Repairing scorched voice coils...

[stewey]

Ok, so I have this pair of HPM 40's with scorched voice coils. I bought them this way intending to repair or replace the woofers. Unfortunately you can't get recone kits for these speaks, and I haven't found replacements yet so I'm stuck...

...or so I thought. With nothing to lose I cut off the dust caps and started cleaning out the gap between the cylinder and coil. I started with a little piece of paper and just ran it around and around scraping out the gap. The paper would get dirty and I would start again with a fresh piece. Gradually I increased the thickness to clean more thoroughly.

Now I'm at a point where the cones move with no scratching or resistance at all. Before they were fairly stiff. I've slowly broke them back in, increasing the volume bit by bit over the last couple of days. Now they seem to play as well as my good pair of HPM 40's.

It's a little early to claim victory, but they really do seem to sound good. More listening will tell for sure. Here's my question: has anyone done this before? ...and if so, what can I expect in terms of performance? Will they return to their scratchy state? What kind of permanent damage have they likely suffered? Thoughts please

Stew.

 

[GordonW]

Yep, done this before. It's called "cleaning the gap".

Depends on what the prior damage came from- if it was simply a small crinkle at the bottom of the voice coil (ie, someone bottomed out the woofer and dinged it) you've probably fixed it. If it was a bubble from overheating, or a bent/kinked voice coil former itself somewhere in the middle, it might cause problems again later... it will probably have little tolerance for over-driving, IOW.

I'd just use it, and not worry about it, unless it screws up again... then if it does, find a speaker reconer that is patient/talented enough to attempt a recone, re-using the old woofer cone. I've reconed a few speakers myself that way at my job at work (last pair was some Genesis Physics 8", that I recovered the original cone, replacing the surround, spider and voice coil, they worked great), and have had generally good results, other than it being more time-consuming than simply making up a kit from new parts (cleaning the old stuff is delicate work that can't be rushed)...

Regards,
Gordon.


Regards,
Gordon.

 

[grumpy]

Just incase your fix does not work The www.circuitshop.com has repaired many pairs of HPM's in the past.

Grumpy

 

[stewey]

Ah, good news.

I'll glue the caps back on and keep my fingers crossed. They'll be serving as rear speakers in my surround setup so hopefully they won't be overdriven any time soon.

Thx.