First, sound insulation
There are many sources of external noise, such as the sound of car horns on the road, the noise of people, and so on. There are two ways to transmit these noises: by air or by inherent objects (such as doors, windows, etc.). Therefore, when designing the listening room, the door and window should be strengthened as much as possible. For example, the door and window of the listening room should be double-layered, or the thick curtain should be hung on the indoor side of the window, or the door should be wrapped with sealing material. If the wall of the room is thin, you should consider using soundproofing materials. For sound rooms in high-rise buildings, sound insulation measures for ceilings and floors should also be considered. The above measures are effective in preventing noise transmitted through the air.
Noise propagating through solids refers to noise generated indoors due to vibrations caused by internal objects (such as doors, windows, walls, etc.) on the building. This type of noise is generally difficult to eliminate, but some measures can be taken to reduce its impact. For example, the window is made of thick glass and is tightly packed; a double wall is used, and a gap is left between the two walls or a sound insulating material is filled in the gap.
Second, sound absorption
In order for the listening room to have an excellent reverberation effect, some acoustic processing is required. As can be seen from the foregoing discussion, the frequency characteristics and reverberation time of the room are related to the shape and size of the room, and are related to the sound absorption performance of the indoor building materials. Therefore, the proper use of sound absorbing materials to adjust the reflected sound to control the reverberation time, eliminate the echo, and avoid the acoustic dyeing is an important part of the acoustic design of the listening room.
The sound absorbing material utilizes the viscous resistance of the air and the vibration and friction of the sound absorbing material to convert the sound energy into potential energy and absorb the sound. Different sound absorbing materials have different absorption coefficients for sounds of different frequencies, and the selection and placement of sound absorbing materials should be based on the principle that the sound absorption characteristics of the frequencies in the listening room are uniform. The desired acoustic properties can be obtained by reasonable selection and matching of sound absorbing materials and the use of appropriate sound absorbing methods.
Commonly used sound absorption methods can be divided into three categories according to their sound absorption principles: porous material sound absorption, thin plate vibration type sound absorption and resonator type sound absorption.
Porous sound absorbing materials such as felt, plant fiberboard, etc. have a lot of small and deep holes. When the sound waves encounter these materials, it is easy to enter these pores, causing the air particles to rub against the pores and causing some of the sound energy to become heat, which weakens the sound.
Thin plate vibration type sound absorption is to use the frame to fix the thin plate or plywood to keep a certain distance from the wall surface. When the sound wave encounters the thin plate, the sound can be changed into a thin plate due to the alternating pressure of sound waves. It is consumed by vibration. Obviously, when the acoustic frequency resonates with the mechanical vibration frequency of the thin plate, it can consume a lot of sound energy. At this time, the sound absorption effect is the best.
Resonator type sound absorption is the use of a resonator to absorb the acoustic energy near its resonant frequency. When the sound wave enters the resonator, the air at the narrow entrance of the resonator resonates at a resonant frequency that causes friction on the neck wall of the resonator to consume acoustic energy.
The porous sound absorbing material has a large sound absorption coefficient and is a commonly used sound absorbing material. The thickness, weight and installation of the porous material have an effect on the sound absorption effect. As the thickness of the material increases, the sound absorption to the low frequencies increases. In general, the best sound absorbing ability of a porous material is about 1/4 wavelength at the lowest frequency of the absorbed sound wave.
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