What hole size and spacing should I start with?

Small holes (3–8 mm) on a pitch a few times their diameter is the typical range — it's what keeps the open-area ratio in the few-percent band this design targets. Fresnelcut solves the exact combination for your target frequency rather than requiring you to guess.

Can I drill this by hand instead of using a laser or CNC?

A regular grid of small holes is realistic with a drill press and a marked template, though a laser or CNC will be faster and more consistent, especially at higher hole counts.

How is this different from acoustic pegboard?

Pegboard uses a fixed, off-the-shelf hole size and spacing that wasn't chosen for any particular target frequency. Fresnelcut solves the hole size, pitch, and cavity depth together for the frequency you actually want to treat.

Do I need a fabric facing over the holes?

It's optional but common — a light acoustically-transparent fabric keeps the fill contained and dust out without materially changing the tuned response, since the fabric itself is a much smaller acoustic resistance than the cavity fill.

Should I fix the hole pattern or the cavity depth first?

Fix the hole diameter and pitch to whatever your drill, laser, or CNC handles comfortably, then let the target frequency solve for the cavity depth — hand-tuning frequency via hole size alone is fiddly because it shifts both the open-area ratio and the end correction at once.

Will more holes always absorb more?

Not necessarily — past a point, more open area pushes the resonance to a different frequency rather than deepening the absorption at your original target. It's a tuned trap, not a porous absorber where more open area straightforwardly means more absorption; the target frequency and the open-area ratio move together.

Perforated-Panel Absorber

How it works

The holes' open area, the panel thickness, and the cavity depth set the resonance; a porous fill damps and widens it. Fresnelcut picks the geometry for your target band and reports the peak absorption estimate plus the backing materials to buy. It is the drilled-hole sibling of the slat absorber.

Worked example: 5 mm holes on a 20 mm grid

Take a 6 mm panel drilled with 5 mm holes on a 20 mm square pitch, over a 50 mm cavity. The open-area ratio is p = π·5² / (4·20²) ≈ 0.0491 — about 5% open. The effective hole length adds roughly 0.8 × the hole diameter to the panel thickness for the end correction:

t_eff ≈ t + 0.8d = 6 + 4 = 10 mm

A shorthand form of the full end-correction term for a round hole in this open-area range.

With t_eff = 10 mm and D = 50 mm, f_res = (343.2/2π)·√(0.0491/(0.010·0.050)) ≈ 541 Hz. Open this build in the designer to retarget it to your own frequency — Fresnelcut solves the hole size, pitch, and cavity depth together rather than making you iterate by hand.

What you'll need to build it

A laser or CNC router makes short work of a repeating hole grid — this is usually the faster of the two absorber types to cut. As with the slat absorber, the holes alone give a narrow resonance; a porous fill or resistive facing in the cavity behind the panel is what turns that into a usefully broad absorption band, and Fresnelcut's bill of materials specifies it alongside the panel geometry.

Perforated vs. slat

Same resonant-absorber physics, different opening shape. A round-hole grid is typically the quicker cut and reads as a cleaner, more uniform surface; the slat absorber's parallel slots are the more traditional wood-slat look and are easy to cut without a laser or CNC at all.

Getting the target frequency right

As with the slat absorber, the three levers here — hole open-area ratio, effective hole length, and cavity depth — interact, so hole diameter and pitch are usually fixed to whatever's practical to drill or laser-cut, and the cavity depth is solved to hit the target frequency. Smaller, more closely-spaced holes push the open-area ratio and the end correction in opposite directions, which is why hand-picking a hole pattern for a specific frequency is fiddly compared to letting the geometry solve for it.

Finishing and mounting

The drilled face is the visible surface, so sand and finish it before assembly — paint or veneer over the holes afterward risks partially closing them and shifting the open-area ratio away from what was designed. Mount the finished panel with a standoff equal to the cavity depth solved above; mounting it flush to the wall removes the cavity entirely and the resonance won't land where the calculator said it would.

The math

f_res = (c / 2π) · √( p / (t_eff · D) )

p = hole open-area ratio, t_eff = effective hole length (with end correction), D = cavity depth.

Best for

Low-mid resonance and boxiness
A clean, uniform look that's simple to fabricate

Not the tool for

High-frequency echo (use a diffuser)
Deep bass without a large cavity