Hi,
I have couple set of drivers without specs. I like to know if anyone knows how to measurement Xmax as it is usually given by the manufacturers. I understand it is the distance traveled by the cone to the max of it's range. But how exactly one is to measure it? The Linkwitz website suggested a method but did not elaborate. For example how do you drive the speaker to it's maximum level so that one can measure how far the cone is to travel?
Peter
I have couple set of drivers without specs. I like to know if anyone knows how to measurement Xmax as it is usually given by the manufacturers. I understand it is the distance traveled by the cone to the max of it's range. But how exactly one is to measure it? The Linkwitz website suggested a method but did not elaborate. For example how do you drive the speaker to it's maximum level so that one can measure how far the cone is to travel?
Peter
I think you are refering to X-suspension. The full possible travel of the cone.
In measureing X-max it is a rather well thought out idea. X-max is the height of the voicecoil minus the thickness of the top plate divided by two. That measurement will get you the classic Thiele/Small definition of X-max. Without a spec sheet it is possible to make an informrd guess. It requires a good light source and you looking at the driver through the spider. Move the cone back and forth and try to add up the length of the viocecoil winding. Alternately you could count the number of windings and figure it out that way. THe top plate thickness is easy. Just measure it!
Hope this helps!
Mark
In measureing X-max it is a rather well thought out idea. X-max is the height of the voicecoil minus the thickness of the top plate divided by two. That measurement will get you the classic Thiele/Small definition of X-max. Without a spec sheet it is possible to make an informrd guess. It requires a good light source and you looking at the driver through the spider. Move the cone back and forth and try to add up the length of the viocecoil winding. Alternately you could count the number of windings and figure it out that way. THe top plate thickness is easy. Just measure it!
Hope this helps!
Mark
No, he is suggesting you look at the coil through the spider using a strong light. Sometimes this is possible and sometimes it is not.
Another way to arrive at a useful xmax number is to measure distortion while increasing the drive signal to the speaker. Use a wedge micrometer (as Linkwitz describes) to determine what the excursion is at your chosen distortion. 10% THD is usually a good place to start if the THD is mostly low order (2nd and 3rd harmonics). On overhung coils (most woofers and midranges), that usually correlates fairly well to an xmax value calculated from the coil overhang.
Another way to arrive at a useful xmax number is to measure distortion while increasing the drive signal to the speaker. Use a wedge micrometer (as Linkwitz describes) to determine what the excursion is at your chosen distortion. 10% THD is usually a good place to start if the THD is mostly low order (2nd and 3rd harmonics). On overhung coils (most woofers and midranges), that usually correlates fairly well to an xmax value calculated from the coil overhang.
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