Room Modes in an 11x29 ft Room with a 9 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 : 1.22 : 3.22) fall outside the Bolt area because the room is long and narrow for its height, so modes bunch up along the length.
• Below about 140 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

The modes from your 29 ft length and 11 ft width land on top of each other near 153.5 Hz. That stack means one specific low note gets reinforced twice, so it jumps out over everything nearby.

For a home theater, expect that stacked note 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 : 1.22 : 3.22) fall outside the Bolt area, the range room ratios usually spread modes best over, because the room is long and narrow for its height, which bunches modes up along the length. 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.
2. At 153.5 Hz the quarter wavelength is about 1.8 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 140 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: 104 in all, 16 axial, 50 tangential and 38 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?

Start in the four floor-to-ceiling corners; every mode in this room peaks there. The 153.5 Hz mode itself would need about 1.8 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 153.5 Hz.

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 104 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 140 Hz.

Similar room sizes

• 12x29 ft, 9 ft ceiling
• 11x28 ft, 9 ft ceiling
• 11x30 ft, 9 ft ceiling
• 11x29 ft, 8 ft ceiling