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
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