Silent room (silent room)lt is not only a special laboratory for acoustic testing, but also an important part of the testing system.

In fact, it is also one of the acoustic testing equipment, and its acoustic performance index directy afects the testing

accuracy Silent room (silent roomThe main functions of):

●Provide acoustic semi-free field environment.

●Low noise measurement environment

Hal-field space

Silent room (silent roomThe main function of) is to provide a semi-free field space for acoustic testing. Half-free field means

that when sound waves propagate in ininite space, there is no reflector (surface) except the ground.

The semi-free field space in nature means that the free space has a total reflection surface, and the sound wave can only be at

180? Azimuth free propagation. Common semi-fee space such as large open-air parking lot on concrete floor, outdoor

basketball court, apron, etc.

Sound wave propagation in semi-free field space has a specific physical definition as fllows:

●The sound pressure of a point sound source decreases with distance, which is the inverse square law of sound energy;

●Sound pressure level is equal to sound intensity level at room temperature. This is the theoretical basis of measuring sound

power in anechoic chamber.

background noise

Silent room (silent roomAnother function is to provide a low background noise environment to meet the requirements of the

test environment According to. IS03745-2003 acoustics-determination of sound power levels of noise sources using sound

pressure. precision methods for anechoic and hemi-anechoic rooms、ANSI S12 55-2006 Acoustics - Determination of sound

power levels of noise sources using sound pressure - Precision methods for anechoic and hemi-anech Oic rooms and

GB6882 "Measurement of Sound Power Level ofAcoustic Noise Sources-Precision Method ofAnechoic Room and Semi-

anechoic Room", in the test frequency range, the sound pressure level of background noise is at least 6dB lower than thatof

the measured sound source, preferably 12dB lower.

cut-of frequency

Silent room (silent room)ln order to simulate the semi-free field space indoors, the sound absorption cofficient of each

surface in the room is required to be above 99%. It is impossible to design a sound absorber which can achieve 100% of the

half frequency band (20 Hz-20Hz-20000Hz). Because common materials can easily absorb high-frequency sound waves,

while low-frequency absorption is related to the thickness of the material (the length of the wedge). Cutof frequency means

that above this frequency, the sound absorption system of the wall can guarantee 99% sound absorption cofficient. In

practice, the semi-free sound field space refers to the sound wave above the cut-off frequency. The lower the cut-of frequency,

the greater the length requirement of the wedge. Generally speaking, the length of the wedge is suitable for the 14

wavelength theory.

Above the cut-off frequency, the soundless chamber (soundless chamber) meets the conditions of free field, while below the

cut-off frequency, Silent room (silent room)The fee-field condition cannot be guaranteed, and the fee-field correction is

required according to GB 6882 when measuring.

Silent room (silent room)ldentification method of

In practical engineering, the free space of sound field is the key basis to identify the soundproof chamber. ISO 3745.. ANSI