Sound in rooms

Direct and reflected sound

A mic hears the source once directly, then off every surface.

One clap, many arrivals

Move the mic and clap: the direct sound arrives first.

Try it

  • Clap with the mic close to the source
  • Move the mic near a wall and clap again
  • Get the direct sound at least 6 dB above the reflections
More on this

A microphone hears the source once, directly, and then again and again off every surface of the room.

Move the mic. The direct path is first and loudest; each bounce arrives later and quieter. Closer to the source, the direct sound wins.

Sound travels about 343 metres a second in air at room temperature, so each metre of extra path adds about 2.9 ms.

Level falls with distance: twice as far is a quarter of the power, 6 dB down. That inverse square law is why moving a mic a few centimetres near the source changes a recording more than moving it a metre across the room.