Think you know the difference between room acoustics and soundproofing when you’re working on a home theatre or studio? Think again, because this is one of the biggest areas where installers go wrong. Dimi Kyriakou explains.

It’s easy to fall in to the trap of thinking that the addition of some good acoustic foam, carpets or even curtains will do the trick, but sound insulation is not something that should be taken lightly in any project.

The importance of soundproofing in a building is cemented by its presence in the National Construction Code (NCC) series. The sound insulation requirements in the Building Code of Australia (BCA) aim to safeguard occupants in residential buildings from illness or loss of amenity which may result in excessive noise. The minimum requirements are there to reduce noise transmission between attached dwellings and units, as well as other areas within the building.

It is important to remember that the BCA deals only with sound insulation between dwellings that fall into the relevant Classes of building. It does not take into account external factors such as noise produced by traffic nearby, household appliances or home theatre rooms; nor does it recommend which materials should be used in preference over others.

The BCA also measures sound insulation in the Weighted Sound Reduction Index (Rw), which is a number used to rate the effectiveness of a soundproofing system or material. Increasing the Rw by one translates to a reduction of approximately 1db in noise level; therefore, the higher the Rw number, the better a sound insulator will be.

In the case of the BCA, it works between 100Hz and 3,500Hz, which is fine for a normal house or apartment wall. If you are working on a studio or home theatre, this is not satisfactory as most problems in soundproofing occur below 100Hz and you need to work with data that goes much lower in frequency, so Rw values can’t be used.

During our research for this article, it became clear that many custom installers don’t always give sound insulation the credit it deserves during a project. Some may believe they know what to do in terms of soundproofing, but most are not aware of the select difference between ‘soundproofing’ a room versus ‘room acoustics’, which can result in a vastly different experience in a client’s home theatre – and leave your reputation as a quality installer in tatters.

SOUNDPROOFING – WHAT IS IT?
Keeping your sound in the room you are in, or keeping someone else’s sound from getting into your room. There are three general rules to increasing soundproofing:

• More mass.
• More air gap.
• More air tightness.

As well as this there are specialised compounds that have different mechanisms. For example, Green Glue, available in Australia from Ultrafonics, works effectively as a constrained layer damping system.

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 the overall reverb time as well as fl utter, 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 fl utter, slap etc) while keeping the room from being too dead.

IN SUMMARY
There are a number of different measurements for soundproofing, because of the number of different factors to consider. The most effective way to measure how effectively soundproofing works is by playing a series of sounds of varying frequency on one side of a wall or ceiling and using special equipment to measure how much sound carries through to the other side. The difference in the amount of decibels (dB) is what’s known as the ‘sound transmission loss (STL) value’.