Speaker delay calculator

Type the extra distance the main speaker’s sound travels to the listener, beyond the speaker you are delaying, and the air temperature. The result is the delay in milliseconds. It also shows that delay plus 5 to 15 ms, so the stage speaker arrives first and the sound seems to come from the stage.

How it works

The speed of sound here is the dry-air line used in live sound: 331.3 + 0.606 × temperature in °C, in meters per second. One foot is 0.3048 meters. Delay in milliseconds is the distance in meters, divided by that speed, times 1,000. A temperature entered in °F is converted with (°F − 32) × 5/9 before it goes into the line. Humidity and altitude are left out.

At 20 °C the speed is 343.42 m/s. One hundred feet is 30.48 m, which is 88.75 ms. The stage offset on that number is 93.75 ms to 103.75 ms.

Merlijn van Veen, “Sonic Atmosphere,” Live Sound International, May 2016, gives this linear form and says it stays within 0.5 percent of 331.3 × √(1 + °C / 273.15) for ordinary temperatures. Delay Card uses the same line.

Helmut Haas measured speech from two loudspeakers in 1951 (Acustica, volume 1, pages 49 to 58). In that study, a second speaker delayed by up to about 30 ms was heard as part of the first sound rather than as a separate echo, and the sound seemed to come from the speaker that played first. An English translation ran in the Journal of the Audio Engineering Society, volume 20, issue 2, March 1972. The 5 to 15 ms added here sits inside that window so the stage speaker is the first arrival. It is a setup range, not a single figure from the paper.

If the delay speaker is not next to the listener, subtract that short hop from the main-speaker distance, and type what is left.

The phone app that measures this with the microphone is Delay Card. It is not on the App Store or Google Play yet.