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
What are you measuring?
For building acoustics, the degree of sound insulation achieved by constructions inside buildings is measured. The objective is to know how much insulation is offered by a wall (including doors/windows), that divides two spaces inside a building.
Each value determined is actually based on multiple measures
- Insulation – measures frequency dependent sound insulation curves, defined by ISO and ASTM standards (ASTM E332:TL, ISO16283, ISO140)
- SRI/STC – expresses sound insulation in a single number measure
How it works?
The procedures differ depending on the measurement conditions, whether it is a field measurement, or a laboratory measurement.
Typically, field measurement can be done with a sound analyser to pick up the measurements, whereas in laboratories, they use a more complete system with more components involved. Both have similar concepts but laboratory measurements will have more procedures to take note on, in accordance to the standards.
Here is a video showing how a field measurement for airborne sound insulation can be done by using a sound analyser:
- Set up a noise source in the sending room
- In Real-Time Analyser (RTA) Mode (or equivalent), measure the noise at multiple locations in the sending room (at least 5 measurements to be taken)
- Measure at least 5 locations in the receiving room
- Measure the reverberation time in the receiving room, in Reverberation Time (RT60) mode. This is needed for corrections applied in calculations of insulation values
- Measure or estimate the volume of the receiving room and the surface area of the dividing wall (also for corrections)
- Compile a table of all sending and receiving RTA measurements in the insulation or SRI/STC modules
- Enter the RT60 measurement number and the receiving room measurements
For laboratory measurements, users can consider using a complete system setup for Building Acoustics applications that is user-friendly and can be operated by a person who has undergone basic trainings on how to operate the system. Some system upgrades can include:
- Multiple microphones or rotating microphone booms
- Multiple loudspeakers with individual signal generator or a movable single loudspeaker on a controllable slide
- Remote on/off switching of tapping machines based on software
- Automated read-in of test chamber temperature, humidity and air pressure
- Manually operated test sequences, or automated measurements based on a pre-programmed Scheduler
- Larger laboratories with several measurement chambers for parallel testing controlled from multiple PC via overall LAN network
Below is an example of a typical setup for airborne testing with microphone booms, two parallel loudspeaker system for level measurements and one dedicated loudspeaker system for reverberation time measurements.
AVCM offers various products relevant to building acoustics measurements. Please do not hesitate to get in touch with us should you wish to know more about them.
Audio, B. (Director). (2020). Measuring airborne sound insulation (building acoustics) [Motion Picture].
Buildings, D. (2021, November 2021). Building Acoustics. Retrieved from Designing Buildings – The Construction Wiki: https://www.designingbuildings.co.uk/wiki/Building_acoustics#:~:text=Building%20acoustics%20is%20the%20science,of%20sound%20within%20spaces%20themselves.
Norsonic. (n.d.). Measurement System Nor850. Retrieved from Norsonic: https://web2.norsonic.com/wp-content/uploads/2021/02/PD-850-Ed1Rev3En-0318-web.pdf
Written by Khei Yinn Seow
Posted on May 13, 2022