Speaker grille and acoustic foam.

Putting anything in front of a driver is a risk, so it is worth being precise about why this material is the accepted answer. A reticulated foam is mostly void: the membranes between cells have been removed, leaving a skeleton of thin strands with air between them. There is very little material present to reflect sound or absorb it, so at the grades used for grilles the effect on the output is very close to nothing.

What does audibly dull a speaker is the wrong foam. Ordinary unreticulated foam still has its cell windows intact — thousands of thin membranes across the sound path — and those do attenuate high frequencies noticeably. This is the usual cause of a replacement grille foam making a speaker sound veiled: not that foam was used, but that the wrong kind was.

The foam is also doing real work. It hides the driver, which is usually half the industrial design intent, and it keeps dust and debris off the cone and out of the surround — where over years it does measurable damage.

Between 30 and 60 PPI covers nearly every driver, and the choice within that band is a straightforward trade:

• 30 PPI — most open, least acoustic effect, longest life between cleans in dusty environments. The driver is slightly more visible through it.
• 45 PPI — the usual default. Hides the driver properly, still effectively transparent, holds dust well.
• 60 PPI — most opaque and finest capture. Reaching the point where the grade starts to matter acoustically, and it dust-loads faster.

Finer than 60 PPI is not recommended in front of a driver. If the environment is dusty, stay at the coarse end and rely on the foam being washable rather than reaching for a finer grade. See choosing a PPI for the underlying trade-off.

• Discs — to the driver or grille diameter, the most common order.
• Rings — with a centre cut-out, protecting the surround while leaving the cone clear.
• Rectangles and panels — for bar speakers, cabinet fascias and in-wall installations.
• Perforated-panel backing — cut to sit behind a metal or plastic grille and hide the driver through the holes.
• Microphone wind screens — finer grade, thicker section, cut to the basket.

Send the diameter and thickness, or the perished original, or the housing dimensions if the original has gone entirely. See die-cutting to your drawing for what we need and how tooling is priced.

Foam grilles from the 1980s and 1990s have almost all failed by now, and they fail the same way: the polyurethane embrittles with years of heat and light until the sheet turns to orange dust at a touch. It is not a defect, it is the material reaching the end of its life — and it is entirely fixable.

Fresh reticulated foam behaves as the original did when new. Where the original has disintegrated past measuring, send the cabinet aperture or grille frame dimensions instead and we will cut to those. Ordering a spare set at the same time costs very little, given that the tooling is already made.