Together with other parameters, VAS at some part dictates some range of net volume for a meaningful design.
I'd call it medium, some 12" drivers have lower number for VAS while other ones have some more of it.
Within meaningful net volume for a given driver, larger cabs will produce larger cone movement in the range of ~50..100Hz while for smaller cabs (same driver) the cone movement wil be reduced.
Larger cabs - lowish tuning
Smaller cabs - highish tuning
Besides Cms paramter (the compliance) and Bl (the motor strength) the essential thing that largely effects cone movement (in the range of ~50..100Hz) does simultaneously relate to radiation impedance and Fb for the Helmholtz resonator.
Radiation impedance is determined by cone surface in first instance, and second by frequency. Radiation impedance goes down when frequency goes down, thus producing rather highish cone movements at the low end side of the bandwidth.
The Helmholtz resonator helps to improve total radiation impedance of the cab system where radiation impedance of alone the driver is already down.
The larger the cab volume then the lower the tuning within the range of a "meaningfull" cab design will be. Once Fb goes down then the "enlarged gap" between Fb and still good radiation impedance of the driver cone surface (above ~200Hz) will result in an noticeable enlarged cone movement in the range roughly ~50..100Hz.
But not every driver is just the same, and there is no general statement valid in this regard.
For just the same cab volume and tuning, some drivers may perform some more of cone movement while others may perform noticeable less of it, at just the same input power provided to the cab.
Modelling for cone movement for two different drivers at just the same cab volume and same tuning, and similar F3 points.
View attachment 4771542
I strongly suggest to clearly distinguish between total group delay and normalized group delay numbers.
A group delay number that is equal to 10msec. at 50Hz may have just the same meaning as a group delay that is equal to 5msec. at 100Hz.
The normalized group delay was just the same on both 50Hz and 100Hz.
Thus, a larger group delay number does not automatically mean an increase of normalized group delay!
Modelling of group delay for the same two different (as above) drivers at same cab volume and tuning
View attachment 4771548
Rather than pure cab volume and tuning numbers it's the loaded driver in interrelationship WITH the cab design (volume and tuning) that determines the (normalized) number of group delay.
Furthermore most of all DIY guys do totally mismatch group delay with pure time related "delays". IMO that's totally missing the point.
Although group delay at some content may have a slightly similar effect to the signal such as pure "delay", yet its not the same, at least as long as there was no modulated "signal group" distributed to the (HPF filter-)system.
However, the amount of group delay may tell something about the damping of the cab system.
highish group delay - underdamped
lowish group delay - overdamped
For a "desireable" critical damped property you may figure the group delay somewhere in the middle of highish and lowish.
Thus, some group delay isn't all that bad as it may look alike (to some DIY folks)!
The suggestion I did above for 212 with 12PR320 was done with lots of care, even with lots of respect to group delay and its directly relating damping property for the cab system.
It depends cause a group delay equal to 10msec. may provide the same normalized group delay as a group delay that was equal to 8msec.
Both cabs might provide just the same "filter alignment" and therefore just the same damping characteristic, therefore just the same "percussive punch".
As usual, it all depends! Probably it depends rather on "knowledgement" than really on total group delay numbers
As I told above, some peaking isn't as bad and "boomy" as some DIY folks frequently try to discuss.
Its hard to believe that Bill might ever have told these words.
I'm pretty sure he knows better
If any, I couldn't even tell what was the right damping assumption, and as well there may arise other unwanted effects if too much of damping material does affect internal functionality of the port.
