Surround Speaker Layout Calculator

How the speaker layout calculator works

Surround sound is laid out by angle, not by distance. Every speaker is placed at a set angle seen from the main seat, measured from the line straight ahead to the screen, and the room then decides where on the walls those angles land. This calculator puts the seat in the room first, then turns each angle into a position you can measure with a tape.

The angles come from Dolby's Dolby Atmos Home Theater Installation Guidelines and its 7.1.4 speaker setup guide. Front left and right sit 22 to 30 degrees either side of the centre line, the surrounds 90 to 110 degrees, the rear surrounds of a 7.1 system 135 to 150 degrees, and the overhead speakers of a 7.1.4 Atmos system 45 degrees up from the seat, allowed between 30 and 55. The international broadcast standard, Recommendation ITU-R BS.775, uses the same front angle of 30 degrees and puts 5.1 surrounds between 100 and 120 degrees; its layout is reproduced in ITU Report BS.2159. Both place listener-level speakers at seated ear height, about 1.2 m (3.9 ft).

Where the seat goes

The calculator puts the main seat at 60% of the room depth from the screen wall. The reason is bass. Low notes set up standing waves between the front and back walls, and the pressure of the first few follow cos(nπx/D), where x is the distance from the front wall and D the depth. Each has dead spots: the first at the middle of the room, the second at a quarter and three quarters, the third at a sixth, a half and five sixths. At 60% the three come to -0.31, -0.81 and +0.81 of their peak, so none of them drops out. The same reasoning is behind the familiar advice to sit at about 38% of the length from the back wall, which is 62% from the front. It is a starting point; a measurement with the receiver's room correction microphone is what settles it.

From angles to wall positions

With the seat at a distance s from the screen wall, the front pair at 30 degrees sits 2 × s × tan 30° apart, or about 1.15 × s. In a narrow room that can put the speakers into the side walls, so the calculator leaves 0.3 m (about 1 ft) for each cabinet and pulls the pair in, showing the angle it ends up at. Below 22 degrees it warns you: the seat is too far back for the room's width, and moving it forward or accepting a narrower picture of sound are the options.

Side surrounds go on the side walls, from level with the seat (90 degrees) to a point (W ÷ 2) × tan 20° behind it (110 degrees), where W is the room width. Rear surrounds sit on the back wall, (D − s) × tan 30° from the centre line at 150 degrees and (D − s) × tan 45° at 135 degrees. In a long, narrow room those points fall outside the room, so the calculator moves them onto the side walls behind the seat instead. For Atmos, the top front and top rear speakers go (H − 1.2 m) ÷ tan 45° ahead of and behind the seat, where H is the ceiling height, and Dolby wants them about as far apart side to side as the front pair.

A worked example

Take a room 4 m wide and 5 m deep. The seat goes 0.6 × 5 = 3.0 m from the screen wall. At 30 degrees the front pair would be 2 × 3.0 × tan 30° = 3.46 m apart, but the room allows 4 − 2 × 0.3 = 3.40 m, which gives 29.5 degrees, well within Dolby's range. The side surrounds run from level with the seat to 2 × tan 20° = 0.73 m behind it. The back wall is 2.0 m behind the seat, so the rear surrounds of a 7.1 system go 2.0 × tan 30° = 1.15 m to 2.0 × tan 45° = 2.00 m either side of the centre. With a 2.4 m ceiling the Atmos overheads sit 1.2 m ahead of and behind the seat, anywhere from 0.84 m to 2.08 m if the joists get in the way.

In US units, a room 13.12 ft wide and 16.4 ft deep puts the seat 9.84 ft from the screen wall and the front pair 11.15 ft apart, again held in by the side walls. A room 2.5 m wide and 7 m deep shows the warning: the seat lands at 4.2 m, the front pair can be no more than 1.9 m apart, and that is only 13 degrees each side.

Height, distance and the ceiling

Dolby puts the front, surround and rear speakers at seated ear height, and lets the rear pair rise to no more than 1.25 times the height of the front ones where furniture is in the way. Overhead speakers belong two to three times higher than the listener-level ones, which with a 1.2 m ear height means a ceiling of roughly 2.4 to 3.6 m. A steeper angle brings an overhead closer to the seat, so where 45 degrees would put the top rear pair past the back wall, the calculator shows the position at Dolby's 55 degree limit, and says so if even that does not fit. Dolby Atmos enabled speakers, the upward-firing kind that sit on top of the front and surround speakers, should be at least 0.9 m from the listener and ideally 1.5 m or more.

What this tool does not do

It places one main seat. Extra rows sit in the same field but further from the ideal, so check the seating rows calculator for sightlines and keep the main row where this tool puts it. It does not measure frequency response, set levels or delays, or allow for doors, windows and furniture, all of which force compromises. The receiver's calibration sets the distances and levels once the speakers are in; this tool gets them to the right places first. Ceiling and wall fixings need to suit the speaker weight and what is behind the plasterboard, and new cable runs and sockets must follow the electrical rules where you live.

Using this calculator with other BuildMetricLab tools

The TV size and viewing distance calculator sets the screen size for the seat this tool picks, and the seating rows calculator works out risers if more than one row is going in. All BuildMetricLab tools run in your browser with no sign-up, and the formula is on the page so the maths can be checked.