I colect and fix speakers and amps vintage and new have lots of speakers at home RUBBER is the way to go because it does not like to rot, but I do have a pair of Realistic Mach One's they have foam surrounds from the 70's the foam is just started to show the signs of rotting last year nothing much because they are really thick, but I got some stuff from canadian tire it's a handy thing called " GOOP " (the auto goop works the best) but not to good if the surrounds already rotted really bad but if you get it at an earily stage it works pretty good 
hope i helped some of you
Jake
hope i helped some of youJake
Foam vs Rubber in high-end sound - u may b surprised!
A speaker surround is more than just a gasket, it has a big effect on a driver's T/S parameters, and is therefore an important part of how the speaker performs overall. I would imagine that speakers with foam surrounds tend to have a lower Qms and are likely to sound better than equivalent speakers with rubber surrounds for other reasons too. The Qms is a simplified representation of how well/badly the speaker's cone is damped when it's not plugged in. There are usually 3 other methods used for damping a vibrating cone:
1)An electrically damped voice-coil (plugged into an amp or short-circuited),
2)A metal voice-coil former,
3)The spider.
Notice that all 3 are near the middle of the cone, but damping around the edge solely relies on the rubber/foam surround? It affects a lot more than just the theoretical f.r. of the speaker. It affects midrange colourations and distortion too.
Just what do we want from a speaker's surround?
It makes sense for the surround to be soft and acoustically absorbant, to damp mechanical resonances and overshoot. Most resonances occur above the speaker's optimal frequency range and we want to absorb those as much as possible. At low frequencies however, we only want the surround to "tune" the speaker's Qms and not do much else. Obviously it also has to be an effective gasket. And we don't want it to be problematic by adding a variable mass to the cone, creating resonances by having an inertia that's different from the rest of the cone, or changing the Vas in a non-linear way...
So how do foam and rubber compare?
Rubber is usually quite dense compared with most speaker-cones, and therefore its mass allows only poor compromises. Either the surround is very thin, and has low absorption and may leak sound pressure from behind, or it's too heavy and reflects vibrations and makes resonances worse. A foam surround can be relatively thick and absorbant, and have have an inertia that's equalized with the cone's inertia. A rubber surround behaves a bit like a spring: it may appear soft and flexible but due to its low damping coefficient, stretch or compress it and it will bounce right back. Therefore its absorbant properties are relatively poor and not good for absorbing cone resonances at high frequencies.
Foam has very good absorbant properties because it has the unfair advantage of not being entirely a solid. Unlike solids, the tiny gas bubbles in foam are easily compressed/expanded, and as that happens the temperature difference is immediately equalized with the "solid" part of the foam. This makes foam almost "malleable" and it won't reflect as much of the energy that's directed at it, but instead the vibrations are absorbed and turned into heat.
I can only conclude that the only reason rubber is more popular as a surround material is because its far superior longevity that others have mentioned. If foam lasted longer, its use would be a lot more widespread.
CM
A speaker surround is more than just a gasket, it has a big effect on a driver's T/S parameters, and is therefore an important part of how the speaker performs overall. I would imagine that speakers with foam surrounds tend to have a lower Qms and are likely to sound better than equivalent speakers with rubber surrounds for other reasons too. The Qms is a simplified representation of how well/badly the speaker's cone is damped when it's not plugged in. There are usually 3 other methods used for damping a vibrating cone:
1)An electrically damped voice-coil (plugged into an amp or short-circuited),
2)A metal voice-coil former,
3)The spider.
Notice that all 3 are near the middle of the cone, but damping around the edge solely relies on the rubber/foam surround? It affects a lot more than just the theoretical f.r. of the speaker. It affects midrange colourations and distortion too.
Just what do we want from a speaker's surround?
It makes sense for the surround to be soft and acoustically absorbant, to damp mechanical resonances and overshoot. Most resonances occur above the speaker's optimal frequency range and we want to absorb those as much as possible. At low frequencies however, we only want the surround to "tune" the speaker's Qms and not do much else. Obviously it also has to be an effective gasket. And we don't want it to be problematic by adding a variable mass to the cone, creating resonances by having an inertia that's different from the rest of the cone, or changing the Vas in a non-linear way...
So how do foam and rubber compare?
Rubber is usually quite dense compared with most speaker-cones, and therefore its mass allows only poor compromises. Either the surround is very thin, and has low absorption and may leak sound pressure from behind, or it's too heavy and reflects vibrations and makes resonances worse. A foam surround can be relatively thick and absorbant, and have have an inertia that's equalized with the cone's inertia. A rubber surround behaves a bit like a spring: it may appear soft and flexible but due to its low damping coefficient, stretch or compress it and it will bounce right back. Therefore its absorbant properties are relatively poor and not good for absorbing cone resonances at high frequencies.
Foam has very good absorbant properties because it has the unfair advantage of not being entirely a solid. Unlike solids, the tiny gas bubbles in foam are easily compressed/expanded, and as that happens the temperature difference is immediately equalized with the "solid" part of the foam. This makes foam almost "malleable" and it won't reflect as much of the energy that's directed at it, but instead the vibrations are absorbed and turned into heat.
I can only conclude that the only reason rubber is more popular as a surround material is because its far superior longevity that others have mentioned. If foam lasted longer, its use would be a lot more widespread.
CM
hi
i am a transducer design engineer and have been moulding my own rubber surrounds in various shapes and sizes for quite a few years
i have moulds for foam surround s too in various densities
rubber
initially in this thread there was mention of 1970 s woofers rubber surround which are yet intact
well
natural rubber has a very long life
the models in which the surround has deteriated they will be 90 % synthetic based rubber surround
natural rubber - low loss rubber surrounds are the best and are used by the top companys (also the most expensive) as reflected in the $ 600 above spks
all audiobahn produts are exterme engineered
the compond for a surround material is speacially prepaired and it has no elastic properties they are formed / cured and remain that way , they are not springs or rubber bands
to explain this , industry depends on rubber o - rings if they start behaving like rubber bands we will have no power and diy audio will be history !
they may elongate when you pull it with force , so will foam _ and my foams do more than rubber
while a rubber is moulded various chemicals are mixed including some for easy handling / forming _ which has nothing to do with the surround _ is a catalyst to the process of moulding , cheaper the speaker more likely to be have been through a fast manufacturing process , therby indicating lesser life
plus they mort probably will be synthetic based
suranjan
transducer design engineer
i am a transducer design engineer and have been moulding my own rubber surrounds in various shapes and sizes for quite a few years
i have moulds for foam surround s too in various densities
rubber
initially in this thread there was mention of 1970 s woofers rubber surround which are yet intact
well
natural rubber has a very long life
the models in which the surround has deteriated they will be 90 % synthetic based rubber surround
natural rubber - low loss rubber surrounds are the best and are used by the top companys (also the most expensive) as reflected in the $ 600 above spks
all audiobahn produts are exterme engineered
the compond for a surround material is speacially prepaired and it has no elastic properties they are formed / cured and remain that way , they are not springs or rubber bands
to explain this , industry depends on rubber o - rings if they start behaving like rubber bands we will have no power and diy audio will be history !
they may elongate when you pull it with force , so will foam _ and my foams do more than rubber
while a rubber is moulded various chemicals are mixed including some for easy handling / forming _ which has nothing to do with the surround _ is a catalyst to the process of moulding , cheaper the speaker more likely to be have been through a fast manufacturing process , therby indicating lesser life
plus they mort probably will be synthetic based
suranjan
transducer design engineer
Have transducer engineers done much experimentation with multilayer surrounds? It seems to me that you could do a sandwich of several materials to provide a barrier to the degrading atmospheric gases or to tune the mechanical properties. For example, if you have a coextruded or laminated sheet with a thin layer of Saran, a thicker layer of a foam, and another thin layer of Saran, then thermoform it to make the surround, you could greatly extend the foam's life. Or have a layer which provides springiness sandwiched by layers which provide damping...
I recently treated some foam surrounds that were about to fall apart. They had gone soft, and were compressible, and would have disintegrated, had I not treated them.
What I did was to carefully coat them with some self-levelling (flowable) silicone, which I applied with an artist's paint brush. Reckon I saved my father-in-law the cost of replacing those surrounds...
The treatmrent did not cause a noticeable difference in sound quality.
What I did was to carefully coat them with some self-levelling (flowable) silicone, which I applied with an artist's paint brush. Reckon I saved my father-in-law the cost of replacing those surrounds...
The treatmrent did not cause a noticeable difference in sound quality.
Modern foam surrounds are quite durable. We've got Shivas in operation in SE Asia (Singapore) for over 6 years now without a problem.
Any more, durability isn't an issue, as long as it's a good quality foam (likewise with rubber). Because foam has a lot of distinct advantages over rubber (mass versus thickness, compliance versus temperature, termination) you'll see it used more and more.
Dan Wiggins
Adire Audio
Any more, durability isn't an issue, as long as it's a good quality foam (likewise with rubber). Because foam has a lot of distinct advantages over rubber (mass versus thickness, compliance versus temperature, termination) you'll see it used more and more.
Dan Wiggins
Adire Audio
Speaker Surrounds
I had to replace the surrounds on my Scan Speak drivers just recently and I found Speakerbits http://www.speakerbits.com/devdefault.aspx extremely helpful. Tom Manning is well qualified to give you all the advice you need.
I had to replace the surrounds on my Scan Speak drivers just recently and I found Speakerbits http://www.speakerbits.com/devdefault.aspx extremely helpful. Tom Manning is well qualified to give you all the advice you need.
DanWiggins said:
I don't know about "any more", but it seems to me the foam surounds used even in the seventies lasted the speakers 10 years or so.
I know people who had their Advents, etc that long and the foam didn't shred for even longer than that.
Watch, now I am going to get a string of horror stories from people whose foam surrounds went bad after 3 years.
Frankly, I prefer the rubber because they seem to last forever. but it seems to me that the problem with foam that I have been reading here seems overstated. Perhaps these people live in an area where the atmospheric conditions just seem to rot them quicker. I know of one person who lived near the shore in Connecticut who bought a pair of good speakers whose voice coils kept rotting after a few months because of the salt air. After several replacements, the dealer had to give him his money back.
Actually, Saran resins are polyvinylidene dichloride, somewhat different than PVC. Their main virtue is fabulous barrier properties- they just don't let anything diffuse through. The disadvantage is that sometimes a tie layer is required to bond them properly to another polymer. But that's all pretty well worked out stuff; people have been using PVDC as a barrier layer in multiple layer structures for many decades.
No, the resins are the raw polymer, usually supplied in pellets or powder. There is one powder grade that's soluble in some organic solvents (Dow F-310; I use it as a base for my ESL coating goop), but suitable solvents will also eat through most surround materials. Normally, Saran is melt-processed using some pretty fancy equipment. A speaker manufacturer would go to one of the companies that produce laminated or coextruded structures, specify the sandwich construction, take the sheets and thermoform them, then die-cut. Not exactly diy stuff.
Pure Saran polymer wouldn't make a very good surround by itself- you want something more amorphous and elastomeric. But as outer layers on an elastomer, the Saran can provide very effective barrier.
Pure Saran polymer wouldn't make a very good surround by itself- you want something more amorphous and elastomeric. But as outer layers on an elastomer, the Saran can provide very effective barrier.
reply
Well talking about foam and rubber surrounds:
My mum has a pair of wharfedale hifi speakers with 12 inch bass and 2 inch purple mylar cone tweeter.And the rubber surround on the 50 yr wharfedales with alnico magnet [made from a kit] are still fine,not rot yet!!!
And I've got 2 crappy car subwoofers laying around which were too poorly made to use in my car[Tornado and Fury] and they are 8 years old now and no foam rot yet.
So I think where it's used plays a part how long the surround lasts.UV and direct sunlight is a cone and surround killer,and so is moisture for foam surrounds.
Well talking about foam and rubber surrounds:
My mum has a pair of wharfedale hifi speakers with 12 inch bass and 2 inch purple mylar cone tweeter.And the rubber surround on the 50 yr wharfedales with alnico magnet [made from a kit] are still fine,not rot yet!!!
And I've got 2 crappy car subwoofers laying around which were too poorly made to use in my car[Tornado and Fury] and they are 8 years old now and no foam rot yet.
So I think where it's used plays a part how long the surround lasts.UV and direct sunlight is a cone and surround killer,and so is moisture for foam surrounds.
hi sy
could you please let me know the protective coating is most effective when used on thermo formed surrounds
orsurrounds which have been made from thermo formed foam sheets which have been heat pressed to form surrounds
as far as my experience goes heat pressed surrounds tend to last a lot longer _
though these will not be as accoustically dead and may be not uniform unless u ve got the densities the thickness of the sheet and heat to be pressed all worked out
i would be obliged if dan wiggens could shed some light here too
thanks
suranjan
could you please let me know the protective coating is most effective when used on thermo formed surrounds
orsurrounds which have been made from thermo formed foam sheets which have been heat pressed to form surrounds
as far as my experience goes heat pressed surrounds tend to last a lot longer _
though these will not be as accoustically dead and may be not uniform unless u ve got the densities the thickness of the sheet and heat to be pressed all worked out
i would be obliged if dan wiggens could shed some light here too
thanks
suranjan
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