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Old 26th June 2008, 05:42 PM   #11
Wizard of Kelts
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The above applied to linear Xmax. That's the distance the cone travels before distortion levels get high-generally 5% or 10% is the standard.

But others have pointed out that there is another type of Xmax-the distance a cone travels before the speaker becomes damaged. This is somewhat greater than the linear Xmax. This stat is variously given as X damage, or Xsus, (for suspension limit), or Xmech, (for mechanical limit).

In normal woofers, Xmech is normally about 50% longer than the linear Xmax. So a home woofer with a linear Xmax of 6mm will likely have an Xmech of 9mm.

In PA speakers, the Xmech is normally much, much greater than linear Xmax. If the linear Xmax of a 15 inch PA speaker is 5mm, you can count on the Xmech being at least 12mm, and very often it will a full inch, (25mm). Happily, most PA manufacturers give you the Xmech in the stats, so you know what the limits are when you buy the speaker. They may call it X damage or whatever, but the mm at which damage occurs usually is listed.
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Old 23rd July 2008, 07:46 AM   #12
ente is offline ente  Germany
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Default Xmax

... the geometric calculation is sometimes a little optimistic

Have a look on this:

http://www.fesb.hr/~mateljan/arta/Ap...8-EngRev01.pdf

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Old 2nd August 2008, 09:02 PM   #13
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Their is only one professionally accepted definition of Xmax. Period. Other standards have been proposed, but none have gained any wide spread acceptance.

It is, as quoted above, Xmax=(top plate thickness-VC winding height)/2

If you find a driver manufacturer using double this value. Run. Don't touch their stuff. They are probably making up other specs and/or fabricating measurements also.

Regarding grille cloth to surround clearance, there are some other things you need to consider. When the driver starts moving at high excursion, the air movement will start to move the grille cloth also. If their is anything underneath the grille cloth (usually the frame) that the cloth can hit, it will make twacking noises bouncing against it.

If the grille cloth is not tensioned enough, its motion can become out of phase with the woofer motion and hit the surround also.
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