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Driver thudding at medium volume

T

TrashCanSam

New Member
Speakers: definitive technology bp-20 with bp-30 woofers. 6ohm impedance 500w max.
Amp: adcom gfa 5500 200w/ch @8ohms

Hey all, I ran into an issue today after sitting down to have a listening session. About halfway through a song that's pretty heavy on the bass, two of the mid-range drivers on the right speaker started thudding very loudly on the hard notes but sound okay otherwise.
They still measure 3ohms each(bipolar speakers) and the other two drivers in the cabinet as well as the whole left speaker still sound perfect at much higher volume.

My question: Would a deteriorating or damaged spider/cone or some other part of the driver cause it to bottom out much more easily? Visual inspection showed no noticable damage to any parts of them.
They're pretty old speakers but I love them and would like to keep them running if I can.
Any thoughts, comments, or questions are greatly appreciated. Thanks
 
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The spider could have weakened. I've had a few pairs of speakers that when the volume was turned up higher than a out 9:00 they would thud or pop. One pair a woofer coil was bad. Another the coil had bottomed out or over extended and deformed the coil tube. One pair had rubber surrounds and the surrounds had started to sag causing the coil tube to either hit the pole, or outer edge. I turned that driver 180° and the cone and coil re-centered, no more pop.
Put an ohm meter across the terminals on each speaker. They should read close to the same.
 
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Lavane said:
The spider could have weakened. I've had a few pairs of speakers that when the volume was turned up higher than a out 9:00 they would thud or pop. One pair a woofer coil was bad. Another the coil had bottomed out or over extended and deformed the coil tube. One pair had rubber surrounds and the surrounds had started to sag causing the coil tube to either hit the pole, or outer edge. I turned that driver 180° and the cone and coil re-centered, no more pop.
Put an ohm meter across the terminals on each speaker. They should read close to the same.
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Thanks for the information, both speakers measure the same on the multimeter. I'll take a closer look at the spiders :)
 
TrashCanSam said:
Thanks for the information, both speakers measure the same on the multimeter. I'll take a closer look at the spiders :)
Click to expand...
What kind of surrounds on the woofers? Also, you can put a.couole fingers on each side of the cone and gently press down evenly. I used my thimb and forefingers. There shouldn't be any scraping, or catching. That can be a sign of the coil tube being deformed.
 
Lavane said:
What kind of surrounds on the woofers? Also, you can put a.couole fingers on each side of the cone and gently press down evenly. I used my thimb and forefingers. There shouldn't be any scraping, or catching. That can be a sign of the coil tube being deformed.
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They appear to use rubber surrounds and are very smooth when pressed. I may have found some small cracking with the internal surround seal, I'll attach a picture. There are multiple spots around the surrounds like this.PXL_20240122_034051540~2.jpgPXL_20240122_034354363.jpg
 
Sgt Shultz said:
Try swapping the speakers to see if the issue follows the speaker or stays on the right channel.
Click to expand...
Good idea. That and try turning them 180° after that. It doesn't take much of a sag for the cone to get off center. There isn't much of a gap around the coil. It does look like some slight cracking where the surround meets the cone. Maybe some surround glue applied around the cone would help
there? Just enough to cover the cracks.
 
Sgt Shultz said:
Try swapping the speakers to see if the issue follows the speaker or stays on the right channel.
Click to expand...
So, funny thing, swapped it to the left speaker and had the same issue but when I threw the good speaker from the left one into the right speaker it started doing the same thing. I think I'm defeated at this point
 
Ya, but the one driver he was having issues with still made the noise in the other cabinet. Now the other is. Does the noise go away from the one when you put it back in it's original cabinet? I wonder of those cracks are deeper than they look. Loose surrounds can make noises. You could connect the woofers directly to your amp or reciever by themselves and see if they're both still making that noise. Maybe hold them up so they're not pointed straight up, but pointed horizontally like they would be in the cabinet.
 
Lavane said:
Ya, but the one driver he was having issues with still made the noise in the other cabinet. Now the other is. Does the noise go away from the one when you put it back in it's original cabinet? I wonder of those cracks are deeper than they look. Loose surrounds can make noises. You could connect the woofers directly to your amp or reciever by themselves and see if they're both still making that noise. Maybe hold them up so they're not pointed straight up, but pointed horizontally like they would be in the cabinet.
Click to expand...

I believe he swapped the speakers left to right and the issue followed, then replaced one of the drivers in the offending cabinet with one from the good speaker and it's now having the same issue. So this shows the issue is consistent with the same speaker cabinet unless I misunderstood his post.
 
Sgt Shultz said:
I believe he swapped the speakers left to right and the issue followed, then replaced one of the drivers in the offending cabinet with one from the good speaker and it's now having the same issue. So this shows the issue is consistent with the same speaker cabinet unless I misunderstood his post.
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Sorry for the confusion, I swapped one of the "bad" drivers to the good(left) cabinet as well as one of the "good" drivers to the bad (right)cabinet. They both started having that noise. Now that all of the drivers are back in the original cabinets the issue is back to being only in the right speaker. It is very odd. Could the crossover circuitry on the speakers (whole cabinet unit) be going bad?
 
TrashCanSam said:
Sorry for the confusion, I swapped one of the "bad" drivers to the good(left) cabinet as well as one of the "good" drivers to the bad (right)cabinet. They both started having that noise. Now that all of the drivers are back in the original cabinets the issue is back to being only in the right speaker. It is very odd. Could the crossover circuitry on the speakers (whole cabinet unit) be going bad?
Click to expand...

Try swapping the right speaker enclosure for the left to see if it follows, this will rule out an amplifier issue or not.
 
TrashCanSam said:
Sorry for the confusion, I swapped one of the "bad" drivers to the good(left) cabinet as well as one of the "good" drivers to the bad (right)cabinet. They both started having that noise. Now that all of the drivers are back in the original cabinets the issue is back to being only in the right speaker. It is very odd. Could the crossover circuitry on the speakers (whole cabinet unit) be going bad?
Click to expand...
Ok, that clears things up. It does seem like there is a problem with the one cabinet. Try and get a picture of the crossover in that ca inet when you get a chance.
 
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