dispersion rings

[paso100]

Bought some AR 91s. Beautiful sounding speakers compared to my original AR 38s that I've had since new. The tweeters on the 91s have a thin felt dispersion ring around them, but I've seen the thicker original foam around others' speakers. I'm also looking for the rectangular dispersion foam that surrounds the mid-range driver for the 91. Has anybody used a good replacement material for these or do you know of anybody who sells these precut?

— John

[ar_pro]

They do turn up on ebay, and can be quite expensive, and are usually very fragile from age.

Both the tweeter and midrange surrounds were large-cell, open foam. The inserts were held in place by round adhesive stickers, attached at the drivers' perimeter. The stickers had teeth that gripped onto the surface of the foam inserts.

Because of the flared nature of the cutouts, replicating them would be a bit more of a challenge. You might try contacting some of the people who make replacement foam grills for the JBL Century speakers - maybe they'd be able to fix something up.

I've seen brand-new AR-9 speakers come out of the box without the foam, and the inserts are missing in many catalog photos, although the 1980 blueprint definitely shows the inserts.

[KlausDK]

I have made them myself from acoustic foam, like this:

https://www.madisound.com/store/product_info.php?products_id=767

It is a little thicker than the one I used, ideally it should be ½" thick. I have made a template in cardboard I use for cutting the foam. I also used it to make new foam grilles for my AR-10Pi, gluing two layers together, and cutting wholes the inner layer for the speakers.

BRgds Klaus

[Carlspeak]

I agree, Klaus's approach is sound - no pun intended. The thicker the better.

Download the paper I wrote at post #5 here:

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=4758

Madisound sells the felt diffraction ring I used in my study.

https://www.madisound.com/store/product_info.php?cPath=404_116&products_id=770

[paso100]

Thanks for the tips. Horse blanket material?? lol It's the simplest solutions that work best, right? But wouldn't lama hair in a cross-weave stitch sound even better? ;}

Great to see the test results on the different materials. I remember lining my old Dodge pickup bed (with a shell) with some artificial carpet for the kids to play on. It reminds me of the original AR foam. I'll most likely order the foam from Madisound and follow Klaus's approach.

Thanks again to all,

John

[deek]

The rectangular and circular foam dispersion rings (photos below) around the tweeter and upper mid-rage are fabricated from reticulated polyurethane foam. It's most common use these days is water filtration for outdoor features. (Koi ponds, etc.)

The features of the pieces (the hole for the driver and the beveled edges) were most certainly molded in, not cut after the fact so fabricating them would require some investment in a mold. Not out of the question, but expensive. I looked into it when I wanted to fabricate replacement grilles for my AR17's which are made from the same material.

One guy suggested submersing them in water and freezing them, then using a mill to cut the shape I wanted. I think it would have worked okay, but what a mess!

-Deek