Building Acoustics – Airborne Insulation Measurements

Building acoustics is defined as the science of controlling noise in buildings, covering the control of noise transmission between spaces, and the control of sound within a single space. It is very important to consider building acoustics in the process of design, operation and construction of buildings because it may significantly impact a person’s health, wellbeing, communication and productivity.

Building acoustics is particularly stressed on in spaces such as theatres, concert halls, recording studios etc., whereby the acoustical quality and intelligibility of speech are crucial.

In general, acoustics in buildings can be affected by:

• Room/space geometry
• Sound absorption/transmission/reflection properties of the surfaces in the room
• Airborne sound transmission
• Impact noise
• Structure-borne sound transmission

Building Acoustics – how does sound travel in the building?

Sound energy does not remain in the room where it is produced. Instead, sound propagates throughout the building by any possible transmission path hence intrudes into other rooms, which will end up being considered as noise. Sound energy transmits through the air and via the structure of the building structure. In homogeneous structures of low loss factors (e.g. a solid concrete wall) sound energy is transmitted with very little attenuation. The acoustic parameters to be measured to describe the sound insulation provided by a wall or a floor are the airborne and the impact sound insulation.

Airborne sound insulation

The airborne sound insulation between two rooms is calculated based on the difference between sound pressure levels in the source and receiving rooms, plus a factor taking into account the absorption in the receiving room. In a laboratory, the correction factor involves the area of the test specimen, S, and the equivalent absorption area of the receiving room, A, which can be determined from the volume and the reverberation time of the receiving room. In actual buildings, the correction factor depends on the way the room insulation is defined. The two most usual definitions are: the Standardized Level Difference, DnT, involving the reverberation time of the receiving room referred to a standard reverberation time of 0,5s, and the Apparent Sound Reduction Index, R’, involving the area of the common partition, the reverberation time and volume of the receiving room. Since the reverberation time in a furnished room is about 0,5s, DnT-corresponds to the actual sound insulation experienced by people in a living-room or a bedroom. (R’, on the other hand, takes into account the dimensions of the room.) For small rooms, like bathrooms, R’ is the less stringent requirement of the two.

What you need

Generally speaking, to carry out a BA measurement for airborne sound insulation, you will need to have at least one for each of the following instruments:

• Sound source (a.k.a. loudspeaker + power amplifier)
• Microphone (with pre-amplifier) & DAQ systems, OR

A sound analyser with built-in modules and microphone