Sound Insulation is the name that is given to describe the reduction of sound which passes through a structure.
When sound is carried between two spaces the sound energy takes two routes. The first is directly
through the wall/floor. The second is indirectly through the surrounding structure and this is called 'flanking'
noise. This type of noise often takes deceptive routes around a structure such as the walls and floor which flank a partition
or an open window, air ducting, doorway or corridors etc. This is why it is extremely important, when building an acoustic partition, to make
sure that everything is airtight as the smallest crack or hole can let huge amounts of sound through.
If you have a noise problem the first thing to address is the weakest part of the structure in question.
The sound insulation of walls is normally only related to airborne sound such as speech or the TV but floors usually need to
protect against the transmission of impact sound such as heavy footsteps etc.
Generally the average airborne sound insulation of a solid structure is governed by its mass.
The heavier the material the greater it is at resisting airborne sound transmission.
The soundproofing performance of any additional structure will always be better if the additional higher
mass layers are isolated from the existing structure.
Remedial actions for Improving Wall Acoustic Performance.
If you are having noise problems with an existing partition wall the first thing to do is inspect the wall and
adjoining areas of abutting walls closely to ensure that optimum sound insulation is being achieved. Any small holes
or cracks will let significant amounts of sound through so these need to be sealed with mastic if small or mortar if large.
DO NOT USE EXPANDING FOAM FILLERS for this purpose.
The area of the wall in the roof space should also be examined. Any missing bricks should be replaced. Any small holes, cracks or unfilled mortar joints
should be sealed with sand and cement mortar mix. There may also be holes, cracks or bad mortar joints in concealed
areas such as behind skirting boards, in the space between the floor boards and ceiling or underneath a wooden ground floor.
You will need to lift the floorboards to check these areas.
If the joists run into the wall then check for gaps between
the joists and wall. If any are found they too should be sealed with the appropriate material. Any cracks at the junction
of the wall with the ceiling or floor should be sealed.
To give you an idea of the difference this alone can make:-
Any hole or gap will reduce the performance of a partition SIGNIFICANTLY.
A 25mm square hole, in an otherwise acoustically sound partition, can reduce the performance by up to 15dB!.
A sound leak, amounting to one-tenth of one percent of a partition area, will limit the effective performance to
around 30dB even if the partition was rated to be around 55dB.
For example, in a wall of area 10m² a gap this size
would have an area of 10cm² and would be obvious as a hole. HOWEVER a crack 1mm wide by 1m long at a periphery
point would be just as detrimental. Cracks such as these can often go un-noticed especially where a mastic seal has
been omitted or incorrectly applied.