Is there any hope for a driver with a rubbing 39mm voice coil? - diyAudio
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Old 6th May 2009, 11:49 PM   #1
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Default Is there any hope for a driver with a rubbing 39mm voice coil?

I have 3 (maybe 4) drivers that are very dear to me that all have rubbing VC's when you push on the cone. Some are worse than other (as far as friction and the point at which they begin to rub). Also, at least two of them seem to go through their entire stroke without rubbing if i push at a specific (off center) point on the cone so i'm guessing the VC has shifted. Honestly I've been trying to contact driver manufacturers to see if they have any recones for this driver or have a kit similar enough so i can experiment and make some frankenwoofers. Any ideas?
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Old 7th May 2009, 01:38 AM   #2
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Hello kappa, A couple ideas I can think of;

1) the expensive one, send the drivers to Bill Legall at Miller Sound. Haven't dealt with him myself, but everything I have heard is good.

2) www.matelectronics.com. They have the various raw components to recone a driver, i.e. voicecoils on formers, cones, dust caps, surrounds. One possibility.

Peace,

Dave
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Old 7th May 2009, 02:27 AM   #3
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Hopefully it isn't the magnet that has shifted. It's possible the VC windings are separating, in which case they'll need reconing. But first see how bad the problem is in practice by driving them with very low frequency signals, while rotating them to see if gravity has an effect. Then slice off the dust cover and have a peek at the VC to see what's happening (like a piece of grit or deformed VC edge).

Possibly the VC can be shimmed to encourage the spider to pull harder to one side. It's possible that manually distorting the spider can fix a light rub. If I were desperate and could reach the spider I might even try a stitch (like a surgeon would place a suture) in the spider to pull on it.
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Old 7th May 2009, 05:49 AM   #4
rjb is offline rjb  New Zealand
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Its impossible to give advice unless you tell us what the speakers are, preferably with pictures. Given the size of the vc, I guess they are modern bass drivers. In which case the position of the magnet and of the voice coil is permanently fixed relative to the chassis by glue or similar, rather than by bolts as was the case for older drivers

There re four possibilities, dirt in the gap, cone shifted relative to chassis, magnet shifted relative to chassis, voice coil disintegrating.

With modern drivers, only 1 and 4 is likely. As all four do it I guess 4 is most probable, in which case a re-cone is needed.
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Old 7th May 2009, 06:29 AM   #5
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VC diameter is in the title, 39mm. Driver is peerless 830491 aka XLS8.
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Old 7th May 2009, 10:53 AM   #6
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Default Re: Is there any hope for a driver with a rubbing 39mm voice coil?

Quote:
Originally posted by kappa546
I have 3 (maybe 4) drivers that are very dear to me that all have rubbing VC's when you push on the cone. Some are worse than other (as far as friction and the point at which they begin to rub). Also, at least two of them seem to go through their entire stroke without rubbing if i push at a specific (off center) point on the cone so i'm guessing the VC has shifted. Honestly I've been trying to contact driver manufacturers to see if they have any recones for this driver or have a kit similar enough so i can experiment and make some frankenwoofers. Any ideas?
Hi,

You should try the drivers with some synthetic signal from Your soundcard. PC->amp->driver. May be 10Hz..30Hz or so. No box needed. Does the rubbing change whith driver orientation in room (upside down/on side ...)? Once I moistured (?? small amount of water) the suspension down at the magnet a bit and let it dry. It worked. The driver had been lying around to long face up.

As far as I know reconing is not possible. It has to be done with original parts. Any other would most probably make a different (worse) animal.

Good luck!
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Old 7th May 2009, 03:40 PM   #7
sklimek is offline sklimek  United States
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Hi, I re-coned a pair of JBL 4313Bís following this excellent thread:

http://audioheritage.csdco.com/vbull...=NEW+SURROUNDS

I followed it step by step and had no problems. Whatís key is introducing a 30Hz tone as the new surrounds dry and centers on the voice coil either through an oscillator or a walkman on repeat (at very low volume). You will be able to hear if the surrounds are centering (the scratching sounds you have heard) it should be a clean 30Hz tone, you will have time to adjust before the glue dries and sets up the new register, the 30Hz tone plays for the complete drying process at least 8 hours.

http://audioheritage.csdco.com/vbull...5&postcount=16

If you are able to get some surrounds for your speakers this is a low cost solution that is quite possible will do the trick.

Stan
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Old 7th May 2009, 06:59 PM   #8
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Well, after testing with tones and music there is indeed rubbing and noise.

One of the woofers rubs almost immediately with very little input. At the lowest of volumes and little motion, it still sounds clean with my ear up to it but as soon as i turn it up even just a little and the cone begins to move more than a few mm's then it begins to distort.

The other two can actually get quite a bit louder before any noise sets in. one is moving roughly 11-12mm before noise (so a bit over half it's linear stroke) and the other is clean to about 7-8mm.
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Old 7th May 2009, 09:21 PM   #9
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Over the years, voice coils in high compliance suspension drivers can get off centered due to wear out of suspension materials (surrounding, spider), cone mass and gravity.
Case c.) in the attached picture illustrate this nicely.
Therefore in not so severe cases of VC rubbing (or to prevent that it happens at all) sometimes it does help to simply move around the driver in the opposite mounting direction once in a while (every few years or so).

When this doesn`t seem to help, at least it doesn`t cost anything.

IMO reconing is worth it only for very rare / unavaiable or expensive drivers.
I have once reconed a Scan-Speak 8" driver. The (original) recone kit did cost 2/3 of a new driver. Taken in account the effort it was do get it done right (and the risk to mess it up), I`ll rather buy a new driver next time this happens.
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Old 7th May 2009, 09:24 PM   #10
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arrgh, picture did not show up
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File Type: jpg chassis dezentriert.jpg (77.5 KB, 60 views)
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