First Reflection Point Finder
Enter your room and your speaker/seat positions to find exactly where the first reflections land on the side walls, ceiling and floor — the spots to treat with acoustic panels — using mirror-image geometry and a top-down diagram.
ℹ This is exact specular (mirror) geometry for a rectangular room with the speakers on the front wall. Real reflections are broadband and a little spread out, so centre a generously-sized panel on each point rather than a tiny patch. Confirm with the mirror trick: sit in your seat while a helper slides a mirror along the wall — wherever you can see a tweeter is a first-reflection point. Treating the side walls and ceiling tightens stereo imaging, but don’t over-deaden — leave some liveliness and consider diffusion. Metric; everything runs in your browser.
Top-down view: green = speakers, cyan = your seat, red = side-wall first-reflection points, with the reflection paths drawn.
How It Works
Sound from each speaker reaches your ears twice: once directly, and a moment later after bouncing off a nearby surface. Those early reflections arrive within a few milliseconds of the direct sound, so your ears can’t separate them — they smear the stereo image and colour the tone (comb filtering). The fix is to absorb (or diffuse) the sound at the exact spot where it bounces. To find that spot, this tool uses the image-source method: a reflection behaves as if it came from a “mirror” speaker on the far side of the wall, so the reflection point is simply where the straight line from that mirror image to your ears crosses the wall. For the side walls it works in plan view; for the ceiling and floor it works in the vertical plane through each speaker and your seat. Because the layout is left/right symmetric, the two side-wall points are mirror images at the same distance from the front wall, and likewise for the ceiling and floor points.
The geometry is exact, but treat the results as centres, not pinpoints: real reflections cover a patch, low frequencies wrap around small panels, and your head moves, so use a panel at least 60 × 120 cm (thicker absorbs lower) centred on each point at listening-axis height. The quickest sanity check is the mirror trick — slide a mirror along the wall while seated and mark wherever a tweeter appears. Side-wall and ceiling treatment sharpens imaging the most; the floor bounce is usually handled by a rug. Don’t treat every surface to death, though — a completely dead room sounds unnatural, so balance absorption with some diffusion and live surfaces.