Partially faulty bass driver - diyAudio
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Old 28th February 2012, 09:51 PM   #1
dmsims is offline dmsims  United Kingdom
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Join Date: Oct 2007
Default Partially faulty bass driver

Keesonic Kubs

1 works fine - the other sounds like it has no bass

Tried swapping cables and amps - same result

Drivers out and both measure 6.9 Ohms, foam surround appears in good order

The faulty driver does produce sound but in the mid region and the movement of the driver is much less compared to the good driver

Applied cable direct from amp to bass driver - sound but still no bass

Pic of connection and crossover

Click the image to open in full size.
Click the image to open in full size.

Any suggestions?
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Old 28th February 2012, 09:54 PM   #2
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nigelwright7557's Avatar
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Location: Carlisle, England
Its odd both measure the same.
I have always found voice coil faults to show as a lower impedance.
Murton-Pike Systems PCBCAD51 pcb design software.
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Old 28th February 2012, 10:05 PM   #3
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It is possible the back plate glue failed, causing the pole piece to pinch the voice coil in the gap.

I just fixed a speaker that happened to, used a C clamp to re-position the back plate until the cone was free (took about 6 tries to find the right angle) then used JB Weld epoxy to re- glue the back plate to the magnet.

Speaker went from only playing 1K up to working normally.
Good luck!
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Old 28th February 2012, 10:16 PM   #4
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Cal Weldon's Avatar
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Location: Near Vancouver
Do both speakers.

Put the magnet side down on a counter. Push the cone in with your fingers spread apart right where the dust cap meets the cone . Then reach around to the backside of the cone and with fingers spread to disperse the force, push the cone upward. Not too hard, pretend that it's about 10 watts of power. Tell us what you hear and feel.
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Old 28th February 2012, 10:22 PM   #5
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Location: Oakmont PA
It most likely is the voice coil is stuck and cannot move. That is what Cal is asking you to test. Both cones should move freely when pushed. Of course if you push too hard or in the wrong place you dent the cone or dust cap.

The second but less likely cause is the voice coil has detached from the cone and form. Check your amplifiers to be sure there is no DC out.
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Old 28th February 2012, 10:58 PM   #6
dmsims is offline dmsims  United Kingdom
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Thanks for all the replies

Under "Cal's test" the good driver is free to move the other one is stuck

Amps are fine (I did check! they drive other speakers and 'phones as well)
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Old 28th February 2012, 11:05 PM   #7
sreten is offline sreten  United Kingdom
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Location: Brighton UK

Its stuck because either the magnet has moved, trapping the coil, or
the coil has delaminated due to excess heat and jammed in the gap.

rgds, sreten.
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Old 29th February 2012, 02:57 AM   #8
puppet is offline puppet  United States
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.. am I the only one that sees a bent basket in the top pic?
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Old 29th February 2012, 11:42 AM   #9
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I think so - yes !


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Old 29th February 2012, 12:35 PM   #10
dmsims is offline dmsims  United Kingdom
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With regards to the basket - it's straight

I took the pic at wide angle (macro) and there is a bit of barrel distortion
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