So I finally have the DATS v3 to measure my custom made field coil full range driver. And most of it is ok, but I get a way too high Vas. My guess is that it has to do with the phase plug that doesn't move, while a dust cap does. So entering the diameter the usual way, might overestimate the Vas. And using the Vas that I have now in WinISD results in hideously huge boxes. How to correct for this?
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If you can share the measured TSPs and the enclosure type it might help point to a solution.
Vas is a product of the suspension compliance (Cms) and radiator surface area (Sd), and two constants. Depending on how leaky the phase plug is, it mostly impacts the mechanical damping (Rms). You didn’t mention the driver size nor the phase plug size, assuming the driver is large (from the large Vas) and the phase plug is small, the surface area difference may be negligible.
Cms is combined surround and spider compliances- typically the spider is much stiffer and dominates the overall compliance (think of two springs connected in parallel and one is much stiffer than the other). If you want a smaller Vas you would need to stiffen the spider (lower compliance) but this would also increase the resonance frequency.
Vas is a product of the suspension compliance (Cms) and radiator surface area (Sd), and two constants. Depending on how leaky the phase plug is, it mostly impacts the mechanical damping (Rms). You didn’t mention the driver size nor the phase plug size, assuming the driver is large (from the large Vas) and the phase plug is small, the surface area difference may be negligible.
Cms is combined surround and spider compliances- typically the spider is much stiffer and dominates the overall compliance (think of two springs connected in parallel and one is much stiffer than the other). If you want a smaller Vas you would need to stiffen the spider (lower compliance) but this would also increase the resonance frequency.
