Room Modes in a 13x20 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 28.1 Hz, set by the 20 ft length.
• Your 20 ft length and 13 ft width both resonate near 84.4 and 168.8 Hz, so bass at those notes will be much louder than its neighbours.
• Your 20 ft length is exactly twice your 10 ft ceiling height, so their modes stack at 56.3, 112.5 and 168.8 Hz and bass at those notes will be much louder than its neighbours.
• Your 13 ft width and 10 ft ceiling height both resonate near 168.8 Hz, so bass at that note will be much louder than its neighbours.
• Between 28.1 Hz and 43.3 Hz there are no modes at all, so notes in that 15.2 Hz gap will sound thinner than the bass around them.
• The proportions (1 : 1.30 : 2.00) fall outside the Bolt area because the room is long and narrow for its height, so modes bunch up along the length.
• Below about 147 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

The modes from your 20 ft length and 10 ft ceiling land on top of each other near 56.3 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 : 1.30 : 2.00) 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, including the ones set by your ceiling height.
2. Full absorption at 56.3 Hz would take about 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. Do not sit dead-center on the 20 ft length. Start near 7.6 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 147 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 94 modes below 200 Hz, 14 axial, 43 tangential and 37 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 13x20 rooms

Will a 13x20 room work for a home theater?

You can use this room as a dedicated home theater or media room, but its bass will fight you: a 29/100 modal score, mainly because two of its dimensions reinforce the same note near 56.3 Hz, means committed corner trapping and careful seat placement are not optional here.

Where should I put bass traps in a 13x20 room?

The four vertical corners first. Full absorption at 56.3 Hz would take roughly 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.

What subwoofer size is right for a 13 by 20 ft room?

There is no fixed sub size tied to 260 sq ft; that number mostly sets this room's mode frequencies (94 of them under 200 Hz). At this size you will want more headroom than a small room needs, and two subwoofers usually beat one at keeping bass even from seat to seat.

Why does my 13x20 room have one loud bass note?

The short answer for this room: two of its dimensions reinforce the same note near 56.3 Hz. Bass unevenness like that is built into the shape of the room and shows up regardless of what speakers or sub you use.

How do I fix bass problems in a 13x20 room?

Put bass traps in the four floor-to-ceiling corners first, as thick as you can fit (6 to 12 in) plus a membrane trap tuned near 56.3 Hz, since that note's own quarter wavelength (about 5 ft) is too deep for any panel. From there, move your seat to about 7.6 ft from the front wall, then measure with REW below 147 Hz to see what still needs work.

Similar room sizes

• 12x20 ft, 10 ft ceiling
• 14x20 ft, 10 ft ceiling
• 13x20 ft, 8 ft ceiling
• 13x20 ft, 9 ft ceiling