Bass Trap Calculator

How the bass trap calculator works

Use this bass trap calculator to estimate the absorber depth needed to treat low-frequency problems in a room. It can help with studio corners, rear wall treatment, porous absorbers and tuned low-frequency absorption planning.

Bass traps target low-frequency energy that broad-spectrum panels cannot effectively absorb. This calculator handles two trap types: a quarter-wave resonator (a panel-and-air-cavity resonator tuned to a specific frequency) and a porous absorber (a thick fibrous material that converts sound energy to heat through viscous friction). Enter your target frequency and the speed of sound, and the calculator returns the required air cavity depth for a resonant trap or the minimum wool thickness for a porous trap. A cross-section diagram helps visualise the construction geometry.

Porous absorbers: how thick is thick enough?

A porous absorber becomes effective at the frequency whose quarter wavelength equals the material thickness. To absorb 100 Hz efficiently, a free-hanging panel needs to be at least 860 mm thick — clearly impractical. In corner placement, however, the effective path length doubles at the room boundaries, allowing a 100 mm panel to contribute usefully down to 200 Hz and a 200 mm panel to reach below 150 Hz. For deeper bass treatment, panels are stacked, placed in corners with an air gap behind them, or supplemented with resonant traps. Flow resistivity (measured in Pa·s/m²) determines how much friction the fibres create — higher resistivity works better at lower frequencies but can begin to reflect high-frequency energy.

Resonant traps: tuned panel absorbers

A quarter-wave resonator consists of a rigid backing wall, a sealed air cavity, and a face panel. When the cavity depth equals λ/4 at the target frequency, a pressure maximum forms at the back wall and a velocity maximum at the face — exactly the conditions for maximum energy absorption. These traps are frequency selective, with a bandwidth of roughly one octave either side of the tuning frequency. They are most useful for addressing a specific room mode that survives broadband porous treatment. The face panel material, mass, and any damping material inside the cavity all affect the peak absorption coefficient and bandwidth.

Placement matters more than quantity

Low-frequency pressure builds up in room corners where two or three boundaries meet. Placing bass traps in corners maximises their effectiveness because pressure is highest there. Floor-to-ceiling corner treatment is more effective per unit of material than isolated panels on flat walls. For a control room or home studio, the four vertical corners behind and beside the listening position are the highest-priority locations. Wall-ceiling junctions (tri-corners where three boundaries meet) are the most efficient single locations in the room. Once corners are treated, adding broadband panels to the front wall, sidewalls, and ceiling reduces flutter echo and mid-frequency RT60.

Key terms

• Quarter-wave resonator — a cavity whose depth is λ/4 at the target frequency; creates maximum acoustic velocity at the mouth for peak energy dissipation.
• Porous absorber — fibrous or open-cell material that converts sound into heat through viscous friction; effectiveness increases with thickness and correct flow resistivity.
• Flow resistivity — resistance to airflow through the material (Pa·s/m²); typical mineral wool for acoustic use is 5,000–20,000 Pa·s/m².
• Corner placement — positioning a trap where two or three room boundaries meet; pressure buildup in corners increases the absorber's coupling to low-frequency energy.
• Air gap — space between the back of a porous absorber and the wall; shifts the effective absorption lower in frequency without adding more material thickness.

Frequently asked questions

• How deep should a bass trap be? Broadband porous bass traps are usually at least 100–200 mm deep, and deeper corner traps work lower in frequency. A tuned trap can be shallower or deeper depending on the target frequency and resonator design.
• What frequency should bass traps target? Start with measured room modes or the strongest low-frequency decay problems. In small studios, common targets are often between 40 Hz and 150 Hz, with broadband corner traps covering as much of that range as practical.
• Are porous bass traps enough for very low frequencies? Porous traps help, especially when thick and placed in corners, but very low frequencies may need large depths or tuned absorbers. Below roughly 60–80 Hz, Helmholtz or membrane-style resonant treatment is often more practical than only adding thin panels.
• Where should bass traps be placed first? Start in vertical corners and wall-ceiling boundaries because low-frequency pressure builds up near boundaries. Rear wall and front wall treatment are next priorities when measurements show long bass decay there.
• What is the difference between a bass trap and a Helmholtz resonator? A bass trap is a broad term for low-frequency absorption. A Helmholtz resonator is a tuned bass trap that absorbs strongly near one frequency using a cavity and neck, while porous traps absorb across a broader range as thickness increases.
• Where should bass traps go? Corners and wall-ceiling junctions are the highest-priority locations because low-frequency pressure peaks there. Floor-to-ceiling vertical corner treatment gives the best return. After corners, address the front wall behind the speakers, the rear wall behind the listening position, and the sidewall first reflection points.
• How thick does a porous bass trap need to be? 100–200 mm mineral wool panels placed in corners with a 50–100 mm air gap behind them provide useful absorption down to 80–100 Hz. Thicker is always better for low-frequency reach. Stacking two 100 mm panels is acoustically similar to a single 200 mm panel.
• What is the difference between a resonant trap and a porous trap? A porous trap broadband-absorbs mid and high frequencies along with bass, and its low-frequency reach improves with thickness. A resonant trap is frequency selective — it absorbs strongly near its tuning frequency with limited broadband effect. Use porous traps for general treatment; use resonant traps to address a specific problem mode that survives broadband treatment.
• How many bass traps do I need? Most small rooms benefit from floor-to-ceiling treatment in at least two opposite vertical corners and the two tri-corners behind the listening position. Treat all four vertical corners with 200 mm mineral wool panels before adding flat-wall panels — corner area per unit of material gives the most low-frequency absorption.
• Can I build my own bass traps? Yes — DIY bass traps are common and cost-effective. Build frames from 50 × 100 mm timber, fill with high-density mineral wool or rockwool (45–60 kg/m³), wrap in acoustically transparent fabric, and mount in corners floor to ceiling. Leave a 50–100 mm gap between the panel back and the wall to extend low-frequency absorption.
• What frequencies do corner bass traps affect? A 200 mm mineral wool panel in a corner with a 50 mm air gap typically provides useful absorption from roughly 80 Hz upward. Corner placement extends the effective frequency range by approximately one octave compared to free-field placement. Below 80 Hz, dedicated resonant traps or very thick broadband panels (400 mm+) are required for meaningful absorption.