Acoustic Calculations & Engineering

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When a new construction, or the conversion of an old construction results in two adjoining dwellings being separated by party elements (wall or floor), it is a Building Regulations requirement for this or these elements to be tested in terms of their sound insulation performance.

Which elements require testing?

The simplest scenarios to imagine are those where two flats are separated by a single partition, be it a wall or a floor.

Single Wall Test:

In the case of a single wall example, two pairs of rooms connected by the wall are chosen as the test rooms.  These should all be living areas (bedrooms, lounges, dining rooms etc.) where possible, rather than bathrooms or kitchens etc.  For each pair of rooms, the larger of the two should be chosen as the source room and an airborne sound insulation test carried out.

In this way, two individual airborne acoustic tests are undertaken to generate the insulation performance results.

airborne sound test
  • Test done between two pairs of rooms about the party element
  • Rooms should be living areas
  • Larger space should ideally contain the testing noise source

NB: This is an ideal case, exceptions can be made where certain criteria cannot be met.

Single Floor Test:

Similarly to the single wall testing scenario, two pairs of living areas about the party element are chosen.  However, for each pair of rooms, two types of sound insulation tests are required; one airborne (tests insulation from lower to upper storeys) and one impact (tests insulation from upper to lower storeys).

In this way, a total of four individual tests are required for a standard floor sound insulation test.

floor test
  • Tests done in two pairs of rooms about the party element
  • Rooms should be living areas
  • Airborne tests upwards if possible (in order to avoid vibrating the floor with the noise source), impact tests always downwards

Multiple Walls or Floors

If a single construction has either multiple separating walls or multiple separating floors, a 10% sample of the party elements may need to be tested.  When there are up to ten of either element, only one partition needs to be tested (two pairs of rooms).  It may give a better idea of average sound insulation performance to take one pair around one element and the other pair around a different element, although this is not compulsory.

multiple sound tests
  • For up to 10 flats, 1 element is tested
    • Walls: 2 Individual tests
    • Floors: 4 Individual tests
  • For 10 to 20 flats, 2 elements are tested
    • Walls: 4 individual tests
    • Floors: 8 Individual tests
  • For 20 to 30 flats, 3 elements are tested etc.
    • Walls: 6 Individual tests
    • Floors: 12 Individual tests


When a number of flats are separated by walls and floors, testing should occur on each type of element as if it were a single partition.

wall and floor tests

Test Procedures

In order to have analysable results, two measurements are needed in order to correct the results for receiver room characteristics. These are the background noise of the receiver room and the reverberation time of the receiver room. As well as these characteristic data, the actual airborne or impact tests are undertaken.

Background Noise

The background noise in the receiver room is measured so that the sound insulation test results are corrected for external sound, such as traffic noise. The background noise is taken into account when calculating the sound insulation rating for the party element.

Reverberation Times

The reverberation time of receiver rooms is measured so that corrections can be applied to account for the characteristics and absorptiveness of the room.  In each room, the reverberation time is calculated six times and an average is taken.

To measure the reverberation time, a speaker is used to generate white noise in such a way to create a diffuse field. The speaker is then instantaneously switched off, and the time taken for the noise in the room to drop by 60dB is measured.  The average of the six measurements is applied to the calculations to determine the sound insulation performance.

Airborne Testing

In order to rate the airborne sound insulation of a party element, speakers are used to generate white noise, usually at levels of around 100 decibels, in the source room.  Then, using a moving microphone technique, the average sound pressure level is measured.

The same procedure is used to measure the average sound pressure level in the receiver room.

From these measurements, combined with the background and reverberation time measurements, the airborne sound insulation of the party element can be calculated.

Impact Testing

Impact tests require a tapping machine to create impact sound directly on the floor construction in the source room.  Measurements are taken in the receiver room, in third octave bands from 100Hz to 3150Hz. The impact sound pressure level is calculated, giving the floor an impact sound insulation rating.

Measurements are taken with the tapping machine in at least four different position and at least six measurements are taken.

This gives six results which can be used along with the background noise and reverberation time of the source room, to calculate an impact sound insulation rating.

Testing Requirements to be Met

In order to meet resistance to the passage of sound standards, the flats must meet values set in Building Regulations 2000 Approved Document E 2003.

This document presents the following criteria to be met:


Test Element

Airborne Sound Insulation 
DnT,W + Ctr dB
(Minimum Values)

Impact Sound Insulation
L’nT,W dB
(Maximum Values)

New Build














Impact tests are designed to test an element’s performance against footfall, therefore this test is not necessary for a wall

Airborne Values (DnT,W + Ctr dB) represent the weighted, standardised level difference between a source room and receiver room (i.e. how much quieter the receiver room is) (DnT,W) with an added correction term (Ctr), which characterises the level difference with respect to urban traffic noise.

As the airborne result is in terms of a level difference, the higher it is, the higher the acoustic attenuation and therefore the better the performance.

Approved Document E 2003 states that in a new build, the party element must achieve an Airborne Sound Insulation result of at least 45dB and a conversion must achieve a result of at least 43dB.

Impact Values (L’nT,W) are given as the weighted, standardised impact sound pressure level (i.e. how much impact noise can be heard in the receiver room.

As this result is given in terms of level, the higher it is, the less of an effect the party element is having, and the worse the sound insulation performance.

Approved Document E 2003 states that a new build must have an impact sound insulation result of no more than 62dB, while the result for a conversion must be no more than 64dB.


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