JBL K120 voice coil debris question

JBL K120 voice coil debris question

Postby slipknott » Mon Jan 26, 2015 12:46 pm

I have a question about debris in the voice coil cavity of a JBL K120 speaker. On the back side of the JBL K120 there is a metal grill of 6 metal strips that has a thin black fabric attached on the inside. I recently purchased one of these speakers that had not been used in a long time, and this fabric has detached from the grill and fallen inside the chamber in several pieces. it seems to be very thin, and crumbly. My question is this: should I fish these pieces out before they crumble into smaller pieces and drift down into the space between the magnet and coil? This could be done, but it's an awkward position--holding the speaker above the eyes to do this-- and there is always the risk of damaging the speaker. But, worth the risk, if the cloth is going to cause rubbing problems in the future. Or, is this kind of thing common, and not a problem? If anyone has an opinion, or experienced this cloth deteriorating, your comments would really be appreciated. Other than this problem, the speaker appears to be essentially unused. And it works, although I've not used it since testing until I decide what to do about the deteriorated grill cloth pieces.
slipknott
Vince
Vince
 
Posts: 8
Joined: Thu Jun 03, 2010 12:37 pm

Re: JBL K120 voice coil debris question

Postby tatittle » Mon Jan 26, 2015 7:40 pm

Hmm... that's a good question slip. I am not sure how likely it is that stuff will cause future problems. I am pretty sure I would delicately try to get it out just bc I am one of those folks who never leaves stuff alone even when its time too! Note: the dustcap you see from the rear hole is much closer than it looks. I wouldn't stick anything sharp or liable to leave residue in there either.
tatittle
Senior Member
 
Posts: 688
Joined: Tue Jul 10, 2012 8:44 am
Location: Johns Island, SC via NJ; Bklyn; Detroit; Charleston; Boulder; Miami; D.C.; etc

Re: JBL K120 voice coil debris question

Postby tatittle » Tue Jan 27, 2015 7:58 am

I just realized it sounds like the grill is intact, which would make fishing very difficult/impossible. I might not risk screwing things up given the lack of accessibility.
tatittle
Senior Member
 
Posts: 688
Joined: Tue Jul 10, 2012 8:44 am
Location: Johns Island, SC via NJ; Bklyn; Detroit; Charleston; Boulder; Miami; D.C.; etc

Re: JBL K120 voice coil debris question

Postby Jon S. » Tue Jan 27, 2015 12:49 pm

Interesting serendipity (see my latest post in my own K120 problem thread).
/ `--'(
< [] []////////|::: )
\_.--.(
User avatar
Jon S.
Senior Member
 
Posts: 1742
Joined: Wed Apr 30, 2008 12:34 pm

Re: JBL K120 voice coil debris question

Postby slipknott » Tue Jan 27, 2015 2:14 pm

my sincere thanks to both posters for their comments. I checked out the related JBL k120 thread that was mentioned, and the referenced ebay link in that thread. This seems to confirms what I feared-that if the foam covering the grill became detached, it could get stuck and cause rub problems. In my case, I think most, if not all, of the foam or fabric is in 3 or 4 large pieces. When I first noticed this, I placed the speaker so that the grill faced down and the dustcap faced upwards, and the foam pieces settled on to the surface of the grill. What I am going to try is this: I'll support the speaker in that position, in a way that lets me look up into the grill, and use a paperclip with a small hook bent at the end to fish these pieces out through the spaces in the grill. Hopefully without making them crumble during the process. I'll post later after I try this.
slipknott
Vince
Vince
 
Posts: 8
Joined: Thu Jun 03, 2010 12:37 pm

Re: JBL K120 voice coil debris question

Postby tatittle » Tue Jan 27, 2015 4:17 pm

For posterity pasted info below. I learned something new, gotta check mine now :)

That's indeed a factory original K120. Here's what might be the problem: ... The foam filter under the foilcal is rotted and lots of pieces have migrated into the gap causing the rub. It'll be a challenge to clean it out without invasive work. I'm sure this is probably the culprit. Either the foilcal needs to be removed and cleaning from the rear vent hole, or the dome needs to be removed to attempt to clean the goo out of the gap. No guarantees it can be cleaned successfully. The second ebay photo shows the foam filter is rotted.
tatittle
Senior Member
 
Posts: 688
Joined: Tue Jul 10, 2012 8:44 am
Location: Johns Island, SC via NJ; Bklyn; Detroit; Charleston; Boulder; Miami; D.C.; etc

Re: JBL K120 voice coil debris question

Postby slipknott » Wed Feb 25, 2015 3:02 pm

So here's what happened with the K120. I think I got 99%+ of the foam out of the voice coil vent. And the speaker sounds great. Hopefully no related problems will surface down the line. In case someone finds themselves in this situation, here's how I went about extracting the foam.
I set the cabinet on two chairs with speaker facing up so that there was about 2 feet of room underneath the voice coil vent and crawled underneath. With a flashlight I could through the back of the cabinet, to the vent, where 2 scraps of foam were sitting on the vent grill. These seemed to add up to the one third entire size of the vent- which is a circle about the size of a half dollar. I laid underneath with a flashlight, bent paperclip, and a pair very thin forceps and was able to pull the foam out in very small pieces. The foam crumbles very easily, so I used a vacuum cleaner every so often to suck out the dust & small pieces. (I was careful to not cover the entire vent opening with the vacuum- I thought too much sustained and complete suction might cause damage by moving the speaker/coil too abruptly.) Then I turned over the speaker a few times and checked again. 2 much larger pieces of foam were now on the grill-these added up to about three fourths of the size of the grill opening. I repeated the above, and was able to remove all traces of these pieces. I checked three more times (turning the speaker, getting underneath, etc), but no more foam pieces appeared.
All together, I the pieces I was able to remove added up in size to just a bit more than the size of the grill opening. So, I think I got it all, and before it had a chance to crumble and work it's way into the small spaces to cause coil rub. What may have helped here is that the speaker had been stored unused for a long time according to the owner. It was in a 10 watt harp amp, that he said was never used much. The owner lived in a very dry area, with low humidity (I know this because I live in the area), which may also have helped to prevent any existing foam dust from collecting into sticky clumps that could cause rubbing problems. Thinking back on the day I bought this, I may even have jarred the foam loose by doing the battery test on the speaker. That caused a big cone displacement when the leads were briefly connected.

For additional info on this and related problems, I'm including these RUKind subject headings for related JBL posts that I read through that might be helpful to others in this situation. The first one is already mentioned in this thread, and is also a topic at TGP, with a lot of good comments there as well.
Burned on K120 w/voice coil rub - what are my options?
Blown K120 blues :(
Dented dust cap?
E120 Blues
Re: Whats In The Box ?
K120 question
Q's on JBL D120Fs.
slipknott
Vince
Vince
 
Posts: 8
Joined: Thu Jun 03, 2010 12:37 pm


Return to Loudspeakers

Who is online

Users browsing this forum: No registered users and 3 guests