4 BL port length

[J2phat4u 9]

I just built a new enclosure and was wondering if 118 inches of port tuned around 31hz ok for my 4 fully loaded BL 12's?

[ricksi30 923]

I just built a new enclosure and was wondering if 118 inches of port tuned around 31hz ok for my 4 fully loaded BL 12's?

That should be good. Use a bit more if you can though.

[ricksi30 923]

Wait you already built it?

[J2phat4u 9]

Yes its built and done.

[ricksi30 923]

Yes its built and done.

You should be fine.

[ncc74656 2]

so when you add more than one woffer to a box you need to increase the size of the box itself for cubic feet but not the port area?  so a sub that needs 5 cubic feet, when putting 2 i a box they would need 10 cubic? but they both would use the same port area for single or dual right? assuming they are sharing a single port.

 

is that right?

[Julian 641]

port area depends mainly on 3 things, tuning. Xmax and sub size. The higher the tuning the more port area.. Also the more you can displace the more port area you will need.

[J2phat4u 9]

This question is really technical. The 4 BL subs I have were from when FI made them available with 4 inch coils. I recently had them reconed but I believe they were reconed with maybe SP4 coils since they are 4 inch. If so does this alter how I should build my enclosure since the SP4 coil is longer than the standard BL coil?

[ssh 924]

port area depends mainly on 3 things, tuning. Xmax and sub size. The higher the tuning the more port area.. Also the more you can displace the more port area you will need.

 

Vas, Tuning, and Power.

 

*The lower the tuning, more port area is needed.

Edited May 30, 2013 by stefanhinote

[ssh 924]

This question is really technical. The 4 BL subs I have were from when FI made them available with 4 inch coils. I recently had them reconed but I believe they were reconed with maybe SP4 coils since they are 4 inch. If so does this alter how I should build my enclosure since the SP4 coil is longer than the standard BL coil?

I wouldn't sweat it.

[Quentin Jarrell 671]

port area depends mainly on 3 things, tuning. Xmax and sub size. The higher the tuning the more port area.. Also the more you can displace the more port area you will need.

Vd, Tuning, and Power.

*The lower the tuning, more port area is needed.

Power can be completely removed (its literally not in the equation). If you do then you might as well include box volume which affects Q and affects power needed to accelerate the piston to xmax.

[ssh 924]

 

port area depends mainly on 3 things, tuning. Xmax and sub size. The higher the tuning the more port area.. Also the more you can displace the more port area you will need.

Vd, Tuning, and Power.

*The lower the tuning, more port area is needed.

Power can be completely removed (its literally not in the equation). If you do then you might as well include box volume which affects Q and affects power needed to accelerate the piston to xmax.

I should have said vas instead of vd.

 

I've been using this: http://s0.wp.com/latex.php?latex=\frac{13.7\sqrt{\frac{9.64+\times+10^{-10}+*+fs^3+*+vas+*+power}{qes}}}{Fb+*+R^2}&bg=ffffff&fg=000&s=3

from the loudspeaker book.

 

Is there another equation that implies the driver reaches full excursion, so it doesn't require power?

Edited May 30, 2013 by stefanhinote

[Quentin Jarrell 671]

I don't remember that formula. WHat's it for?

 

 

 

 

I prefer to let Mathcad do the work being that it is frequency dependant but here you go.  Im going off a file off my phone but I think this is all of it.

 

Pmax= (k1/Gno)(Fn4 - C x Fn2 + A)^2 + Fn2 x (D x Fn2 - B) / Fn4 - E x Fn2 + A^2

 

K1= (4 x pi^3 x Ro / c) * Fs^4 x Vd^2

        Ro= density of air (1.18 kg/m^3)

        C= 1 + A + (vas/vb) + Fb / 7 x Fs x qts)

 

Gno= 10^((spl-112)/10)

          spl= reference efficiency

 

Fn4= Fn2^2

 

Fn2= (F/Fs)^2

         F= frequency

 

C= 1 + A + (Vas/Vb) + Fb / (7 x Fs x Qts)

 

A= (Fb/Fs)^2

 

D= 1/Qts + Fb / (7 x Fs)

 

B= A/Qts + Fb / (7 x Fs)

 

E=  (97 / 49) X A

[ssh 924]

I don't remember that formula. WHat's it for?

 

 

 

 

I prefer to let Mathcad do the work being that it is frequency dependant but here you go.  Im going off a file off my phone but I think this is all of it.

 

Pmax= (k1/Gno)(Fn4 - C x Fn2 + A)^2 + Fn2 x (D x Fn2 - B) / Fn4 - E x Fn2 + A^2

 

K1= (4 x pi^3 x Ro / c) * Fs^4 x Vd^2

        Ro= density of air (1.18 kg/m^3)

        C= 1 + A + (vas/vb) + Fb / 7 x Fs x qts)

 

Gno= 10^((spl-112)/10)

          spl= reference efficiency

 

Fn4= Fn2^2

 

Fn2= (F/Fs)^2

         F= frequency

 

C= 1 + A + (Vas/Vb) + Fb / (7 x Fs x Qts)

 

A= (Fb/Fs)^2

 

D= 1/Qts + Fb / (7 x Fs)

 

B= A/Qts + Fb / (7 x Fs)

 

E=  (97 / 49) X A

It's the formula for vent mach from the loudspeaker cookbook. Pretty close if not the same as WinISD iirc.