A semi anechoic chamber is an important facility for conducting sound quality testing, providing a space close to a free field, making the test results more accurate. The following are the requirements for semi anechoic chambers based on the provided search results:
 
Wall sound absorption coefficient
 
The walls of the semi anechoic chamber need to be covered with efficient sound-absorbing materials or structures to absorb incident sound waves. Generally speaking, the sound absorption coefficient needs to reach over 99% to ensure that indoor reflected sound is as small as possible.
 
Reflection coefficient
 
For semi free field space, the reflection coefficient should be above 95%. This means that most of the sound waves will be absorbed by the wall, and only a small amount of sound waves will be reflected.
 
Cut off frequency
 
The cutoff frequency of a semi anechoic chamber is usually 125Hz, but it can be specially designed and extended to 150Hz as needed. The cutoff frequency refers to the lowest frequency at which the anechoic chamber is in free field space, and sound waves below this frequency are considered to propagate in free field space.
 
Spike length
 
Sharp splits are commonly used sound-absorbing structures, and their length should be suitable for the theory of 1/4 wavelength. This means that the length of the spike needs to be determined based on the frequency range of the test to ensure effective absorption of sound waves.
 
Soundproof doors, windows, and lighting systems
 
In order to facilitate workers' entry and observation, soundproof doors and windows need to be set up in reasonable positions in the semi anechoic chamber, and a lighting system needs to be installed inside the room. These facilities need to have good sound insulation performance to avoid external interference.
 
The above are the basic requirements for a semi anechoic chamber. It should be noted that these requirements may vary depending on the standards of different countries and regions, so when designing and constructing semi anechoic chambers, it is necessary to refer to the corresponding standards and specifications.