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Hello, I’m Ian Rees, I am a consultant with Adrian James Acoustics based in Norwich
and today I am going to talk about sound insulation testing.
We have carried out hundreds of these tests to date
but it seems there is not a lot of information out there
on what exactly is involved in the tests and it is something we are frequently asked
by prospective clients.
So in this short video I will take you through the
sound test procedure and explain some of the requirements for the tests.
Firstly, a little on why we need sound insulation testing.
Testing is required to demonstrate compliance with Part E
of the Building Regulations, which deals with ‘Resistance to the Passage of Sound’.
Testing must be carried out by a UKAS accredited or ANC registered test organisation.
In its current form, Part E has been in place since 2003
in England and Wales. Part E sets out standards for sound insulation across walls and floors
between houses, flats and rooms for residential purposes.
The Regulations apply to both new-build and converted dwellings.
So what is required? Firstly we have to determine the number of tests needed for a particular
development. Testing is done on a sampling basis,
so not every wall and floor may need testing. Typically, at least 1 in 10 of
each type of construction, be that wall, floor, masonry or dry-lined, would be tested.
We work out what tests we think would be required when we provide a quotation but we always
recommend that you check this with Building Control.
A little bit on test conditions. Sound insulation is
heavily dependent on quality of construction and workmanship;
a small hole in a brick wall, for example, can seriously compromise sound insulation
so we need to test when the building is essentially complete.
When we do test we need to ensure that sound transmission
is just through the wall or floor we are testing so all other elements, particularly doors
and windows, must be in place.
The test rooms should ideally be empty and unfurnished.
Crucially for impact tests on floors, soft coverings
such as carpet and vinyl should not be down; we need to test directly onto the
permanent structural floor surface. The only exception to this is where carpets
are to be permanently glued to solid concrete floors.
So on to the tests, and we’ll start with the airborne test.
Essentially the test procedure involves setting up a loudspeaker
on one side of the wall or floor, making a lot of noise
and measuring the difference in noise levels on each side of the wall.
Now, we don’t have a tame building site to work on here
so I am going to demonstrate this between our meeting room
and the small office next to it.
Here is the loudspeaker then, set up ready to go,
and here is the sound level meter; it’s a bit of a brick, but it’s good to
show off the display.
Now, we test using a pink noise signal; it’s a bit like white noise,
which most people are familiar with, but with more bass or low frequency content.
The pink noise signal has roughly equal energy in all
frequency bands, so we can test the complete spectrum in one hit,
which is quick and efficient. For sound insulation, we are testing in one-third
octave bands, between 100Hz, which sounds like this
[tone]
and 3.15KHz, which sound like this [tone]
A quick word of explanation about frequencies. We can think of the audible frequency spectrum
like a piano keyboard, with low frequencies, or bass,
towards the left hand side and high frequencies, or treble,
towards the right. This is also how it is represented on a sound
level meter.
An octave is a doubling of frequency; on a piano this is twelve semi-tones,
say between C and the C above. A third-octave covers roughly 4 semi-tones
or a major third, for example between C and E.
Back to the room then, and we are ready to make some noise.
To test accurately, we need to make a lot of noise
in the source room here, so I need to wear ear defenders,
but we will need very quiet conditions in the receiving room next door.
For this reason we must keep background noise to a minimum,
so if we are working on a building site we usually need all work to stop while we
take the tests.
So here we go…
[noise]
First we take a measurement in the source room.
Room acoustics are quite complex, particularly in small rooms,
and as a result noise levels can vary in different parts of the room.
We therefore need to take an average level over a broad area of the room.
Some testers do this using a series of measurements at fixed microphone positions,
but we use a continuous sweep method like this.
Having finished our measurement in the source room, we move into
the receiving room and take a similar measurement in there.
Like most other branches of science, in acoustics we seldom measure anything just
once. So we move the loudspeaker to a different
position and repeat the measurements all over again.
Measured levels in the receiving room can be
affected by background noise, say from traffic or building works elsewhere on the site,
but also by the reverberation in the receiving room.
So we take some further measurements to compensate for these.
Firstly, we measure background noise.
For this, we turn off the loudspeaker in the source room
then take a measurement in the receiving room.
To measure reverberation time we need to move the loudspeaker into the receiving room.
We fire a short burst of pink noise through the loudspeaker
and when we stop it, the meter measures how long the sound takes to die away.
This waterfall graph shows how the sound decays at different frequencies.
Then as before, we rinse and repeat. A lot.
Now, let’s look at impact noise measurements, which are required through separating floors
where there are flats or residential rooms below.
Impact noise measurements on floors are done a little differently to airborne
measurements. For these we use a tapping machine like this,
which has a row of 5 hammers on a crank. As the crank turns, each hammer is lifted
and then drops. This generates structure-borne noise through
the floor, a bit like footsteps.
We measure this noise with the machine in several different positions around the
room, then measure background noise and reverberation
times in the receiving room, as before.
Once we have finished our measurements, we download and process the results.
Each test generates 176 individual measurements, which ultimately get boiled down
to a single figure result.
The airborne sound insulation result is expressed in terms of DnTw + Ctr,
a weighted standardised level difference. The higher the figure,
the better the standard of sound insulation. The Ctr term is a spectrum correction,
which gives more weight to the low-frequency performance of the wall or floor.
This was introduced in 2003 to give some consideration to the bass generated
by modern hi-fi’s.
The impact result is expressed in terms of L'nTw,
which is the weighted standardised impact sound level.
Unlike airborne sound insulation, which is a level difference,
impact sound is expressed as an absolute level, so a lower figure is better in this case.
We calculate the results on site and will give you an answer
on whether you’ve passed or failed before we leave.
We then provide a written test report, which we will
usually forward to you within a couple of days of the test.
If the tests do fail, we can diagnose the problem
and advise on remedial treatment to bring it up to standard.
Building Control will then usually require a retest
once the work has been carried out.
Don’t panic though – the majority of tests do pass.
Provided that the design is right, the key to success is good workmanship
and attention to detail. We can of course provide advice on acoustic
design and detailing if required before you start.
I hope this video has been helpful and given you an idea of what we do.
You can find out more information on our website at www.adrianjamesacoustics.com
but please do give us a call if we can be of any further assistance.
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