I get asked alot if the "xmax" is as far as the speaker moves?..
No, the xmax rating is given at which point the driver is at a 30% loss of b/l.
If you don't know what bl is then feel free to use the search function, and read a little.
Thank you
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dont be a pet monkey ..use your dmm
This is another thing that goes by manufacturer a lot. Any good manufacturer will give you two numbers. A mechanical X-max (xmech) and a linear x-max. The linear is as you stated above 30% loss of b/l, or the real good manufacturers will show you a bl curve. I love to see bl curves that dont even come close to what a manufacturer claims. Cracks me up.
Xmech is really only useful in judging the spl of the sub though. Because after a driver goes below 70% of it's b/l it sounds like arse.
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fiberglass reminds me of peanut brittle... but fiberglass tastes better!
It is actually a little different than that. DUMAX, an independant large signal measurement system invented by David Clark, uses the lesser of 70% of BL or 400% of Kms (the inverse of Cms) as their Xmax rating. These points were selected because they represent the point where each produces around 10% THD. There are a few companies that use this standard to rate their speakers Xmax. But the more common practice is to rate the driver based on top plate and coil length measurements. That isn't very accurate though as it ignores the stray flux in the motor. Others, like Eclipse, use an Xmech rating.
Also note that another popular independant large signal measurement system, the Klippel machine, defines Xmax at the point when both the BL and Kms plots are producing 10% THD. Generally this measurement system produces lower Xmax numbers than the DUMAX machine.