To build a bass trap you take a thick slab of mineral wool or rigid fibreglass, mount it across a room corner with an air gap behind, and wrap it in breathable fabric. Bass traps are the single most important piece of treatment in any small room, because low frequencies cause the worst problems and pile up exactly where the walls meet. Get the corners under control and everything else gets easier.
🔧 Free tool: try our Frequency to Wavelength Calculator.
This is treatment that controls bass inside the room. It will not stop bass travelling to the neighbours — that’s soundproofing, and it works on completely different principles of mass and decoupling.
Why Corners and Why Bass Is the Problem
Small rooms suffer from room modes and standing waves: certain low frequencies reinforce and cancel at fixed points, making bass boom in one spot and disappear in another. Pressure builds up highest at the room boundaries, and corners are where multiple boundaries meet, so a corner is where a trap does the most good. A thick absorber straddling the corner soaks up that low-frequency energy and smooths the response. Background on this is in how to treat room corners.
Thicker Is the Whole Point
Bass has long wavelengths, so you need depth to absorb it. A thin panel does almost nothing below the low mids. That’s why a bass trap is built much thicker than a wall panel — typically 100 mm (4″) or more of mineral wool, and ideally straddling the corner so there’s a large air cavity behind it. The bigger the effective depth, the lower the frequency it controls. This is also why foam “corner” wedges and egg cartons are useless for bass: no mass, no depth.
What You’ll Need
- Thick rigid mineral wool or fibreglass — Rockwool (Rockboard) or Owens Corning 703, 100 mm slabs (stack for more depth).
- Timber to build a triangular or rectangular frame that sits across the corner.
- Breathable fabric, a staple gun, screws/brackets, a saw and drill.
- Dust mask, gloves and eye protection — mineral fibres irritate, so wear them while cutting.
Step by Step
- Decide the style. The simplest effective trap is a flat panel mounted diagonally across the corner, leaving a triangular air cavity behind. Alternatively, fill the corner more fully by stacking slabs. The straddle-with-air-gap approach gives excellent low-end control for the material used.
- Build the frame. Make a frame deep enough to hold your slab(s) and to span the corner. A triangular frame sits cleanly into the corner; a simple rectangular frame mounted across the corner works just as well.
- Fit the wool. Set the slab(s) into the frame snugly without crushing them. Stacking two 100 mm slabs gives you a serious low-frequency absorber.
- Wrap in fabric. Pull breathable fabric taut over the front and staple to the back, folding the corners neatly.
- Mount across the corner. Fix it floor-to-ceiling if you can — tall traps catch more of the vertical mode energy. Anchor into studs, not bare drywall, because these are heavy.
Go Floor to Ceiling and Use the Front Corners First
Bass collects along the full vertical edge of a corner, so a tall trap beats a short one. If you can only build a couple, put them in the front corners (behind your monitors) first, then the rear corners. The vertical wall-ceiling edges also hold bass and respond well to traps if you have material to spare. You can even mount a thick absorber across the wall-ceiling junction as a hybrid trap and acoustic cloud.
How This Fits Your Wider Treatment
Bass traps come first, then broadband panels at the reflection points. Build the flat panels using how to build acoustic panels, place them per where to place acoustic panels, and fit it into the overall scheme in acoustic treatment for home studios. Once traps are in, measure the result with the free Room EQ Wizard (REW) to confirm the low-end response actually smoothed out — see how to measure your room acoustics.
Frequently Asked Questions
How thick does a bass trap need to be?
At least 100 mm of mineral wool, and more is better for low frequencies. Straddling the corner so there’s a large air cavity behind effectively increases the depth and pushes absorption lower.
Do foam bass traps work?
Foam corner wedges are too thin and light to absorb real low-frequency energy; they mostly touch the highs. For genuine bass control you need thick, dense mineral wool or fibreglass, not foam.
Where should I put bass traps first?
The vertical corners of the room, prioritising the front corners behind your monitors. Run them floor to ceiling where possible, since bass pressure builds along the whole corner edge.
