Speaker Distance and Delay AVR speaker distance and time-delay settings

What speaker distance does

Every speaker in a layout sits a different distance from the seat, yet the soundtrack assumes they all reach your ears at the same instant. The receiver's distance table fixes this. You enter or measure each speaker's distance, and the receiver delays the nearer speakers so their sound lines up with the farthest one. Dolby's Atmos installation guidelines state the ideal: all speakers in the listener plane should be equidistant from the listener, and where that is not possible, distance compensation may be used to time-align arrivals.

ITU-R BS.775-4 sets the same rule at the standards level. Side and rear loudspeakers should be no closer to the listener than the frontal loudspeakers unless a compensating time delay is introduced, and when the front speakers must sit on a straight line, delay is added to the center channel.

The math: 0.89 ms per foot

The conversion is the speed of sound. Wikipedia gives about 343 m/s at 20 C, roughly 1,125 ft/s. Dividing, one foot takes 0.889 ms and one meter takes 2.92 ms. Temperature moves it slightly: about 331.3 m/s (1,087 ft/s) at 0 C and about 355 m/s (1,164 ft/s) at 40 C, which works out to 0.92 ms per foot in a cold room and 0.86 ms per foot in a hot one. Over a normal 12 ft path the spread between those extremes is under 1 ms, so a fixed constant is a reasonable approximation.

Denon's manual shows the practical limits. On the AVR-X4700H, the distance range is 0.0 ft to 60.0 ft (default 12.0 ft), and the difference between speakers must stay under 20.0 ft (6.00 m), about 17.8 ms of delay at 0.889 ms per foot.

How auto-EQ sets distance

Audyssey MultEQ XT32 measures it. Denon's manual says the main-position measurement is used to calculate speaker distance, level, polarity and the optimum subwoofer crossover, with six or more measurement positions recommended and up to eight allowed. The test tones come from the speakers and subwoofer during measurement. The result is an arrival-time estimate, not a tape measure, as the subwoofer case below shows.

The subwoofer shows why. Marantz's SR7009 manual warns that subwoofers may measure a greater reported distance than the actual distance because of added electrical delay common in subwoofers. If a sub 10 ft away reported 14 ft, the extra 4 ft would be 3.6 ms of real internal delay, and the receiver compensating for it is the point of the measurement.

The subwoofer distance trick

Rythmik's phase guide turns this into a tuning tool. It equates three actions: adding delay in the time domain, adding negative phase angle, and subtracting physical distance in the receiver. Its worked example uses an 80 Hz crossover with the main speaker at +135 degrees and the sub at -180 degrees, so the sub needs a further -45 degrees, one eighth of a cycle. At 80 Hz the wavelength is 4.3 m, so one eighth is about 0.5 m. With the sub 4 m from the seat, enter 3.5 m: the receiver then thinks the sub is closer and delays it by the time sound takes to cross 0.5 m. Rythmik stresses that the sign matters.

The shape of the trick: one full cycle at 80 Hz is 12.5 ms, so an eighth of a cycle is about 1.56 ms, or roughly 1.75 ft at 0.889 ms per foot. The guide rounds that to 0.5 m. A 3 ft change moves the sub by about 2.7 ms, roughly a fifth of a cycle (77 degrees) at 80 Hz, well beyond the 45 degrees in the example. Because distance delays the sub across its full range while phase matters mainly near the crossover, measure after each change with an SPL meter or a sweep rather than trusting the arithmetic alone.

Worked example

A 5.1 layout has the fronts at 11 ft, center at 9.5 ft, surrounds at 6 ft and the farthest speaker at 11 ft. The receiver delays the center by 1.5 ft x 0.889 = 1.3 ms and the surrounds by 5 ft x 0.889 = 4.4 ms; the fronts get none.

The same logic applies upward in Atmos. Dolby's guidelines place overhead speakers at two to three times the height of the listener-level speakers, which makes their path to the seat longer than a wall speaker at ear level. Take a 45 degree elevation, the Dolby reference, from a seated ear height of 3.9 ft to an 8.5 ft ceiling: the speaker sits 4.6 ft above the ears, so it is 4.6 ft out horizontally and 6.5 ft away along the slant. Against 11 ft fronts, that overhead needs about 4.5 ft x 0.889 = 4.0 ms of delay. Dolby also says most receivers need the speaker locations and types set through the menu or microphone detection so objects land where intended, and Dolby Atmos enabled speakers should sit at least 3 ft (0.9 m) from the listening position, ideally 5 ft (1.5 m) or more. Run the receiver's measurement again after moving any speaker, and re-check speaker levels, because the distance and level tables are calibrated together. If lip sync drifts after changing delays, see lip-sync audio delay.