I ordered a pair of the 2216nd woofers for my new build (2way vented cabinet with a horn tweeter). They finally arrived.

For the bass bin, two obvious candidates to model are the M2 and s-4700, since they are both vented designs and use the same 2216nd woofer.

So far my reading has uncovered the s-4700 is a 4.8 cu ft (135 liter) cabinet with a vent tuned at 32 Hz (shown in the EDS sheet posted elsewhere).

The specifics on the M2 are more elusive. It looks like the cabinet is about 10% larger (perhaps 5.2 cu ft). Folks have suggested the vent tuning might be in the mid-20 Hz region. This seems low since the free resonance of the woofer is either about 36 Hz or 39 Hz (I have seen both specs on the EDS sheet). However the comments about the vent tuning seem to be more speculative or second hand.

So my question is: has anyone measured the impedance in the region around the vent tuning (say 20-40Hz) with a RMS meter, power resistor and tone generator? Of course the DSP filters would need to set on bypass for the the measure to be meaningful.

It is actually fairly easy to measure, but requires access to an M2 cabinet which I do not have. Maybe someone has already made the measure.

Thanks for any assistance or reference.
-Tom