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-   -   Partially faulty bass driver (http://www.diyaudio.com/forums/multi-way/207764-partially-faulty-bass-driver.html)

dmsims 28th February 2012 09:51 PM

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

http://www.zen183332.zen.co.uk/connect.jpg
http://www.zen183332.zen.co.uk/crossover.jpg

Any suggestions?

nigelwright7557 28th February 2012 09:54 PM

Its odd both measure the same.
I have always found voice coil faults to show as a lower impedance.

weltersys 28th February 2012 10:05 PM

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!

Cal Weldon 28th February 2012 10:16 PM

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.

simon7000 28th February 2012 10:22 PM

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.

dmsims 28th February 2012 10:58 PM

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)

sreten 28th February 2012 11:05 PM

Hi,

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.

puppet 29th February 2012 02:57 AM

.. am I the only one that sees a bent basket in the top pic?

phase_accurate 29th February 2012 11:42 AM

I think so - yes !

Regards

Charles

dmsims 29th February 2012 12:35 PM

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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