The anechoic chamber is immensely quiet and with no room reflections. This makes it ideal for testing very quiet products or hearing very quiet sounds.
This is a room which is acoustically like being high above the ground in the open air because there are no reflections from the walls, floor or ceiling. This means it is ideal for testing the response of loudspeakers or microphones because the room doesn’t affect the measurements. It is also the best place for virtual acoustics – generating auralisations of concert halls, city streets and other spaces.
Final year project student, Patrick Froment wanted to simulate the sound of rain on roofs. He needed to measure the sound of a single raindrop landing on a roof section without the effect of a room, so he used the anechoic chamber. He also needed a very quiet acoustic to measure the sound.
Anechoic Chamber Design
The background noise level in the chamber is immensely low; this is probably the quietest place you’ll ever experience. We need to prevent sound getting into the room and this usually can pass through the walls, or through the foundations of the building. The anechoic chamber is actually a room, within a room, within the Newton building. The walls, floor and ceiling of the inner chamber are made of heavy Accrington brick and concrete to prevent sound getting into the room. Two heavy acoustic doors with rubber seals are used to minimise airborne sound.
Careful design is needed to deal with structure-borne sound, for example, vibrations through the foundations. The whole inner chamber is mounted on a set of springs – neoprene rubber mounts – to reduce vibration, as is done for major concert halls, but this chamber is very much quieter than even the grandest auditorium. The design is very exacting, for instance the bridge leading into the chamber is attached to the outer but not to the inner wall, to prevent the vibration isolation being bypassed.
To remove reflections from the walls of the chamber, every surface is covered in absorbing materials. The inside of the chamber is lined with foam wedges to absorb sound; this includes the floor. The floor you walk on is a wire trampoline stretched between the walls with an acoustically transparent catch net below. The wire floor is safe, but you shouldn’t enter if you are wearing high heels!
Background noise level -12.4dBA
Working area 5.4 × 4.1 × 3.3m
Cut-off frequency 100Hz
- Loudspeaker Testing – Directivity/EASE measurements
- Microphone Testing
- Hearing Protection
- Sound Power including low background
- Noise Emission including low background