Articles and whitepapers

Residential Sound Proofing (4/7/2005)

By Mike Ervine, Acoustiblok UK

'Pumping up' the volume may be top of the list in planning a home media room, but ask any sound consultant, and you will soon discover that how quiet the room should be is just as important.

After all, no one wants a film's cliff hanger moment to be punctured by a ringing telephone, or a favourite piece of music accompanied by the whir of the washing machine. Those who invest in a home theatre want the best sonic experience, and this comes from a quiet room. Similarly, the rest of the household and neighbours should be spared the muffled dialogue and machine-gun fire of an action movie, or the booming base from a rock anthem. There is no getting away from it, acoustic insulation is as important as the sound system itself.

Sound proofing the walls

How sound travels

Sound waves move in all directions, travelling at 1,130 feet per second. They look for any means available to travel along, and can be transmitted by a home's structure, for example through wood, steel, masonry, concrete, pipes and plumbing fixtures. Vibrations can excite wood studs, or a concrete floor slab and then race through the house. Heating, ventilating and air conditioning ducts can also move sound along from one part of the house to another. As we all know, bass noise is particularly insidious. Its low frequencies are non-directional and find their way through the tiniest of holes and into the next room, and every bit of bass that escapes the room diminishes the overall effect that you are hearing and feeling.

Controlling sound

There are four ways to control sound as it travels through the air: break it up, absorb it, block it and isolate it. Walls and ceilings break up sound, and gypsum plasterboard can stop a certain amount of noise leakage. But plasterboard alone does not stop sound dead. Adding more layers of plasterboard will help to seal in upper frequencies but will not do much for the bass.

The best results are gained by separating the walls from each other. This prevents the sound from resonating through the studs and into the other rooms. Basically, building two walls with an air space in between is the best way to isolate the sound, and what is put in between the space in terms of acoustic treatment, is key.

Stud wall with acoustic treatment

Acoustic treatments

There are various acoustic treatment systems which come with pre-sandwiched layers of fibreglass wool. They can provide varying levels of noise abatement as they aim to reduce both airborne and impact noise. Preventing noise continuing through the substrates of the building in the first place, is as important as absorbing sound to prevent vibration and distortion.

To achieve this with open-cell materials to the desired degree would increase the thickness of the wall greatly. However, placing a pressed poly-vinyl noise-barrier-type material into the existing cavity with loose fibreglass, not only reduces the cost of extra bespoke building materials, labour and time, but also ensures the wall dimensions almost remain the same. With Document E of the Building Regulations placing an increased demand on builders to reduce the passage of sound through dwellings, such solutions are now being used not only the AV industry, but in normal building practice.

The actual sound insulation component of the system can also vary enormously. Some products to be placed in stud walls can be inches thick, therefore shaving a significant amount of space off the room - a consideration if space saving is crucial. For thinner solutions with hefty noise abatement, the U.S. is leading the way with products such as Acoustiblok 3mm and 6mm vinyl. The 3mm flexible barrier is installed between the stud and dry wall. Each layer reduces sound transmission by an average of 26dB, and an impressive 19dB @100Hz - which is more effective than lining your room with thick sheets of lead.

Acoustiblok being used in a stud wall

To prevent sound from entering or leaving a room, it is also essential to caulk all openings around electrical boxes, light switches, doors, windows, and air ducts. Be attentive to in-wall or in-ceiling speakers, since their large mounting cavities can pass along a good deal of sound. Windows and doors will also require attention, as they leak a fair amount of sound. An airtight gasket or seal around the door frame, and double-paned windows made of thick plate glass with a heavy inert gas between the panes, work best.

Sealing wall outlets

Conclusion

Any custom installer worth their salt, who wants to provide their client with a media haven where they can play music and movies as loud as they want, at any time of day or night, must not only pay attention to the design of the system, but give careful consideration to noise control too. This should be planned and budgeted for, from the outset. While it is beyond the scope of this article to go into costs - as each media room is individual - what I will say is, if you're investing in a meaty sound surround system, don't skimp on the sound control!

Mike Ervine is the Managing Director of Acoustiblok UK Ltd, provider of space-saving high dB noise control system from the US.

www.acoustiblokuk.com