Insight into onsite acoustic testing of glass systems
01 September 2016
PETER LONG, technical manager at UK-based Optima Group*, looks at how acoustic testing of glass partitions is carried out on site.
On-site acoustic tests of glass partitions are carried out in accordance with BS EN ISO 16283 and generate a value for the whole room front. This means the value of the door and screen are effectively rolled into a single composite (aggregate) result.
Breeam (BRE Environmental Assessment Method) also considers acoustic testing in Clause Hea 05 – Acoustic Performance. Here it makes reference to BS 8233:2014, which sets out acceptable levels of sound insulation between rooms, measured in dB (Dw).
To arrive at the desired Dw value, the standard considers three key factors:
• The required speech privacy level (SPL);
• The extent of background noise from mechanical service, among other aspects (NR value); and
• The occupancy type for the space on each side of the screen.
On-site performance can be measured in a number of ways, which can be summarised as:
Dw dB (weighted level difference): This field method of measurement simply measures the difference in sound levels on either side of the partition and will include any losses from flanking. Depending on the individual circumstances, the measured value could be up to 8 dB lower than the lab-tested value for the partition.
DnT,w dB (weighted standardised level difference): A field measured value, derived in the same way as Dw and including the effects of flanking transmission, but corrected for the amount of absorption within the receiving room. The result would be expected to be at least 5 dB (Rw) lower than the lab-tested value for the partition on its own.
R’w dB (weighted apparent reduction): A field measured value, expressed in decibels, using the same method of measurement as Rw (weighted sound reduction index – laboratory measurement), again including the influence of flanking sound.
This method of measurement would not be expected for typical office partition scenarios and is used for testing walls and partitions which have very large surface areas.
There are a number of components in a finished fit-out that can cause the on-site performance of a partition to be poorer than the laboratory-tested value. This is known as Flanking Transmission and can occur through the ceiling or floor plenum, curtain-wall mullions, abutments, around the partition via penetrations and around the door leaf.
All elements of a room dividing construction need to perform in tandem. Any under-performing element will cause a failure against the specified performance.
* UK-based Optima specialises in designing, developing and installing office partitions. The group says it has become the first choice for providing commercial workspace through innovative design, superior installations and excellent customer service.
