spots at the back of a woofer paper cone?

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daemonsgr

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Joined 2014
#1
Hi,

One of the JBL woofers has some extra material on the back of the paper cone.
Is this common or a manufacturing problem?
I can send it back if needed.

Thanks
 

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#2
I would regard this as normal and part of the coating process applied to the rear of the cone.

This old Bose woofer coating looks even lumpier. Perhaps it helps break up cone resonances!
 

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#4
You're most welcome. Maybe they were scraping the bottom of their 'paint' pot!

I certainly wouldn't go to the trouble of returning the driver - more chance of heavy drivers being compromised through transit damage.
 
#5
All my JBLs (2206 and 2226) have that as well and also my Beyma 15LX60v2s (of which I suspect, that they have cones from the same manufacturer).
I would say that this is coming from the process used to manufacture these cones. They are not made by cupping some wet sheets of paper into shape but rather by a process like the one that is used for hand paper making with a paper/glassfiber slurry and a fine mesh. Maybe someone whose mother-tongue is english might properly describe it. But you can rest assured that it is basically a sign of quality.

Regards

Charles
 
#8
Those are a completely normal part of the cone making process.

Some driver companies purposely do similar things to help with rigidity and resonance control.

Just take a look at the highly regarded SB Acoustics Satori papyrus mid.

mw16p-4--1.jpg
 
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