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Strange rattling noise from woofer

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Jo bg View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jo bg Quote  Post ReplyReply Direct Link To This Post Topic: Strange rattling noise from woofer
    Posted: 29 July 2021 at 10:13am
Hi
Anyone knows what this noise could be? 
B&c 18 sw115-4 ohm , has been spanked hard  in a th118 for 5 years, so we can say it did it's job, but still I would like to know what's up, second driver developing this issue in a th118.
No voicecoil rubbing, everything moves right without frictions, there is just this high pitched metallic rattling that rises with level .
They are going in for a recone next week, but still don't knowing what is happening drives me mad.
If someone can enlighten me I would be grateful!

Video of driver making such noise

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Jo bg View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jo bg Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2021 at 10:22am
Ps it's not the grille...
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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2021 at 10:41am
have you checked for tiny tears in the surround/suspension? Dust cap glued all around?
Kevin

North Staffordshire

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Jo bg View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jo bg Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2021 at 11:41am
Thanks for the hints, I will check this evening!
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Earplug View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2021 at 11:53am
Have you tried "tapping" around the cone?

There might not be any rubbing, but a loose winding on the coil that might be heard if you hit the cone at different points around the thing close to the center/coil.




Edited by Earplug - 30 July 2021 at 5:43am
Earplugs Are For Wimps!
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Tinnitus Rex View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tinnitus Rex Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2021 at 1:46pm
Have a close look at the spider suspension to see if has detached from the voice coil stem underneath the cone , pushing the cone full forward  usually reveals this .if it has this can be fixed.a stitch in time saves a recone
"couldn't we just like... use headphones?"
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Peter Jan View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Peter Jan Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2021 at 1:55pm
Check if the spider is still properly glued to the chassis.

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Wikl109 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Wikl109 Quote  Post ReplyReply Direct Link To This Post Posted: 29 July 2021 at 11:07pm
Originally posted by Earplug Earplug wrote:

Have you tried "tapping" around the cone?

There might not be any rubbing, but a lose winding on the coil that might be heard if you hit the cone at different points around the thing close to the center/coil.



I'd say this is a good shout. I had one of the bass drivers on my home system develop a problem exactly like this some years back.
No rubbing when pushing the cone and it played fine at a low volume. However when turning the system up and play anything with really deep rumbling bass there was a slight high frequency rattle from the drive unit.
I could only come to the conclusion the winding on the former had come loose.
It was replaced under warranty as it was a manufacturing fault.
Cheers, Chris.
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Tinnitus Rex View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tinnitus Rex Quote  Post ReplyReply Direct Link To This Post Posted: 30 July 2021 at 12:27pm
This is exciting,when are you drawing the result? I bet 90dB  on the spider and 50 on the surround


Edited by Tinnitus Rex - 30 July 2021 at 2:08pm
"couldn't we just like... use headphones?"
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APW View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote APW Quote  Post ReplyReply Direct Link To This Post Posted: 30 July 2021 at 12:53pm

I'd put money on the bottom few turns of the coil have broken loose (come off the coil former), seen it a few times on customers kit when the coil assembly has clouted the motor backplate... normally due to lack of or incorrectly set HPF. 


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smitske96 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 30 July 2021 at 3:58pm
@APW
The 18SW series should not get damaged that way. Excursion is eventually limited by the suspension and can't reach Xdamage.
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Wikl109 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Wikl109 Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 12:21am
In my case it was clearly a manufacturing fault and not caused by over excursion. Rather annoyingly the other bass driver in the other speaker developed the same fault a couple of years later.
By that time it was out of warranty and I had to fork out £100 for a new 8" bass driver to be shipped over from America.
Both replacement drivers have been playing fine for 10 years plus now so it was probably a problem with the adhesive being used at the time of original manufacture on that batch. I still have the second faulty unit here somewhere.
It could be one of a number of things that's caused Jo bg's problem but I think a loose winding from the coil is quite possible.
Cheers, Chris.
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