JBL LE 14A Woofer Specs Off?

dc270

dc270

Now Off the Reservation
Accordeing to what is published and what I have meausred with the WT 3 the specs on my original Le 14A's seem to be off a fair amount!
Example;
FS=28 hz (published)
FS= 20hz (meaured)
Qts= .32 (published)
Qts= .22 (measured)
Qms= both the same

The Lansaloy surrounds were very stiff yesterday, I treated them with a couple coats of brake fluid which did free them up quite a bit...to much?
Should I look into replacing the (still good) surrounds with new replacements to get my Q's to fall back into line? Maybe re- break in them in for a while?
Thanks for any idea here.
DC
 
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Yes, that's a problem with the brake fluid approach, as I've discussed with others previously. The only way to get the compliance right is to measure as you apply it incrementally. Steve O, I believe it was, did the same thing with substantially the same result.

It will evaporate over time (~6 months,) and for some indeterminate period will be in the correct range until they become overly stiff again. Install new surrounds and be done with it. Whatever they come out will at least be stable.

You can certainly use them the way they are now, but your tunings will be, well, "indefinite" for the duration.

http://audiokarma.org/forums/showthread.php?t=117517
 
Well to avoid the BF evaporation problem and the variable "Q's" making stable tuning a problem it pretty much makes sense to re-foam now and start with a stable platform.
The 14A is a great woofer worthy of a good clean slate to re-start with- I read with interest on Duffinator's project and will consider doing something like it as well. Finding those HF drivers cheap enough will be a challenge however!
Thanks again for the support Zilch- yew da man...
 
Duff's doing his Barzilays, I'm building S99 towers, and Jackgiff upgraded his Santanas, all using the same LE14/PT waveguide formula. BMS like Jack used is also a good option for the HF driver. I'll probably use those as well and save my 2452H-SLs for another little project I'm cooking here.... ;)
 
Zilch has to know I was going to jump in here...

...While what he notes is true about my results of applying brake fluid mostly parallel your experience (fs~20Hz) there is another issue that I consider unresolved WRT aftermarket refoam materials. Specifically, the currently avail foam was designed for later versions of the LE14A. These foam kits can be made to fit the old style LE14A with inverted surrounds (which most seem to be these days) but IME they introduce a physical offset into the cone geometry. Personally, I find this offset theoretically annoying and consider it about equal in deviation from original operating parameters as the lower and varying fs produced by brake fluid. FWIW, the refoam job I performed on one set of LE14As resulted in an fs~24Hz, still not spec and probably drifting lower as they break in.

Bottom line is that either way, there are compromises to consider when attempting to refurb these older speakers. I've chosen to go the brake fluid route while I await release of a dimensionally correct replacement surround...and I'm not holding my breath. I don't believe that the occasionally avail JBL recone kit is close to being a practical alternative due to extreme cost.

Ultimately, I have to wonder if maybe the best solution to using these old drivers is to not use them at all but rather replace them with something modern and less hassle prone. OTOH, as a hobby, “practical” doesn’t need to be a prime consideration.
 
I've got a gaggle of refoamed LE14As here, all playing quite nicely.

For the cost of a new recone, you can almost buy new LE14H-1s or H-3s, but you may wait as long as a year to land any of those.

Recone's only rational for blown voice coils and thrashed cones, in my view.

LE14As are plentiful, and serviceable.

Pick your pleasure, and just do it. There's not much value in agonizing over cone centering issues 'til someone actually measures the outcome with various available aftermarket surrounds and generates some meaningful data, but that's not likely to happen, either....
 
Once again I appreciate the help here! I will poke around, ask some questions and see who had the real deal for the correct foam kit.
DC
 
Zilch said:
New PE catalog lists what they claim are "exact replacement" surrounds for LE14s, Part#260-980:

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=260-980&CFID=12513770&CFTOKEN=77710486
Click to expand...

Unless they've recently changed the physical product represented by that PN, they are like all other LE14 replacement surrounds I've investigated: They are not an exact replacement for early LE14As with inverted Lansaloy surrounds as original equipment. They must be installed in a non-inverted config and introduce the physical offset I've described elswhere.

Maybe someday...
 
I've taken early LE14s, and after installing the "generic" foam surrounds, removed the offset by heating the foam surround with a heat gun (be careful to no over-do it, naturally!) and letting the suspension "re-center" to proper rest position, before the foam cools and re-sets. It's worked fine for several sets. Yes, it's time consuming and requires care, but it WILL make the speaker work as it should...

Regards,
Gordon.
 
GordonW said:
I've taken early LE14s, and after installing the "generic" foam surrounds, removed the offset by heating the foam surround with a heat gun (be careful to no over-do it, naturally!) and letting the suspension "re-center" to proper rest position, before the foam cools and re-sets. It's worked fine for several sets. Yes, it's time consuming and requires care, but it WILL make the speaker work as it should...

Regards,
Gordon.
Click to expand...

Very interesting!!! I wasn't aware the foam could be "reset" with heat. This might be the next best thing to a purpose designed LE14A surround. :thmbsp::thmbsp::thmbsp:

Do you reposition the cone physically where you want it to end up prior to heating or just let it naturally move into a position of equilibrium thru restoring force provided by spider? Also, any idea of actual temperature or range of temperature to be used? Or is it just by sight and feel?


BTW, as a "speakerfixer" any insights as to why the early LE14s with inverted surrounds are seemingly ignored by the foam mfgrs? You'd think that if say a Bose 901 warrants a custom refoam kit, surely the mighty inverted LE14A deserves one too. There must be enough of them out there in need of replacement to make the volume worthwhile.
 
I put a small amount of weight on the center of the dustcap (it varies, but a couple of ounces of weight is usually plenty) and heated the surround until it dropped just past where the center position would be (like 1 millimeter or so past "dead center". Let it cool, remove the weight... and it should spring up to centered.

I think, realistically, the number of later model LE14s dramatically outnumber the early model ones... that's the reason the surrounds tend to cater to the later ones...

Regards,
Gordon.
 
Well, once again, I'm just not getting this.

Factory recone kits for LE14A use convex surrounds attached to the rear of the cone.

If a convex surround is attached to the front of a vintage LE14A cone per the convex original Lansaloy, it would push the cone rearward, not forward, no?

And any "resetting" of the foam would require biasing the cone forward in the process?

In any case, I would not rely upon a 40-year-old spider of indeterminate history to center the alignment. If it's been stored in anything but a vertical position, it's likely sagged one direction or the other, although if the Lansaloy is hard, I suppose that wouldn't occur. :dunno:

And how does one determine that, anyway? Flatness of the spider folds?

Well, I've got a poo pot of them around here, and I suppose I could make an organized empirical study of it with the proper motivation. :p:

Of note: For some period of time (several years, perhaps,) recognizing the problem with Lansaloy, JBL reconed LE14As for free under warranty with foam surrounds....
 
Well, I'd be interested in whatever you come up with. As I mentioned, I've got a pair of LE-14C's that are perfect except for hard Lansalloy surrounds. I'm not in a huge hurry, because I really need to do some more practice on simpler surround replacements before I tackle these.

I would love to know, however, if the available surrounds will work without heatgunning them!
 
Fisherdude said:
I would love to know, however, if the available surrounds will work without heatgunning them!
Click to expand...
I use the generic aftermarket surrounds. I glue them to the front of the cone, per the original Lansaloy. (Or, rather, my reconer/refoamer, an authorized JBL service center, does.) It's never been an issue.

I believe Mxlews, Jackgiff, and Duffinator are presently using the same.... :dunno:
 
How tough is it to get the old surround off? It obviously isn't going to just rub off with your thumb the way rotten foam does. I'm terrified of pulling off some of the white sandy surface on the cone.
 
Zilch said:
I use the generic aftermarket surrounds. I glue them to the front of the cone, per the original Lansaloy. (Or, rather, my reconer/refoamer, an authorized JBL service center, does.) It's never been an issue.

I believe Mxlews, Jackgiff, and Duffinator are presently using the same.... :dunno:
Click to expand...

Yep, if they're originally on the front of the cone, by all means put the new ones there. Will definitely reduce the offset issue.

Fisherdude said:
How tough is it to get the old surround off? It obviously isn't going to just rub off with your thumb the way rotten foam does. I'm terrified of pulling off some of the white sandy surface on the cone.
Click to expand...

I use a sharp razor blade, and lightly score the cone right where the surround edge meets the cone on the inside. That way, if anything does try to peel off from the white surface, it's got a "barrier" that stops it from going any further into the cone. Then, once I've put the new surround on, I put a very small amount of white glue, smeared into the crease, to seal it and make sure it doesn't propagate.


Regards,
Gordon.
 
GordonW said:
...I use a sharp razor blade, and lightly score the cone right where the surround edge meets the cone on the inside...
Click to expand...

Oooh, that's kinda scary.

GordonW said:
...Then, once I've put the new surround on, I put a very small amount of white glue, smeared into the crease, to seal it and make sure it doesn't propagate.

Regards,
Gordon.
Click to expand...

By "crease" do you mean the scored slit in the cone? Make sure what doesn't propagate? The slit you cut? Oooh, that's kinda scary.
 
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