Driver Mechanical, Electrical and Total system Q

[JonJT 10+ year member]

VAS represents the Amount of air compressed in a specific space(one meter cubed) that is takes to equal the same stiffness that the diaphragm/soft parts comply at rest. larger spiders and cones have more surface area and present a higher VAS for the same CMS(greater efficiency). this is true because your larger drivers have more surface area, hence they can displace more air and have less stiffness per inch^2 against the moving parts at rest for equal CMS over smaller drivers...
simple explanation... take a tire. both same sized tires. one tire has 25PSI and the inner volume measured one cubic foot... the other has 30PSI and it also measures 1 cubic foot in volume... the tire with the lower VAS is simply the tire that has the higher PSI... why? because the amount of volume is equal(SD), but the compression of air is greater for that given surface area( lower Vas) there for the tire with the higher PSI lends to have a higher Quality or is HARDER to distort(lower CMS) from its original shape. now in woofers.....

when the woofer resonates its trying to have the correct amount of damping to have the most efficient movement possible with a given input and a given amount of airspace.. having too much stiffness(low vas) causes the driver to want to deceleration before optimal excursion limits are reached where as too soft or too high a VAS it doesn't have the ability to properly stop the mass to change direction..

did that help a bit?

Yes it does, I understand now. Thank you.

 

[JonJT 10+ year member]

The addition of the box amplifies the pressure air exurts on the cone for a given amount of excursion. its like adding more spring to the cone. this lowers compliance.
Looking at the equations for Qms and Qes and Qts, this has the effect of causing changing all three. Qms increase, Qes increases, and Qts increases.

Does this make sense? yes. The system has added more energy storage elements, but has not changed lossy elements. keep in mind that at resonance, where Q is defined, energy is efficiently transfered from compliance to inertia -- the mass of the cone and the compilance of the box/spider are in harmony so to say.

and as compliance drops due to the small box, the resonant frequency increases as well.

as for another example, lets say you pulled the cone outward to some arbitrary position. the cone will now have MORE potential energy due to the increased spring constnat. further, it requires more force to hold the cone outward, thus when released the spring will exurt more force on the same amount of mass, causing it to move to rest faster. because the spring has no potential energy when the cone is at rest, and because the the mass has a higher acceleration, it is clear that the cone will reach its rest point faster and with a higher velocity. Thus higher Fs is expected. without increased losses, the cone will tend to wobble for more cycles.

Thank you, I better understand the effect of box size on speaker Q now.