Troubleshooting B&W DM 302 - possible crossover issue. - AVS Forum
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post #1 of 7 Old 07-26-2014, 08:04 PM - Thread Starter
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Troubleshooting B&W DM 302 - possible crossover issue.

I just bought a pair of B&W DM 302 bookshelf speakers at a yard sale for $4. This was a group yard sale for a school sports team fundraiser and all the stuff was donated and combined into one lot so the owner of the speakers wasn't around for me to ask questions. I figured $4 was worth a gamble.

If you're not familiar with this speaker, it's a late 1990's/early 2000's two-way bookshelf speaker with a 1" tweeter and a 5" midrange driver. That's all I know about it though.

Now that I've got the speakers home I tested them out with some music and one of them seems to work fine, but the other one only produces sound from the tweeter. I switched the L and R wires and got the same results, so I don't think it's an issue with my amp. I'm guessing this means something is wrong with the crossover circuit, maybe? Or the internal wiring to the driver between the driver and crossover?

If you had a speaker doing this, where would you start? Does anyone know how to dismantle this particular speaker to get a better look at what might be happening? I don't really know much about speaker design, and my knowledge of electronic circuits is pretty basic, but I'm willing to mess around with this since I only invested $4 in this pair of speakers. I'm thinking I should try to open the enclosure and look for anything obvious, and then maybe test some of the wires for continuity, etc. Beyond that I'm not sure.


Thank you for your thoughts!
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post #2 of 7 Old 07-26-2014, 09:21 PM
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It looks like the front cover is plastic and could possibly be removed by screws hidden behind the rubber boots for the grill pegs. You should then be able to remove the woofer and check the wiring/crossover. It is also quite possible that the woofer is bad (fried), if you remove the woofer check for continuity with a multimeter or take a 9 volt and touch it across the terminals if the woofer jumps it's ok.
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post #3 of 7 Old 07-26-2014, 10:33 PM - Thread Starter
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Quote:
Originally Posted by mtg90 View Post
It looks like the front cover is plastic and could possibly be removed by screws hidden behind the rubber boots for the grill pegs. You should then be able to remove the woofer and check the wiring/crossover. It is also quite possible that the woofer is bad (fried), if you remove the woofer check for continuity with a multimeter or take a 9 volt and touch it across the terminals if the woofer jumps it's ok.
Thank you for the tips. I looked under the rubber grill boots and didn't find anything. Upon further inspection I found holes on the BACK of the cabinet that have screws for the FRONT of the cabinet... meaning I'll need a screw driver long enough to stretch the entire depth of the cabinet. So far I haven't found a screw driver that long, but I'm going to dig through some stuff in the garage and maybe locate one.

Side note: When I press the woofer with my finger to move it in and out, I hear a faint crunching sound (like delicate paper or something) coming from behind it that I don't hear with the working speaker. But everything visually looks the same on the outside. Must be something going on behind it. If it's something simple, could just be a loose wire rubbing against it... or could be something bad. Hopefully it's not some kind of creepy insect nest or something!
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post #4 of 7 Old 07-26-2014, 10:48 PM
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I hate to say it but there is a 90% chance you have a burned up woofer voice coil in that one. The woofer cone should move freely when pressed upon without any scratching sounds. While there is a chance something else is brushing the back of the cone causing that noise it is a very slime one.
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post #5 of 7 Old 07-26-2014, 10:51 PM
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Crunchy sound could mean a bad voice coil, sorry for the bad news.
The good side the cabinets are worth way more than $4, maybe find a new comparable woofer and pop that in?
Pay attention to the mounting dimensions see what happens.
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post #6 of 7 Old 07-26-2014, 10:59 PM - Thread Starter
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Ahh I think you guys are right. I found an extension for my screw driver and got the thing opened. I tried that 9v battery test and nothing happened.

I would be interested in trying to replace the woofer though with another one if I can narrow down the specs to get something that will match the other speaker (or replace the good one too to get them to match?).
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post #7 of 7 Old 07-26-2014, 11:23 PM - Thread Starter
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Looks like it's not even screwed in directly, just held in place by two pressure bars. I think replacing it wouldn't necessarily require any major modification, but I guess I would need to figure out the specs of the original woofer if I want to respect the intended design of the unit and possibly match the other speaker I have.

Edit: Looks like I might even be able to buy an original part. It's over $70 though. Not sure if that's a good deal or not. I mean, the total price for my speakers would still be under $100, but kinda tarnishes the fun of finding a good deal.
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