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Room mode calculator

Three dimensions and a tape measure. You get every mode your room will have, which musical notes they land on, how your proportions compare to the ratios people recommend, and a map of where the bass is smoothest, which is the part most mode calculators leave you to work out yourself.

Measure to the inside faces of the walls. Getting within about 5 cm is close enough.

Room
m

front wall to rear wall

m

side wall to side wall

m

floor to ceiling

Listening seat
m

to your ears, not the sofa back

m

seated

Speakers

Assumed symmetric. If yours are not, measure the one that sounds worse.

m

to the woofer, not the grille

m
m

centre of the bass driver

Advanced

Sets the speed of sound, which shifts every predicted mode by about 0.2% per degree.

Proportions score

72

out of 100

Volume

49.4m³

Modes below 300 Hz

109

Modal region ends

191Hz

Decay target

0.20s

  • −3Mode spacing. Widest gap between axial modes is 22 Hz, between 69 and 90 Hz.
  • −9Mode density. 1 third-octave band(s) hold fewer modes than the band below them.
  • −16Coincident modes. 2 pair(s) of modes land on top of each other in a band that has too few modes to spread the energy out.

Where to sit

Predicted bass smoothness across the room

Every point on the floor, modelled at ear height with both speakers driven together. Dark blue is even bass; bright yellow means large peaks and holes. The dashed line is the centre line, which is where a stereo seat has to go.

FRONT WALLREAR WALLseen from above5.20 m × 3.80 m × 2.50 m high
5 dB: even bass22 dB+: peaks and holes
your seatsuggested seatspeakers

At your seat

11.9dB swing

Best on the centre line

8.3dB swing

The smoothest usable seat is 2.70 m from the front wall, on the centre line. That is a 3.6 dB reduction in level swing compared with the seat position you entered, for the price of moving a chair.

The very smoothest points on the map are usually jammed against a wall. They are excluded from the suggestion: against the front wall you are level with the speakers and there is no stereo image, and against the rear wall every mode is at maximum pressure, which measures flat and sounds boomy.

Proportions

How your ratios compare

Room proportions decide where the modes land. You usually cannot change them, so treat this as context for the rest rather than as something to act on, unless you are building the room.

1.01.21.41.61.82.02.21.01.52.02.53.0Sepmeyer ASepmeyer BSepmeyer CLoudenVolkmannBoneryour roomwidth ÷ heightlength ÷ height

1 : 1.52 : 2.08 (height : width : length). Inside Bolt's region of favourable proportions. Closest published ratio is Louden, 8% away.

Green blob: Bolt 1946, digitised. Blue band: the EBU Tech 3276 proportion limits.

Predicted modes

Where the resonances land

FreqModeNote
33.0 Hz1st length modeC1 +16¢
45.2 Hz1st width modeF♯1 -41¢
66.0 Hz2nd length modeC2 +16¢
68.6 Hz1st height modeC♯2 -16¢
90.3 Hz2nd width modeF♯2 -41¢
99.0 Hz3rd length modeG2 +18¢
132 Hz4th length modeC3 +16¢
135 Hz3rd width modeC♯3 -39¢
137 Hz2nd height modeC♯3 -16¢
181 Hz4th width modeF♯3 -41¢
  • length (5.20 m) is close to 2 times height (2.50 m), so every 2nd mode of the length lands on a height mode instead of falling between them.

This is what your room should do. Now find out what it actually does.

Everything above is predicted from three dimensions and an idealised rectangular box. It cannot know about the doorway, the bay window, the sofa, or the fact that your left speaker is 20 cm closer to a wall than your right one. A measurement can. Feed a REW export in alongside these dimensions and the report names the cause of each real bump, sorts the fixes by what they cost, and tells you which problems no equaliser will ever solve.

Analyse a measurement

Questions

How do I calculate room modes by hand?
Divide 343 by twice each dimension in metres, or 1130 by twice each dimension in feet. That gives the fundamental resonance between each pair of opposite surfaces, and every whole-number multiple of it also resonates. A 3.4 m width gives 50 Hz, 101 Hz, 151 Hz, and so on. The calculator above does this for all three axes plus the tangential and oblique modes that involve more than one pair of surfaces.
What is a good room ratio?
One where the modes end up spread out rather than piled up. Sepmeyer, Louden and Volkmann each published ratios that achieve this, and EBU Tech 3276 gives limits as inequalities. The score above is not read off a chart, though: it counts your room's actual mode spacing, how evenly the modes fill each third-octave band, and whether any land on top of each other.
Can I fix a bad room ratio?
Not without moving a wall, which is why this page treats proportions as context rather than as advice. What you can change is where you sit and where the speakers go, and those move the response at your ears far more than most people expect. That is what the smoothness map is for.
Why does the map say the best seat is not the smoothest point?
Because the smoothest point in almost every room is pressed against a wall. Every mode is at a pressure maximum there, which flattens the predicted curve and sounds boomy and closed-in. Against the front wall you are also level with the speakers, so there is no stereo image. The suggestion is restricted to positions you would actually want to sit in.
How accurate is this without a measurement?
The mode frequencies are exact for a sealed rectangular box, and real rooms usually land within a few percent. The smoothness map is a modal summation, so it gets the shape of the problem right but not the exact depths: it assumes rigid walls, no furniture and no openings. Use it to choose where to sit, then measure to find out what is really happening.

More on what the numbers mean: why your room has a bass peak at 60 Hz / what room EQ can and cannot fix