The issue with this is that when you run a "parameter test" once a speaker is installed in
a box, the software doesn't know that the 1st impedance peak is not a raw-driver's Fs (remember, Fs= free-air(!)
resonance)----and since it doesn't know, it still goes ahead uses that 1st peak to calculate what it thinks
is the driver's free-air resonance, and spits out the results without alerting you that the driver is not really suspended in free-air.
But it is flawed because there is no Fs
once a driver is enclosed. There is nothing "free air" about a driver "enclosed"---a kind of oxymoron. The reason for this is that once a driver is enclosed it now forms one
driven resonant system with the enclosure and vent, that are now inseparable from each other. This goes back to University Physics 101 with the studies of a driven damped double-mass double-spring harmonic oscillator.
This is why a vented enclosure's primary system is called Fb
, not Fs (similarly for a sealed box, the system resonance is Fc). Rest assured, the primary system resonance (Fb, or "port tuning" as it is known) for that enclosure you posted is just slightly below 40Hz, right where the impedance dip is.