A room that creates free field conditions but above a reflective plane. Above a certain frequency, all sound waves that hit the walls or ceiling of the chamber will be absorbed. This type of chamber is normally used in Auto Parts Testing, Vehicle testing with a rolling round so that the vehicle may be driven. The semi-anechoic chamber then forms a controlled environment with the surrounding acoustic conditions behaving as a sterile version of the real world. In this way, accurate measurements of the sound inside and outside the vehicle can be made under operating conditions.

A semi-anechoic chamber is a type of chamber that combines the characteristics of an anechoic chamber and a reverberation room. The chamber has one or more walls that are lined with sound-absorbing materials to prevent sound reflections, while the other walls, ceiling, and floor are reflective, allowing sound waves to bounce around.

The purpose of a semi-anechoic chamber is to provide a controlled acoustic environment for testing and measurement of audio equipment, such as speakers and microphones, where a full anechoic chamber may not be necessary or practical.

The absorptive materials used in a semi-anechoic chamber are typically placed on the walls facing the equipment being tested, while the remaining surfaces are covered with reflective materials such as concrete, metal, or glass. This creates a partially isolated space with reduced reflections, allowing for more accurate measurements of sound pressure levels, frequency response, and other acoustic characteristics.

Semi-anechoic chambers are commonly used in the automotive and aerospace industries for testing vehicle and aircraft noise emissions. They are also used in the electronics industry for testing the acoustic properties of consumer electronic products.