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 :D

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? :blink:

[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! :applaud: :applaud:

[JBLROCKS]

What are peoples opinions about replacing foam with rubber in general?
I posted the question to SimplySpeakers but they never responded.

Thanks:applaud:

[Mr. Widget]

Why would you even consider it? These drivers are designed the way they are for very good reasons.

I don't really understand why people get so weirded out about foam that only lasts 10-15 years. Who will still be using their computer, cell phone, or even DVD player in 10-15 years? I like the fact that for a nominal fee these can last nearly a lifetime... there are few products made today that can even be repaired!

Widget

[pmakres1]

Why would you even consider it? These drivers are designed the way they are for very good reasons.

I don't really understand why people get so weirded out about foam that only lasts 10-15 years. Who will still be using their computer, cell phone, or even DVD player in 10-15 years? I like the fact that for a nominal fee these can last nearly a lifetime... there are few products made today that can even be repaired!

Widget

Before I reconed my LE14H's, I had a refoam job that only lasted 3 years. I know that is unusual..Maybe it was old stock or something, but I know I wasn't very happy about that.

Peter

[Steve Gonzales]

I think what gets lost in translastion by the site's experts is that that longevity is NOT the main issue!. A foam surround is ENGINEERED to have a SPECIFIC compliance, mechanical resistance and other factors. Going from a foam to a rubber, butyl rubber, santoprene-etc FROM an original JBL factory foam is going to drastically change things to your drivers response. I don't think it is a good idea except when going from Lansaloy to the newer foam . I mean no disrespect to any other answers. I just felt that alot of people (As I did), NEED to know the bottom line in no uncertain terms. Unless you have what equipment JBL did when they designed and tested their drivers (R&D), trust them that the best performace you could possibly ever achieve for your driver is a JBL RECONE kit, then if you can't afford that, a good quality replacement in the CORRECT and Original "type" material (FOAM). I hope this helps those who still had a question mark in their mind as I once did. Steve G.;)

[Tom Loizeaux]

Why would you even consider it? These drivers are designed the way they are for very good reasons.

I don't really understand why people get so weirded out about foam that only lasts 10-15 years. Who will still be using their computer, cell phone, or even DVD player in 10-15 years? I like the fact that for a nominal fee these can last nearly a lifetime... there are few products made today that can even be repaired!

Widget

I agree with this, except JBL doesn't offer re-foam kits. They only offer full re-cone kits, often at prices well over $100.00 each. If JBL offered the correct re-foam kits, then I would agree that the foam surrounds were replaceable. Now your only refoam choice is an aftermarket kit, at that doesn't sit well with me. I believe in quality products that last. That's why I love the 43XX JBL studio monitors. Short-lived surrounds don't follow this philosophy. JBL should not only make these foam surround kits available, but should make them, and authorized JBL service installation VERY inexpensive (maybe just slightly above cost)...as a way of saying "Thanks for using JBL and keeping or products going".

Tom

[Steve Gonzales]

It depends on who you by your kit from (foam). I agree that there are low quality kits out there for sure. There are EXCELLENT ones too. Do your homework and ask around here on the LHS, or ask me. I have have 12 years on a pair of L166's and they where fresh as new so it all depends. As for the price suggestions, well, I wish that too, BUT we can wish in one hand and %^&* in another and see which one fills up first! :D

[Steve Gonzales]

I have a Porsche, big deal, but I own one. I had to change the shocks after 12years and they are $1000.00 EACH pair!!. I could have got knock off's for a third of the price. I asked if they would make it handle as new and they said maybe, well, yeah, sort of. I layed out the $$ and now I'm back carving around corners like I should. Worth EVERY PENNY!! (Factory new)

[pmakres1]

I never griped about the cost of recone kits...GETTING the kits was another matter, a repair center/JBL relationship issue that I won't go into here. Suffice it to say I don't deal with that center any more. But, I was surprised when a previous refoam job only lasted 3 years.

The trouble and expense of properly rehabing a JBL product is worth every minute of trouble and every penny of expense. It appears from my experience that having a genuine recone kit installed by a qualified service center is the way to go.

Peter

[Mr. Widget]

Most of the cheapo and even expensive alternatives do not have proper recone kits available. They wear out and will never be truly as new again. I am damn glad that JBL still makes recone kits available!:applaud:

I was at a local repair shop and the guy was having to piecemeal a Franken woofer to repair an older $40K Wilson Audio WAMM. Wilson said that they no longer supported it!!! That's what $40K will buy you from someone else.

Widget

[Mr. Widget]

But, I was surprised when a previous refoam job only lasted 3 years.

I hope after that experience you opted for a proper JBL recone kit. When properly installed by an authorized technician they come with a warranty.

Widget

[pmakres1]

Most of the cheapo and even expensive alternatives do not have proper recone kits available. They wear out and will never be truly as new again. I am damn glad that JBL still makes recone kits available!:applaud:

Widget

Agreed!! :applaud: :applaud: Go Widget!

[pmakres1]

I hope after that experience you opted for a proper JBL recone kit. When properly installed by an authorized technician they come with a warranty.

Widget

Yes, I did.

[Steve Gonzales]

Some people have great drivers with rotten foam. I had a pair of 2235H woofers that sat unused for 15 years in some sumo B380 knock-offs. New high quality foams were installed and wha-la. Ask porshedpm about them, they're good as new. Nothing is an absolute if you get the right supplier and installer.

[Steve Gonzales]

Sometimes $$$ factors in Mr.Giskard. Plain and simple. I for one have had to go with just quality foams at times. I do AGREE, JBL recone is the absolute BEST WAY to GO-- if it is in your budget to do so.

[Steve Gonzales]

God what an absolute BARGIN a Factory Recone kit is if you can lay out the cash!!!!.

[pmakres1]

God what an absolute BARGIN a Factory Recone kit is if you can lay out the cash!!!!.

Yep!! :D

[Maron Horonzakz]

So who is going to sell me a JBL LE8T recone kit so I can do my own?

[57BELAIRE]

There seems to be some devisiveness on this subject...to all you foam "devotees" out there...if you're buying aftermarket foam for your JBL drivers, how can you be assured that that you'll have the correct "F's" , the correct compliance, the necessary excursion, damping, blah, blah.... Unless JBL was offering exact factory replacement foam kits for your particular driver, it's pretty much a crapshoot out there.

Just because a particular aftermarket foam kit is "half-roll" and looks the equivilent, doesn't make it so. It could be a poor substitute for a quality cloth surround.

I think the PRIMARY consideration with foam kit mfgs. is simply...will it fit? They could care less about performance characteristics which is what this discussion is all about.

I stand by my original decision to replace foam with pleated cloth on my 136H's and until JBL offers an exact foam replacement kit for them...status in quo.

rbh

[4313B]

I stand by my original decision to replace foam with pleated cloth on my 136H's and until JBL offers an exact foam replacement kit for them...status in quo.I guess my response would be "Who cares?"
Feel free... ;)
The recone kits are available to those who do it right.

[Mr. Widget]

"There seems to be some devisiveness on this subject...to all you foam "devotees" out there...if you're buying aftermarket foam for your JBL drivers... Just because a particular aftermarket foam kit is "half-roll" and looks the equivilent, doesn't make it so."

You are absolutely right!

I personally wouldn't do a refoam unless I could verify the measured results afterwards to confirm that the driver was still in spec. With a cloth surround you have excellent odds of it being quite out of spec. In any case a complete recone while more costly is the best way to go. For me it isn't about being a devotee... I am after quality and performance... that is why I use JBL drivers. I also use other brands when appropriate.

You have every right to experiment and if it makes you happy to create Franken woofers... feel free. To me it is similar to my high school bud who bought an old Jag E Type and replaced the engine with a Ford small block... It ran very differently, sounded like a truck, and the handling went to hell, but he could get parts for it just down the street...

Widget

[57BELAIRE]

I guess my response would be "Who cares?"
Feel free... ;)
The recone kits are available to those who do it right.

EXACTLY!....who cares if you you use .."paper or plastic".

What sounds good to YOUR ear is what counts..... Right?

If a total recone isn't required , I'd rather keep the original cone and voice coil.

Great responses!

Russ


:applaud: :applaud: :applaud: :applaud:

[4313B]

Well, that wasn't my point, but whatever. :p

This thread was answered in post #2 and everything after that is pretty much filler.

[Titanium Dome]

MMM-M-mm-mmm! filler. :homer:

[GordonW]

To me it is similar to my high school bud who bought an old Jag E Type and replaced the engine with a Ford small block... It ran very differently, sounded like a truck, and the handling went to hell, but he could get parts for it just down the street...

Widget

Why exactly would the handling go to hell? The Ford 289/302/351W engines are actually LIGHTER WEIGHT then the Jag 3.8 or 4.2 6-cylinders! And to boot, you can actually put the weight EVEN CLOSER TO THE CENTER of the car, as in further behind the front wheels... which should make the turn-in response of the car even QUICKER...

And as for spring rates- the reduction in weight, should make the front springs proportionally "stronger"... which should, to an extent, counteract the tendency for oversteer that moving the center of gravity rearward might cause... it should mostly cancel out, unless we're talking a real butcher job here...

Regards,
Gordon.
who's worked on a few engine-swaps over the years...

[Mr. Widget]

Why exactly would the handling go to hell? ...unless we're talking a real butcher job here...

We're talking... high school kids, of course it was a butcher job!



Gordon ...who's worked on a few engine-swaps over the years...
Why does that not surprise me?:applaud:

Widget

[57BELAIRE]

Well, that wasn't my point, but whatever. :p

This thread was answered in post #2 and everything after that is pretty much filler.

OOOOOHHHH....looks like I struck a nerve!
:bouncy: :banana: :dancin: :yes:

When I opened this thread I purposely chose a controversial subject of interest to me and hopefully others. It seems enough readers weighed in with their own opinions to make for some thought provoking discourse. To dismiss these opinions as "filler" is doing your fellow forum members a disservice...I don't know about you but I'm interested to hear what others have to say on this subject. ;)

[4313B]

OOOOOHHHH....looks like I struck a nerve!
:bouncy: :banana: :dancin: :yes:

When I opened this thread I purposely chose a controversial subject of interest to me and hopefully others. It seems enough readers weighed in with their own opinions to make for some thought provoking discourse. To dismiss these opinions as "filler" is doing your fellow forum members a disservice...I don't know about you but I'm interested to hear what others have to say on this subject. ;)I've been told you guys really like my responses so I have come to expect being trolled. :p
These opinions are filler - JBL never offered cloth surrounds for 136H's. There is no controversy. Everything after post #2 is irrelevant. :)
Dismissed... :rotfl:

[57BELAIRE]

I've been told you guys really like my responses so I have come to expect being trolled. :p
These opinions are filler - JBL never offered cloth surrounds for 136H's. There is no controversy. Everything after post #2 is irrelevant. :)
Dismissed... :rotfl:

Well, you heard it here first folks...no more discussion, end of story....
:banghead:

I think you missed the whole point of the thread....anyway, it must wonderful to inhabit such an exalted position among your peers. I'm impressed! :snore:

[4313B]

peersNOT! :D

I think you missed the whole point of the thread...Wasn't it to argue about cloth being better than foam on the 136/2231 transducer and that you wanted definitive proof? The 2235H, with it's foam surround, is still in limited production... and this is 2005.



I'd just hate to see a whole bunch of people start putting cloth surrounds on these transducers and then think they can eBay them for anything more than core prices ($40 to $80 each depending on condition).

[GordonW]

WRT the "uniformity" and "correctness" of aftermarket foam surrounds:

IME, and I've refoamed (and re-fabric'ed, here and there) probably 1500 drivers in the last 5 years- the biggest differences between a foam surround and a fabric surround are the acoustic differences arising from the DIFFERENT SHAPE and DAMPING PROPERTIES of the material. A foam surround will have LOWER DISTORTION at high excursion, because it has a more LINEAR STIFFNESS VS EXCURSION behaviour characteristic than fabric. Also, the roll-shape of foam surrounds, means they will "oil-can" (ie, vibrating counter to the motion of the cone movement) less than fabric surrounds, reducing noise production by the surround.

As for the whole stiffness issue- I've been working with these for a LONG while, and I've seen VERY FEW cases where ANY aftermarket foam surround was FAR ENOUGH out of spec, stiffness-wise, to make even a remotely significant effect on the driver response. In the vast majority of cases, the aftermarket foams resulted in a driver that was within +- 10% of stock, from a free-air resonance (Fs) standpoint, after refoaming. And the cases where that WASN'T going to be true, it was OBVIOUSLY NOTICABLE, before the foam was even installed, that the foam was THICKER or MUCH STIFFER than stock.

In fact, the last time I had this problem, was over 3 years ago, with a certain batch of LE10 foam surrounds we got, and sent back because they were stamped too thick and stiff. They probably would have worked OK on a 2121 or 2122 (drivers that don't have to handle low bass), but they were inappropriate for LE10, LE111 or PR10 applications. After that, I've not got a single batch that would violate the +- 10% tolerance thing above...

Also, the modern foam (that made in the last few years), is an improved composition... made from, for the most part, a polyether-based material rather than the old polyurethane-based foam. The new foam is MUCH LESS vulnerable to air-borne attack (bacteria, humidity, heat, etc) and therefore will dry rot at a MUCH LOWER rate than the old stuff. So, modern foam surrounds, at least according to the "scientists", should last significantly longer than the stuff we were using 10 years ago.

So, it's MUCH MORE the GEOMETRY and MATERIAL PROPERTIES of foam vs. fabric, than it is any variation in foam stiffness or the life-span of a foam surround, that most people should be worrying about. Those geometric and material properties are what's going to make the SIGNIFICANT difference in the performance of the driver...

Regards,
Gordon.

[4313B]

I recently refoamed a pair of 2214H's using Rick's kits and they came out fine.

[57BELAIRE]

NOT! :D
Wasn't it to argue about cloth being better than foam on the 136/2231 transducer and that you wanted definitive proof? The 2235H, with it's foam surround, is still in limited production... and this is 2005.

I'd just hate to see a whole bunch of people start putting cloth surrounds on these transducers and then think they can eBay them for anything more than core prices ($40 to $80 each depending on condition).

Not argue, but have an intellegent debate on the pros and cons with hopefully some difinitive scientific or empirical information from some of the more learned members on this forum.

So far there has been some interesting propositions...I'm now leaning toward a form of butyl rubber. Who knows?

Who said anything about eBay?
:blink:

[4313B]

an intellegent debate on the pros and cons with hopefully some difinitive scientific or empirical information from some of the more learned members on this forum.Oops! I'm out then... :slink:


Who said anything about eBay? :blink:That was for the benefit of the eBayers. :p We all see the hack jobs that show up on eBay. Frankenwoofers - I like that. :rotfl:

[Earl K]

57BELAIRE

( cool moniker BTW )

- I don't think there'll be much of any sort of enlightening discussion ( on this subject of cloth vs foam ) until you fess up and publish the newly acquired Fs for your cloth surrounded 136H woofers .

- Ya never know, you might be enjoying the sound of a 136HS wannabe woofer ( which would then redirect this discussion in a whole different direction / since there are a few members here who consider the 40hz Fs of a 2225H as low enough to produce decent bass, when placed into a 5 cu' enclosure ) .

:cheers:

[57BELAIRE]

WRT the "uniformity" and "correctness" of aftermarket foam surrounds:

IME, and I've refoamed (and re-fabric'ed, here and there) probably 1500 drivers in the last 5 years- the biggest differences between a foam surround and a fabric surround are the acoustic differences arising from the DIFFERENT SHAPE and DAMPING PROPERTIES of the material. A foam surround will have LOWER DISTORTION at high excursion, because it has a more LINEAR STIFFNESS VS EXCURSION behaviour characteristic than fabric. Also, the roll-shape of foam surrounds, means they will "oil-can" (ie, vibrating counter to the motion of the cone movement) less than fabric surrounds, reducing noise production by the surround.

As for the whole stiffness issue- I've been working with these for a LONG while, and I've seen VERY FEW cases where ANY aftermarket foam surround was FAR ENOUGH out of spec, stiffness-wise, to make even a remotely significant effect on the driver response. In the vast majority of cases, the aftermarket foams resulted in a driver that was within +- 10% of stock, from a free-air resonance (Fs) standpoint, after refoaming. And the cases where that WASN'T going to be true, it was OBVIOUSLY NOTICABLE, before the foam was even installed, that the foam was THICKER or MUCH STIFFER than stock.

In fact, the last time I had this problem, was over 3 years ago, with a certain batch of LE10 foam surrounds we got, and sent back because they were stamped too thick and stiff. They probably would have worked OK on a 2121 or 2122 (drivers that don't have to handle low bass), but they were inappropriate for LE10, LE111 or PR10 applications. After that, I've not got a single batch that would violate the +- 10% tolerance thing above...

Also, the modern foam (that made in the last few years), is an improved composition... made from, for the most part, a polyether-based material rather than the old polyurethane-based foam. The new foam is MUCH LESS vulnerable to air-borne attack (bacteria, humidity, heat, etc) and therefore will dry rot at a MUCH LOWER rate than the old stuff. So, modern foam surrounds, at least according to the "scientists", should last significantly longer than the stuff we were using 10 years ago.

So, it's MUCH MORE the GEOMETRY and MATERIAL PROPERTIES of foam vs. fabric, than it is any variation in foam stiffness or the life-span of a foam surround, that most people should be worrying about. Those geometric and material properties are what's going to make the SIGNIFICANT difference in the performance of the driver...

Regards,
Gordon.


:applaud:GREAT!!!! Now we're talkin'....this is exactly what I was looking for!

Gordon....Thanks for your input.

"FRANKENWOOFER'S"....gotta love it!

[4313B]

http://www.lansingheritage.org/html/jbl/reference/notes/tech1-3a.htm

[spkrman57]

Giskard,
Is there a authorized reconer/refoamer in the central to northern part of Ohio that you would recommend.

You can PM me the info also if you would like.

Ron

[Mr. Widget]

So, it's MUCH MORE the GEOMETRY and MATERIAL PROPERTIES of foam vs. fabric, than it is any variation in foam stiffness or the life-span of a foam surround, that most people should be worrying about. Those geometric and material properties are what's going to make the SIGNIFICANT difference in the performance of the driver...



Gordon, glad to see you weigh in here... I was surprised you hadn't popped in earlier... then when you did it was to chat about cars! Not that cars are bad mind you, but you seem to have the greatest experience with Frankenwoofers, so I thought you could shed some light on the subject.

I have a question that is probably more for old timers but you might have some experience here. When this thread first popped up I grabbed a book I have that I remembered comparing cloth surrounds with foam rolled surrounds. Hi-Fi Loudspeakers and Enclosures by Abraham B. Cohen... well as it turned out this book written in 1956 and my copy from 1968 wasn't comparing cloth accordion surrounds with foam half roll surrounds... they were cloth half roll surrounds! Specifically those developed by AR in their early acoustic suspension designs... for the most part the comparison was the same as pleated cloth vs. foam, but the question is, Why did EVERYONE go to foam and stop using a rolled cloth surround? The geometry is the same, but the foam must be better at centering or something...

Widget

[Mr. Widget]

- I don't think there'll be much of any sort of enlightening discussion ( on this subject of cloth vs foam ) until you fess up and publish the newly acquired Fs for your cloth surrounded 136H woofers .

Excellent point. I meant to ask Belaire myself. You own a speaker tester... so what does it say? Factory stock 16Hz? NOT!

But seriously what is the new Fs?

Widget

[4313B]

Giskard,
Is there a authorized reconer/refoamer in the central to northern part of Ohio that you would recommend.

You can PM me the info also if you would like.

RonI don't know of anyone. Sorry.

[Don McRitchie]

Why did EVERYONE go to foam and stop using a rolled cloth surround?

I don't know if the following was universal, but this is what was described to me by an Altec engineer about the 411-8A that originally used a cloth roll surround. When the driver was pushed hard, the cloth surround deformed from its normal half roll shape. As these deformations were streched out, it would cause an audible crackling sound since the material was inelastic. The driver was re-engineered with a foam half roll surround and the problem went away.

[Ian Mackenzie]

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

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? :blink:

A couple of text references I have discussed the merits of different surround materials, I am happy to scan and email to you, just pm your details.

However I would be more interested to pursue why this happened and over what period.

From you avator I assume you on the on Gold Coast Aust.
In areas like this high humidity and salt air will rot foam more quickly. I imagine this is similar to Florida and New Orleans.

It may be simpler to correctly air condition the listening room. A very humid climate with heat and other air contaminants is not going to help any speaker system. The acoustic properties are also subject change under such conditions.

Another alternative maybe to consider a soa driver like the JBL 1500AL assuming it is available.

Ian

[GordonW]

I don't know if the following was universal, but this is what was described to me by an Altec engineer about the 411-8A that originally used a cloth roll surround. When the driver was pushed hard, the cloth surround deformed from its normal half roll shape. As these deformations were streched out, it would cause an audible crackling sound since the material was inelastic. The driver was re-engineered with a foam half roll surround and the problem went away.


... and there you have it. Same thing I've observed... a variation on the "oil-can" effect I mentioned earlier. You NEED an elastic material...

Regards,
Gordon.

[Ian Mackenzie]

I have found a great reference on surrounds, here it is:

Ian

[57BELAIRE]

Whew! This outpouring of expertise is mindboggling...

Giskard: thanks so much for that tech bulletin (1-3A). It appears that the double half-roll cloth surrounds that I installed on my 136H 's may not have been the optimum choice after all. Fascinating reading!

There was an interesting section ( Producers vs. Reproducers) which explained the differences in musical instrument (E130) and sound reinforcement (2220) transducers....I learned a long time ago the two are mutually exclusive and this spelled it out.

Widget brought up an excellent point regarding the half-roll cloth surrounds that were used in early acoustic suspension designs (AR, KLH).
These were noted for their neutral characteristics and extremely long excursion....have these gone the way of the dinosaur?

Ian...you're close...actually, the Gold Coast I'm refering to is S.Fl. not Aus. but similar in climate...hot and humid.

All in all, some great info and kudos to all for staying with this rather mundane subject :applaud:

[4313B]

Whew! This outpouring of expertise is mindboggling...Sometimes you just have to shake the trees and rustle the bushes.

[JuniorJBL]

This does not apply directly to this thread but does explain some of the problems with surrounds

"With cone diaphragms, the outer surround can be a major cause of problems. Its primary purpose is to maintain an air seal and help keep the voice coil aligned in the narrow magnet gap as the cone moves back and forth. It must be flexible enough to cope with the maximum required movement of the cone. However, this very flexibility is the reason why the surround doesn't always follow the movement of the cone in a coherent manner. Problems start to occur at the so-called surround dip frequency, where the surround begins to move in the opposite direction to the cone and partially cancels its output. There are various design tricks that enable you to smooth out this effect to some extent, but it would be nice to avoid it altogether."
More reading here:

http://www.bwspeakers.com/index.cfm/fuseaction/products.techfeatures/ObjectID/3808A556%2D3AB8%2D11D4%2DA67F00D0B7473B37