Gypsum board (drywall) absorption coefficient
Gypsum board on studs absorbs α 0.29 at 125 Hz and almost nothing above it — NRC 0.05. That single pair of numbers is the most misunderstood thing in a small room: your bare walls are already the biggest bass absorber you own, and the standard rating hides it completely. Here are the sourced octave-band coefficients (α) for drywall and the other hard surfaces around it, pulled straight from our absorption database, plus the panel-resonance arithmetic that explains the shape. We don't sell panels or building materials.
Gypsum board and hard-surface absorption coefficients by octave band
Random-incidence coefficients measured per ISO 354 / ASTM C423. α is the fraction of incident sound energy absorbed (1.00 = fully absorbed). NRC is the average of the 250 / 500 / 1000 / 2000 Hz values. Read down the 125 Hz column: the stud-framed sheet is in a different league from solid masonry, and every row collapses toward zero as the frequency rises.
| Surface | 125 Hz | 250 Hz | 500 Hz | 1k Hz | 2k Hz | 4k Hz | NRC |
|---|---|---|---|---|---|---|---|
| Gypsum board (12 mm on studs) | 0.29 | 0.10 | 0.05 | 0.04 | 0.07 | 0.09 | 0.05 |
| Gypsum board ceiling | 0.15 | 0.10 | 0.06 | 0.04 | 0.04 | 0.05 | 0.05 |
| Plaster on masonry | 0.01 | 0.01 | 0.02 | 0.03 | 0.04 | 0.05 | 0.05 |
| Brick, unglazed | 0.03 | 0.03 | 0.03 | 0.04 | 0.05 | 0.07 | 0.05 |
| Concrete or terrazzo floor | 0.01 | 0.01 | 0.01 | 0.02 | 0.02 | 0.02 | 0.00 |
Source: Standard architectural-acoustics coefficient tables (ISO 354 / ASTM C423 measured). See every value and its source in the full database or download the CSV (CC BY 4.0). These are nominal published values for planning — a specific wall's behaviour depends on its cavity depth, board thickness, fixings and whether the cavity holds insulation.
Drywall absorbs bass, not treble — the opposite of foam
Every porous absorber on this site has the same shape: near-zero at 125 Hz, climbing steeply toward the treble. Gypsum board runs the other way. Put them side by side and the 125 Hz column inverts the ranking you would expect.
| Material | 125 Hz | 250 Hz | 500 Hz | 1k Hz | 2k Hz | 4k Hz | NRC |
|---|---|---|---|---|---|---|---|
| Gypsum board (12 mm on studs) | 0.29 | 0.10 | 0.05 | 0.04 | 0.07 | 0.09 | 0.05 |
| Mineral wool, 50 mm, on wall | 0.15 | 0.55 | 0.90 | 1.00 | 1.00 | 1.00 | 0.85 |
| Open-cell acoustic foam, 50 mm | 0.08 | 0.25 | 0.60 | 0.90 | 0.95 | 0.98 | 0.70 |
| Carpet, heavy, on foam pad | 0.08 | 0.24 | 0.57 | 0.69 | 0.71 | 0.73 | 0.55 |
Why: panel resonance, not porosity
Porous absorbers work by letting air move through a fibrous layer and turning that motion into heat, which is why they need physical depth comparable to the wavelength. Gypsum board is not porous and has no depth to speak of. It absorbs by a completely different mechanism: a relatively limp sheet mounted over a sealed air cavity behaves as a mass-spring system — the board is the mass, the trapped air is the spring. Around its resonant frequency the sheet is driven into motion by incident sound and dissipates energy in the board, the fixings and the cavity. That is why drywall's absorption is a low-frequency bump rather than a rising curve, and why it disappears once the sheet is glued flat to solid masonry with nothing to flex against.
The standard approximation for that resonance is f₀ ≈ 60 / √(m · d), with m the panel's surface mass in kg/m² and d the cavity depth in metres. Taking gypsum board's nominal density as 750 kg/m³, common build-ups land here:
| Wall build-up | Surface mass | Cavity | f₀ (approx.) |
|---|---|---|---|
| One 12.5 mm sheet on 25 mm battens | 9.4 kg/m² | 25 mm | 124 Hz |
| One 12.5 mm sheet on 45 mm battens | 9.4 kg/m² | 45 mm | 92 Hz |
| One 12.5 mm sheet on 90 mm studs | 9.4 kg/m² | 90 mm | 65 Hz |
| Two 12.5 mm sheets on 90 mm studs | 18.8 kg/m² | 90 mm | 46 Hz |
Planning estimate only, from the limp-panel approximation given in Cox, T. J. & D’Antonio, P. — Acoustic Absorbers and Diffusers (3rd ed., CRC Press). and Bies, D. & Hansen, C. — Engineering Noise Control, appendix absorption tables. It assumes a sealed air-filled cavity and ignores stud stiffness, board damping and edge fixing, all of which broaden and flatten the peak in a real wall — filling the cavity with insulation in particular damps the resonance and spreads it over a wider band. See our methodology & sources.
Every one of these build-ups resonates between roughly 46 and 124 Hz — squarely inside the range where small rooms have their worst modal problems, and inside or just below the 125 Hz measurement band. That is the direct explanation for the α 0.29 figure at the top of this page. It also explains a detail worth knowing: heavier board on a deeper cavity tunes the absorption lower, so a double-boarded wall helps further down the spectrum than a single sheet on thin battens.
NRC 0.05 hides all of it
NRC averages only the 250, 500, 1000 and 2000 Hz coefficients. Gypsum board's entire useful absorption sits at 125 Hz — the one octave band NRC never looks at. The result is that a wall which genuinely removes low-frequency energy from a room is rated NRC 0.05, identical to unglazed brick (NRC 0.05) and plaster on masonry (NRC 0.05), materials that absorb roughly 10× and 22× less bass respectively. If you are comparing materials by a single number, this is the failure mode to watch for — see what NRC actually measures for the general case, and always read the 125 Hz column yourself.
Why a masonry room booms and a stud-framed room doesn't
This is the practical payoff, and it explains an experience most people have had without knowing why. Two rooms of identical size can sound completely different bare, because their surfaces return different amounts of low-frequency energy. A stud-and-plasterboard room gives back 71% of the bass energy hitting its walls; a plastered masonry room gives back 98.7% and a concrete floor 99%. That is why converted basements, garages and concrete-framed apartments are notorious for booming, sustained low-end while a stud-framed spare bedroom of the same dimensions sounds comparatively controlled before anything is put on the walls.
Absorption is not soundproofing — and here they conflict
Gypsum board is where the usual "absorption ≠ soundproofing" caution becomes sharper than usual. On the other material pages the two are simply unrelated. Here they actively trade off, because drywall absorbs bass by flexing, and a panel that flexes easily is by definition a poor barrier. Everything you do to improve isolation — adding mass, doubling the board, decoupling the leaves, damping the cavity — stiffens or damps the very resonance that produced the α 0.29 figure, and moves it elsewhere in the spectrum. A wall built to keep sound out is usually a slightly worse bass absorber for the room inside. Neither goal is wrong; they are just different projects, and it is worth knowing which one you are doing.
What this means for treating your room
- Don't count drywall as treatment. Its absorption is real but narrow and already present — it is the room's starting condition, not something you can add more of.
- Do account for your structure. A masonry or concrete room needs materially more low-frequency absorption than a stud-framed one of the same size.
- Ignore NRC for hard surfaces. At NRC 0.05, drywall and brick look identical and are not. Read the 125 Hz coefficient.
- Porous panels remain the job. Above 250 Hz the wall does essentially nothing — that whole range is what your panels and traps are for.
Plan the rest of your room
Your walls handle a slice of the bottom octave; everything above it is up to the treatment. Size that with the acoustic panel calculator, then check the result against a reverberation target with the RT60 calculator — it lets you set gypsum board (or any material in the database) as a surface and see the per-band effect, so you can compare a stud-framed room against a masonry one directly. If the low end is the complaint, find the problem frequencies first with the room mode calculator and compare them against the f₀ table above.
Frequently asked questions
What is the absorption coefficient of gypsum board (drywall)?
For gypsum board (12 mm on studs) the sourced octave-band coefficients are α 0.29 / 0.10 / 0.05 / 0.04 / 0.07 / 0.09 at 125 / 250 / 500 / 1000 / 2000 / 4000 Hz, giving an NRC of 0.05. The number that matters is the first one: 0.29 at 125 Hz, falling to 0.04 by 1 kHz. Drywall is a low-frequency absorber and a mid/high-frequency reflector — the exact opposite shape to foam or carpet.
Does drywall absorb sound?
Yes, but only bass, and only when it is mounted on studs or battens over a cavity. A sheet of plasterboard fixed directly to solid masonry has almost nothing to flex against and behaves like the masonry underneath it (plaster on masonry is α 0.01 at 125 Hz). It is the stud cavity, not the gypsum itself, that does the work.
Why is the NRC of gypsum board only 0.05?
Because NRC averages the 250, 500, 1000 and 2000 Hz coefficients and ignores 125 Hz entirely. Gypsum board's only meaningful absorption (α 0.29) sits in the one band NRC does not look at, so a wall that genuinely removes bass energy scores NRC 0.05 — the same as unglazed brick (NRC 0.05), which absorbs almost nothing at any frequency. This is a known blind spot in the NRC metric, not a quirk of this dataset.
Does drywall absorb more bass than acoustic foam?
At 125 Hz, yes — by a wide margin. Gypsum board on studs is α 0.29 at 125 Hz, against 0.08 for 50 mm acoustic foam, 0.08 for heavy carpet on a pad and 0.15 for 50 mm mineral wool. Above 250 Hz the ranking reverses completely and the porous materials win by an order of magnitude. The wall and the treatment are solving different halves of the spectrum.
Why does a concrete or basement room boom more than a stud-framed room?
Because the walls themselves are absorbing very different amounts of bass. Gypsum board on studs takes α 0.29 out of the 125 Hz band; plaster on masonry takes 0.01 and a concrete floor 0.01. A masonry or concrete room hands nearly all of its low-frequency energy back into the room, so modes ring longer and the room sounds boomier before any treatment is added.
Does gypsum board soundproof a room?
No — and here absorption and isolation actually pull against each other. Drywall absorbs bass by flexing on its cavity, and a panel that flexes easily is a poor sound barrier. Building for isolation means adding mass, decoupling the leaves and damping the cavity, which stiffens and damps exactly the resonance that produced the α 0.29 figure. A better wall for keeping sound out is usually a slightly worse bass absorber for the room inside.
Related material guides
- Acoustic foam absorption coefficient — NRC by thickness and foam type — and why it barely touches bass.
- Mineral wool absorption coefficient — Thickness and an air gap beat density — the panel-builder’s material.
- Carpet absorption coefficient — Tames echo, not bass — and why it is not soundproofing.
- Curtains absorption coefficient — Fullness and an air gap are the levers — “soundproof” curtains do not block noise.
- Cork absorption coefficient — Rated the same as bare brick — sold as treatment, measured as a hard surface.
- Concrete absorption coefficient — Four different materials share the name — and painting the block costs you most of it.
What the numbers mean: what is the sound absorption coefficient? · New here? Start with Acoustic Treatment 101 · Browse all material absorption data · See our methodology & sources.