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Acoustic Panel Calculator

This acoustic panel calculator predicts the absorption coefficient - the fraction of sound energy a surface soaks up rather than reflects back - of any porous panel from 20 Hz to 8 kHz. Set the thickness, flow resistivity, and air-gap depth - the tool plots the full curve, computes NRC and SAA, and tells you exactly where the panel will and will not work in a room.

Fixing echo in a normal living room? The OC 703 2" preset with a small air gap is the classic starting point.

My designs

Save panel designs as you iterate. Useful for planning a treatment plan across multiple panels and comparing variants.

NRC - Noise reduction coefficient (250/500/1k/2k Hz avg).
SAA - Sound absorption average (200-2500 Hz, more accurate than NRC).
Effective from
- Lowest frequency where the panel reaches α ≥ 0.7, the level below which absorption is too shallow to treat a room.

Panel preset

recipe

Pick a panel to auto-fill thickness, material, and air gap.

Material

flow

Pick the product you own or plan to buy - thickness and density set what it can absorb.

Pa·s/m²

How hard air has to push through the material - the spec that matters most for absorption. Sweet spot: 5,000-30,000 Pa·s/m². Too low slides through, too high reflects.

Incidence

Random incidence predicts real-room performance, and is the estimate a reverberation-room datasheet approximates; normal incidence matches impedance-tube measurements. Use Normal only when comparing to an impedance-tube figure.

Dimensions

depth

2" / 50 mm absorbs from about 630 Hz up. 4" / 100 mm reaches into mid-bass.

0 = on wall. A gap as deep as the panel itself shifts bass absorption nearly an octave lower.

Quick gap recipes

Absorption coefficient across the audible band

hover to read

The curve is the absorption coefficient α at each 1/3-octave center frequency from 20 Hz to 8 kHz. Above 1.0 means the panel absorbs more than its surface area (lab edge-diffraction artefact; capped at 1.0 here for the NRC). Hover or tap the curve to read values - it snaps to the nearest measured 1/3-octave point.

The shaded band on the left is where the prediction is extrapolated. The Delany-Bazley-Miki regression behind this curve is published as valid for f / σ between 0.01 and 1.0, so its lower bound moves with the material: about 165 Hz for OC 703, 300 Hz for the denser OC 705. Below that line the shape is still the right shape, but it is the model running past its own bounds - treat it as an indication, not a figure to specify against.

Why these numbers

How a porous panel actually absorbs sound

The Delany-Bazley-Miki model in plain English

Porous absorbers (fiberglass, mineral wool, open-cell foam) convert sound energy into heat via viscous friction as air molecules push through the fibers. The efficiency depends on one number: flow resistivity, measured in Pa·s/m². Too low and the air slides through without losses. Too high and the panel reflects like a wall. Sweet spot: 5,000-30,000 Pa·s/m².

The calculator runs the Delany-Bazley-Miki empirical model. It computes the complex propagation constant and characteristic impedance at every frequency, transfers them through the panel and air gap to get the surface impedance, then the absorption coefficient.

The Miki part matters. The original 1970 Delany-Bazley regression is the one most calculators still use, and below its published validity floor it returns a surface impedance whose real part goes negative - a passive slab of fiberglass apparently generating energy. For OC 703 that floor is 165 Hz, so any tool plotting plain Delany-Bazley into the bass is reporting numbers the model cannot support. Miki's 1990 revision keeps the same form with corrected coefficients chosen to stay physical down there, which is why the curve here is drawn from it.

Thickness moves the low end, air gap moves it further

A porous panel only starts absorbing where its thickness equals roughly a quarter wavelength of the sound. At 500 Hz a quarter wavelength is 17 cm - so a 5 cm panel is well past its low-end limit. At 100 Hz it's 86 cm; three feet of fiberglass for a single octave.

The air-gap trick: mounting the same panel a few inches off the wall puts an empty chamber behind it. The panel sits where particle velocity is highest (the absorber needs velocity, not pressure), shifting the effective absorption an octave or more lower. A 5 cm panel with a 10 cm gap absorbs nearly as well at 200 Hz as a 15 cm slab on the wall would - and the gap is free.

Acoustic panel NRC chart: common materials compared

NRC is a single-number summary at 250/500/1k/2k Hz - useful for paperwork, useless for bass. "Effective from" is the lowest frequency at which the panel reaches α ≥ 0.7, the same effectiveness floor the calculator above uses; below it the curve has rolled off into absorption too shallow to change a room.

Why the calculator reads lower than a datasheet. The NRC column here is the maker's published figure, measured in a reverberation chamber. Those measurements routinely return α above 1.0 because sound diffracts around the exposed edges of a finite test sample, so the panel absorbs more than its own stated area - real, but not something a flat wall of the stuff reproduces. The calculator predicts the material itself, with no edge bonus, so a modeled NRC of 0.70 against a published 0.95 is not a contradiction: it is the difference between a lab sample and a mounted panel. Specify against the model, then treat the datasheet number as the optimistic end.

PanelThicknessNRCEffective from (α ≥ 0.7)
Auralex Studiofoam 2" wedge50 mm0.55From 800 Hz. Nothing usable below 500 Hz.
Auralex 4" wedge100 mm0.95From 250 Hz. Still misses real bass.
OC 703 2" direct mount50 mm0.95From 630 Hz. The studio standard for mids up.
OC 703 4" direct mount100 mm1.05From 250 Hz. Mid-bass capable.
Rockwool RW3 50 mm on wall50 mm0.90From 800 Hz. UK/EU OC 703 equivalent.
Rockwool RW3 100 mm on wall100 mm1.00From 250 Hz.
GIK 242 (4" + cloth, no gap)100 mm1.00From 250 Hz. Broadband mid panel.
GIK 244 Bass Trap (4" + 4" gap)200 mm1.05From 160 Hz. The default bass-trap shape.
DIY corner trap (100 mm RW3 + 50 mm gap)150 mm1.00From 200 Hz. Floor-to-ceiling stacks lower still.
Polyester batting 50 mm on wall50 mm0.65From 2 kHz. Cheap, fire-safe, mediocre.
2 cm carpet on concrete20 mm0.302 kHz - 8 kHz only. Negligible for music.
Painted concrete wall (reference)-0.02Nothing. 98 % reflects.
Ekustik Woody Queen 15 cm (PET felt)150 mm0.94From 100 Hz up - maker-rated, and the reason to buy the deep one.

Treatment we have reviewed on this chain: Ekustik Woody Queen (broadband absorber, 0.75 NRC at 5 cm rising to 0.94 at 15 cm) and Ortvik Parametric Tower (freestanding diffuser and absorber, no bass trapping). The rest of the room kit is on the accessories hub.

What a porous absorber can and cannot do

A porous absorber works on air velocity, not on pressure. Sound moving through the fibers is slowed by friction and turned into a tiny amount of heat. That only happens where the air is actually moving, which is why the same panel behaves completely differently depending on where it sits in the wave.

Air velocity is highest a quarter of a wavelength from a hard surface, and effectively zero at the surface itself. A panel mounted flat on a wall therefore does very little for any frequency whose quarter wavelength is deeper than the panel. That single fact explains why thin panels only absorb treble.

The consequence is unavoidable: low-frequency absorption costs depth. A 5 cm panel starts working around 1 kHz, 10 cm reaches into the low midrange, and treating 60 Hz with porous material alone needs depth measured in tens of centimeters - or an air gap behind the panel, which buys some of the same effect for free.

Acoustic panel calculator showing NRC and SAA figures for a panel and the frequency below which it stops absorbing

Worked example

A 50 mm rigid fiberglass panel (OC 703, flow resistivity 16500) mounted flush to the wall, with no air gap behind it.

NRC 0.70, SAA 0.68, and a low-end cutoff around 630 Hz.

NRC and SAA both describe mid-band absorption and they agree here. The cutoff is the number that decides where a panel stops working: below roughly 630 Hz this one thins out fast, which is why flush-mounted 50 mm panels kill flutter and do nothing for bass.

The ideas behind the controls

Absorption coefficient
The fraction of incident energy a surface absorbs at a given frequency, from 0 to 1. It is frequency-dependent, so a single number is always a summary.
NRC and SAA
Single-figure ratings averaged over a band of frequencies. Useful for comparing panels, useless for knowing what happens at 50 Hz.
Flow resistivity
How hard it is to push air through the material. Too low and sound passes straight through; too high and it reflects off the face.
Air gap
Space left between panel and wall. It moves the panel towards the velocity maximum and extends absorption downwards without extra material.

Explained in depth Comb Filtering

Acoustic panel design FAQ.

What thickness actually absorbs bass, why air gaps work, when foam is enough, and how to read the NRC number on a panel data sheet.

  1. What absorption coefficient counts as actually useful?

    About 0.70 and up. Below that the panel reflects more energy than it absorbs at that frequency, and the treatment is not changing what you hear so much as slightly softening a wall. This calculator marks a build "effective" only from the frequency where it clears 0.70, which is a stricter bar than the 0.5 a lot of product marketing implies - so expect the honest answer to be a higher frequency than a datasheet suggests.

  2. What is an acoustic panel absorption coefficient?

    The absorption coefficient (α) is the fraction of sound energy that a surface absorbs rather than reflects, on a scale from 0 (perfect reflector) to 1 (perfect absorber). It is frequency-dependent: most porous panels absorb strongly above 500 Hz and weakly below 200 Hz. The calculator plots α from 20 Hz to 8 kHz at 1/3-octave centers, and treats α 0.7 as the floor below which a surface is not absorbing enough to treat a room.

  3. How thick does an acoustic panel need to be to absorb bass?

    A porous absorber begins to work where its thickness equals about one quarter of the wavelength. A quarter wavelength at 100 Hz is 86 cm of solid absorber, which is impractical. The shortcut is the air gap: a 10 cm panel mounted 10 cm off the wall reaches an octave lower than the same panel on the wall, because the panel sits where the air-particle velocity is highest.

  4. What is flow resistivity and why does it matter for acoustic panels?

    Flow resistivity is how strongly a porous material resists air being pushed through it, measured in Pa·s/m². The Delany-Bazley-Miki model used here takes flow resistivity as its single material input. Optimal broadband absorption sits between 5,000 and 30,000 Pa·s/m². Lower and sound slides through; higher and the panel reflects like a wall.

  5. What is the difference between NRC and SAA?

    NRC (Noise Reduction Coefficient) averages absorption at 250, 500, 1k, and 2k Hz, rounded to 0.05, the legacy US specification. SAA (Sound Absorption Average) averages the twelve 1/3-octave centers from 200 to 2500 Hz, rounded to 0.01, the modern replacement standardized in ASTM C423. Both are visible in the tool, and both ignore the bass-trap behavior below 200 Hz that often matters most in rooms.

  6. Is Owens Corning 703 better than Rockwool RW3?

    They are near-equivalents. OC 703 is the US studio standard rigid fiberglass at roughly 6 lb/ft³ (96 kg/m³) with flow resistivity around 16,500 Pa·s/m². RW3 is the closest UK/EU equivalent in mineral wool at 60 kg/m³ and roughly 14,000 Pa·s/m². At 50 mm direct-mount, both produce nearly identical absorption curves; pick whichever ships locally.

  7. Does acoustic foam actually work for bass?

    No. Open-cell foam in the 2 to 4-inch (50-100 mm) thicknesses sold for studio panels rolls off below 400-500 Hz. It is effective on early reflections and sibilance but does nothing at room-mode frequencies. For bass, the tool will show you the difference between 100 mm foam on the wall (almost no bass absorption) and 100 mm mineral wool with a 100 mm air gap (real low-end absorption).

  8. How big do I need to build my DIY acoustic panels?

    Cover at least 15-25% of room surface area for music listening, more for control rooms. Distribute panels across first reflection points (side walls, ceiling above the desk) and corners (bass traps). The calculator will tell you the absorption depth you need for the frequencies you want to treat; the wall-coverage percentage is set by how much absorption the room needs overall. Use the room mode tool to find what frequencies to target first.

  9. Why does the absorption curve go above 1.0 in published panel specs?

    Lab-measured α can exceed 1.0 because edge diffraction at the panel boundaries effectively captures sound from beyond the panel's geometric area, so the panel absorbs more energy than is incident on its face. The calculator caps at 1.0 for the NRC calculation. In a real installation with many panels side-by-side this edge effect disappears and the absorption sits closer to 1.0 maximum.

  10. Does the Delany-Bazley-Miki model account for cloth covering or perforated facings?

    Not directly. The model treats the absorber as a homogeneous porous layer in front of either a rigid wall or an air cavity. A breathable speaker-grille cloth has negligible effect. A perforated panel with low open area starts to act as a Helmholtz resonator and shifts the curve. That is a different model. For typical cloth-wrapped panels the calculator is accurate to within 5-10% of measured data.