• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Unrestored JBL LE10A Fs is 100 hz, S/B 30 Hz

Bauhausler

Bauhausler

Rational Subjectivist
I just measured an unrestored JBL LE10A with hardened Lansoloy surround. The WT3 plot is shown below. This driver's Fs spec is 30 hz. The unrestored one measures at 100 hz, showing the effect of the hard surround.
This driver will not perform remotely like it was designed to unless the foam is replaced.
I plan to refoam 2 of these when I have time. I'll update this thread with a new plot showing the original and refoamed versions.

attachment.php
 

Attachments

  • JBL LE10A BEFORE REFOAM.jpg
    JBL LE10A BEFORE REFOAM.jpg
    121.8 KB · Views: 135
Register to hide this ad
If it's that white rubber surround material, yes they become stiff and raise the resonant frequency. It turns them into big midranges.
 
Nearly all rubber surrounds age poorly. They stiffen and lose compliance, with the resulting loss of performance, as the graph indicates.

Just because there is no cracking of the surround does not mean that the surround is up to spec.
 
luvvinvinyl said:
Nearly all rubber surrounds age poorly. They stiffen and lose compliance, with the resulting loss of performance, as the graph indicates.

Just because there is no cracking of the surround does not mean that the surround is up to spec.
Click to expand...

I've used a rubber treatment on my polks for years. More for looks than anything. Maybe this helps keep the rubber as intended?
 
This is a well known fault with these drivers. The surround material was unique to JBL. The problem is discussed a lot but I couldn't find any actual before/after measurements. It was simple enough to record this for posterity to shed some light on the issue.
There are people who try to restore the elasticity of the aged, cement like original surround by smearing various things on them but I sincerely doubt that a degraded material will ever work the way it originally did no matter what you pour on it.

Anyone who has corrected this problem with an original hard JBL surround is invited to post documentary proof here.
 
This material isn't rubber. It's some kind of polymer foam.
conventional grey foam surrounds degrade as well, but in a different way. They become weak as the material breaks down and the surround thins from loss of material on the surface. This goes on until it falls apart. I doubt that degradation of grey foam surrounds changes the performance. I have measured woofers with and without surrounds. Adding a thin grey foam surround only changed the Fs by about 10%, from 15.5 to 17 hz. Those drivers have their 'springiness' dominated by the spider if they're using a conventional thin grey foam surround, apparently.

In contrast, the difference in Fs of using a thick versus a thin surround on the same driver was 42 Hz (way off) versus 17 hz (on spec)
 
Damage said:
Having not seen any in person, are you saying the surround gets hard over time?
Click to expand...

That particular driver has lansalloy surrounds. So does LE14A. As they age, they get hard and stiff. You can temperarly loosen them up with break fluid, but the real cure is foam replacement surrounds from looney toons.

russellc
 
Bauhausler said:
I just measured an unrestored JBL LE10A with hardened Lansoloy surround. The WT3 plot is shown below. This driver's Fs spec is 30 hz. The unrestored one measures at 100 hz, showing the effect of the hard surround.
This driver will not perform remotely like it was designed to unless the foam is replaced.

***
and
***
This is a well known fault with these drivers. The surround material was unique to JBL. The problem is discussed a lot but I couldn't find any actual before/after measurements. It was simple enough to record this for posterity to shed some light on the issue.
There are people who try to restore the elasticity of the aged, cement like original surround by smearing various things on them but I sincerely doubt that a degraded material will ever work the way it originally did no matter what you pour on it.

Anyone who has corrected this problem with an original hard JBL surround is invited to post documentary proof here.
Click to expand...

See above
 
Russellc said:
That particular driver has lansalloy surrounds. So does LE14A. As they age, they get hard and stiff. You can temperarly loosen them up with break fluid, but the real cure is foam replacement surrounds from looney toons.

russellc
Click to expand...

So the lansalloy being some kind of foam composite? I know this is probably well known to you JBL guys, but I just haven't had that much experience with the more "special" JBL stuff.
 
Yes.

For some period of time, JBL reconed Lansaloy-surround woofers under warranty, once the issue was verified. Few owners took advantage of this at the time, and thus most vintage LE woofers must be re-surrounded -LE8, LE10, LE14, and LE15....
 
You must log in or register to reply here.
Back
Top Bottom