Help with Bowers and Wilkins CDM7 speakers

Dedicated to those large boxes at one end of the room
Post Reply
bostod
User
Posts: 177
Joined: Wed Nov 02, 2011 6:12 pm

#1 Help with Bowers and Wilkins CDM7 speakers

Post by bostod »

hello guys. My friend has a problem with one of his Bowers & wilkins CDM 7se speakers. He heard a loud pop and the 2 main drivers stopped working. Only the tweeter works now. I tried to bypass the crossover by placing the speaker wire directly onto the woofer. No sound from it. the other matching speaker is working fine. Can anyone reccomend someone in the Doncaster area that might be able to help diagnose and maybe repair it.
Thank you in advance.
User avatar
Paul Barker
Loony Bin!
Posts: 9010
Joined: Mon May 21, 2007 9:42 pm

#2 Re: Help with Bowers and Wilkins CDM7 speakers

Post by Paul Barker »

Drivers not my area of knowledge but from you’re description the coil sounds dead.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
User avatar
Nick
Site Admin
Posts: 15793
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#3 Re: Help with Bowers and Wilkins CDM7 speakers

Post by Nick »

Hmm, but before fixing them, I would try and find what the cause was. Check the amp for DC on its output, was there anything odd going on when it happened? The amp is the likely culprit if both base drivers in the box have gone. The tweeter is protected with a cap.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
Nick
Site Admin
Posts: 15793
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#4 Re: Help with Bowers and Wilkins CDM7 speakers

Post by Nick »

Just realised its both speakers. May be the source into the amp then maybe.

If the maker cant offer spares, there is this lot in the states

https://reconingspeakers.com/speaker-re ... zz12199-6/
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
ed
retired
Posts: 5387
Joined: Thu Jun 21, 2007 4:01 pm
Location: yorkshire
Contact:

#5 Re: Help with Bowers and Wilkins CDM7 speakers

Post by ed »

I'm not 100% sure I'm understanding whether it's both drivers in one loudspeaker or one of the bass drivers in both speakers......either way I'm betting the cheapest way out of this if a) he really loves them and b) there is a coil burned out then a new(old) pair from hifi shark or ebay etc is the way to go. They seem to be advertised between £300 and £500, but there will be cheaper. Re-coning and postage to the US may cost more than that...are there replacement drive units available?
There's nowhere you can be that isn't where you're meant to be
bostod
User
Posts: 177
Joined: Wed Nov 02, 2011 6:12 pm

#6 Re: Help with Bowers and Wilkins CDM7 speakers

Post by bostod »

So the problem is just with one speaker. His set up is an Audiolab 8000a feeding an Audiolab 8000p power amplifier. He was watching TV connected to beresford Dac. He said he was listening at low volume and heard a loud popping sound. I went down and listened to the damaged speaker, only the tweeter was working. I then unscrewed the top woofer and placed the speaker cable directly onto the woofer terminal. Neither woofers worked but the tweeter still fired up. I didn't directly test the second woofer in this way. If they are both damaged would this suggest the amplifier has a fault.
He seemed to think tge 8000a made a "fizzing" sound. I took this out of his system and played it for a short time in an alternative system. Both channels worked without distortion. Haven't tested the 8000p yet. Would there be any telltale sign of DC leakage. Apart from a speaker blowing ;)
karatestu
User
Posts: 138
Joined: Fri Mar 03, 2017 1:34 pm
Location: Leeds/York

#7 Re: Help with Bowers and Wilkins CDM7 speakers

Post by karatestu »

You need to put a multimeter in the speaker outlets on the back of the amp and measure dc Should be below about 50 mA.

B&W are no longer the company they used to be. I think they were bought out by money worshippers. I don't think they will still have drivers for these speakers which are probably about 20 years old but you can try. B&W drivers on ebay are not cheap if you can find the exact model. Are they kevlar or something else ?
:bigsmurf:
bostod
User
Posts: 177
Joined: Wed Nov 02, 2011 6:12 pm

#8 Re: Help with Bowers and Wilkins CDM7 speakers

Post by bostod »

Tested both the top keeler driver and the bass driver. Nothing on a multimeter. Getting the amps tested tomorrow.
Does anyone know if Bowers and Wilkins had individual numbers for each driver. I cant seem to find the exact match but some look close with the first 2letters and digits matching but last 3 don't. I was wondering if they gave a different id number for each set back then.
karatestu
User
Posts: 138
Joined: Fri Mar 03, 2017 1:34 pm
Location: Leeds/York

#9 Re: Help with Bowers and Wilkins CDM7 speakers

Post by karatestu »

Yes there are lots of different part numbers. If you can find the part number online that would be ideal. I looked on b&wsupport in usa but their site is down. Drivers do come up on ebay but they are usually taking the piss with the pricing.

Good luck with your quest.
:bigsmurf:
User avatar
Toppsy
Shed dweller
Posts: 2401
Joined: Mon Jul 23, 2007 12:10 pm
Location: red rose country

#10 Re: Help with Bowers and Wilkins CDM7 speakers

Post by Toppsy »

Have you tried speaking direct to B&W Group Ltd., Hi-Fi and Audio Repairs and Parts, Dale Road, Worthing, BN11 2BH. Tel 01903 221800.
Info found here: https://www.yell.com/ucs/UcsSearchActio ... 1997723503

Might be worth a phone call to be if replacement drivers are available or if the dead drivers could be repaired.
bostod
User
Posts: 177
Joined: Wed Nov 02, 2011 6:12 pm

#11 Re: Help with Bowers and Wilkins CDM7 speakers

Post by bostod »

Thank you all. I was able to find some B&W drivers from ebay that were the same dimensions that are from the dm 601 series. Replaced the originals with 2 kevlar units. Sound is good enough to my ears. I cant tell a difference from the other original speaker. When testing the damaged drivers, there is no movement at all they are stiff. I was wondering if they could have been damaged by previous owner. Got the amplifiers serviced. He said there was no problem with DC current.
karatestu
User
Posts: 138
Joined: Fri Mar 03, 2017 1:34 pm
Location: Leeds/York

#12 Re: Help with Bowers and Wilkins CDM7 speakers

Post by karatestu »

Hello. Glad that you found a solution that is acceptable to you. The DM series is of lower quality than the CDM but don't let that worry you the drivers are still B&W kevlar. Many of their kevlar drivers use the same basket and look very similar.

They have stopped using kevlar in their drivers now I believe. There are reports that the break up resonances are rather nasty and so need to be crossed low or with a high order filter. All the 2 way B&W speakers I have been inside have had a single inductor low pass. However kevlar drivers respond well to the application of lashings of contact adhesive dope.
:bigsmurf:
Post Reply