View Full Version : Purpose of sheet of foam on inside of L212 front grill?

03-14-2010, 08:11 PM
Just getting around to rehabing some L212's and noticed that there was a thin sheet of foam on the inside of the front grills around the transducer cutouts. Is this an acoustic thing or is it just to keep the grill box from rattling? As the foam had deteriorated it needs replaced. If it is not an acoustic thing a replacement will be much easier to fashion.

03-14-2010, 08:29 PM
This was added later, possibly to the "L212C" revision as I recall. The original units did not have it. I had one with it and one without and couldn't hear any difference.

03-15-2010, 05:19 AM
The idea AFAIK was to reduce edge diffraction of the sound waves, though this would have no effect in the lower frequencies.

03-15-2010, 07:47 AM
It's a 1/4" peel-n-stick foam sheet that covers the entire back side of the grill with holes where the drivers are. Basically it's supposed to fill the space between fabric and baffle.

03-15-2010, 07:59 AM
like this ??? ...

Not really. Here is a picture of the inside of the grille. As RD says, it was a foam sheet that covered everywhere except the transducer cutouts and grill pegs holes. (These are L212 C models.)

03-15-2010, 09:28 AM
My advice is to forget the foam. As stated, it was intended to reduce edge diffraction off the cutouts in the grill. I doubt it was very effective, since the edges are still "there". Best option is to run them naked anyway. That said, I'll bet you'll find similar peel-n-stick stuff at a fabric or hobby store.