Room Modes in a 28x29 ft Room with a 10 ft Ceiling

Mode spectrum

Each line is one standing wave. Axial modes, the strongest kind, stand tallest; tight bunches and wide empty stretches are where the bass will sound uneven.

Axial modes by dimension

What this means for your room

• The lowest room mode is 19.4 Hz, set by the 29 ft length.
• Your 29 ft length is almost the same as your 28 ft width, so their modes fall close together without quite stacking.
• Your 29 ft length is almost exactly three times your 10 ft ceiling height, so their modes fall close together without quite stacking.
• Between 44.6 Hz and 55.9 Hz there are no modes at all, so notes in that 11.3 Hz gap will sound thinner than the bass around them.
• Mode density drops in the 25 and 50 Hz third-octave bands, where fewer modes fall than in the band below, so bass will sound uneven from note to note.
• The proportions (1 : 2.80 : 2.90) fall outside the Bolt area because the floor is close to square, which concentrates bass problems on fewer notes.
• Below about 83 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

This room has a hole of 11.3 Hz between 44.6 Hz and 55.9 Hz where no mode helps the bass along. Anything tuned to that range reads weaker than its neighbors.

For a home theater, expect that gap to color explosions and sub-bass hits unevenly rather than smoothly. For a music room, it means you cannot fully trust what you hear in the low end at the listening position, since a note that sounds loud in the room may be perfectly balanced on the recording.

The proportions (1 : 2.80 : 2.90) fall outside the Bolt area, the range room ratios usually spread modes best over, because the floor is close to square, which piles bass problems onto fewer notes instead of spreading them out. That does not rule the room out, but treatment is doing more of the work here than shape is.

How to fix it, in order

1. Start with bass traps in the four floor-to-ceiling corners; every mode in this room peaks there, including the ones set by your ceiling height.
2. At 25.0 Hz the quarter wavelength is about 11.3 ft, deeper than any practical panel, so a porous trap alone will not fully absorb that note. Build corner traps as thick as you can fit (6 to 12 in, straddling the corner with an air gap behind) to take the edge off, then handle the note itself with a membrane or pressure trap tuned near it, careful seat position, and more than one subwoofer with EQ.
3. Do not sit dead-center on the 29 ft length. Start near 11 ft from the front wall, about 38% of the way back, and adjust from there.
4. For the subwoofer, try a few spots before settling: a front corner usually gives the most output but also the most uneven bass, while pulling it off the wall or adding a second sub often smooths out peaks like the ones this room has.
5. After treating, run an REW sweep from the seat. Everything below 83 Hz is where these modes live, so that is the range worth checking before you call the room done.

Every mode below 200 Hz

The table below lists every mode under 200 Hz for this room: 266 in all, 22 axial, 115 tangential and 129 oblique. Axial modes bounce between just two parallel surfaces (say, the two side walls) and are the loudest and most audible; tangential modes involve four surfaces and are quieter; oblique modes bounce off all six surfaces and are the faintest. Start with the axial rows; they cause most of the boomy or thin spots you will actually hear.

Questions about 28x29 rooms

Will a 28x29 room work for a home theater?

This size suits a dedicated home theater or media room, though the 60/100 modal score signals some work ahead, mainly because there is a gap of 11.3 Hz between 44.6 Hz and 55.9 Hz with no mode in between.

Where should I put bass traps in a 28x29 room?

Start in the four floor-to-ceiling corners; every mode in this room peaks there. The 25.0 Hz mode itself would need about 11.3 ft of depth to fully absorb, more than any panel can give, so build corner traps as thick as you can fit (6 to 12 in) and pair them with a membrane trap tuned near 25.0 Hz.

What subwoofer size is right for a 28 by 29 ft room?

There is no fixed sub size tied to 812 sq ft; that number mostly sets this room's mode frequencies (266 of them under 200 Hz). At this size you will want more headroom than a small room needs, and two subwoofers usually beat one at keeping bass even from seat to seat.

Why does my 28x29 room have weak bass notes?

The short answer for this room: there is a gap of 11.3 Hz between 44.6 Hz and 55.9 Hz with no mode in between. Bass unevenness like that is built into the shape of the room and shows up regardless of what speakers or sub you use.

How do I fix bass problems in a 28x29 room?

Put bass traps in the four floor-to-ceiling corners first, as thick as you can fit (6 to 12 in) plus a membrane trap tuned near 25.0 Hz, since that note's own quarter wavelength (about 11.3 ft) is too deep for any panel. From there, move your seat to about 11 ft from the front wall, then measure with REW below 83 Hz to see what still needs work.

Similar room sizes

• 27x29 ft, 10 ft ceiling
• 29x29 ft, 10 ft ceiling
• 28x28 ft, 10 ft ceiling
• 28x30 ft, 10 ft ceiling
• 28x29 ft, 8 ft ceiling
• 28x29 ft, 9 ft ceiling