A human ear can detect frequencies between 16Hz to 20000Hz. When considering acoustics for building or architecture it is generally the range between 50Hz and 5000Hz that we are concerned with and which will affect the comfort levels of those working or living inside a building or structure.
The acoustic insulation property of a glass unit or frame is defined by R which represents the acoustic power difference from one side of the glass to the other. This value is measured in specific laboratory settings under BS EN standards in order to achieve a constant, corresponding acoustic index across all building materials.
It is the Rw value that is the most common method of rating the sound insulation of any glass item. It incorporates the weighted corrections for the human ear as a receptor and is expressed in dB (decibel).
As Rw values are measured in factory settings they cannot always give a true reflection of the sound insulation of a building when incorporating things like roof joints, hollow flooring and connections and how the whole installation will perform under various ‘real-life’ acoustic situations and sources. Corrections to the Rw value can be included to give a more accurate determination of the sound insulation of an installation.
These two corrections are broken down by EN ISO 717-1 as ‘pink noise’ (C) which represents outside background noise and ‘road traffic noise’ (Ctr) and are incorporated with Rw to create a common index of Rw(C;Ctr). Both C and Ctr are generally a negative value, detracting from the total sound insulation of the whole installation to give a more realistic noise reduction factor.
Every glass type and thickness will vibrate differently at different frequencies meaning that at certain frequencies the noise reduction value of a glass installation can be very low. By changing the composition and thickness of the glass you can move this dip in sound insulation towards lower frequencies making the noise more comfortable to hear but in order to reduce the critical frequency to below 100Hz, making it insignificant enough to be ignored, the glass would have to be 12cm thick!
Acoustic interlayers in glass work by changing the oscillating nature of the glass panel and therefore removing this critical frequency effect, allowing the glass to maintain a steady acoustic reduction up all frequencies. Using an acoustic interlayer into a glass unit will increase the sound insulation factor (R) from around 3dB to 5dB depending on the glass installation, and depending on the glass composition will give you an overall Rw value of anywhere from 35dB to 49dB.
These high acoustic value glass units can be used on internal uses to reduce sound transference between spaces or on external faces. Acoustic interlayers can be laminated in the largest glass panels available in the UK giving much greater freedom with design.
If you are installing acoustic glass into a framing you will need to consider the acoustic rating of the framing system itself to determine how the whole installation will insulate against sound pollution. Talk to IQ Glass for more information.