Room Modes in a 17x23 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 24.5 Hz, set by the 23 ft length.
• Your 23 ft length and 17 ft width both resonate near 97.9 and 195.7 Hz, so bass at those notes will be much louder than its neighbours.
• Your 23 ft length and 9 ft ceiling height both resonate near 122.3 Hz, so bass at that note will be much louder than its neighbours.
• Between 48.9 Hz and 59.1 Hz there are no modes at all, so notes in that 10.2 Hz gap will sound thinner than the bass around them.
• The proportions (1 : 1.89 : 2.56) fall inside the Bolt area, the range of room ratios that spreads modes most evenly.
• Below about 127 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

Your 23 ft length and 17 ft width share a mode near 97.9 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 : 1.89 : 2.56, 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

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. At 97.9 Hz the quarter wavelength is about 2.8 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 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 127 Hz is where these modes live, so that is the range worth checking before you call the room done.

Every mode below 200 Hz

Below are all 123 modes this room produces under 200 Hz: 17 axial, 58 tangential, 48 oblique. Axial modes, which only involve one pair of opposite surfaces, ring the loudest. Tangential modes (four surfaces) come next, and oblique modes (all six surfaces) are the weakest of the three.

Questions about 17x23 rooms

Will a 17x23 room work for a home theater?

This size suits a dedicated home theater or media room, though the 68/100 modal score signals some work ahead, mainly because two of its dimensions reinforce the same note near 97.9 Hz.

Where should I put bass traps in a 17x23 room?

Start in the four floor-to-ceiling corners; every mode in this room peaks there. The 97.9 Hz mode itself would need about 2.8 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 97.9 Hz.

What subwoofer size is right for a 17 by 23 ft room?

There is no fixed sub size tied to 391 sq ft; that number mostly sets this room's mode frequencies (123 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 17x23 room have one loud bass note?

The short answer for this room: two of its dimensions reinforce the same note near 97.9 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 17x23 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 97.9 Hz, since that note's own quarter wavelength (about 2.8 ft) is too deep for any panel. From there, move your seat to about 8.7 ft from the front wall, then measure with REW below 127 Hz to see what still needs work.

Similar room sizes

• 16x23 ft, 9 ft ceiling
• 18x23 ft, 9 ft ceiling
• 17x22 ft, 9 ft ceiling
• 17x24 ft, 9 ft ceiling
• 17x23 ft, 8 ft ceiling