First Reflection Point Calculator
The first reflection point is where sound bounces once off a surface on its way from speaker to listener. Treating it tightens the stereo image and reduces colouration. Using the mirror-image method, this calculator finds that point's position along the wall from the listener, the direct and reflected path lengths, and the extra delay of the reflected sound. Enter the perpendicular distances from the speaker and the listener to the surface, and the separation between them measured parallel to the surface.
Mirror-image formula
reflection point = separation * listener distance / (listener distance + speaker distance)
direct path = sqrt(separation^2 + (listener distance - speaker distance)^2)
reflected path = sqrt(separation^2 + (listener distance + speaker distance)^2)
delay (ms) = (reflected path - direct path) / speed of sound * 1000
The reflected path equals the straight-line distance from the listener to the mirror image of the speaker behind the wall. The reflection point divides the wall in proportion to the two perpendicular distances.
Early reflection facts
- Reflections within about 10 to 20 ms of the direct sound fuse and cause colouration.
- Absorption or diffusion at the first reflection point sharpens the stereo image.
- The mirror-image method applies to side walls, ceiling and floor alike.
- The reflected path is always longer than the direct path, so it arrives later.
- A simple mirror trick: a helper slides a mirror along the wall until you see a speaker.
First reflection point: frequently asked questions
What is the first reflection point?
It is the spot on a wall, floor or ceiling where sound from a speaker bounces once on its way to the listener. Treating that spot with absorption or diffusion reduces early reflections that blur the stereo image and colour the sound.
How do you find the first reflection point?
Use the mirror-image method. The reflection point lies on the line between the listener and the mirror image of the speaker behind the wall. Geometrically it sits a fraction listener-distance / (listener-distance + speaker-distance) of the way along the wall from the listener.
What is the reflected path delay?
The reflected sound travels farther than the direct sound, so it arrives later. The delay equals the path-length difference divided by the speed of sound. This calculator returns both the path difference in metres and the delay in milliseconds.
Why does early reflection delay matter?
Reflections arriving within roughly 10 to 20 milliseconds of the direct sound fuse with it and cause comb filtering and image shift. Longer delays are perceived more as spaciousness. Knowing the delay helps you decide whether to absorb the reflection.
Does this work for the ceiling and floor too?
Yes. Enter the perpendicular distances from the speaker and the listener to whichever surface you are treating, and the along-surface separation between them. The geometry is identical for side walls, ceiling and floor.
Official sources
- National Institute of Standards and Technology: SI units and length.
- Acoustical Society of America: room acoustics references.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.