Acoustic treatment

How many acoustic panels do I need?

The answer you will find everywhere — six panels and four bass traps — is not an answer. It is an average of rooms that are not yours. The number is calculable, the arithmetic fits in a paragraph, and in a normal American bedroom it says something most panel listings do not.

By the Acustega engineering team · October 6, 2026

The short answer

Work out the absorption you need with A = 0.049 · V / RT, subtract what the room already has, and divide by the panel’s coefficient minus the coefficient of the surface it covers. In a 14 × 11 × 8 ft bedroom with a wood floor and drywall walls, hitting 0.40 s takes about 14 panels of 2 ft × 4 ft × 2 in. Six panels gets you a third of the way.

Why the rule of thumb fails

“Cover 20% of your walls” ignores three things that change the result completely: the volume of the room, what the floor and furniture already absorb, and the real coefficient of the material you are about to buy. A carpet contributes as much mid-frequency absorption as several panels. A hardwood floor contributes almost nothing. Two rooms with the same 20% coverage can end up with reverberation times that are nowhere near each other.

The correct calculation is not harder. It just has one more step, and that step is the one that decides whether you buy nine panels or nineteen.

The four steps

1. Pick a target.How long you want the tail to last. A small mixing room wants 0.25–0.35 s. A room you record voice or take calls in is comfortable at 0.35–0.45 s. A living room that also happens to host a microphone can live at 0.5 s. Choosing a control-room target for a bedroom is the single most common way people end up with an unpleasant, over-damped space.

2. Work out the absorption that target needs. A = 0.049 · V / RT with the volume in cubic feet, or A = 0.161 · V / RT in cubic meters. The result is in sabins: square feet of perfect absorption.

3. Add up what you already have.Every surface times its coefficient in that band — floor, ceiling, walls, window, door. This is the step almost nobody does, and the one that changes the final number most.

4. Divide the shortfall by the material.The missing sabins, divided by the coefficient of the panel you plan to use. And here is the detail that is rarely mentioned: subtract the coefficient of the wall the panel is going to cover. That surface was already absorbing something. Adding the panel without discounting it is the standard way to overbuy — and at low frequencies, as you will see below, it can flip the sign of the result.

A worked example, with every number shown

A 14 × 11 × 8 ft spare bedroom: 1,232 ft³ of volume, 708 ft² of surface. Wood floor on joists, drywall on studs for the walls and ceiling, one 12 ft² window, one hollow-core door — which, acoustically, behaves like a thin panel over an air cavity, not like a wall. Target: 0.40 s. Material: 2-inch mineral wool board of the kind sold at any American building supplier, in homemade 2 ft × 4 ft panels.

Before any treatment, that room measures like this:

Band	Reverberation time
125 Hz	0.32 s	already fine
250 Hz	0.68 s
500 Hz	0.99 s
1 kHz	1.34 s
2 kHz	1.40 s
4 kHz	1.53 s	worst band

Read that column from the bottom up. The problem in this room is the top end, not the bottom. That is the opposite of what a corner-bass-trap bundle assumes, and the reason is structural: drywall on studs is itself a low-frequency absorber. It flexes. At 125 Hz it absorbs roughly five times more than it does at 1 kHz, and in a room built that way, the bass tail is already short before you hang anything.

What six panels actually does

Rather than argue with the usual answer, run it. Here is the same room with six, twelve, sixteen and twenty panels, in seconds of reverberation time:

Panels	125 Hz	250 Hz	500 Hz	1 kHz	2 kHz	4 kHz
none	0.32	0.68	0.99	1.34	1.40	1.53
6	0.33	0.52	0.55	0.65	0.69	0.71
12	0.33	0.42	0.38	0.43	0.46	0.47
16	0.34	0.37	0.32	0.35	0.37	0.38
20	0.34	0.34	0.27	0.30	0.31	0.32

Six panels take the worst band from 1.53 s to 0.71 s. That is a large improvement and you will hear it the day you hang them. It is also still roughly double a sensible target for a room you record in. Six panels is not wrong. It is unfinished — and sold as a complete answer, it is the reason so many people conclude that treatment “didn’t really do much.”

Around fourteen panels puts every band from 250 Hz up inside the target. Twenty pushes 500 Hz to 0.27 s, which in a bedroom is past useful and into dead. The room stops sounding controlled and starts sounding like a closet.

The row that surprises people: 125 Hz

Look at the 125 Hz column across that whole table. It barely moves — 0.32 s to 0.34 s — and what movement there is goes the wrong way. The arithmetic explains it: the 2-inch panel absorbs about 0.22 at 125 Hz, and the drywall it covers absorbs about 0.30. The panel is slightly worse at that frequency than the wall it is hiding.

Which leads to the most useful conclusion in this whole exercise: low frequencies are not solved by more thin panels. They are solved by thickness, by an air gap behind the panel — a 2-inch absorber spaced 4 inches off the wall performs close to a 6-inch one — or by traps tuned to the problem frequency. Run the same six panels in a 6-inch thickness and 125 Hz drops to 0.26 s while every other band improves too. Same count, same wall area, different physics.

What this math cannot tell you

Two honest limits, because a number without its limits is worse than no number.

Sabine’s formula is a statistical model, and it assumes sound is evenly distributed and absorption is evenly spread. Neither is true in a small, heavily treated room. Treat the figures above as sizing, not as a prediction of what a measurement microphone will read — especially once you are below about 0.3 s.

Reverberation time is not the same as room modes. At 125 Hz the wavelength is about 9 feet, comparable to the room itself, and the sound field is not diffuse at all: it is a pattern of peaks and nulls set by the dimensions. A short 125 Hz reverberation time does not mean your bass is even. It means the tail is short. Those are different problems, corner absorption still helps the second one, and no amount of Sabine arithmetic will describe it. That is what a modal calculation and a real measurement are for.

Where they go, in order

The number tells you how much. It does not tell you where, and the order matters as much as the count. First reflection points on the side walls come first: have someone slide a mirror along the wall while you sit in your listening position, and wherever you see the speaker reflected, that is a panel. Then the ceiling, between the speakers and your head. Then the back wall. And the corners, always, for low frequencies — that is where pressure is highest and where a thick absorber finally earns its thickness.

Start with your own number, not ours

Every figure above depends on what your room is already doing, and that takes thirty seconds to find out. Clap once and your phone measures the decay. Free, no sign-up, and it tells you which of the rows above your room actually looks like.

Measure my room →

To run the four steps with your own dimensions and finishes, the calculator does the arithmetic against a catalog of materials with published coefficients.

Frequently asked questions

How many acoustic panels do I need for a 14 by 11 foot room?

In a 14 × 11 × 8 ft bedroom with a wood floor, drywall walls and ceiling, one window and a hollow-core door, reaching 0.40 s takes about 14 panels of 2 ft × 4 ft × 2 in mineral wool. The number moves with your floor, your target and the material you buy: a carpeted version of the same room needs roughly half as many above 1 kHz. There is no single answer, but there is a calculation.

Is six acoustic panels enough?

Six 2 ft × 4 ft panels in that room take the 4 kHz reverberation time from 1.53 s to 0.71 s. That is a large, audible improvement — and still roughly double a sensible target for a room you record or take calls in. Six panels is not wrong. It is unfinished.

How do I calculate how much acoustic treatment I need?

Four steps. Pick a target reverberation time. Compute the absorption that target requires with A = 0.049 · V / RT in cubic feet, or A = 0.161 · V / RT in cubic meters. Add up the absorption your room already has, surface by surface. Divide the shortfall by the panel's absorption coefficient minus the coefficient of the wall it covers — that subtraction is the step most people skip, and it is why they overbuy.

Do I need bass traps in the corners of a drywall room?

For reverberation time, often not: drywall on studs is itself a low-frequency absorber, and in the worked example 125 Hz already sits at 0.32 s untreated, below the target, while the top end is at 1.53 s. That does not mean the bass is fine. Reverberation time and room modes are different problems, and corner absorption still helps the modal peaks and nulls that Sabine's formula cannot describe.

Is it better to overshoot or undershoot on panels?

Undershoot. An over-treated room sounds dead, tires your ears and cannot be fixed by removing material without redoing the work. Size against the upper end of your target range, listen, and add later.

Are thicker panels better than more panels?

Below about 500 Hz, yes, and not marginally. Six 6-inch panels outperform six 2-inch panels in every band in the worked example, and at 125 Hz the 2-inch panel absorbs less than the drywall it covers — adding it makes that band slightly worse. Thickness, an air gap behind the panel, or tuned traps are what move low frequencies. Quantity of thin panels does not.

Keep reading

Panel coefficients are the manufacturer’s published ASTM C423 figures for 2-inch and 6-inch mineral wool board. Surface coefficients come from Acustega’s material catalog. Run the same calculation with a different material and you will get different numbers — which is the entire point. We do not sell panels.