96civ

12-30-2006, 02:07 AM

Ok I must be missing something here. I see the sticky, "Box Plans," and the plans that Moe Lester has honorably stuck on this forum, but I must be missing something. I'm confused on how some of these plans work, because I've crunched them into a calculator several times to no avail. For instance the 1.25ft^3 tuned at 32Hz with 21in^2 port area has a 40.5" port length (and not to his discredit because I'm sure I'm missing something here), but after putting those variables into either the equation:

Lv = [(Av*1.84*10^8)/(1728*Vb*(Fb/.159)^2)] - 0.823*sqrt(Av)

or the equation:

Lv = [(23562.5*Dv^2*Np)/(Fb^2*Vb)]-(k*Dv)

I do not come to a value of 40.5"... what's wrong here?

Also when you have the winding ports as in this case, why is that bit of extra port length accounted for? It must not be end correction, or is it?

Lv = [(Av*1.84*10^8)/(1728*Vb*(Fb/.159)^2)] - 0.823*sqrt(Av)

or the equation:

Lv = [(23562.5*Dv^2*Np)/(Fb^2*Vb)]-(k*Dv)

I do not come to a value of 40.5"... what's wrong here?

Also when you have the winding ports as in this case, why is that bit of extra port length accounted for? It must not be end correction, or is it?