offset.


4. measurement of acceptance
Standards are as follows:
(1) above Acoustics: 55dB
(2) the frequency of the reverberation time: T = 0.4s (125Hz? 4kHz allows +-0.1s error)
(3) listen to the tempo of the frequency response: no uniformity of control within the 3dB