By space
How a home theatre is designed
How the physics is applied in a dedicated cinema room: isolation first, then layout, then bass, then reflections — in that order.
8 min read6 sourcesChapter 21 of 24
Schematic
A dedicated theatre in plan. Isolation shell around everything. Front three channels behind the acoustically transparent screen, subwoofers against the front wall, surrounds and heights at their angles, first reflection zones on the side walls and ceiling treated, deep traps in the corners, and the rear wall diffusive or absorptive depending on depth.
Animated illustration of the principle. Not measured data.
A home theatre is the most demanding small room there is. It has to reproduce a mix made in a controlled studio, with bass that shakes the seat, in a room a fraction of the size of the cinema it imitates, without waking the house. Every chapter on this site applies to it at once.
1. The shell
A theatre is loud by design, and its bass travels through structure. If the room has to coexist with bedrooms, a study or a neighbour, isolation is settled before anything else: a double-leaf wall build, a resiliently hung ceiling where the slab above is occupied, a solid sealed door, and any window either removed or rebuilt as acoustic glazing. This is the expensive, invisible part, and it cannot be added afterwards without tearing out the finishes.
2. The layout
Screen size and seating distance are decided together, and they set the loudspeaker positions. With a large screen the front three channels go behind it, on an acoustically transparent fabric screen, so that dialogue comes from the mouth speaking it. Subwoofers — usually two or more — are placed for even bass across the seats, not for convenience. Surrounds and height channels go at their designed angles, and then disappear behind fabric so the room reads as a room, not a rack.
The primary seat avoids the centre of the room’s length. Second and third rows are raised so the screen is seen over the row in front, and their bass is checked, not assumed.
3. The bass
Below about 120 Hz the room behaves increasingly as a set of modes. Multiple subwoofers driven against each other, deep porous traps in every corner, and — if the measurement shows a stubborn mode — a tuned absorber built into the front wall. This work is done and measured before the reflection treatment, because it is the hardest to change later and it sets the character of every explosion and every note of the score.
4. The reflections and the reverberation
With a full surround array the room’s own reflections mostly get in the way, so a theatre leans towards absorption: thick panels at the side-wall and ceiling first reflection zones, an absorbent front wall around the screen, and a floor with carpet. The rear wall is the one place diffusion often earns its keep, so that the back of the room does not slap and does not feel dead. The target reverberation is short — the EBU and ITU formula for critical listening rooms puts a typical home theatre at about 0.2–0.3 s — and, crucially, even across the range.
All of this is then hidden. Stretched fabric over the whole wall surface lets the treatment be sized by what the room needs, and lets the room look like a cinema.
The sequence is the whole method: shell, layout, bass, reflections, then measure and calibrate. Rooms that skip a step spend the budget correcting for it later.
5. Calibration
Only once the room is built and measured does the system get tuned to it: levels, delays, crossovers, and cut-only equalisation of what the seats share. The calibration is the final adjustment, not a substitute for the four steps before it.
For integrators and architectsThe numbers, the standards, and what to specify
- References
- Loudspeaker positions from ITU-R BS.775 / BS.2051 and the format makers’ public guides; screen and seating geometry from viewing-angle and sightline calculations; background noise to an NC criterion. Record any deviation with the reason.
- Isolation target
- Set a transmission-loss target per octave band to the adjacent rooms, with 63 and 125 Hz included, and review flanking through the slab before the room location is final.
- Screen
- Acoustically transparent screens attenuate high frequencies slightly; the front loudspeakers are equalised for it in calibration. Woven and perforated types differ in that attenuation and in moiré risk with the projector.
- Reverberation
- Design curve from the EBU Tech 3276 / ITU-R BS.1116 formula Tm = 0.25 × (V / 100 m³)^⅓ s averaged from 200 Hz to 4 kHz — about 0.21 s at 60 m³, 0.25 s at 100 m³, 0.29 s at 150 m³ — low bands held within ~1.45× mid, no cliff at the top. Full-wall fabric systems allow treatment depth to vary by location behind a continuous finish.
- Verification
- Frequency response, waterfall and ETC at every primary seat, before treatment and after, then post-calibration. Deliver the files.
- Calibration
- Levels, delays, crossovers, subwoofer alignment and cut-only EQ set at the seats and documented at handover — see the calibration chapter.
What to write into the brief
- Design in the order shell → layout → bass → reflections → calibration, with a measurement gate between each.
Sources
- 01Dolby — Dolby Atmos Home Theater Installation Guidelines (2018)
- 02SMPTE RP 141-2005 — Background acoustic noise levels in theaters and review rooms
- 03EBU Tech 3276 — Listening conditions for the assessment of sound programme materialControl-room RT: Tm = 0.25 (V/100)^⅓ s, 0.2–0.4 s.
- 04ITU-R BS.1116-3 — Methods for the subjective assessment of small impairments in audio systemsSame reverberation formula for critical listening rooms.
- 05Warnock, NRC Canada Building Digest CBD-239 — Factors affecting sound transmission lossMass law, double-leaf walls and coincidence, from Canada’s National Research Council.
- 06Toole, Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms, 3rd ed. (Routledge, 2017)Textbook on loudspeakers, reflections and small rooms.
External links open in a new tab. Figures quoted in this chapter are taken from these sources; a Science of Sound measurement is only ever presented as one, with its file, date and instrument.
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