First Time JBL 128H Refoaming Help

[VintageUT]

Hello, I picked up a pair of JBL L112 speakers and the 128H’s needed new foam. I refoamed both of the 128H drivers using a 30hz tone generator on both and followed the same steps. I ended up using Simply Speakers surrounds and Aleene’s Tacky Glue. I didn’t hear any rubbing during the process, but after the glue dried I hear some distortion in one as I tested on very low volume, no bass. Also, when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise. Does this mean the voice coil on this driver is not centered? Could it be anything else? Thanks

[VintageUT]

[gasfan]

deteriorated foam 'goo' is not indicative of "scratchy" sound, but rather frozen/stiff cone movement which is silent. I would suggest there's an issue with geometry somehow. just sayin.

[Mr. Widget]

I didn’t hear any rubbing during the process, but after the glue dried I hear some distortion in one as I tested on very low volume, no bass. Also, when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise. Does this mean the voice coil on this driver is not centered? Could it be anything else? Thanks

Either not centered or there is debris in the gap.



Widget

[SEAWOLF97]

I've done a handful of those. Remember them as pretty much "self centering".

IF it was OK when you worked it in & out, then something went wrong, obviously.

you've gotta strip the new foam off anyway. "crap in the gap" seems likely, so dustcap needs to come off too.

IN the past I've refoamed drivers w/o testing them and wasted the time/supplies on bad ones. Now all drivers get tested before refoams. Just lay them on their backs on the floor (so gravity does not put them off center) and apply low signal.

[VintageUT]

I've done a handful of those. Remember them as pretty much "self centering".

IF it was OK when you worked it in & out, then something went wrong, obviously.

you've gotta strip the new foam off anyway. "crap in the gap" seems likely, so dustcap needs to come off too.

IN the past I've refoamed drivers w/o testing them and wasted the time/supplies on bad ones. Now all drivers get tested before refoams. Just lay them on their backs on the floor (so gravity does not put them off center) and apply low signal.

Thanks for the info. Now I think if it, I did press the center of the cone before and there was a slight rub. Wonder if there is the foam parts in the gap? Is it easy to remove the dust cap or should I leave it to a pro?

[VintageUT]

Either not centered or there is debris in the gap.



Widget

That’s what it seems. I guess I’ll have to remove the surround and start from scratch.

[RMC]

Earl's post # 12 raises an interesting question here.

RE "To the best of my knowledge all JBL woofers with ceramic magnets, having a single back vent, sport this internal foam filter. If one looks through the back vent ( looking past the foilcal screen if present ) and doesn't see the internal filter, one should still assume bits of it are present ( until proven otherwise )."

I took JBL's word as God's word so to speak regarding their own products on screen vs foam on/in back vent. But nevertheless suggested to OP in post # 11 to check under the screen to see if there's foam, just in case. The potential problem with "until proven otherwise" is that one MAY be cutting the dustcap legitimately (foam present) or not (no foam)?

Earl's post also raises a concern for me with the 2205H having ceramic magnet. Not a blame nor his fault. I knew for the 2214H and corrected the foam issue. Simply wish the matter of screen/foam would be one OR the other as mentioned by JBL in the pic below, instead of one AND/OR the other Earl appears to refer to. The 2205H do have a foil cal and a screen, peace of mind I thought, up to this point with the above mention which may imply they could also have foam cancer. Better learning it "late" than never, however I don't have time these days to check "on site". Later will try. Regards,

Richard

P.S. The pic below is JBL data shown on a JBL related Web site here, so I assume copyright issues (if any, none indicated) aren't applicable in this context.

[Earl K]

Richard,

Nice pic!

I'd need to check but I think the ( noted ) screen was dedicated to JBL's M.I. drivers ( after around 1980 and the intro of ferrite magnets ).

Previous to that time period all the alnico type drivers ( Home, Pro + M.I. ) used a plastic-like mesh screen over the internal vent ( "blow-hole" ).



PS; Here's a shot of my adhoc vacuum attachment used for foam bit removal inside the dust-cap area ( one can see that suction can be adjusted by a fingering the open area where the two portion of attachments meet.



From this thread over at AK

[RMC]

Hi vintageUT,

RE "when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise."

When you push on a cone you should be pushing at the center of the cone, not at various places.

Pushing elsewhere may lead to a little sideway displacement which in turn may aggravate your issue.

Remember, the natural movement of a cone is from the middle of it, in or out, so that's where you ought to push.

Clever idea btw to use clothespins. Regards,

Richard

[VintageUT]

Hi vintageUT,

RE "when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise."

When you push on a cone you should be pushing at the center of the cone, not at various places.

Pushing elsewhere may lead to a little sideway displacement which in turn may aggravate your issue.

Remember, the natural movement of a cone is from the middle of it, in or out, so that's where you ought to push.

Clever idea btw to use clothespins. Regards,

Richard

Very helpful, thanks. I’m new to this hobby and will definitely follow this guidance. Appreciate it!

I stole that idea from someone else.

[RMC]

Hi Earl,

Thanks for the input.

I don't dispute your previous statement that ferrite magnet drivers may also have foam inside in addition to screen, since I don't really know, never opened the rear nor dustcap, all original. The point is simply it pisses me off that I might have to do another tedious foam rot removal job... Maybe I felt overly safe, secured or comfortable about it in view of JBL pic I posted here. Could be that cruel reality may catch-up with me.

RE "I'd need to check but I think the ( noted ) screen was dedicated to JBL's M.I. drivers ( after around 1980 and the intro of ferrite magnets )."

I'm a bit confused now with that statement since my 2205H are not M.I. driver but from sound reinforcement 2200 series and I purchased them new Aug 6, 1980 just checked invoice (been with me 6 years longer than wife! LOL). So mine not MI, have ferrite and 1980 but have a screen.

Your adhoc vacuum attachment is pretty clever. Another proof that necessity is the mother of all inventions.

If you want to try the large straw attachement extention to suck up foam rot let me know, I can send you a free long blue or black straw, as you wish, in the mail, they're easy to cut to proper length, modify the end of it or even make two of them. I kept various plastic ones (see pics).

Probably would be shorter than what you use now. Just tape straw in corner of original vacuum attachment, like your computer attachment, and you keep the fingering adjustment for suction force. Plastic straws are out, not eco friendly, people throw them left and right polluting, getting banned everywhere now.

Regards,

Richard

[gasfan]

Hello, I picked up a pair of JBL L112 speakers and the 128H’s needed new foam. I refoamed both of the 128H drivers using a 30hz tone generator on both and followed the same steps. I ended up using Simply Speakers surrounds and Aleene’s Tacky Glue. I didn’t hear any rubbing during the process, but after the glue dried I hear some distortion in one as I tested on very low volume, no bass. Also, when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise. Does this mean the voice coil on this driver is not centered? Could it be anything else? Thanks

Is the spider centered on the top plate? It's possible it may not be. If it isn't, you need to follow that same asymmetry to the basket flange. The gap on those drivers and other 3" vc drivers is very tight ime. You definitely need to find center by shifting it around with the test tone first.

[VintageUT]

Is the spider centered on the top plate? It's possible it may not be. If it isn't, you need to follow that same asymmetry to the basket flange. The gap on those drivers and other 3" vc drivers is very tight ime. You definitely need to find center by shifting it around with the test tone first.

Yes, the spider looks centered, just like the other speaker. I really wonder if there is crap in the gap as mentioned below.

[RMC]