Most of us have probably lived in a house where the walls are so ‘paper thin’ you can hear your neighbours. But constructing walls to resist sound prevents the sound of neighbours and other noise such as traffic intruding on our lives. The transmission suite is used to test wall constructions to ensure they are good enough.
The source room contains two dodecahedral loudspeakers which create high level noise. Some of this sound then passes through the test partition into the receiving room. The noise levels in the source and receiving rooms are measured on six microphones and the difference in the sound level between the two rooms, after a correction for the reverberance of the receiving room, gives a measure for how good the test partition is at resisting sound.
Amongst many other applications, the transmission suite has been used for:
- The facade of Portcullis House which provides offices for MPs next to the Houses of Parliment
- Investigating sound going around partitions or through window supports
- Measuring the transmission loss and absorption of roadside barriers used on British motorways
- The development of high performance double glazing units
- The development of lightweight plasterboard partitioning
- Testing acoustic doors for hotels, executive offices, studios and cinemas.
How is it made?
When measuring the sound transmitted through the test partition, we don’t want to measure sound that has bypassed it and gone through the walls, ceiling and floor of the transmission suite. For this reason, the transmission suite consists of two adjacent rooms structurally isolated from each other and from the surrounding building.
The adjacent walls are each 33cm thick, set 5cm apart and the cavity is filled with mineral wool. This massive construction must resist sound better than any test partition we might want to measure. The rooms have double doors and all services are fed via flexible connections to maintain the integrity of the vibration isolators. You can see the flexible connectors on the service ducts above you.
When measuring absorption, it is important that the sound strikes the test sample from all directions. To achive this ‘diffuse field’ the rooms are constructed with non-parallel walls and have plywood diffusers hung in the space. The measurement of absorption examines the change in reverberance when a test sample is put into the room. To get accurate measurements, the room must be very reverberant to begin with, and so the walls, floor and ceiling are made of massive and dense concrete and brick.
Receiver room surface area of 224m^2
Receiver room volume of 220m^3
Source room volume of 136 m^3
Test aperture surface area 2.40m x 3.60m
Mid frequency (100Hz-2kHz) reverberation time 3.4s (controlled)
The steelwork supporting the floor is located on four anti-vibration mounts with a natural frequency below 10 Hz.
Tests and Standards
Sound insulation testing to BS EN ISO 140-3/ BS EN ISO 717-1 (UKAS accredited).
Vibration surveys can be carried out on partitions using the laser interferometer. Measurement of sound insulation to BS EN ISO 140-3:1995 (UKAS Accredited) Laboratory Measurements of the reduction of transmitted noise by floor coverings on a standard floor to BS2750 Pt.8:1980 / ISO 140-8:1978