Sound Insulation
Sound insulation describes the reduction in sound across a partition. The sound insulation across a good conventional, lightweight, office to office construction is typically in the order of 45 dB Dw. This means that if the sound level in the source room is around 65 dB, (a typical level for speech) the sound level in the adjacent room, the receiver room, will be approximately 20 dB (barely audible). If sound levels are increased in the source room to 75 dB (raised voice), sound levels within the adjacent room will also increase to around 30 dB (audible). Sound insulation therefore describes the level of sound lost across a partition and not the level of sound within a adjacent room.
Privacy
Privacy describes the perceived sound reduction across a wall. Privacy is a function of both sound insulation and background noise. Background noise is made up of services noise and environmental noise sources breaking in through the facade or open windows, vents etc.If the background noise within a room is increased by 5 to 10 dB, the perceived level of privacy across a partition is also increased by 5 to 10 dB. Therefore, when looking at required sound insulation levels on-site, it is important to consider both the background noise in the receiver room and the sound insulation across the partition.
Subjective Description of Sound Insulation
The table to the right provides an illustrative representation of privacy. This table specifes two Dw levels for a partition, Column 1. Two levels are provided in this column, one for background noise levels in the receiver room of 35 dBA1, and the second for background noise levels of 40 dBA2. Please see the text above for an explanation.
Rw (Lab Tested Sound Reduction Index) and Dw (On Site Sound Reduction Index)
Two parameters are used to describe the sound insulation of a partition, Dw and Rw. Dw represents the sound insulation between rooms on-site. Since these figures describe the fnal site requirements, Dw levels are specifed by clients and Building Regulations. Rw represents the lab tested sound insulation of an element making up a partition wall/foor type. Due to fanking and other factors, lab rated sound reduction levels will not be achieved on-site. Conventionally, there is a 5 to 10 dB reduction between a Rw lab tested fgure and an on-site Dw fgure. The conversion between Dw and Rw is relatively complex and takes into consideration receiver room volume, receiver room reverberation times and the area of the separating partition. The conversion between Rw and Dw should always be calculated.
| Dw | Subjective description | |
|---|---|---|
| 30dB1, 25dB2 |  |
Most sentences clearly understood |
| 40dB1, 35dB2 |  |
Speech can be heard with some effort. Individual words and occasional phrases heard |
| 50dB1, 45dB2 |  |
Loud speech can be heard with some effort. Music easily heard |
| 60dB1, 55dB2 |  |
Loud speech essentially inaudible. Music heard faintly; base note disturbing |
| 70dB1, 65dB2 |  |
Loud music heard faintly, which could be a problem if the adjoining space is highly sensitive to sound intrusion, such as a recording studio, concert hall, etc |
| 75dB1, 70dB2 and above |  |
Most noises effectively blocked |