strange speaker breakdown

makeb4break · 18th March 2009, 12:28 AM

hey gang!

i got a wierd one in my shop. a nice ol' B&W DM620 came by with a woofer that have a 1,4R DC resistance

it works, but of course, sounds funny. there's no other apparent damage to the loudspeaker. so i replaced the driver (nice of B&W to have replacements in stock for such an old box, i'd say)

all is well

until the customer comes back two weeks later, saying it STILL sounds funny

this time it's the _other_ lf unit that's dropped to 1,3-4R. what gives? i've never seen anything like this in twenty years of messin' around with loudspeakers

any clues, gentlemen? i've asked him to come by with his amp. maybe it's putting out an unhealthy dose of DC?

the vc looks okay. kicking myself for throwing the first one out, it could do with a proper autopsy now .. alas, i'm flabbergasted

any advice or tales appriciated!

cheers,

mb4b

pedroskova · 18th March 2009, 12:53 AM

He could have brought them in each time in "partial" failure due to excessive DC on the voice coils...i.e., they both shorted from layer to layer on the voice coil, but were brought in before they shorted open.

seems kind of unlikely

...don't know the amplifier...but it would have to be designed in such a way as to allow a single component failure to cause DC offset in both channels.

clemualb · 29th March 2009, 08:58 AM

Don't have any input on how this might have happened but I do have a DM620 with a bad woofer. The coil broke. I've had no luck finding a replacement part. B&W doesn't make it anymore and have been no help with an alternate solution. If you can still get this part or if your customer has a good one they want to sell let me know.

18th March 2009, 12:28 AM	#1
makeb4break diyAudio Member Join Date: Jan 2009	strange speaker breakdown hey gang! i got a wierd one in my shop. a nice ol' B&W DM620 came by with a woofer that have a 1,4R DC resistance it works, but of course, sounds funny. there's no other apparent damage to the loudspeaker. so i replaced the driver (nice of B&W to have replacements in stock for such an old box, i'd say) all is well until the customer comes back two weeks later, saying it STILL sounds funny this time it's the _other_ lf unit that's dropped to 1,3-4R. what gives? i've never seen anything like this in twenty years of messin' around with loudspeakers any clues, gentlemen? i've asked him to come by with his amp. maybe it's putting out an unhealthy dose of DC? the vc looks okay. kicking myself for throwing the first one out, it could do with a proper autopsy now .. alas, i'm flabbergasted any advice or tales appriciated! cheers, mb4b

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18th March 2009, 12:53 AM	#2
pedroskova RIP Join Date: Dec 2002 Location: C'ville VA, USA	He could have brought them in each time in "partial" failure due to excessive DC on the voice coils...i.e., they both shorted from layer to layer on the voice coil, but were brought in before they shorted open. seems kind of unlikely ...don't know the amplifier...but it would have to be designed in such a way as to allow a single component failure to cause DC offset in both channels.

29th March 2009, 08:58 AM	#3
clemualb diyAudio Member Join Date: Mar 2009	Don't have any input on how this might have happened but I do have a DM620 with a bad woofer. The coil broke. I've had no luck finding a replacement part. B&W doesn't make it anymore and have been no help with an alternate solution. If you can still get this part or if your customer has a good one they want to sell let me know.

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