Refoam answer from OC speaker repair (over/under)

[badman]

I snagged a pair of LE8T (Lancer 33, actually) with a recent (04) refoam from OC speaker repair. I was touching them, feeling them, and getting all kinds of tweaky, so decided to give them a call.

Because, the foam's on the cone! OH NO! All the lansalloys were on the back, so what if this throws my alignment off? I only have +/- 4mm to work with here!

Not to worry, sez OC man (in a helpful tone!), the restoring force is provided in the Z axis by the spider, in vast majority (within excursion limits of the surround, natch), and JBL sez to recone most of their Lansalloys on the front. One interesting point, I didn't realize the lansalloys were integral in manufacturing, pretty cool.

I also got confirmation that rubbing when pushing on the periphery is normal, due to the tight tolerance.

So, I just need to test these puppies when I get home with a nice impedance sweep and some tunes

[4313B]

Ok...


In any case, the reason people refoam on the front of the cone is because it's easy (and because they know that most people would never know the difference anyway). Many of JBL's newest transducers have the surround mounted on the front of the cone. They use a Klippel machine to optimize offset.

[JBLCanuck]

Ok...

LOL!

[badman]

I thought it might be a point of interest for some. I know I redid a foam job on 122As after finding that it should have been rear-mounted, and given that the suspension is dominated by the spider, (and was very old anyway) I probably didn't have to bother.

[Earl K]

Hi Badman,

- I didn't find 4313Bs response snarky . It was an accurate assessment of this ongoing question/dilemma .

- FWIW, I always find it interesting what others endup reporting about OCs' views on the matter ( so keep those reports coming ).
- From my long-distance perspective, OC will say almost anything to justify their "flip of the coin" approach ( as to whether they have just mounted foams to the back or the front of a customers' cone ) .

- Therefore, I take with a healthy grain of salt any "Gawds Truth" view-point that they might profure up . I certainly don't buy their argument that voice-coils are "self-aligning" in the "Z axis" . They'll need to provide "Klippel" measurements before I'll change my mind on that .

>< cheers

[4313B]

I thought it might be a point of interest for some. I know I redid a foam job on 122As after finding that it should have been rear-mounted, and given that the suspension is dominated by the spider, (and was very old anyway) I probably didn't have to bother.

We've gone over this ad nauseum.

Properly refoamed transducers retain their desirability.
Improperly refoamed transducers don't.

See this new thread for an example:

LE10H-1 surrounds

Some people couldn't care less if their surrounds are on front of the cone or on the back of the cone. Some guys redo their surrounds with duct tape. Some guys think that surrounds aren't required at all. :dont-know

[badman]

Well, all things being equal I would have preferred the rear mounting. But, my concerns being performance driven rather than nostalgic, it's nice to know that the effect of the surround tends to be much less than that of the spider, so any influence on the klippel tests for Kms will tend to be minimal. I was just glad to get confirmation that it's not going to throw away my already limited Xmax with this driver.

Regarding their "flip of the coin" methodology, I hadn't heard this (though this experience tends to point towards it), and my experiences with them have been largely positive (couple foam kits, some replacement diaphragms, etc) but glad to have a grain of salt POV to think about. Next time they (the le8t) need foam I'll clean them up and move it back to the rear unless I have a really hard time getting the face clean.

Note: I did some legwork on the contribution of the surround to the suspension compliance prior to my discussion with OC but was glad to have my findings confirmed. It's not that the voicecoil is self-centering in the z-axis, it's that the mechanicals are dominated by the spider rather than the surround, especially regarding z-axis behavior.

I've seen surround-less and spider-less speakers, and many feel that the more you can eliminate springs and let the motor dominate cone motion the better, even at the potential cost of more even-order rocking-mode distortion.

Anyway, the point of my post is that from a performance standpoint, front foams will tend to be an extremely minor effect on drivers even if the factory was rear-foamed.

[4313B]

Anyway, the point of my post is that from a performance standpoint, front foams will tend to be an extremely minor effect on drivers even if the factory was rear-foamed.

True, but from my point, just do it right.

None of us really cares where you glue your foam just so long as you don't try and dump it on us as original or desirable. We don't pay JBL prices for crap jobs. The arguing about where to glue the surrounds is beyond boring at this point. We've even had this discussion at JBL and the long and short of it is, just do it right.

Or don't; Whatever... We're all familiar with the "it's good enough" attitude.

[badman]

Your caustic and accusatory attitude and implication that I am one who espouses the "Good Enough" philosophy are offputting. I get the impression you think I'm advocating moving the foams when doing a refoam. That's not the case at all. Had I done the refoam (this was done in 04, with the last owner) I'd have done it behind the cone. As I say, I did so with 122As.

Foam on top is not original to be sure, but to my way of thinking, still very desirable. The big motors, excellent build quality, etc, are still present, it's just not 'original' from a collectors standpoint.

The point is, if someone's interested in hearing a classic JBL driver, and it was refoamed top rather than bottom, they shouldn't let it prevent them from giving them a shot due to performance concerns. If this had been stated explicitly here before, it didn't come up in searches, so I posted to try and add something of value to some. Not to restorers but to DIYers.

[robertbartsch]

I don't want to start a war, but, I would send them back and ask them to install new surrounds to the factory specification.

This is what they were supposed to do and that is what you paid for; right?

I had a well known speaker repair shop tell me there is no difference between factory diaphragms and cheap imports from Communist China.

[4313B]

I don't want to start a war, but, I would send them back and ask them to install new surrounds to the factory specification.

It would require a recone. Besides, he seems perfectly happy with the results. If he wants to carry the banner of doing refoams the quick and dirty way then more power to him. He'll have plenty of company. I personally don't do refoams because, frankly, they can be a real bitch to do right and I just don't have that kind of time to waste. Most reconers just slap them on the front because, frankly, they don't have the time to eff around with them either. And like I said several posts ago, most people just don't care. The JBL enthusiast, however, does care. Go figure...

1. Some guys don't care where their surrounds are.

2. Some guys do care where their surrounds are.

3. Service Centers should notify their customers when they are going to change the physical appearence of a JBL transducer. It does matter.

Alot of these old JBL drivers aren't low rent drivers. They're actually viewed as nice collectables. For instance, an LE8T-H is good enough to rate a top quality recone in my book.

I had a well known speaker repair shop tell me there is no difference between factory diaphragms and cheap imports from Communist China.

Well, alot of people can't hear for shit so maybe that well known speaker repair shop has a point. Besides, these days alot of stuff is getting watered down; JBL outsources alot of drivers...

[badman]

This has gotten quite ridiculous. I've been nothing but clear but you continue on your disingenuous path of making it out that I'm advocating foam on the top.

I didn't refoam these, I explicitly stated so several times. I also said that I DID refoam 122As to match factory mounting.

Why do you misrepresent what I've repeatedly, clearly said?

If he wants to carry the banner of doing refoams the quick and dirty way then more power to him.

Care to point out where I said anything of the sort? I have said I would have preferred on the rear. I've only said that for a DIYer, like me, it's not going to mess with your alignment. I'd prefer a more original look, but it's more of a cosmetics/historical issue, not a performance one. I'm not a historian, I appreciate JBL for the performance and quality it (once) represented.

Your distortions have worn thin. You get no 'street cred' for acting this way.

[4313B]

'Street cred'!? Good grief...

I think you might want to read over your first post, determine the kind of message it might be sending and then ask a moderator to whack the whole thread... I mean really, what was the point?

[badman]

I don't want to start a war, but, I would send them back and ask them to install new surrounds to the factory specification.

This is what they were supposed to do and that is what you paid for; right?

I had a well known speaker repair shop tell me there is no difference between factory diaphragms and cheap imports from Communist China.

Hi Robert:

They had already been refoamed when I purchased them. I think I'd have a tough time getting a full-on recone out of OC speaker for the sake of cosmetics. If I'd been the one getting them done, I might have pushed for it upon seeing them installed wrong, but as a second owner, I don't think I really have a case. I bought them for the driver performance. I wanted the underhung Alnico motor with a silver shorting path. I wanted wide bandwidth via the center radiator coupled directly to the voicecoil former.

I got those things, they sound great, and I'm happy. I'd prefer the proper foam location, but it's a small issue to me, they look and sound great. OC should have installed it under the cone, but I think I'm out of any reasonable timeframe to push on them about it.....

[rdgrimes]

Hi Robert:

They had already been refoamed when I purchased them. I think I'd have a tough time getting a full-on recone out of OC speaker for the sake of cosmetics. If I'd been the one getting them done, I might have pushed for it upon seeing them installed wrong, but as a second owner, I don't think I really have a case. I bought them for the driver performance. I wanted the underhung Alnico motor with a silver shorting path. I wanted wide bandwidth via the center radiator coupled directly to the voicecoil former.

I got those things, they sound great, and I'm happy. I'd prefer the proper foam location, but it's a small issue to me, they look and sound great. OC should have installed it under the cone, but I think I'm out of any reasonable timeframe to push on them about it.....

I'd be betting that OC did call the owner of the drivers and got his OK to front mount the surrounds. That's been my experience with them. I've also had this conversation with them and was told that they sometimes do front-mount especially when the cone has tears or issues on the edge that one might want to cover up, or with specific drivers where it's closer to spec. But in any case, they've always done what was asked of them and I will continue to use them. Getting rabid over what is "to spec" and what isn't is always a bit silly. As a wise person once said: a difference that doesn't make a difference is no difference. Enjoy your fine drivers.