Room Modes in an 11x15 ft Room with an 8 ft Ceiling
At 11 by 15 ft with an 8 ft ceiling, this room works well as a bedroom theater or dedicated music room. Its first room mode, the lowest note the walls naturally reinforce, falls at 37.5 Hz, set by the 15 ft length.
That puts its modal score at 81 out of 100, a strong score for an untreated room. The main thing to plan around: two of its dimensions reinforce the same note near 150.0 Hz.
Mode spectrum
7 dense clusters (≤5 Hz apart) — overlapping resonances are harder to treat evenly.
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
| Dimension | 1st | 2nd | 3rd | 4th |
|---|---|---|---|---|
| Length (15 ft) | 37.5 Hz | 75 Hz | 112.5 Hz | 150 Hz |
| Width (11 ft) | 51.2 Hz | 102.3 Hz | 153.5 Hz | 204.6 Hz |
| Ceiling height (8 ft) | 70.3 Hz | 140.7 Hz | 211 Hz | 281.3 Hz |
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.
- 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 : 1.38 : 1.88) fall inside the Bolt area, the range of room ratios that spreads modes most evenly.
- Below about 207 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.
Your 15 ft length and 11 ft width share a mode near 150.0 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.
Height, width and length work out to 1 : 1.38 : 1.88, which lands inside the Bolt area. Rooms with that proportion usually need less correction than a room shaped like a cube or a hallway.
How to fix it, in order
- Treat the four floor-to-ceiling corners first; they are common to every mode this room produces.
- At 150.0 Hz the quarter wavelength is about 1.9 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.
- 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.
- 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.
- Once traps are in, measure with REW from the listening position. Focus on frequencies below 207 Hz (this room's Schroeder frequency); that is where individual modes, not general reverb, are running the show.
These numbers assume an empty rectangular 11x15 room with hard walls. Draw your real room, add furniture and speakers, and simulate the bass at your seat.
Every mode below 200 Hz
The table below lists every mode under 200 Hz for this room: 49 in all, 10 axial, 24 tangential and 15 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.
| Frequency | Type | Mode (length, width, height) |
|---|---|---|
| 37.5 Hz | axial | (1,0,0) |
| 51.2 Hz | axial | (0,1,0) |
| 63.4 Hz | tangential | (1,1,0) |
| 70.3 Hz | axial | (0,0,1) |
| 75 Hz | axial | (2,0,0) |
| 79.7 Hz | tangential | (1,0,1) |
| 87 Hz | tangential | (0,1,1) |
| 90.8 Hz | tangential | (2,1,0) |
| 94.7 Hz | oblique | (1,1,1) |
| 102.3 Hz | axial | (0,2,0) |
| 102.8 Hz | tangential | (2,0,1) |
| 109 Hz | tangential | (1,2,0) |
| 112.5 Hz | axial | (3,0,0) |
| 114.9 Hz | oblique | (2,1,1) |
| 123.6 Hz | tangential | (3,1,0) |
| 124.1 Hz | tangential | (0,2,1) |
| 126.9 Hz | tangential | (2,2,0) |
| 129.7 Hz | oblique | (1,2,1) |
| 132.7 Hz | tangential | (3,0,1) |
| 140.7 Hz | axial | (0,0,2) |
| 142.2 Hz | oblique | (3,1,1) |
| 145.1 Hz | oblique | (2,2,1) |
| 145.6 Hz | tangential | (1,0,2) |
| 149.7 Hz | tangential | (0,1,2) |
| 150 Hz | axial | (4,0,0) |
| 152.1 Hz | tangential | (3,2,0) |
| 153.5 Hz | axial | (0,3,0) |
| 154.3 Hz | oblique | (1,1,2) |
| 158 Hz | tangential | (1,3,0) |
| 158.5 Hz | tangential | (4,1,0) |
| 159.4 Hz | tangential | (2,0,2) |
| 165.7 Hz | tangential | (4,0,1) |
| 167.4 Hz | oblique | (2,1,2) |
| 167.6 Hz | oblique | (3,2,1) |
| 168.8 Hz | tangential | (0,3,1) |
| 170.8 Hz | tangential | (2,3,0) |
| 172.9 Hz | oblique | (1,3,1) |
| 173.4 Hz | oblique | (4,1,1) |
| 173.9 Hz | tangential | (0,2,2) |
| 177.9 Hz | oblique | (1,2,2) |
| 180.1 Hz | tangential | (3,0,2) |
| 181.6 Hz | tangential | (4,2,0) |
| 184.7 Hz | oblique | (2,3,1) |
| 187.3 Hz | oblique | (3,1,2) |
| 187.6 Hz | axial | (5,0,0) |
| 189.4 Hz | oblique | (2,2,2) |
| 190.3 Hz | tangential | (3,3,0) |
| 194.4 Hz | tangential | (5,1,0) |
| 194.7 Hz | oblique | (4,2,1) |
Questions about 11x15 rooms
- Is an 11x15 room good for a home theater?
- At 165 sq ft, this size works well as a bedroom theater or dedicated music room, and its modal score of 81/100 is solid for an untreated room. Expect only minor bass trapping to clean up.
- Where do bass traps go in an 11 by 15 ft room?
- Start in the four floor-to-ceiling corners; every mode in this room peaks there. The 150.0 Hz mode itself would need about 1.9 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 150.0 Hz.
- 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 49 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 150.0 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 150.0 Hz, since that note's own quarter wavelength (about 1.9 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 207 Hz.
Similar room sizes
How these numbers are calculated
Modes use the rectangular-room equation f = (c/2)·√((nx/L)² + (ny/W)² + (nz/H)²) with c = 343 m/s, for an empty room with rigid walls. The Schroeder frequency is fs = 2000 x sqrt(RT60 / V), assuming RT60 = 0.4 s. The modal score starts at 100 and subtracts penalties for stacked modes, density dips, gaps, proportions outside the Bolt area and dimension multiples. Doors, openings and furniture shift real rooms away from these values, which is what the room mode calculator and the 3D editor are for.