We get a huge number of calls for acoustic foam for soundproofing. Adding acoustic foam to one side of a wall is not the way to make the wall more soundproof. The following description explains why.

Soundproofing – what is it?

Keeping your sound in the room you are in, or keeping someone else's sound from getting into your room.

3 general rules to increase soundproofing –

• More mass
• More air gap
• More air tightness

As well as this there are specialised compounds that have different mechanisms e.g. Green Glue works as a very effectively as a constrained layer damping system.

Make sure you know whether you want soundproofing like the building code uses. This is measured in Rw values and works between 100Hz and 3500Hz. If you are doing a studio or home theatre this IS NOT satisfactory as most problems in soundproofing occur below 100Hz. If it is a normal house or apartment wall Rw is fine. Otherwise you need to work with data that goes much lower in frequency and Rw values can not be used.

This means you use thicker layers on walls i.e. more plasterboard, bigger distance between the layers of plasterboard (with insulation in the cavity) and seal every possible edge and gap with a good sealant like non hardening mastic.

Things that DON'T work –

Curtains, acoustic foam, carpet etc are really not the way to improve soundproofing. They may have a slight benefit due to the reduction in sound build up in the room but the first choices should always be those above.

Room Acoustics – what is it?

How things sound inside the room. This means overall reverb time as well as flutter, slap, echoes, comb filters etc. It affects how well sounds are heard in the room compared to how they were meant to be heard i.e. when recorded or played. In other words how realistic and clear things sound, how natural, tight and even the low frequencies sound.

This is generally improved with the use of absorbent or diffusive things. Absorption reduces the amount of sound reflected around the room after the original sound is heard. Too much of this makes it too dead so it must be used in key places. The alternative to more absorption is diffusion which is designed to reflect sound but not in the hard direct manner a wall would. Diffusion is used to make many small reflections in different directions to eliminate problems (like flutter, slap etc) whilst keeping the room from being too dead.