foam vs cloth

[57BELAIRE]

In a recent post concerning my choice to replace the disintegrated foam surrounds on my L300's 136H to pleated cloth raised some eyebrows

This was done after the second pair of foam surrounds on this speaker fell apart. It was performed by an authorized JBL repair shop with quality parts.

I wonder if there have been any studies comparing the switch from foam to cloth in select woofers (LE14, LE15, LE10 etc. ) and the results.

I assume if the excursion and damping characteristics are similar in both, the cloth would be a logical upgrade

Anyone?

[Don McRitchie]

I wouldn't do it. There is a reason why drivers designed for hi-fi and monitoring applications almost universially use half roll foam or rubber surrounds. They have the most linear response and most desirable damping characteristics. The cloth surrounds have always been a compromise whereby some level of linearity and distortion has been sacrificed for increased power handling and ruggedness. Just some of the physical differences include increased mass for the cloth surrounds, higher stiffness and a non linear restoring force as the pleated cloth is streched. All of these characteristics will audibly change the response of a driver.

Even if you did decide to pursue cloth surrounds, I don't think they could be made to fit with the 136H. That driver uses a very narrow surround with a cone diameter that is not much smaller than the inside rim diameter. Cloth surround speakers such as the 2226 have a smaller diameter cone to allow room for the pleated cloth. You could recone your drivers as 2220's or 2225's if you are really adamant on no maintenance surrounds, but I don't see the point. They are just not designed to work in an L300.

I don't know when you last had the surrounds replaced, but the current materials have a much longer design life than the 70's and early 80's era originals. Properly done, new surrounds should last at least 15-20 years. Personally, I would not trade off sound quality to avoid a $100 repair every couple of decades.

Don

[57BELAIRE]

Thanks Don....when it comes to bass I'm very critical...that's my job.


You mention distortion, are you speaking in terms of lab measurements or actual subjective listening tests?

Bass frequencies, by their very nature, can masquerade a whole host of gremlins. For instance, during a live performance I can play a bass passage 1/2 step flat and most listeners won't hear it. You couldn't get away with that with a trumpet. The ears perceive bass differently.

I can't recall how my woofers sounded back in 1980 with their original foam surrounds, but I can say I can't imagine them sounding that much better than they do today.

Again, I would love to see some difinitive text on the subject. I'm willing to bet (not much) the differences from foam to cloth surrounds are barely perceptable. :dont-know

[57BELAIRE]

"I'm willing to bet (not much) the differences from foam to cloth surrounds are barely perceptable."

The guys at JBL are on a whole different level than most of us. I can say that one of them in particular has a real disdain for the foam but realizes it is a necessary evil to obtain the performance they desire from certain transducers. They have worked extremely hard to come up with a viable alternative and that alternative can be found in the newest transducers such as the LE14H-3, SUB1500, and 1500AL. No cloth surrounds on those bad boys.

Great point!...if cloth were an upgrade they'd be using it.

[Steve Gonzales]

What I've noticed is that by and large, the free air resonace is at least a half octave higher for most pleated surround JBL woofers when compared to their foam surround cousins. I am not an expert but can tell just by this one difference that they (pleated surround) will not perform as well on the bottom given the same enclosure.

[pmakres1]

What I've noticed is that by and large, the free air resonace is at least a half octave higher for most pleated surround JBL woofers when compared to their foam surround cousins. I am not an expert but can tell just by this one difference that they (pleated surround) will not perform as well on the bottom given the same enclosure.

So does the rubber surround used on the LE14H-3 perform as well as the foam surround? Does it "last forever"? What other differences are there between the LE14H-2 and its predecessors? I've never heard one, but the PS1400 sub looks like a real nice powered sub with the LE14H-3.

Peter

[mike]

I've encountered both L19's and 124A's that were resurrounded with butyl rubber. Whether or not they perform the way they should I don't know. I own a few pairs of older A/D/S speakers from the early 80's that use butyl surrounds and they are still in excellent condition.

Mike

[RickL166]

Looks like they did a fine job!! Looks very nice!!

[Maron Horonzakz]

It really depends on the woofer/ enclouser application. If its a horn enclouser a pleated cone will do better than rubber or foam. Some feel a foam or rubber surround on the woofer in a sealed or ported enclouser due to lower Freeair resonence will go deeper. But not really true. But its cheaper to make than a full horn system.

[57BELAIRE]

Looks like they did a fine job!! Looks very nice!!

Thanks! ... after the new foam surrounds fell apart the second time it wasn't a difficult decision to try cloth.

I can honestly say I can't hear any difference with foam vs. cloth and I'm a very critical listener.

rbh

[tomt]

does the foam on altec 411's belong on the front/top or the back/bottom
of the cone ?

http://img2.uploadimages.net/398689411sur2.JPG

[stpower]

Tom,

The foam on the 411 goes on the front/top. Early versions of the 411 used a nice cloth half roll surround. I have a pair of these I bought new in the early 70's that are still going strong in my HT system. To bad the bean counters got them to go to foam later on.

stpower

[Don McRitchie]

The surrounds on the 411-8A weren't re-engineered to reduce costs, it was done to address accoustical problems with the cloth surround. This came from one of the engineers involved.

[Steve Gonzales]

So does the rubber surround used on the LE14H-3 perform as well as the foam surround? Does it "last forever"? What other differences are there between the LE14H-2 and its predecessors? I've never heard one, but the PS1400 sub looks like a real nice powered sub with the LE14H-3.

Peter

I was speaking mostly to original spec drivers in the same size, like the difference between a 2235H vs 2225, when in fact, you could put a 2235H cone kit in a 2225 basket. I would dare to say that the lower FS is due to the 2235H's foam surround and other factors. If JBL makes a new driver, as in the LE14H-3 and they've figured a way to have the best of both designs, well, that is just another reason IMO, that we have such a high regard for those three little letters JBL!

[pmakres1]

If JBL makes a new driver, as in the LE14H-3 and they've figured a way to have the best of both designs, well, that is just another reason IMO, that we have such a high regard for those three little letters JBL!

Yes! Yes!