Sound Tests Explained by an Acoustic Consultant
There are many Building Regulations requirements that a new or refurbished residential development must meet. The specific acoustic performance requirements for new builds and conversions are set within Approved Document E ‘resistance to the passage of sound’, as shown in the table. This is an important regulation, as we seek some level of sound privacy from our neighbours, ensuring we can live and sleep in peace.
As shown above, the criteria for refurbishments are slightly more lenient than for new builds.
What is Airborne Sound Insulation and a DnT,w + Ctr?
Airborne sound insulation relates to sound that travels via the air and through separating structures between rooms. It relates to noise sources such as speech, music, television sound…any noise source that radiates into the air, rather than directly into the structure.
The DnT,w + Ctr relates to a level of on-site sound insulation. In simple terms, put a noise source in one room (the ‘source room’), measure the noise level, then go next door (the ‘receiver room’) and measure again, then calculate the difference.
The higher the DnT,w + Ctr, the better the level of airborne sound insulation.
What is Impact Sound Insulation and an L’nT,w?
Impact sound insulation relates to noise generated by actual impact on a structure. Hence this typically is only assessed for intermediate floors, to consider noise such as footsteps, chair scrapes and any other object being dropped or impacting on the floor.
The L’nT,w is determined from measuring sound levels within a room where the floor above is being excited by an impact.
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The lower the L’nT,w, the better the level of impact sound insulation.
What does Sound Testing involve?
Airborne sound insulation tests are conducted by placing a loudspeaker, or two loudspeakers in the ‘source’ room. The acoustic consultant will use their sound level meter to make a series of measurements in the source room. They will then go to the adjacent room (with the loudspeaker still on) and take a series of measurements within the ‘receiver’ room.
After turning off the loudspeaker, two other tests will be made in the receiver room. One is to measure the reverberation time, the other is to measure the background noise level.
Putting these all together, the measurements of level difference, reverberation time, and background noise, enables us to calculate the result DnT,w + Ctr.
Impact sound insulation tests as alluded to earlier, are conducted using a ‘tapping’ machine. This machine is placed upon the floor and set to work, where the acoustic consultant will then move downstairs to measure in the room below. As per airborne sound tests, the acoustic engineer will measure reverberation time and background noise in the receiver room. Putting all this together enables the consultant to calculate the L’nT,w.
How many Sound Tests do I need?
In large scale residential developments, we’re going to have a certain level of repeatability. Do we need to test every single wall and floor? No. Lets say for example, we have a building containing 10 very similar flats, with the same constructions and construction detailing between them. For this, ADE indicates that we would only need 1 ‘set’ of tests, as it suggests that at least ‘one set of tests for every ten dwelling-houses, flats or rooms for residential purposes in a group or sub-group’.
So what defines a ‘set’ of tests?
I hope you enjoyed this short article, and keep an eye out for more articles on the common questions that I get asked by clients in my job as an acoustic consultant. Feel free to connect and message me through LinkedIn, send me an email at chris@parkerjonesacoustics.com, or through our Contact Us page.
