Thiele-Small: QLv Help

[Rob]

Hello,

I am in the process of modeling a speaker project using BassBox Pro
and some good old pen and paper. I am building a vented loudspeaker,
and in on of the vent sections of the program it asks for the QLv
(loss of the vent) aned gives an entry field (ie it is not affected by
any other variables).

The problem is I don't know how to derive QLv! Any suggestions?

Also, what is the importance of QLv in my design? Is this something I
should be sweating over?

Thanks so much!

Rob