Theater Calculators
First Reflection Point (Mirror Trick) Finder
https://www.theatersizing.com/calculators/first-reflection-point/
Estimate only — not a calibrated SPL meter, an acoustic report or an electrical design. Confirm with measurement.
First Reflection Point (Mirror Trick) Finder
The mirror trick finds the sidewall point where you would see the tweeter. This uses image-source geometry for the same spot, plus a ceiling bounce.
Inputs
Results
- Side-wall mark from front
- 0.80m
- Ceiling mark from front
- 1.60m
Calculation method
Along the side wall, distance from the front = d · s / (s + L) where s is speaker-to-wall and L is listener-to-wall.
Exact formula
x_side = d · s / (s + L). Ceiling uses image height (H − h_sp) over the full bounce path. Limits: rectangular room, flat walls, speakers on the front wall, listener on the centreline, tweeter and ears below the ceiling.
Speakers on the front wall, seat on the centreline
The image-source model puts both speakers on the front wall and the listener on the room centreline. If the towers are pulled into the room or the sofa is offset, the sidewall mark moves. Invalid geometry (speaker inset at or past width/2, tweeter or ears at or above the ceiling) returns no marks.
A mirror still wins with furniture
Bookshelves, a fireplace and a door break the infinite-plane bounce. Use the numbers to buy panel count and a starting height, then sit in the seat with a helper and a mirror on the real wall.
Frequently asked questions
Mirror trick still needed?
Yes on odd walls. The calculator assumes a rectangle.
Floor bounce?
A rug usually handles it. This tool does side and ceiling.
Both sidewalls?
Mirror the same distance on the other side if the layout is symmetric.
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