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First Reflection Point Finder

Enter your room and speaker/seat positions to find each first reflection point 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.

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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 — typically within the Haas zone (5–35 ms) — so your ears can’t separate them. Instead they smear the stereo image and colour the tone through comb filtering: the delayed reflection adds to or cancels the direct sound at different frequencies, creating a characteristic series of peaks and dips. 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 stereo imaging the most; the floor bounce is usually handled by a rug. Good room treatment starts here, with targeted acoustic panel placement at the first-reflection points before considering broader wall coverage. Don’t treat every surface to death, though — a completely dead room (very low RT60) sounds unnatural and fatiguing, so balance absorption with some diffusion and live surfaces. Once panels are placed, you can use the room frequency analyzer to measure how treatment has changed the response, or the RT60 calculator to estimate the resulting reverberation time from your panel material’s absorption coefficients. If you’re still deciding where speakers should go before treating, the speaker placement optimizer helps minimize modal excitation before you start hanging panels.

Frequently Asked Questions

What is the “mirror trick”?
Sit in your listening seat and have someone slide a mirror flat along the wall. Wherever you can see the reflection of a speaker’s tweeter, that’s a first-reflection point — mark it and centre a panel there. It’s the real-world version of the geometry this tool computes.
Why treat first reflections at all?
Early reflections arrive just after the direct sound and your ears blend them in, which blurs the stereo image and adds comb-filter colouration. Absorbing or diffusing them at the bounce point restores a clearer, more focused soundstage.
How big should the panels be?
At least 60 × 120 cm, centred on each point at the height of the speaker-to-ear line. Thicker panels (and an air gap behind) absorb lower frequencies. A point is really a small zone, so err on the larger side.
Do I need to treat the floor?
The floor bounce is usually tamed with a thick rug between the speakers and seat rather than a rigid panel. The side walls and ceiling matter more for imaging.
Can I over-treat a room?
Yes. Absorbing every reflection makes a room sound unnaturally dead and fatiguing. Treat the first-reflection points, then stop and listen — add diffusion and keep some live surfaces for a natural sound.
Should I use acoustic foam, rigid fiberglass, or rockwool panels at first-reflection points?
Thin acoustic foam (25–50 mm) is effective only above roughly 500–1,000 Hz and does little for the critical midrange comb-filter colouration. Rigid fiberglass or rockwool panels at 50–100 mm thickness absorb from around 250 Hz upward and are the preferred choice for first-reflection treatment. Adding a 50 mm air gap between the panel and wall effectively shifts the absorption curve another third-octave lower. Avoid covering entire walls with foam — it excessively kills high frequencies while leaving the low-midrange unaffected, which is worse than no treatment at all.
Does this tool work for non-rectangular rooms or L-shaped spaces?
No — the calculator assumes a simple rectangular room with speakers on one end wall. For L-shaped, sloped-ceiling, or irregularly shaped rooms, the image-source geometry becomes non-trivial and the tool results will not be valid. In those cases, use the mirror trick directly: sit in your listening position and have someone slide a mirror along each wall surface — wherever you see a tweeter is a first-reflection point, regardless of room shape. The mirror trick works for any room geometry.
Should I use absorbers or diffusers at first-reflection points?
Either can work, but they sound different. A broadband absorber (rockwool or fiberglass panel) at the reflection point removes the energy, which tightens imaging and reduces comb filtering but can make the room feel dry. A quadratic-residue diffuser (QRD) or skyline diffuser scatters the reflection in many directions, which preserves a sense of spaciousness while still breaking up the discrete early reflection. Many recording and mixing rooms place absorbers on the side walls at ear height (most damaging for imaging) and diffusers on the rear wall and upper sidewalls to maintain liveliness. Whichever you choose, centre it on the point the tool outputs.
Do first reflections affect mono compatibility?
Yes, indirectly. Untreated side-wall reflections arriving later than the direct sound add frequency-dependent comb-filter cancellations to each ear separately. When you sum the mix to mono, those cancellations may shift — causing a mix that sounds balanced in stereo to appear thin or coloured in mono. Treating the first-reflection points reduces early-reflection colouration, which gives you a more accurate monitoring environment and makes your stereo-to-mono translation more predictable. For a complete room treatment strategy, the acoustic panel placement calculator can help plan the full treatment budget across all surfaces.

Related Tools

Panel Placement Calculator
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Speaker Placement Optimizer
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Reverb Time Designer
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Room Frequency Analyzer
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Room Ratio Analyzer
Check your room proportions.
RT60 Calculator
Reverb time via Sabine & Eyring.
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