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View Full Version : Reconing 15" bass drivers on JBL 4350A's: Need a pro shop



j20056
09-03-2018, 09:37 AM
I have a pair of JBL 4350A's and I had those re-coned by a JBL service center (which I forget where) back about 15-20 years ago. Now, the rubber rim connecting the cones to the frame is frayed and coming apart and it is time to get all 4 of them fixed. I don't see any damage or wear and tear on the membranes themselves (they are pretty thick), and they seem to work OK as far as the electric circuit. The increasingly noticeable sound is distortion (boinking type of sound from woofers) but I don't think the coils or magnets have any issues although maybe worth an inspection when being fixed.
So the question is where am I supposed to do this since I do not remember where I did it 20 years ago.
Any recommendation of a good place is appreciated.

PH

Robh3606
09-03-2018, 10:17 AM
Can you post a picture? Do you have white cones or grey? Stop playing them if you damage the coils it will severely limit your options dependlng on what bass drivers you have in them.

Rob:)

gdmoore28
09-03-2018, 10:22 AM
Where are you located? Great Plains Audio in Oklahoma City is a first rate Altec/JBL service center. Don't bother trying to email them - calling is the only way you will contact them. Talk to Bill.

Great Plains Audioô
7127 Northwest Third St.
Oklahoma City, Oklahoma 73127
Phone/Fax: 405-789-0221 (tel:405-789-0221)

speakerdave
09-03-2018, 10:25 AM
Where are you? Local service is best if available because shipping big heavy woofers is expensive and careful, informed packing is required.

Based on your description of what you are hearing, you should not be using those speakers anymore as they are, since the surround helps hold the voice coil in place, and if it can tip it will rub and that's good-bye.

JBL sells only complete new recone kits, but there are replacement surrounds available which work well. On the other hand, if you are OK with the expense, total recone is best.

The ideal would be an authorized JBL shop (one which follows JBL instructions) which also has the equipment for recharging your Alnico magnets. These are not common, because Alnico magnets are no longer common.

Given your location someone here might be able to tell you about a shop near you. If you end up shipping, legacy Altec specialist Great Plains Audio is now servicing JBL, I believe, and they routinely remagnetize Alnico woofers. Check with them; they are in Oklahoma City.

speakerdave
09-03-2018, 10:27 AM
Three simultaneous helpful posters.

One more thought implied by Robb--it matters whether you have original type cones or not. Some prefer them. If you have them, and they are salvageable, you should give them up only after considering the differences between them and the JBL-provided 2235h replacement.

j20056
09-03-2018, 12:10 PM
I donít think I should have used the word recone. What is damaged and almost fully unglued now is only the rubber rim connecting the cone to the metal frame. There is no damage to the cones nor the coils. I found an online retailer that sells the rubber replacement parts and they have very detailed instruction videos on how to safely remove and clean the old rubber rims and put new ones. Itís $39 for a pair, including specialized glue. There are more than 25 comments from customers (all 5 stars) who bought the product including 2 that used it for 2231Aís like mine as it is made exactly for series of JBL and UREI 15Ē drivers including the 2231. So for $78 I think I am going to try this as it appears quite easy to do. Happy to report afterwards once the repair is hopefully successful. URL is below.

https://www.simplyspeakers.com/jbl-speaker-foam-edge-repair-kit-le15-2235-136a-fsk-15jbl.html

speakerdave
09-03-2018, 12:25 PM
I don’t think I should have used the word recone. What is damaged and almost fully unglued now is only the rubber rim connecting the cone to the metal frame. There is no damage to the cones nor the coils. I found an online retailer that sells the rubber replacement parts and they have very detailed instruction videos on how to safely remove and clean the old rubber rims and put new ones. It’s $39 for a pair, including specialized glue. There are more than 25 comments from customers (all 5 stars) who bought the product including 2 that used it for 2231A’s like mine as it is made exactly for series of JBL and UREI 15” drivers including the 2231. So for $78 I think I am going to try this as it appears quite easy to do. Happy to report afterwards once the repair is hopefully successful. URL is below.

https://www.simplyspeakers.com/jbl-speaker-foam-edge-repair-kit-le15-2235-136a-fsk-15jbl.html

They may be fine (except they seem overpriced), but since you came here and asked I should tell you that we have long used, with consistently good results, foam surrounds from Rick Cobb whose seller moniker on eBay is Looney Tunes.

j20056
09-03-2018, 01:03 PM
I wish it showed up first on a google search, although I thought $39 versus the perspective of having to ship heavy 38cm magnets was appealing versus a full outside servicing. Thanks for the feedback though.

grumpy
09-03-2018, 02:44 PM
Opinion on

If this is your first re-surround rodeo, Iíd strongly suggest you either leave this to a professional that has demonstrated ability and knowledge (not always so easy to determine), or practice on some shit speakers first, before hacking on fairly valuable, no longer available, drivers. It may appear easy, but itís also easy to make a bit of an unprofessional looking mess. If there is no voice-coil rubbing, the 30hz tone method (vs cutting out the dust caps and using shims) is often sufficient. Inexperienced dust cap glue lines are a dead giveaway of a diy-level job (also reducing the value, down the road).

So...nice speakers, worthy of proper maintenance.

Opinion off.

Robh3606
09-03-2018, 03:04 PM
Not sure what videos you have seen but we have a step by step on the site. The suggestion of doing a practice run is not a bad idea. Take your time and you should be fine. If you have any doubts don't.

Rob:)

http://www.audioheritage.org/vbulletin/showthread.php?469-Resurround-Step-by-step

rusty jefferson
09-03-2018, 03:58 PM
What Grumpy said. Not a place to experiment. IMHO. :)

Robh3606
09-03-2018, 05:39 PM
What Grumpy said. Not a place to experiment. IMHO. :)

Yeah I tend to agree but I have seen some real butcher jobs so if you choose a shop you really need to see their work and specify you want the foams installed on the back of the cones. If you get any grief move on. It just extra work to put them on the back. Real easy to just ignore the sticky glop on the back and leave it there and just drop them on the front.

Rob:)

j20056
09-03-2018, 06:27 PM
Thanks Rob.

As mentioned before, I wish i would have met you earlier but upon watching the online video from the place where I bought the surround rims, they indicate that it has to be glued on the rear side of the membrane, and upon inspection, that is clearly how my existing 2231A's are glued. I hope I won't make a mistake but if you have some extra knowledge that you feel is not mentioned in the online video, I am happy to re-purchase the hardware from you and get your extra knowledge. Obviously, I am not going to worry about an additional moderate cost to get this done right.
Am I really supposed to worry here though?

grumpy
09-03-2018, 11:01 PM
Itís mostly in the prep work, like most things. Carefully removing existing gaskets for reuse, cleaning the frame down to metal (access to MEK, a well ventilated space, a lazy susan/turntable) and removing excess glue from the cone without damaging or weakening it, using sufficient glue without being sloppy, cleaning up slop (it happens) with a damp rag right away. Waiting out the recommended drying/centering periods.

Hope it it goes well.

j20056
09-04-2018, 05:40 AM
Thanks all. Between your advice and the instruction video , which are 100% correlated, i feel well equipped to do this.

grumpy
09-04-2018, 08:26 AM
Comments on the vendor video:

Personally, I've found that running a 30Hz tone brings out alignment issues (allowing them to be noticed and corrected) better than finger pushing, but I would expect the latter to be quicker and require less equipment (zero). If there are no alignment issues, either is probably sufficient.

I always cut out the foam surround where the screws pass through the frame (after gluing the foam, and prior to reinstalling the gasket). Last thing you want is to torque down the mounting screw to have the foam rotate and distort. If you're using clamps (vs screws through the frame), this isn't an issue.

Cleaning (and gluing to) the backside of a cone is a bit trickier than what was shown for the C-V front-side example in the video, but take your time. Presumably the written instructions with the kit will describe the process for your drivers.

j20056
09-04-2018, 08:39 AM
Thanks Grumpy, you guys are really great.
I actually highlighted the problem (present on all 4 drivers) by running a 25-30Hz sine wave through the 4350's. But to be honest, I am unfamiliar with the alignment issues that you mention. Is it improper alignment of the coil in the magnet field? presumably, poor alignment would create screeching sounds or worse? The video indeed appears to simply push down on the center of the cone to make sure everything is aligned. But I am unsure if I'm supposed to do more advanced alignment testing?
Lastly, good point on holes where the screws would go but i do use clamps so not relevant here.
Thank you so much again and now, as i am waiting for the parts, I will begin the preparation process, which appears to be the most complex part of the project. I started removing one of the foam surrounds from one driver and they fraying in my hand like sand, I can't believe I didn't notice it before, as the distortion was reasonably low despite playing the speakers well above 110dB. Speaks of the quality of vintage 4350's...

grumpy
09-04-2018, 09:05 AM
non-interference in the gap primarily (throughout travel range). Ideally, the voice coil is both centered concentrically in the gap as well as moving on-axis only
(not tilted). Assuming spider (corrugated suspension connecting the frame to the voice coil area on the cone) isn't worn out, the static position of the voice coil in the gap (height) should be ok. If the spider is obviously not 'flat'... inner corregation bumps are either sunk in or extended out vs the part of it near where the frame attaches... it will take professional (or at least more advanced) help to select and replace that particular part.

Noises can come from other moving parts as well, such as lead tinsels (from wire terminals to where they go through the cone to the voice coil)
needing to be adjusted so they don't hit or rub things. Finger pushing test won't excite this type of non-musical behavior.

SEAWOLF97
09-04-2018, 09:27 AM
Comments on the vendor video:

Personally, I've found that running a 30Hz tone brings out alignment issues (allowing them to be noticed and corrected) better than finger pushing, but I would expect the latter to be quicker and require less equipment (zero). If there are no alignment issues, either is probably sufficient..

there's one nice (but yet to be mentioned) benefit to ordering from RCobb = a CD with the 30hz tone is included with the surrounds order.

j20056
09-14-2018, 12:55 PM
I'm back with a question. I am done cleaning up the first driver, removing rubber and glue. However, my question is about the rim of the paper cone itself. As can (hopefully) be seen on the attitude photo, there is a rather rigid black rim of hardened glue+rubber at the edge of the paper cone, permeably 1/4 wide. I can remove it by softening it with alcohol and cutting carefully, but before I do that I wanted to make sure that it is not a part that needs to be kept. it is definitely harder in consistency (and harder to remove) than the easy to remove black rubber that was about 3/8" wide at the back of the cone.
So wondering if I should remove it, as if I do so, only a clean paper cone edge will be left, prior to gluing to the new rubber surrounds.

Thanks for your feedback.

PS: Although the metal frame is not 100% clean metal, the video from SimplySpeakers states that as long as it well cleaned, it doesn't need to be 100% void of residual glue and rubber.

1audiohack
09-15-2018, 09:06 AM
Hello J

Itís a bit hard to tell from the picture since the immediate background is also black but I believe the felt edge of the cone should be all that is left.

Barry.

Earl K
09-15-2018, 09:29 AM
When I look at this pic, I see a shiny black edge almost 1/2" wide ( close to touching the edge of the basket rim ) that needs to be removed.

NOTE: don't remove anything until you have your new foams in hand so that you can make sure you don't remove too much edge.

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=82301&stc=1&d=1536954575

Google "2235 refoam" + I'm sure one will ( eventually ) see what a properly prepared edge ( of a 2231 or 2235 ) looks like.

:)

Okay, I did it for you;

See ( click the pic for more info );

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=78736&stc=1&d=1508735355 (http://www.audioheritage.org/vbulletin/showthread.php?40234-JBL-2231a-Woofer-refoam-suggestions-thoughts)

Here's a 2231 cone that shows the proper space ( gap ) between edge of paper cone and the metal frame edge ( note: that paper cone still needs some cleanup )

http://file.tubebbs.com/attachments/day_150109/15010915319692e2336d5db20c.jpg