Room Modes in an 11x24 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 23.4 Hz, set by the 24 ft length.
• Your 24 ft length and 10 ft ceiling height both resonate near 164.1 Hz, so bass at that note will be much louder than its neighbours.
• Between 23.4 Hz and 46.9 Hz there are no modes at all, so notes in that 23.5 Hz gap will sound thinner than the bass around them.
• Mode density drops in the 31.5 Hz third-octave band (0 modes against 1 in the band below), so bass will sound uneven from note to note.
• The proportions (1 : 1.10 : 2.40) fall outside the Bolt area because the room is long and narrow for its height, so modes bunch up along the length.
• Below about 146 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

Because your 24 ft length and 10 ft ceiling are close in size, their modes stack near 164.1 Hz. Expect that one note to sound louder, and ring longer, than the rest of the bass in this room.

In a home theater, this shows up as one bass note in an action scene sounding far louder than the rest of the mix, usually a kick drum hit or an LFE cue landing right on that stacked note. In a music room, the same thing means certain bass notes on a track jump out while others next to them feel buried.

At 1 : 1.10 : 2.40, this room sits outside the Bolt area because the room is long and narrow for its height, which bunches modes up along the length. Expect to lean on bass traps and seat position a bit more than in a room with friendlier proportions.

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. Full absorption at 164.1 Hz would take about 1.8 ft of trap depth, well past what any room can fit. Fill the corners as deep as you reasonably can (6 to 12 in, with an air gap behind), then lean on a membrane trap tuned near that frequency, your seat position and a second subwoofer with EQ to tame the note itself.
3. Do not sit dead-center on the 24 ft length. Start near 9.1 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 146 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: 96 in all, 14 axial, 47 tangential and 35 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 11x24 rooms

Will an 11x24 room work for a home theater?

This size suits a dedicated home theater or media room, though the 55/100 modal score signals some work ahead, mainly because two of its dimensions reinforce the same note near 164.1 Hz.

Where should I put bass traps in an 11x24 room?

The four vertical corners first. Full absorption at 164.1 Hz would take roughly 1.8 ft of trap depth, so treat that note with a tuned membrane or pressure trap instead, and use thick porous corner traps (6 to 12 in) for everything above it.

What subwoofer size is right for an 11 by 24 ft room?

There is no fixed sub size tied to 264 sq ft; that number mostly sets this room's mode frequencies (96 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 11x24 room have one loud bass note?

The short answer for this room: two of its dimensions reinforce the same note near 164.1 Hz. 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 an 11x24 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 164.1 Hz, since that note's own quarter wavelength (about 1.8 ft) is too deep for any panel. From there, move your seat to about 9.1 ft from the front wall, then measure with REW below 146 Hz to see what still needs work.

Similar room sizes

• 10x24 ft, 10 ft ceiling
• 12x24 ft, 10 ft ceiling
• 11x23 ft, 10 ft ceiling
• 11x24 ft, 8 ft ceiling
• 11x24 ft, 9 ft ceiling