Design
Acrylic in acoustic applications: where it helps, where it does not
Glass is heavier and polycarbonate is lighter; acrylic sits between them and wins on clarity and on being easy to seal properly.
Design
Glass is heavier and polycarbonate is lighter; acrylic sits between them and wins on clarity and on being easy to seal properly.
Acrylic is the most common clear material in machine noise enclosures and highway noise barriers, and it is chosen for practical reasons rather than acoustic ones: it is light, it machines cleanly, it can be sealed accurately and it stays clear. Its acoustic performance is respectable but it is not the best available by weight.
A single-leaf barrier follows the mass law: transmission loss rises about 6 dB per doubling of surface mass, and about 6 dB per doubling of frequency. Acrylic has a density of roughly 1,190 kg/m³, glass about 2,500 and polycarbonate about 1,200. For the same thickness, glass beats acrylic acoustically because it is heavier.
A second effect matters as much: coincidence. At a particular frequency the bending wave in the panel matches the acoustic wave in the air and transmission loss drops sharply. For acrylic around 6 mm, that dip falls in the 2 to 4 kHz region, which is exactly where a lot of machinery noise sits. Thicker or thinner panels shift the dip; a double-leaf or laminated construction removes it.
| Panel | Surface mass | Rw (approx.) | Note |
|---|---|---|---|
| 5 mm acrylic | ~6 kg/m² | ~26 dB | Common in machine guards; coincidence dip near 3 kHz |
| 8 mm acrylic | ~9.5 kg/m² | ~29 dB | Better at low frequency; dip moves down |
| 12 mm acrylic | ~14 kg/m² | ~31 dB | Practical limit for a single clear leaf |
| 6 mm glass | ~15 kg/m² | ~31 dB | Heavier for the same thickness, brittle |
| Laminated 6+6 acrylic | ~14 kg/m² | ~34 dB | Damping layer improves the coincidence region |
| Double glazed, 20 mm gap | n/a | ~35 dB or better | Best clear option, and much bulkier |
These are indicative figures for comparison, not design values. A real acoustic design accounts for the enclosure geometry, the seals, the flanking paths and the spectrum of the source, and should be done by an acoustic engineer. What follows is where acrylic helps and hurts in that design.
A 30 dB panel in a 15 dB frame gives a 15 dB enclosure. The gap around a panel, a cable penetration, a door without a gasket or a fixing that compresses locally are all leaks, and a leak dominates the result.
8 mm cast acrylic minimum for a machine enclosure; 12 mm for a highway or plant barrier.ALL JOINTS ON CONTINUOUS EPDM GASKET, NO DRY BUTT JOINTS.PENETRATIONS SEALED WITH GLAND, NOT FOAM.FIXING SLOTTED FOR THERMAL MOVEMENT, WASHERS BOTH FACES; a cracked panel is an acoustic hole.LAMINATED PANEL WHERE THE SOURCE HAS STRONG 2–4 kHz CONTENT.We fabricate the panels, machine the gasket grooves and bond the sub-assemblies. We do not perform acoustic design or certify a transmission loss figure for an enclosure. Where a project has a specified Rw or a noise limit to meet, the design and the verification belong with an acoustic engineer; we will build the panels to that design and hold the dimensional and sealing tolerances it needs.
No. For the same thickness glass is heavier and performs better. Acrylic wins on weight, safety, machinability and sealing accuracy, which in a real enclosure often matters more than the panel figure.
8 mm is a practical minimum for a machine enclosure and 12 mm for a larger barrier. Beyond 12 to 15 mm clear acrylic becomes impractical, and a laminated or double-glazed construction is the better route.
More than the panel. An enclosure is only as good as its weakest leak, and the frame, the door seal and the penetrations are usually where the performance is lost.
Yes. A laminated panel with a viscoelastic interlayer damps the coincidence dip and performs better than the same mass of single sheet, at higher cost and slightly lower clarity.
No. We fabricate to a design; acoustic certification requires measurement by an acoustic engineer against the relevant standard.
Acrylic is used in acoustic work for two different jobs, and they get confused with each other. The first is a barrier — a screen that stops direct sound reaching a person. The second is a resonator — a panel that absorbs energy inside a room. A 4 mm sheet is mediocre at the first and useless at the second, and knowing which one your project needs decides whether acrylic is the right material at all.
| Thickness | Mass per m² | Rw (dB) | Speech at normal volume |
|---|---|---|---|
| 3 mm | 3.6 kg | ~24 | Conversation audible, words not clear |
| 5 mm | 6.0 kg | ~27 | Conversation unintelligible at 1 m |
| 8 mm | 9.6 kg | ~30 | Raised voices still transmit |
| 10 mm | 12.0 kg | ~32 | Comfortable privacy screen |
| 15 mm | 18.0 kg | ~35 | Occasional loud speech audible |
Mass law is the whole story here: doubling the thickness buys about 5–6 dB, and doubling the distance from the source buys about 6 dB for free. That is why moving a screen 300 mm further from the talker is often worth more than doubling the sheet thickness, and why a 10 mm screen with a 25 mm gap to a wall outperforms a 15 mm screen fitted flush against it. A sealed air gap is the cheapest acoustic upgrade available to an acrylic assembly, and it costs nothing but a spacer.
The failure mode to design out is flanking. An acrylic screen that stops at the floor, has a 10 mm gap at each end and a 30 mm gap at the top loses most of its rated performance through those gaps — a 1% open area can cap the whole assembly 5–10 dB below the panel's own rating. If the screen is meant to work, it needs a frame with gaskets and a return at the wall, and that is a mechanical design problem rather than a material one.
Where acrylic genuinely wins is the case where you need a barrier that people can see through, clean easily and mount in a thin frame. Where you need absorption inside a room — reducing reverberation, not blocking a line of sight — acrylic is the wrong tool; perforated sheet with a backing, felt or a mineral wool panel does the job at a fraction of the weight. We say so on enquiries, because a screen sold as an acoustic solution that does not absorb anything is a disappointment waiting to happen.
Panel sizes, gasket grooves and sealing detail are what we hold to tolerance. The dB figure belongs with your acoustic engineer.