How is the acoustic performance of glass partitions tested on-site?
Having previously considered laboratory testing in our blog posts, An Essential Tip When Comparing Acoustic Glass Partitions and Acoustic Performance of Glass Partitions – Questions to ask of Your Test Certificate; our Technical Manager, Peter Long, takes a look at what this all means on site.
Understanding On-Site Testing
On-site acoustic tests 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 also considers this 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 services etc. (NR value)
- The occupancy type for the space on each side of the screen
On-site performance can be measured in a number of ways. These 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 8dB 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 5dB (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, 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.
Delivering Acoustic Performance On-Site
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.
Hopefully this has been a useful summary of on-site acoustic testing. Keep an eye out for our next blog post when we will explore Flanking Transmission in more detail.