Fig. 1: A home theatre has two acoustic jobs. Keeping sound in, and making it sound right once it is there.
The quick answer
A home theatre needs isolation and treatment, and they are different jobs. Isolation is mass: MLV and BassBloc built into the walls, ceiling and door. Treatment is what happens inside: absorption on first reflection points, bass traps in every corner, diffusion on the back wall. Foam alone does the second job and none of the first.
Building a home theatre is more than a projector and a speaker package. Without isolation, traffic and household noise arrive during quiet scenes, and your subwoofer arrives in someone else's bedroom. Without treatment, expensive speakers fire into a room that smears everything they produce. This guide covers both, in the order they should be done.
01 /Two jobs that get confused
- Isolation stops sound crossing the boundary, in either direction. It is achieved with mass, damping and sealing. Nothing else does it.
- Treatment controls what happens to sound inside the room: echo, reverberation and bass build-up. Absorption and diffusion do this.
A room can be perfectly isolated and still sound terrible. It can also sound wonderful and still wake the house. You need both, and isolation has to come first because it is built into the wall.
02 /Where sound actually leaks
| Path | Why it fails | Priority |
|---|---|---|
| Doors | Hollow core with an undercut for airflow. A 5mm gap behaves like an open window | Fix first, cheapest win |
| Windows | A few millimetres of glass against 200mm of masonry | High |
| Walls | Brick and gypsum transmit vibration without added mass or damping | The main build |
| Floors and ceilings | Structure-borne transfer, worst in apartments and duplexes | Essential above ground floor |
| Corners | Bass accumulates and muddies dialogue | Treatment, not isolation |
03 /The three-layer wall build
- Barrier layer. SoundBlanket MLV is dense, limp and thin, so it adds blocking mass without eating the room. 2.5mm is rated STC 30, 4mm is rated STC 34. Use 4mm in a theatre. Fix with SR Adhesive or nails.
- Absorption core. BassBloc at 20mm or 40mm, NRC 0.90 under ASTM C423, sits over the MLV to absorb vibration and kill wall resonance before it becomes low-end boom.
- Finish layer. Cover everything. PET felt panels for a clean look, wooden slats for diffusion and warmth, or perforated gypsum where budget is tight. MLV and BassBloc must never be left exposed.
Fig. 2: Barrier, core, finish. Skip the middle layer and the wall rings. Skip the first and nothing is blocked.
04 /Treating the room
- Absorption on walls and ceiling. Acoustic foam at first reflection points controls mid and high frequencies. Do not cover every surface, or the room goes dead.
- Bass traps in every vertical corner. Corners hold the most low-frequency energy. Foam traps floor level as a minimum, wooden bass trap diffusers floor to ceiling for a serious room.
- Ceiling clouds above the seating. These stop the first reflection off the ceiling arriving just behind the direct sound, which is what blurs dialogue.
- Diffusion on the back wall. Wooden diffusers scatter rather than absorb, keeping the room alive instead of flat.
05 /Doors and windows
- Seal the door. Perimeter seals and a bottom drop seal close the gaps. A solid core door with seals outperforms an expensive wall with a hollow door in it.
- Treat the glass. A dense multilayer soundproof curtain handles windows and balcony doors without replacing glazing, and blocks light at the same time.
06 /Why the old approach underperforms
| Traditional method | Three-layer system |
|---|---|
| Mineral wool and upholstery foam | MLV barrier with high-density absorber |
| Covered in low GSM fabric | Finished with tested acoustic panels |
| No performance data | Published STC and NRC values |
| Absorbs, but the leaks remain | Isolates and treats as separate layers |
| Often over-deadened or uneven | Absorption balanced with diffusion |
Related reading: our full home theatre soundproofing guide, and where to place bass traps.
07 /Frequently asked questions
Will acoustic foam alone soundproof my home theatre?
No. Foam improves how the room sounds by reducing echo and reverberation, but it has almost no mass, so it does not stop sound leaving or entering. Isolation needs MLV and a dense absorber underneath the finish. Foam is a good starting point for treatment on a budget, not for soundproofing.
What thickness of MLV should a home theatre use?
Use 4mm. SoundBlanket 4mm is rated STC 34 against STC 30 for the 2.5mm, and the extra mass matters most at the low frequencies a theatre produces. The 2.5mm suits lighter applications where room depth is critical.
Can I install this myself?
Partly. Surface installation is straightforward, but a carpenter familiar with foam and timber will get better results on the framing and finish. MMT Acoustix offers free consultation to installers to make sure the layers go on correctly.
Is any of this removable later?
Mostly. Panels and foams are surface applied and come off or upgrade without damaging the wall behind. Layers fixed with adhesive rather than mechanical fixings are the ones that leave marks, so plan for that if the room is rented.
How do I fix boomy bass and unclear dialogue?
Both usually trace to the same cause. Bass building up in corners masks the speech range. Treat all four vertical corners with bass traps, add ceiling clouds above the seating, and put diffusion on the back wall so the room stays lively rather than dead.
Are the materials fire rated?
The felt finish panels are Class A rated under ASTM E84 and are VOC free, odourless and non-toxic. Ask for the specific rating on any material going into a theatre, since fire performance varies considerably between suppliers.
Sonit writes about practical soundproofing for Indian homes and workplaces, with a focus on what delivers measurable results at sensible cost rather than what simply looks the part.
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