What is the best way to MEASURE speaker displacement?

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What is the best way to MEASURE speaker displacement, i,e volume occupied by speaker inside a box, including cone, magnet, structure etc? I've found a number of 'caculators' and ways to estimate this, but what amount empirical measurements?

- Saran wrap and amount of water displacement?

- How about using a VAS box with the magnet inside, instead of out as would normally be done for the VAS measurement?

- Something else?
 
Odd shape is difficult to measure.

I don't recommend trying to Saran wrap your driver and then playing Archimedes.

Most people are satisfied calculating the cone volume using the formula for a truncated cone, and adding in the magnet volume, which is more or less a cylinder for most woofers.

You don't need to be all that exact. Almost everything about a driver's alignment is subject to variation by temperature (voice coil and ambient) as well as cone excursion so getting the box volume calculated to within +/- 10% is more than good enough (assuming that is why you want to know the driver volume).

If your question pertains specifically to measuring the driver to determine Vas from a resonance change when mounted in a box of known volume, perhaps you should consider the added mass method instead. There is no need to know the driver volume when doing it that way.
 
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