Room Modes in an 8x20 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 28.1 Hz, set by the 20 ft length.
• Your 20 ft length and 8 ft width both resonate at 140.7 Hz, so bass at that note will be much louder than its neighbours.
• Between 28.1 Hz and 56.3 Hz there are no modes at all, so notes in that 28.2 Hz gap will sound thinner than the bass around them.
• Mode density drops in the 40 Hz third-octave band (0 modes against 1 in the band below), so bass will sound uneven from note to note.
• The proportions (1 : 0.89 : 2.22) fall outside the Bolt area because the room is long and narrow for its height, so modes bunch up along the length.
• Below about 198 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

Because your 20 ft length and 8 ft width are close in size, their modes stack near 140.7 Hz. Expect that one note to sound louder, and ring longer, than the rest of the bass in this room.

In a home theater, this shows up as one bass note in an action scene sounding far louder than the rest of the mix, usually a kick drum hit or an LFE cue landing right on that stacked note. In a music room, the same thing means certain bass notes on a track jump out while others next to them feel buried.

At 1 : 0.89 : 2.22, this room sits outside the Bolt area because the room is long and narrow for its height, which bunches modes up along the length. Expect to lean on bass traps and seat position a bit more than in a room with friendlier proportions.

How to fix it, in order

1. Put your first traps in the four vertical corners where floor meets ceiling; that is where every mode in this room reaches its loudest point.
2. Full absorption at 140.7 Hz would take about 2 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. Avoid the exact middle of the 20 ft length for your seat or mix position; try around 7.6 ft from the front wall (38% of the length) as a starting point, then nudge from there by ear.
4. Test more than one subwoofer position. Corner placement drives the most output but also the least even bass; moving it along a wall or using two subs at different spots tends to average out this room’s peaks.
5. Confirm the fix with an REW measurement at the listening position, paying closest attention below 198 Hz; above that, general room reverb matters more than any single mode.

Every mode below 200 Hz

The table below lists every mode under 200 Hz for this room: 56 in all, 12 axial, 28 tangential and 16 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 8x20 rooms

Is an 8 by 20 ft room good for a music room or home theater?

It can work as a bedroom theater or dedicated music room, but do not expect an easy ride: this room scores 55/100 because two of its dimensions reinforce the same note near 140.7 Hz. Treatment will make a real difference here.

What is the best corner for bass traps in an 8x20 room?

The four vertical corners first. Full absorption at 140.7 Hz would take roughly 2 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 8x20 room need?

Subwoofer size is less about this room's 160 sq ft and more about the output headroom you want; room size mainly changes where the 56 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 is bass boomy in one spot in an 8 by 20 ft room?

Here it comes down to this: two of its dimensions reinforce the same note near 140.7 Hz. 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 8x20 room?

Corner bass traps come first, as thick as you can fit (6 to 12 in) plus a membrane trap tuned near 140.7 Hz, since that note's own quarter wavelength (about 2 ft) is too deep for any panel. After that, reposition your seat near 7.6 ft from the front wall and verify with REW below 198 Hz.

Similar room sizes

• 9x20 ft, 9 ft ceiling
• 8x20 ft, 8 ft ceiling