Room Modes in an 18x19 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 29.6 Hz, set by the 19 ft length.
• Between 43.1 Hz and 59.2 Hz there are no modes at all, so notes in that 16.1 Hz gap will sound thinner than the bass around them.
• Mode density drops in the 40 and 50 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 : 2.25 : 2.38) fall outside the Bolt area because the floor is close to square, which concentrates bass problems on fewer notes.
• Below about 144 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

This room has a hole of 16.1 Hz between 43.1 Hz and 59.2 Hz where no mode helps the bass along. Anything tuned to that range reads weaker than its neighbors.

For a home theater, expect that gap 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 : 2.25 : 2.38) fall outside the Bolt area, the range room ratios usually spread modes best over, because the floor is close to square, which piles bass problems onto fewer notes instead of spreading them out. 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.
2. Full absorption at 40.0 Hz would take about 7 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 19 ft length. Start near 7.2 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 144 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 97 modes this room produces under 200 Hz: 14 axial, 47 tangential, 36 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 18x19 rooms

Is an 18 by 19 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 71/100 because there is a gap of 16.1 Hz between 43.1 Hz and 59.2 Hz with no mode in between. Treatment will make a real difference here.

What is the best corner for bass traps in an 18x19 room?

The four vertical corners first. Full absorption at 40.0 Hz would take roughly 7 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 18x19 room need?

Subwoofer size is less about this room's 342 sq ft and more about the output headroom you want; room size mainly changes where the 97 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 18 by 19 ft room?

Here it comes down to this: there is a gap of 16.1 Hz between 43.1 Hz and 59.2 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 18x19 room?

Corner bass traps come first, as thick as you can fit (6 to 12 in) plus a membrane trap tuned near 40.0 Hz, since that note's own quarter wavelength (about 7 ft) is too deep for any panel. After that, reposition your seat near 7.2 ft from the front wall and verify with REW below 144 Hz.

Similar room sizes

• 18x18 ft, 8 ft ceiling
• 18x20 ft, 8 ft ceiling