Bass Trap Calculator
This bass trap calculator sizes a porous bass trap (quarter-wavelength depth rule) or a tuned membrane trap (f₀ = 60/√(m·d)) to tame a low-frequency room mode, with panel thickness by material, a room-mode targeting helper, and corner-placement guidance for DIY acoustic treatment.
ℹ These are standard design approximations, not exact predictions. A porous absorber doesn’t switch on at one frequency — its absorption rolls off gradually, and the real figure depends on the material’s density and flow resistivity and how it’s mounted. A membrane trap is narrowband and must be sealed airtight to work. You’ll usually need several traps, and corners matter most. Use the numbers to size and place traps, then confirm by measuring (Room Frequency Analyzer). Metric; everything runs in your browser.
How It Works
Bass problems come from room modes — standing waves between parallel surfaces that boom at some notes and disappear at others. Two kinds of trap absorb that low-frequency energy. A porous trap (thick mineral wool or rigid fibreglass) absorbs by friction as air moves through it, and air moves fastest a quarter-wavelength out from a wall — so a porous trap of total depth d only starts working well around f ≈ c / (4·d). To absorb a 50 Hz mode that way you’d need roughly 1.7 m of depth, which is why porous traps are mounted thick, across corners, with an air gap behind to add effective depth. A membrane (panel) trap takes a different route: a limp panel of mass m over a sealed air cavity of depth d behaves like a mass on a spring and resonates at f₀ ≈ 60 / √(m·d), soaking up energy near that frequency without needing huge depth. The trade-off is that it’s narrowband and must be airtight.
Both formulas are approximations: a real porous absorber rolls off gradually rather than switching on at the quarter-wave point, and its absorption depends on density and flow resistivity; a real membrane’s tuning shifts with how the panel is fixed and how lossy it is. Use them to size a trap, then place traps where they work hardest — in the corners, because every axial mode has a pressure peak in every corner, so a single floor-to-ceiling corner bass trap attacks them all. Enter your room dimensions above to see your lowest axial modes and target the worst one first, then verify the result with a measurement using the Room Frequency Analyzer.
Choosing the right porous material
Not all foam and insulation is equal for bass trapping. Rigid fibreglass (e.g. Owens Corning 703 or 705) and rockwool / mineral wool (e.g. Rockwool Safe'n'Sound, Knauf Insulation) with a density of 40–100 kg/m³ and high flow resistivity are the most effective broadband porous absorbers. Open-cell acoustic foam of 25–50 mm thickness is useful for mid/high-frequency control but provides negligible bass absorption — it is not a substitute for a thick, dense mineral-wool panel absorber. A minimum depth of 100 mm (with air gap) is needed for meaningful absorption below 200 Hz; 200 mm or more for below 100 Hz.
Room modes vs flutter echo — know which problem you have
Bass traps address room modes (standing waves at specific low frequencies determined by room dimensions). Flutter echo — the rapid, metallic decay you hear when you clap in an empty room — is a mid/high-frequency phenomenon caused by parallel reflective surfaces and is solved by diffusers or thinner panels, not bass traps. If your main complaint is a boomy, one-note bass or certain notes sustaining unnaturally long, you have room modes. If it's a "ping" or slap-back on transients, you have flutter echo. Many rooms have both. Use the Room Mode Calculator to confirm which frequencies are the axial modes before building.