Speed of sound, delay and time alignment

Sound in air travels at roughly 343 m/s at 20 °C. That single number explains delay speakers, microphone alignment and many acoustic problems.

Temperature matters

The speed of sound rises by about 0.6 m/s per °C:

For a rule of thumb, 1 ms of delay corresponds to about 34 cm and 10 m takes about 29 ms.

Delay speakers

In a large venue, loudspeakers placed further back keep the sound level up for distant listeners. If they play without delay, the sound from the main PA arrives later than the local speaker and the image is pulled toward the nearer speaker.

To fix this, delay the fill speaker by the travel time from the main system to the fill's position. Many engineers add an extra 10 to 15 ms so the main system still arrives first and keeps the localisation (the precedence or Haas effect).

Time-aligning microphones

A close microphone and a distant microphone on the same source are offset in time. Delaying the closer one by the travel-time difference reduces comb filtering when they are summed, see Comb filtering.

Tools

• Delay ↔ distance converter
• Frequency ↔ wavelength converter

Draft: written by an AI assistant, awaiting technical review.