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Rubber Surrounds Hardening With Age
Rubber Surrounds Hardening With Age
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Old 10th January 2006, 01:45 PM   #1
PB2 is offline PB2  United States
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Default Rubber Surrounds Hardening With Age

I posted this in another thread, and this is a new thread to discuss measurements:
http://www.diyaudio.com/forums/showt...threadid=57435

Just so happens that most of my better speaker systems have drivers with rubber surrounds. 2 different 10" drivers in commercial systems seem to have become very stiff, one system is over 15 years old the other over 10, both bought used. I measured Fs of one driver and it was close to 50 Hz, 49 IIRC which indicates that the suspension is more than 3 times stiffer than it should be.

Pete B.
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Old 10th January 2006, 01:54 PM   #2
PB2 is offline PB2  United States
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Default KEF B139 Measurements Manufactured in 1975 - Measured in 2006

I pulled out a used pair of KEF B139s (SP1044) from storage with manufacturing dates from 1975 and measured the T&S parameters.
The compliance is 60% of the advertised parameter supplied by KEF. This is better than what I'm seeing in US manufactured drivers, but still a significant change. It's possible that different types of rubber materials were used.

I do not have measurements from ~1979 when I got them, they've been in storage since then. I don't recall if Linkwitz's SB article has measurements of B139s or not, but it would be good to get some older data as a reference:
(tables loose formating here on the forum, am I missing something?)

KEF B139-SP1044 UNIT SAMPLE: PLB#1 1/10/06
UNIT DATE: 28-Apr-1975
KEF
Delta M 15.75 Spec
Fshift -14%
Fs 32.6 25
Vas 98.1 164
Re 6.52 6.2
Qe .52 .4
Qm 4.6 5.5
Mms 42.8 43.5
no .63
SPLref 90.0 (half space) 84 (full space)
Bl 10.5 12.3
Qts .46 .37
Cms .56 .93 (calculated)
Compliance error compared to spec = .56/.93 = .6

================================================== ======================

KEF B139-SP1044 UNIT SAMPLE: PLB#2 1/10/06
UNIT DATE: 7-May-1975
KEF
Delta M 15.75 Spec
Fshift -14%
Fs 31.3 25
Vas 101 164
Re 6.2 6.2
Qe .48 .4
Qm 4.2 5.5
Mms 45.0 43.5
no .63
SPLref 90.0 (half space) 84 (full space)
Bl 10.7 12.3
Qts .43 .37
Cms .58 .93 (calculated)
Compliance error compared to spec = .58/.93 = .6
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Old 10th January 2006, 04:03 PM   #3
inertial is offline inertial  Italy
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Hi PB2,
I have a pair of Focal 8K515 since 1992. Measured Fs was 30-31Hz.
Today, with the same temperature they are Fs= 50Hz !!!!

Another wf, the seas P17RCY declared 37Hz if I well remember, today
is 68 Hz !!!( at 22 celsius)

And the correct bass-alignement with perfect data.........
Indeed fun, don't you know?
Cheers,
inertial
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Old 10th January 2006, 04:26 PM   #4
Joseph Hynes is offline Joseph Hynes  Denmark
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There are a number of detrimental things which happen to polymers with age (and rubber surrounds are polymers also --elastomers).
1
The substance slowly continues to polymerize. Molecules grow larger, connect to each other, and cross-link. this increases the hardness and reduces elasticity. It also leads to shrinking and cracking.

2.
The polymer begins to de-polymerize. Longer molecules break up into smaller ones, again, leading to a degradation of physical properties.

3.
Oxydation. Oxygen permeates the polymer and reacts with some of its molecules resulting in an oxydized product. This product has a higher molecular weight (by incorporating the oxygen atom), and is less elastic.

4.
Microorganisms
Bacteria grow especially well on surfaces, better on porous surfaces. Humidity can allow microbes of all kinds to form a microenvironment in the porous rubber substance, where they may release acids (their waste products), just like they do in your mouth, causing cavities. The acids can slowli degrade the physical properties of the rubber surround.

The above may not be a complete list of the things that happen to a polymer speaker suspension, but there are some steps to reduce or prevent damage.

1.
Avoid exposue to light, especially fluorescent light and daylight. UV destroys ALL polymers effectively.

2.
Avoid temperature extremes, like 85 F summer and 15F winter. Keep speakers in the same living space where a person is comfortable.

3.
avoid high humidity.

4 spray the surrounds with a silicone-based conditioning product (like Armor All) to keep moisture and oxygen out of the rubber. Spray BOTH sides -- you have to get behind the speaker element.

I've started spraying after I've seen my expensive speakers from 1985 die from surrounds that started to crack and crumble.

Joseph Hynes
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Old 10th January 2006, 04:42 PM   #5
inertial is offline inertial  Italy
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Hi Joseph,
I have noted that also cloth-surround ( PRO-drivers) are more stiffer after many years.
I believe that with the right "painting" it can return like "news".
Could you indicate me a generic sostance to apply for the cloth?
Some people talking about silicone, but what type of it ( if it is important, perdone me I understand nada about chemistry).
Thanks advanced,
Inertial
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Old 10th January 2006, 05:06 PM   #6
PB2 is offline PB2  United States
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Thank you Joseph, very informative. Turns out my dad is also a chemical engineer and a retired polymer expert so I hear a lot of this talk. Do you know if silicone oil in general is as good as Armor All?

Any products that might help after the damage is done, I don't have any that are cracked and falling apart just loosing their compliance.

I'd like to ask, if you don't mind what brand drivers those are with surrounds that cracked. I'll try to find out what type of rubber was used.

Thanks again,
Pete B.

Quote:
Originally posted by Joseph Hynes
There are a number of detrimental things which happen to polymers with age (and rubber surrounds are polymers also --elastomers).

....

I've started spraying after I've seen my expensive speakers from 1985 die from surrounds that started to crack and crumble.


Joseph Hynes
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Old 10th January 2006, 05:09 PM   #7
richie00boy is offline richie00boy  United Kingdom
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I don't know if you have the same stuff over there, but over here Armor All car trim spray is NOT silicone based, that's why it's one of the few things I let near my car.
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Old 10th January 2006, 05:13 PM   #8
Joseph Hynes is offline Joseph Hynes  Denmark
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I think every country has on the market some form of silicone spray.

The sprays for waterproofing boots in Northern Europe should work.

In the South, the sprays for conditioning leather shoes, handbags and furniture should have similar composition.

It's important to look for a product containing silicone, because this is a man-made material which lasts almost forever, and does not attract pests. Conditioning products not based on silicone often contain natural waxes and oils which have limited lifetime.

They must have some leather seats inside those Alfa-Romeos and Lamborghinis in Italy, Si? So there must exist products to condition and protect them.

Joseph
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Old 10th January 2006, 05:13 PM   #9
PB2 is offline PB2  United States
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Armor All has gotten some bad press but I don't know if the claims are valid. I wonder if it has additives that do more for the shiny look and take away from the preservative qualities or perhaps cause some damage, this is pure speculation on my part.

How about this product:
http://www.bhphotovideo.com/bnh/cont...goryNavigation

Pete B.


Quote:
Originally posted by richie00boy
I don't know if you have the same stuff over there, but over here Armor All car trim spray is NOT silicone based, that's why it's one of the few things I let near my car.
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Old 10th January 2006, 05:32 PM   #10
inertial is offline inertial  Italy
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Si Joseph, if you say.....I can go( with my Fiat 600)!
Thanks!
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