Room Modes in an 11x15 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 37.5 Hz, set by the 15 ft length.
• Your 15 ft length and 11 ft width both resonate near 150.0 Hz, so bass at that note will be much louder than its neighbours.
• Your 15 ft length and 10 ft ceiling height both resonate at 112.5 Hz, so bass at that note will be much louder than its neighbours.
• Between 37.5 Hz and 51.2 Hz there are no modes at all, so notes in that 13.7 Hz gap will sound thinner than the bass around them.
• The proportions (1 : 1.10 : 1.50) fall outside the Bolt area because the room is long and narrow for its height, so modes bunch up along the length.
• Below about 185 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

Your 15 ft length and 10 ft ceiling share a mode near 112.5 Hz. When two dimensions resonate at the same note, their boosts add up, so that note stacks on top of itself and comes out noticeably louder than the bass around it.

If you use this room for movies, that stacked note tends to show up as boom on specific low-frequency effects rather than an even rumble. If it is a music or mixing room, that same spot makes some bass notes read louder on playback than they actually are on the recording, which makes mixing bass by ear risky here.

This room's ratio (1 : 1.10 : 1.50) is outside the Bolt area: the room is long and narrow for its height, which bunches modes up along the length. Treatment can still get it sounding good, but the shape is not helping as much as it could.

How to fix it, in order

1. Treat the four floor-to-ceiling corners first; they are common to every mode this room produces, and your ceiling height is part of the problem.
2. Full absorption at 112.5 Hz would take about 2.5 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. Move your listening position off-center along the 15 ft length; roughly 5.7 ft from the front wall (38% back) is a common starting spot before fine-tuning.
4. Walk the subwoofer around the front of the room while playing a bass-heavy track and listen from your seat: corner placement is loudest but least even, and a second sub or an off-corner spot often fills in this room’s weak points.
5. Once traps are in, measure with REW from the listening position. Focus on frequencies below 185 Hz (this room's Schroeder frequency); that is where individual modes, not general reverb, are running the show.

Every mode below 200 Hz

The table below lists every mode under 200 Hz for this room: 63 in all, 11 axial, 31 tangential and 21 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 11x15 rooms

Is an 11x15 room good for a home theater?

At 165 sq ft, this size works as a bedroom theater or dedicated music room, but a modal score of 61/100 means it is workable, not effortless: two of its dimensions reinforce the same note near 112.5 Hz, so plan on real bass trapping.

Where do bass traps go in an 11 by 15 ft room?

The four vertical corners first. Full absorption at 112.5 Hz would take roughly 2.5 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.

Do I need a big subwoofer for an 11x15 room?

Room size here mainly shapes where the modes land, not the sub size on its own; this room has 63 modes below 200 Hz to work around either way. Larger rooms like this one ask more of a subwoofer's output, and a second sub in a different spot helps smooth out the peaks and dips across seats.

Why does one bass note boom in an 11x15 room?

In this room, the main cause is that two of its dimensions reinforce the same note near 112.5 Hz. Room modes reinforce specific notes more than others no matter how good your speakers are, and that unevenness is what you are hearing.

How many bass traps does an 11 by 15 ft room need?

Start by treating the four corners with traps as thick as you can fit (6 to 12 in) plus a membrane trap tuned near 112.5 Hz, since that note's own quarter wavelength (about 2.5 ft) is too deep for any panel. Next, shift your listening position toward 5.7 ft from the front wall, then confirm progress with an REW sweep under 185 Hz.

Similar room sizes

• 10x15 ft, 10 ft ceiling
• 12x15 ft, 10 ft ceiling
• 11x14 ft, 10 ft ceiling
• 11x16 ft, 10 ft ceiling
• 11x15 ft, 8 ft ceiling
• 11x15 ft, 9 ft ceiling