Help me reverse engineer this box! Pt. 2

[rc10mike 10+ year member]

Im not to experienced w/ ported enclosures so a little help here. Its a dual 12, single slot port design, with a few small internal braces.

Its external dimensions are (made with .75 mdf)

32"w

14"H

22"D

Slot port dimensions are

3"w

12.5" H

18.25" L1

1.75" L2

I just want to figure out the tuning freq. and net int. volume.

Thinking of throwing my IDMAXs in there, which ID recommends 2.0cuft and 32hz for "Small"

I tried the RE calculator which says Fb 28.98 and Ft3 3.967. How accurate is this?

Thanks for any help!

Click to read more...

 

[miker 5,000+ posts]

Ok here's what I got.

3.99cf tuned to ~29hz before sub or bracing displacement.

 

[rc10mike 10+ year member]

Ok here's what I got.
3.99cf tuned to ~29hz before sub or bracing displacement.

What did you use to get that? Thats what I got with the RE calc! Is it actually accurate?

 

[miker 5,000+ posts]

\/\/\/\/\/\/\/\/\/\/\/\/

http://www.carstereo.com/help2/Articles.cfm?id=31

 

[IDSkoT 5,000+ posts]

Im not to experienced w/ ported enclosures so a little help here. Its a dual 12, single slot port design, with a few small internal braces.
Its external dimensions are (made with .75 mdf)

32"w

14"H

22"D

Slot port dimensions are

3"w

12.5" H

18.25" L1

1.75" L2

I just want to figure out the tuning freq. and net int. volume.

Thinking of throwing my IDMAXs in there, which ID recommends 2.0cuft and 32hz for "Small"

I tried the RE calculator which says Fb 28.98 and Ft3 3.967. How accurate is this?

Thanks for any help!

((32-(.75*2)x(14-(.75*2)x(22-(.75*2))/1728 = 4.52 total

3 x 12.5 x (18.25+1.75) = 750 / 1728 = .43 cuft of port space

Now... to find the frequency we used the formula from JL's website:

Fb = .159*SqRt((Av(1.84*10^8))/(Vb(Lv+.823*SqRt(Av))))

We plug in all the numbers:

Fb = .159 * SqRt(((3*12.5)(1.84*10^8))/(7810.56(20+8.823*SqRt(3*12.5))))

You do the math.

 

[helotaxi 5,000+ posts]

Assuming about .1cf displacement per driver I got 3.7 cf with a tuning of almost exactly 32hz.

 

[helotaxi 5,000+ posts]

((32-(.75*2)x(14-(.75*2)x(22-(.75*2))/1728 = 4.52 total
3 x 12.5 x (18.25+1.75) = 750 / 1728 = .43 cuft of port space

Now... to find the frequency we used the formula from JL's website:

Fb = .159*SqRt((Av(1.84*10^8))/(Vb(Lv+.823*SqRt(Av))))

We plug in all the numbers:

Fb = .159 * SqRt(((3*12.5)(1.84*10^8))/(7810.56(20+8.823*SqRt(3.12.5))))

You do the math.

You forgot to include the thickness of the inner port wall and the width of the port as part of the port length (the effective port length is different than A+B because those are only the lengths of the inner port walls) in your port displacement calculation. I just keyed the box volume and port dimensions into WinISD.

 

[IDSkoT 5,000+ posts]

You forgot to include the thickness of the inner port wall and the width of the port as part of the port length (the effective port length is different than A+B because those are only the lengths of the inner port walls) in your port displacement calculation. I just keyed the box volume and port dimensions into WinISD.

x2

I did forget the inner wall. My bad.

 

[rc10mike 10+ year member]

Assuming about .1cf displacement per driver I got 3.7 cf with a tuning of almost exactly 32hz.

Hmm, ID says 2.0 per sub for "Small". Do you think 3.7 (if thats correct) would still work for two subs? Since they're sharing a common chamber/ 1 port?

My experience with ported is limited at best. Im going to try this box tomorrow, I just want to see if the specs will actually work before I try.

 

[rc10mike 10+ year member]

((32-(.75*2)x(14-(.75*2)x(22-(.75*2))/1728 = 4.52 total
3 x 12.5 x (18.25+1.75) = 750 / 1728 = .43 cuft of port space

Now... to find the frequency we used the formula from JL's website:

Fb = .159*SqRt((Av(1.84*10^8))/(Vb(Lv+.823*SqRt(Av))))

We plug in all the numbers:

Fb = .159 * SqRt(((3*12.5)(1.84*10^8))/(7810.56(20+8.823*SqRt(3*12.5))))

You do the math.

I **** at math!

 

[rc10mike 10+ year member]

I just keyed the box volume and port dimensions into WinISD.

I have WinISD, only messed with it a few times, but I didnt see anywhere on there to calculate enclosure specs..I have WinISD Pro Alpha...

 

[helotaxi 5,000+ posts]

I did the math to figure the box volume manually and then plugged in that volume and the port area and length into WinISD. I use the Alpha as well.