Subwoofer specifications? what do they mean? could someone please explain?

[thadman]

I'd like to know what the exact specifications of drivers exactly mean. I know VAS and QTS has something to do with if you should seal or port the subwoofer and FS equates to roughly how low it will go (lower FS the deeper the sub). Obv xmax has to do with excursion and xmech has to do with peak-peak excursion? Am I right? But what do all of the other specifications mean, there is a lot more to drivers than just watts and xmax.

What do these mean? In english...

Fs
Qms
Qes
Qts
Vas
Re
Le
Sd
BL
Xmax
Pmax4
SPL

[Worlddre]

http://www.diysubwoofers.org/define.htm

http://www.carstereo.com/help/Articles.cfm?id=6

[VereChronicus]

well you do have the xmax and xmech backwards sort of. xmax has nothing to do with excursion, it is nothing more than a measurement of coil overhang. you can have an xmax of 59mm and the cone and coil mounted to a spider system that can only move 1mm peak to peak. it is a measurement of a physical static dimension. xmech is the measurement of the suspensions mechanical maximum flex. it does not necessarily mean excursion, rather than how far the parts can physically be forced to move. excursion is really how far the diaphragm moves by the speakers own motor force. that would be an easier way of looking at it.

Vas tells you the springiness of a volume of air that is the exact same compliance or springiness of the speakers suspension.

SPL is how loud in decibels that the speaker gets at a given distance from the mic and at a given input voltage. most SPL measurements are taken at one watt of input and measured one meter away from the center of the dust cap at rest.

Qts is a formula that involve the electrical Q and the mechanical Q or Qms and Qes.

Sd is the surface area of the effective radiating part of the speaker (inside half of the surround and the entire cone.)

BL is the product of magnetic force and the energy of the coil (determined by number of windings in the magnetic gap), this is a number determined when the speaker is at rest when it is used as a specification of the speaker. as the speaker moves to a point where one end of the coil starts to go into the gap, the number of windings of the coil in the gap decreases, meaning that the coil energy goes down and subsequently the BL drops. so the BL drops every time the speaker moves up and down.