there are some equations.
If there is any mistake, post reply please.

fs=(1/2*3.14)*(Cms*Mms)^-1/2
so fs will be same.

and,
Qms=2*3.14*fs*(Mms/Cms)
=(1/D)*(Mms/Cms)^1/2
so, I thought, D=Cms
if this is right, in compound woofer system, Qms' is not same of single Qms.
because
Mms will be double, and Cms will be half because effective stiffness will be double.
so,
Qms'=(2/D)*(2*Mms/Cms/2)^1/2
=(2/D)*2*(Mms/Cms)^1/2
=4*(1/D)*(Mms/Cms)^1/2 =4*Qms

and
Qes=[Re/(Bl)^2]*(Mms/Cms)^1/2
I think l will be double and if my thinking is right, Bl will be double.
and if wired in series, Re will be 2Re.
so,
Qes'=[2Re/(2Bl)^2]*(2Mms/Cms/2)^1/2
=2/4[Re/(Bl)^2]*2(Mms/Cms)^1/2 = Qes
and, if wired in parallel, Re will be half.
so
Qes'=[(Re/2)/(2Bl)^2]*(2Mms/Cms/2)^1/2
=1/8[Re/(Bl)^2]*2(Mms/Cms)^1/2 = Qes/4

and
Qts=Qms*Qes/(Qms+Qes)
so I can't understand that push-pull or compound woofer system's Qts will be same of single driver.
But that Qts of push-pull and compound woofer system is same og single driver is written on "the Loudspeaker Design Cookbook"(fifth edition by Vance Dickason) page 30 and 32 !

I'm very confused. please somebody help me....

please define...
 

"push-pull" do you mean clamshell isobaric?

like this:

http://www.hakalugi.net/misc/bpiso.GIF

if so, i believe the only changes are:

Vas, Impedence, Power handling.