Best overall to use the added mass method. Don't know what amount DATS recommends, but the pioneers worked it out to a fare-thee-well and arrived at adding enough mass to decrease the measured driver's free air Fs by [at least] 1.56x, but not much more, though IIRC most folks just shoot for a > 1.25x, then use the formula [or one of the many worksheets available on-line] to find the driver's Vas if not automatically done. I assume the DATS does the other calculations such as efficiency, Mms, Mmd, etc., using Fs, Vas, Qes.
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If determined to work from SPL, then the math normally used is based on a 1 kHz mid-band efficiency to allow accurate comparisons between lows-mids-highs, which manufacturers don't necessarily follow for a variety of reasons, but what you should measure, i.e. don't rely on published n0! When I was actively designing, I vetted the published specs as much as I could using the various formulas and most T/S specs were way off, especially n0 and one reason why I always spec [very] large cabs to allow plenty of tuning flexibility. Best overall to just calculate it and if DATS does it, it will be interesting to see if they match: mh-audio.nl - Home
Mmd, etc., calculator: mh-audio.nl - TSP Calculator
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