‘Sound Insulation’ refers to the ability of building materials, or combinations of materials, to inhibit the passage of sound.
When a sound wave impacts a surface, some of the sound is:
Building elements such as walls, floors, doors and glazing all have their sound insulation characteristics, (such that we can determine how much sound energy is transmitted through them. )
Partitioning serves several functions in the built environment, one of which is to stop the passage of sound between areas. Walls should be designed and constructed to allow a minimum of sound energy through them.
If we consider party walls between dwellings, these walls should have a relatively high sound insulation performance because the last thing we want to hear is our neighbour!
For existing buildings, existing partition walls can present an acoustic challenge. These walls may not have been designed and constructed with acoustics in mind, and therefore might not be fit for purpose. Measures would then need to be taken to improve the sound insulating properties of the partition.
The following is a real-world example that highlights three common techniques that Acousticians refer to when improving the sound insulation performance of a wall:
A school decides to repurpose an unused room into a larger meeting room for staff. However, the space in question is situated adjacent to the School’s music room. The concern here is that noise from the music room could disrupt the meeting and negatively impact speech intelligibility. Both rooms could likely be occupied and used at the same time.
A lightweight wall exists between the two spaces, consisting of a 12.5mm plasterboard on either side of a 92mm metal stud, giving a theoretical sound reduction of Rw 36dB. There are no penetrations in the wall for services or sockets, extending from slab to slab.
Musical performances in the music room rendered speech intelligibility very difficult in the adjacent room, making it practically impossible to hold meetings in such conditions.
Clearly, the sound-insulating properties of the existing wall is not good enough and this would need to be improved in order for both spaces to be used simultaneously in their intended purpose.
A significant improvement in the sound insulation performance of the partition would be achieved by changing the existing 12.5mm plasterboard with 2no. Layers of 15mm ‘Acoustic-rated’ plasterboard on either side of the stud; this is the ‘Add Mass’ approach.
Note: every doubling of mass will provide an additional 6dB of attenuation.
Rockwool insulation is easy to install, inexpensive and yields an appreciable improvement in the overall sound insulation performance across the relevant frequency range.
A resilient bar could be installed on one side of the stud. The resilient bar de-couples the plasterboard lining from the stud, inhibiting the transfer of sound through the structure. An even greater improvement in the overall sound insulation performance of the wall is achieved; this benefit is particularly pronounced in the middle and high frequencies.
Implementing all three techniques will significantly reduce the noise transfer between the music room and the future meeting room.
Note: these results are based on theoretically modelling of sound insulation performance. The true performance will differ in real-world scenarios.