Room Modes in an 11x23 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 24.5 Hz, set by the 23 ft length.
• Your 23 ft length is almost exactly twice your 11 ft width, so their modes fall close together without quite stacking.
• Your 23 ft length is almost exactly three times your 8 ft ceiling height, so their modes fall close together without quite stacking.
• Between 24.5 Hz and 48.9 Hz there are no modes at all, so notes in that 24.4 Hz gap will sound thinner than the bass around them.
• Mode density drops in the 31.5 and 63 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 : 1.38 : 2.88) fall outside the Bolt area because the room is long and narrow for its height, so modes bunch up along the length.
• Below about 167 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

No mode falls between 24.5 Hz and 48.9 Hz, a gap of 24.4 Hz. That is a spot where bass naturally loses energy instead of gaining it.

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 gap. 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 : 2.88, 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 31.5 Hz would take about 8.9 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 23 ft length. Start near 8.7 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 167 Hz is where these modes live, so that is the range worth checking before you call the room done.

Every mode below 200 Hz

This room has 75 modes below 200 Hz, 13 axial, 36 tangential and 26 oblique. Read the axial rows as the ones you will hear most clearly. Tangential and oblique modes add texture but usually only become audible when they land close to an axial mode.

Questions about 11x23 rooms

Is an 11 by 23 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 50/100 because there is a gap of 24.4 Hz between 24.5 Hz and 48.9 Hz with no mode in between. Treatment will make a real difference here.

What is the best corner for bass traps in an 11x23 room?

The four vertical corners first. Full absorption at 31.5 Hz would take roughly 8.9 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 11x23 room need?

Subwoofer size is less about this room's 253 sq ft and more about the output headroom you want; room size mainly changes where the 75 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 does bass sound thin in spots in an 11 by 23 ft room?

Here it comes down to this: there is a gap of 24.4 Hz between 24.5 Hz and 48.9 Hz with no mode in between. 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 11x23 room?

Corner bass traps come first, as thick as you can fit (6 to 12 in) plus a membrane trap tuned near 31.5 Hz, since that note's own quarter wavelength (about 8.9 ft) is too deep for any panel. After that, reposition your seat near 8.7 ft from the front wall and verify with REW below 167 Hz.

Similar room sizes

• 12x23 ft, 8 ft ceiling
• 11x22 ft, 8 ft ceiling
• 11x24 ft, 8 ft ceiling