Refoam AER-BD1 (BD-Design)

by werner , Monday, March 09, 2020, 23:13 (1502 days ago)

It must have been about 17 years ago when I bought a used set of AER BD-1 from Bert to put in my DIY wooden ORIS like horn speakers. (see showrooms, Werner's system) Until about a year ago I was more then happy with this set-up, but one day a small rattle crept into the music. First you think it's on the record your playing, or a miscontact somewhere, but hearing it also playing from digital source I took a close look at the drivers to find out that there was a little crack in the foam of the right driver. Pointing with my finger into the paper conus I was able to stop the rattle, and more interested in playing music than repairing things I taped a blunt object into the horn to replace my finger.
For that night and many to come there was no rattle so no problem. But after a few weeks the rattle returned. The crack had grown and, still not motivated to cure the problem, I simply put the horn upside-down for another few weeks of problem free listening. You know that this won't help forever, so I started to find out how to get this driver (or better both drivers, as the other will crack as well in time and changing something in one channel only is never good)) repaired. In the pricelist of AER I found a refoam/check-up option.Sounds good only... 500 euro/driver (ex transport) and six weeks without my favorite toys in the house.....
After another few weeks listening to an upside-down horn with a peace of wood glued in to reduce the rattle a bit I decided to refoam the drivers myself.
missing them for six weeks was no option, 500 euro/driver too much and the sound no longer good enough to listen to.
Browsing the internet I found a company with an enormous collection of foam rings to refoam nearly any known driver, and at least as important, a good manual how to do the refoam. I ordered a pair of foam rings that came very close to the dimensions of the original foam with only one big difference: the original foam is curved inward seen from the front, the new ones curve outward. Apart from that they fit like a glove. It sure is not the price that would hold you from doing this, I payed about 25 euro for 2 foam rings and a small bottle of glue, it's more do you have enough confidence to start working on such an expensive driver.
I removed the driver from the horn and started the process. Most painful (not physical) is to cut away the cracked foamring. Now it will not be usable until fixed. The manual notes that all old glue has to be removed. From the cast frame that is no problem, with knife, screwdriver etc. From the paper cone it is a pain in the .... Very carefully with a razor blade and fingernails it took me about 3 hours. Then I marked with a sharp soft pencil the position of the new ring on the paper. Any glue below this line will be visible forever. Before starting to put the glue on the paper I searched a round object to put some pressure on the edge I had to to glue. A round bowl was fine. Now glue on the paper, foam ring to the marker line and bowl on top. I let it dry overnight.
So far so good. Next I had to glue the foam to the frame. You have to be sure the conus is centered. To do so, you put peaces of plastic (no paper) into the air-gap (see picture) You can center the AER driver afterwards (see Berts maintenance section of his site) but doing this right saves a lot of work. I centered the conus, put glue on the edge of the frame and and kept the ring is place with clothespins. First top-bottom, than left-right and then the rest.
Another overnight dry and ready. Well, almost. As the curve of the foam is towards me now, it hits the edge of the horn. I made a distance-ring out of thin (3 mm) plywood. Problem solved. And the sound... as good as before the foam started to crack. I can not hear a difference between the refoamd driver and the one that is still ok but I also will refoam.
It was a difficult decision to do this job myself but man, am I happy