The case study contents
Five sections below. The constraint section explains why the obvious solutions were not available.
The brief
- Seven seats with a clear sightline from every one of them.
- A 120 in projected image, with the option of a 85 in panel later.
- Usable at 11pm without a complaint from the adjoining flat.
- The room also had to function as a family sitting room in the day.
The constraints
- Two walls shared with a neighbour's bedroom, both single-brick.
- Slab height of 9 ft 2 in, which limits how much acoustic depth the ceiling can give.
- A 210 sq ft room, which is small for seven seats and a 12 ft throw.
- An AC drain that had to cross the room to reach the shaft.
What we did
- Built a decoupled stud wall on both shared faces with a 40 mm cavity and mineral wool.
- Used fabric-wrapped absorbers at the first reflection points rather than treating everything.
- Kept the ceiling treatment to a 100 mm raft over the seating, leaving head height at the screen.
- Stepped the rear row on a 9 in riser with the AC drain run inside the riser.
- Specified 2700K dimmable lighting in three scenes: entry, viewing and cleaning.
Numbers
- Measured 32 dB reduction from the room to the adjoining bedroom at typical viewing level.
- Seven seats at 22 in per person with a 36 in walkway behind the front row.
- Throw distance of 12 ft 4 in for a 120 in image at 16:9.
- Room reverberation brought to 0.32 seconds in the mid band.
What transfers to your project
- Decoupling a shared wall is the only thing that reliably stops noise transfer. Mass alone does not.
- Treat the first reflection points and the rear wall; treating every surface makes the room dead.
- In a 9 ft slab, put the acoustic depth over the seating and keep it away from the screen wall.
- Plan the AC drain route before the riser is built. It is the cheapest time to solve it.
How to apply it
- Decouple the shared walls. Mass alone does not stop transmission; a cavity and a break in the structure does.
- Treat the first reflection points and the rear wall only. Treating every surface produces a dead room that is unpleasant to sit in.
- Put the acoustic depth over the seats in a low slab, and keep the ceiling high at the screen wall.
- Plan the AC drain before the riser is built. Running it inside the riser costs nothing at that moment and is impossible afterwards.
Three lessons that transfer
- Neighbour noise is a structural problem. No amount of soft furnishing solves a single-brick shared wall.
- A riser is useful storage and a useful service route. Nine inches of step hides a lot.
- Throw distance decides the room, not the screen size. Work backwards from the seat, not forwards from the spec sheet.
Download the case study (PDF) →
See the photographs at home theatre Mumbai and read the home theatre planning guide.
Frequently asked questions
What noise reduction is realistic in a flat?+
Twenty-five to thirty-five decibels to an adjoining room with a properly decoupled stud wall, mineral wool and a sealed perimeter. Beyond that you are into floating floors and isolated ceilings, which in a 9 ft slab is not practical. Thirty-two decibels was enough here to run the room at 11pm without complaint.
How many seats fit in 210 sq ft?+
Seven, at 22 inches per person in two rows with a 36 inch walkway behind the front row. Eight would have fitted dimensionally and would have compromised the sightline from the outer seats. Seat count is usually limited by sightline rather than by area.
What throw distance does a 120 inch image need?+
About 12 ft 4 in for a standard-throw projector at 16:9, which was what this room allowed. Short-throw and ultra-short-throw units change the maths considerably, and are worth considering in any room under 14 ft long.
Should the whole room be acoustically treated?+
No. Treat the first reflection points on the side walls, the ceiling above the front seats and the rear wall. Treating every surface removes all reflection and produces a room that feels oppressive and makes dialogue sound unnatural. Reverberation around 0.3 seconds is the target, not zero.
What does a home theatre like this cost?+
The room construction — decoupled walls, treatment, riser, joinery, lighting and finishes — runs Rs 4.5 to 9 lakh for a room of this size at this specification, ex-GST. Projector, screen, audio and seating are separate and can easily exceed the construction cost.