Room Modes in a 15x20 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 15 ft width both resonate at 112.5 Hz, so bass at that note 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 15 ft width and 10 ft ceiling height both resonate at 112.5 Hz, so bass at that note will be much louder than its neighbours.
• The proportions (1 : 1.50 : 2.00) fall inside the Bolt area, the range of room ratios that spreads modes most evenly.
• Below about 137 Hz (the Schroeder frequency) individual modes shape the sound; above it, reflections and reverb matter more.

Because your 20 ft length and 10 ft ceiling are close in size, their modes stack near 56.3 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 a ratio of 1 : 1.50 : 2.00, this room sits inside the Bolt area, the zone where modes tend to spread out rather than pile up. Shape is doing you a favor here.

How to fix it, in order

1. Treat the four floor-to-ceiling corners first; they are common to every mode this room produces, and your ceiling height is part of the problem.
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. Move your listening position off-center along the 20 ft length; roughly 7.6 ft from the front wall (38% back) is a common starting spot before fine-tuning.
4. 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.
5. Once traps are in, measure with REW from the listening position. Focus on frequencies below 137 Hz (this room's Schroeder frequency); that is where individual modes, not general reverb, are running the show.

Every mode below 200 Hz

This room has 106 modes below 200 Hz, 15 axial, 48 tangential and 43 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 15x20 rooms

Is a 15 by 20 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 55/100 because two of its dimensions reinforce the same note near 56.3 Hz. Treatment will make a real difference here.

What is the best corner for bass traps in a 15x20 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 size subwoofer does a 15x20 room need?

Subwoofer size is less about this room's 300 sq ft and more about the output headroom you want; room size mainly changes where the 106 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 a 15 by 20 ft room?

Here it comes down to this: two of its dimensions reinforce the same note near 56.3 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 a 15x20 room?

Corner bass traps come 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. After that, reposition your seat near 7.6 ft from the front wall and verify with REW below 137 Hz.

Similar room sizes

• 14x20 ft, 10 ft ceiling
• 15x20 ft, 8 ft ceiling
• 15x20 ft, 9 ft ceiling