Sound Insulation Test Results & What They Mean

Sound Insulation Test Results and What They Mean.

This guide helps to explain the way Acoustic Test results are displayed and what they mean. We have also added a section offering guidance highlighting common errors which can lead to Sound Insulation Test failures 

Acoustic Testing is often associated with UKAS accredited testing laboratories. It is good practice for those involved in Acoustic Testing be a UKAS accredited. An organisation with this accreditation is valuable, as they adhere to rigorous testing in the above areas. APT Sound Testing is a UKAS accredited Acoustic Testing Company.

This is an excerpt from UKAS;

“Accreditation is increasingly being recognised as a valuable tool across a wide range of Government policy areas including better regulation, good governance, fair markets and public confidence. It is already being used by Government as an effective market-led tool for delivering policy more efficiently and to help deliver on its obligations in areas as diverse as healthcare, food production, energy supply, climate change and personal safety.”

How Sound Insulation Testing is performed in the Field and their Results Quantified

There are two types of sound insulation testing that are most commonly carried out in the field, to help to establish the sound insulation performance of wall and floor partitions for Part E Building Regulations.

Airborne Sound Insulation Testing

Approved document E states the following:

The airborne sound insulation of a separating wall or floor should be measured in accordance with BS EN ISO 140-4:1998. All measurements and calculations should be carried out using one-third octave frequency bands. Performance should be rated in terms of the weighted standardised level difference, DnT,w, and spectrum adaptation term, Ctr, in accordance with BS EN ISO 717-1:1997″

An Airborne sound insulation test is carried out using the following methodology:

1. Check full access is possible to the two properties (or more depending on the testing sequence).
2. A background noise level is taken in the receiving room and used for corrections in the measurement (external noise issues such as traffic noise, weather conditions and other influential noises that are outside the test engineers control).
3. A reverberation test is carried out in which a controlled noise is introduced to the receiver room, the noise is then stopped a measurement is taken  the tail at the end (reverb) to check how long it takes for a sound to reduce below 60dB (RT60).
4. Controlled noise is introduced across a broad range of frequencies is amplified through a large Dodecahedron speaker (which should be on a tripod to prevent it from sitting directly on the floor partition). The noise levels can be in excess of 100dB, so no other operatives should be in the vicinity of the testing location. Multiple readings are taken in various locations within the source and receiving room to investigate any variations in performance.

When undertaking the testing, there is a source room and receiving room – the source is where the sound is being carried out or where the speaker is positioned – usually the larger room – and the receiving room being the recording on the other side of the partition from the speaker. The results of this are referred to as onsite sound testing or Field Measurement.

The measurements are expressed as the following;

The Weighted Standardized Level Difference with Spectrum Adaption Term (DnT,w + Ctr), DnT,w is the measured amount without correction, Ctr is the correction for low frequency interference (traffic etc.) and most commonly used in the expression – you would deduct this from the 1^st number. For example; DnT,w (C;Ctr) =65 (-1;-5) dB = 60dB using the correction methodology.

Impact Sound Insulation Testing

Approved Document E states the following:

The impact sound transmission of a separating floor should be measured in accordance with BS EN ISO 140-7:1998. All measurements and calculations should be carried out using one-third-octave frequency bands. Performance should be rated in terms of the weighted standardised impact sound pressure level, L’nT,w in accordance with BS EN ISO 717-2:1997.”

An Airborne sound insulation test is carried out using the following methodology: 

1. Check full access is possible to the two properties (or more depending on the testing sequence).
2. A background noise level is taken in the receiving room and used for corrections in the measurement (external noise issues such as traffic noise, weather conditions and other influential noises that are outside the test engineer’s control)
3. A reverberation test is carried out in which a controlled noise is introduced to the receiver room, the noise is then stopped a measurement is taken  the tail at the end (reverb) to check how long it takes for a sound to reduce below 60dB (RT60).
4. A UKAS calibrated Tapping Machine is placed, which taps the floor with a concise pattern and pressure. This is measured in various locations in the upper room to highlight any potential deviations in acoustic performance.

The tapping machine is places in the source room with the receiving room being the room directly below the tapping machine. Results of this are referred to as a Field Measurement.

The measurements are expressed as the following;

Weighted Standardized Impact Sound Pressure Level (L’nT,w). No correction is applied to this measurement. For example; L’nT,w = 35dB.

Contributing Factors that may affect Sound Test Results in the Field
There is a huge amount of factors that may affect the sound test results whilst undertaking sound insulation testing in the field (onsite) one of the main factors is the quality of workmanship – The quality of building workmanship is very important, and often the most influential to acoustic test results. If the site construction is of a poor standard/quality the sound proofing would need to be more robust to help alleviate these issues. Some negative contributions to the onsite construction may be:

1. Noise flanking due to the materials bridging cavities etc.
2. Unfilled mortar joints.
3. Gaps within plasterboard joints due to poor cutting and sealing of acoustic plasterboard.
4. Not following manufactures installation guidelines.
5. Butting soundproofing materials up against adjacent walls and fixing elements through a neighbouring partition walls or floors.
6. Dot and Dab plasterboard as a way of ‘soundproofing’ instead introducing a cavity – air gap – between materials.
7. Installing underperforming acoustic mineral wool with poor sound density.
8. Packing dense acoustic mineral wool into a cavity, thus bridging the air gap.

If you would like more information on Sound Insulation Test Results and how to pass your sound insulation test then please contact us at info@aptsoundtesting.co.uk or call us on 01525 303905 or visit our website at www.aptsoundtesting.co.uk