Room Modes in an 11x29 ft Room with an 8 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 and 11 ft width both resonate near 153.5 Hz, so bass at that note will be much louder than its neighbours.
• Between 19.4 Hz and 38.8 Hz there are no modes at all, so notes in that 19.4 Hz gap will sound thinner than the bass around them.
• Mode density drops in the 25 Hz third-octave band (0 modes against 1 in the band below), so bass will sound uneven from note to note.
• The proportions (1 : 1.38 : 3.63) fall outside the Bolt area because the room is long and narrow for its height, so modes bunch up along the length.
• Below about 149 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

Because your 29 ft length and 11 ft width are close in size, their modes stack near 153.5 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 : 1.38 : 3.63, 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.
2. Full absorption at 153.5 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 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 149 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: 92 in all, 15 axial, 44 tangential and 33 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 11x29 rooms

Is an 11 by 29 ft room good for a music room or home theater?

It can work as a dedicated home theater or media room, but do not expect an easy ride: this room scores 55/100 because two of its dimensions reinforce the same note near 153.5 Hz. Treatment will make a real difference here.

What is the best corner for bass traps in an 11x29 room?

The four vertical corners first. Full absorption at 153.5 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 size subwoofer does an 11x29 room need?

Subwoofer size is less about this room's 319 sq ft and more about the output headroom you want; room size mainly changes where the 92 modes below 200 Hz fall. A room this size needs more sub output to reach the same level as a smaller one, and running two subs at different spots evens out the response between seats.

Why is bass boomy in one spot in an 11 by 29 ft room?

Here it comes down to this: two of its dimensions reinforce the same note near 153.5 Hz. That is a property of the room's shape, not your equipment, so treatment, not a better sub, is the fix.

What is the fastest fix for bass in an 11x29 room?

Corner bass traps come first, as thick as you can fit (6 to 12 in) plus a membrane trap tuned near 153.5 Hz, since that note's own quarter wavelength (about 1.8 ft) is too deep for any panel. After that, reposition your seat near 11 ft from the front wall and verify with REW below 149 Hz.

Similar room sizes

• 12x29 ft, 8 ft ceiling
• 11x28 ft, 8 ft ceiling
• 11x30 ft, 8 ft ceiling