Fig. 1: Two goals: keep the sound in, and make it sound right once it is there.
The quick answer
A home theatre runs at 70 to 95 dB with heavy bass, and low frequency is what escapes. Add mass to every surface, walls, ceiling and floor, using MLV with BassBloc over it and a finish layer on top. Then treat the room with absorption at reflection points, bass traps in every corner, and diffusion on the back wall. Seal the door before anything else.
Most home theatre budgets go on the projector, the speakers and the recliners. The acoustics are considered last, if at all, which is why so many finished rooms sound worse than the multiplex they were meant to replace and wake the house every time a film has an explosion in it.
01 /Where the sound escapes
Bass is the problem. High frequencies are relatively easy to stop, but low frequencies carry more energy over longer wavelengths and pass through walls, floors and ceilings with much less loss. Think of a car with the windows up: you cannot make out the lyrics, but you feel the bass from across the street.
That is why a theatre needs mass on every surface rather than just the wall facing the neighbour, and why treating only the walls leaves you with a room that still shakes the floor above.
02 /Measure first
Work out your areas before ordering anything:
- Wall area = (Length x Height x 2) + (Breadth x Height x 2)
- Ceiling area = Length x Breadth
- Floor area = Length x Breadth
- Total = walls + ceiling + floor
03 /Isolation, surface by surface
- Seal the door. A bottom seal and EPDM perimeter tape. A hollow door with an undercut will out-leak an entire treated wall, so this comes first.
- Add the barrier. SoundBlanket MLV at 4mm, rated STC 34, on walls and ceiling. 2.5mm at STC 30 is adequate for the floor. Fix with SR Adhesive or spray adhesive, then nails for final grip. Nails are not needed on floors.
- Add the absorber. BassBloc at 40mm for a theatre, NRC 0.90 under ASTM C423, over the MLV so the surfaces do not resonate once you have made them heavier.
- Cover everything. The barrier and absorber are technical layers and are never left exposed.
04 /Treating the room
Once the room is isolated, the finish layer does the acoustic work. Aim for roughly 80 per cent absorption and 20 per cent diffusion.
- Absorption at first reflection points. Behind the speakers, behind the seating, on the ceiling above the midpoint, and on the side walls level with the listening position. Turbo and other 2 inch profiles are rated NRC 0.90.
- Bass traps in all four vertical corners. Corners hold the most low frequency energy. Four at floor level minimum, full-height columns for a serious room.
- Diffusion on the back wall. SoundaXe wooden panels scatter rather than absorb, so the room keeps some life instead of going flat.
- Carpet the floor, wall to wall. It absorbs and it stops footfall during quiet scenes.
05 /The fabric panelling alternative
Some builds use a timber framework filled with Sound Insulation Pad at 50mm and faced in acoustic fabric. It looks traditional and suits a classic cinema aesthetic. The sequence is the same: MLV first for mass, then the framework, then the infill, then the fabric.
It costs more in labour and depth than surface-mounted panels, and the acoustic result depends heavily on the carpenter. Panels are faster and more predictable. Fabric wins on appearance if that is the priority.
Related reading: the full home theatre guide, and bass trap placement.
06 /Frequently asked questions
Why is bass the hardest part of a home theatre to contain?
Low frequencies carry more energy over longer wavelengths and pass through walls, floors and ceilings with far less loss than speech. It is the same reason you feel a car stereo from across the street without hearing the words. Containing it needs mass on every surface, not just one wall.
Do I need to treat the ceiling and floor as well as the walls?
Yes, for a theatre. Bass will find any untreated surface, and in an apartment the floor and ceiling are usually where complaints come from. Use 4mm MLV on walls and ceiling and 2.5mm on the floor, with BassBloc over it and a finish layer.
How much of the room should be absorption versus diffusion?
Roughly 80 per cent absorption to 20 per cent diffusion. Absorption goes at first reflection points and on the ceiling, diffusion on the back wall. Pure absorption everywhere makes the room feel dead and takes the impact out of a soundtrack.
Panels or fabric panelling?
Panels are faster to install, cost less in labour, take up less depth and give a more predictable result. Fabric panelling over a timber framework filled with Sound Insulation Pad suits a classic cinema look but depends more on the quality of the carpentry.
Sonit writes about practical soundproofing for Indian homes and workplaces, with a focus on what delivers measurable results at sensible cost.
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