I have a set of Bowers & Wilkins CDM1 speakers that I bought maybe 20 years ago. I bought them for the sound they produced first, but also I really liked the way the looked. After years of listening to them, one day I realized they just didn’t sound very good. At the time I did internet queries like “do speakers age?”, but they didn’t immediately lead me to suspect a particular cause. So, by this time I had a bit more money, and was thinking of slightly larger speakers anyway, so bought some DM602 S3 speakers to replace the CDM1. The DM602 S3 speakers sounded much better than my ailing CDM1 speakers, so that was that. I put the CDM1 speakers in storage thinking that someday I might just replace the drivers because I liked the cabinets so much.
Well, a few weeks ago I happened to come upon a post that talked about how many speakers around the era the CDM1 speakers were made used ferrofluid as a coolant and dampener for their tweeters, and that ferrofluid can dry out, causing a sludge that will lock the voice coil to the fixed magnet, meaning that it can’t move, which means no sound.
I pulled my CDM1 speakers out of storage, and tested them. Sure enough, I wasn’t hearing any sound out of the tweeters, so I did some further research specifically on CDM1 tweeters. The first thing I found was that you can’t buy new CDM1 tweeters from B&W anymore. (This was probably OK, because I don’t think I could have spent the kind of money they would have probably asked when I wasn’t 100% sure that the solution would work.) The second thing I found was that there were really three options I could take.
Option 1: Assuming my current tweeters had no damage (voice coil not burnt out, cloth/rubber diaphragm around the metal dome still working, etc.), it is possible that I could clean out all the old ferrofluid, and just replace it with new ferrofluid. (To be honest, not replacing the fluid at all is also an option it seems.)
Option 2: Assuming my current tweeters had damage to the diaphragm and/or voice coil, it is possible to clean out the old ferrofluid, replace it, and also replace the diaphragm/voice coil with an aftermarket one. The instructions for doing this I found on the following site.
Now, the instructions for dealing with the ferrofluid were truly helpful to me (I did Option 1). Unfortunately, this site also said that the aftermarket diaphragm/voice coils were out of stock, so I wasn’t sure that this would be a realistic option as I couldn’t seem to find replacements anywhere.
Option 3: Replace the tweeters entirely with one that would fit well in the available space. I almost went down this path, but decided to try Option 1 first, and only replace the tweeters if the repair got too involved for me to continue comfortably. Now, had I chosen this option, the tweeters that I understood would fit in this space were the Tymphany OC25SC65-04 which are available at Parts Express in the US (seem to have worldwide shipping) or in Japan at Yokohama Bayside Net.
https://www.parts-express.com/peerless-by-tymphany-oc25sc65-04-1-textile-dome-tweeter–264-1018
http://www.baysidenet.jp/c-item-detail?ic=TPSP1953
Now, my understanding is that a bit of work still has to be done on the new tweeters as the posts are not in the same place as the original tweeters, but the size is apparently just right. Honestly I wondered if it would be possible to take the diaphragm/voice coil assembly out of these tweeters and have them fit into the original B&W driver magnets, but you would have to be fairly gutsy to do try this as the diameter of the voice coil may not be the same. (If anyone has done this, please let me know!)
Anyway, after considering my options, and with fingers crossed that my tweeters weren’t already fried, and that I wouldn’t damage them in the process of getting them cleaned up, I embarked on Option 1 above.
Replacing ferrofluid in B&W CDM1 tweeters