Speaker placement calculator for home cinema

What the calculator does

The Cinema Designer is a speaker placement calculator with a drawing attached. You set the room size, the screen, the rows and the seats, and pick a layout from 5.1 to 9.1.6. It places every speaker at a compliant starting position and scores each one for the reference seat. Drag a speaker or a seat and every verdict updates as you move.

It scores three things about placement:

• The window. Each speaker’s angle from the reference seat, checked against the Dolby Atmos placement window for that channel.
• The gap. The angle between neighbouring speakers in the same ring, checked against the RP22 limits.
• The level. The sound pressure each channel can deliver at the seat from its sensitivity, the amplifier power and the distance, checked against the RP22 level targets.

It also checks the viewing angle for every seat, the sightline over the row in front, the first reflection points on each surface, and the reverberation time of the room. This guide covers the speaker part.

The two standards it scores against

Dolby Atmos placement windows. Dolby publishes a window for each channel in a home layout, as an angle from the listener. The designer uses these bands:

The top channels use two angles: how far off the centre line the speaker sits when you look at it from the seat (lateral), and how far around the arc from the front of the room to the back it sits (elevation, where 90 degrees is straight overhead).

SMPTE RP22. RP22 is the recommended practice for immersive audio rooms. The designer uses three of its rules for speakers. The gap between neighbouring speakers in a ring must stay under 80 degrees for Level 2, 60 for Level 3 and 50 for Level 4. Each channel must reach a level target at the seats: 105 dB for the screen channels at reference, with lower targets for surrounds and a higher one for the subwoofer. And the screen should fill 44 to 60 degrees of the viewer’s field at the reference seat.

How to read the verdicts

Every verdict is a badge and a sentence. The badge is one of a fixed set: IN SPEC, MARGINAL and OUT OF SPEC for the numeric checks, FORMAT LIMIT when a layout cannot meet a rule however you place it, and STEEP, CLEAR and TOO LIVE for the seat and room checks. The sentence gives the number, the standard and the miss, so you never have to guess why a colour is red.

A speaker angle line reads like this: “74.0° between Left front and Left surround. Under 80° meets RP22 L2 for the ear-level surround ring.” A level line reads like this: “Right surround 100.2 dB. RP22 L1 surround, 4.8 dB under reference (105 dB) for seat 2, row 1.”

Verdicts are scored at the reference seat: the front-row seat nearest the screen centre. The other seats are measured and reported underneath as a spread, for example “across the other 4 seats it swings 97.7 dB to 103.7 dB”. That is how RP22 treats a room: levels at the reference position, the listening area as an extent.

Successes fold away. The panel opens on the exceptions, with a count of what passed, so a room that is mostly right reads as mostly right.

A worked example

The tool opens on a 5.5 by 7.5 by 2.8 metre room with a 5.1 layout, two rows and five seats, a 150 watt amplifier into 8 ohm speakers and no acoustic treatment.

In that room the speaker angles read 5 of 8 in spec. The two marginal lines are the same gap on each side: 74.0 degrees between the front and the side surround, inside the Level 2 limit of 80 degrees but not the Level 3 limit of 60. The levels read 3 of 6 channels in spec. The side surrounds reach 100.2 dB at the reference seat, 4.8 dB under the 105 dB reference, and the subwoofer reaches 103.6 dB against a 114 dB target.

Switch the layout to 7.1.4 and nothing else. The angles now read 13 of 20 in spec; the new rear surrounds and the four top speakers all land inside their windows because the placer put them there, and the marginal lines are again the ring gaps at 65.6 to 75.0 degrees. The levels read 3 of 12. The four top speakers reach 98.0 dB, 1.0 dB short of their 99 dB target, and the rear surrounds reach 95.7 dB, 3.3 dB short. Same amplifier, longer distances, smaller drivers.

That is the point of scoring placement and level together. Adding height channels to this room is a placement success and a level failure, and the fix is amplifier power or more sensitive speakers. Moving them closes none of it. The SPL calculator does that sum on its own for one speaker.

When to trust it, and when not to

The angles are geometry and the levels are the standard inverse-square sum, both checked against published oracles. If the tool says a speaker is outside its window, it is.

Three limits to keep in mind:

• It scores the reference seat. A wide room with a long row will show a large spread on the side surrounds. That is a real property of the room, and the spread line is there so you can see it.
• The level sum is free field. Room gain is set to zero by default so the tool never hands out decibels the room may not give. Real rooms usually add a few dB at low frequencies.
• It does not hear the room. Reverberation time is an estimate from the room volume and its treatment; no microphone is involved. Frequency response, background noise and the level of each reflection are outside what it can see, and it says so rather than claiming a level it cannot check.

Placement from a calculator is a starting point. A measurement microphone and an afternoon still decide the last few decibels.

Use it

Open the Cinema Designer, set your room, pick your layout and drag the speakers to where they can actually go. The panel on the right tells you what each move costs. When it reads the way you want, Share copies a link you can send to whoever is doing the install.