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Acoustics Testing

Semi-anechoic room

Hemi Anechoic chamber

This is a room where sound reflections only come from the floor because the walls and ceiling are absorbent. The solid floor makes this room much easier to work in than the anechoic chamber, because equipment can be stood on the solid floor. Often, we put absorbent material on the floor to reduce floor reflections.

Example application – diffuser scattering

The standard method for testing room acoustic diffusion coefficients was developed as part of a research project at Salford. The most efficient method is done in a semi-anechoic chamber with all the microphones, the loudspeaker and diffuser sample placed on the hard floor in a boundary plane measurement. The absorbent walls and ceiling then prevent unwanted reflections. The room is quiet so background noise doesn’t affect measurement accuracy.

Example application – public engagement

Television has always enjoyed filming in our anechoic chambers. Our first chamber was used as a mock up of a torture chamber for Granada TV, and more recently, Richard Hammond was filmed by National Geographic breaking a glass using the sound from his guitar. Producers like the anechoic chamber, but often use the semi-anechoic because of problems setting up equipment on a trampoline floor. We filmed high speed footage of acoustic phenomena in this room, and have used it to make videos for use in classrooms. See www.acoustics.salford.ac.uk/schools

Vital statistics

Background noise level 3.8dBA
Working volume 4.2m x 3.3m x 3.0m
Cut-off frequency 250Hz

Tests and standards

Sound power level measurement to BS ISO 3744 / ISO 3745 and BS 4196

Student semi-anechoic room

The student anechoic room is part of the student audio and acoustics laboratory. It is used exclusively for teaching. Typically it is used for noise measurement in the Applications of Acoustics module and for measuring the response of loudspeakers in the Electroacoustic Transducer Design module.