What is this box's volume and port tune? Specs inside

[BassAddictJ 5,000+ posts]

Local pawn shop has a JL "Pro Box" with a 12w3v3 in it. The w3 isn't the ohm value I'm looking for, but the box looks sturdy as **** and might go well with my older mmats procast (p3) 12.

So.....that said. This is a rectangular box, internal specs are 20.5in L x 12in W x 13.5in H

The port is rectangular, runs along the bottom of the box, and ends at the exterior of the box. Internal measurements of the port are 4.5in x 4.5in x 15in long. Looks like the width of the wood throughout is 3/4in, including the body of the port.

Volume of internal space before port volume: 3321in cubed, or 1.9cuf

Volume of internal port: 303.75in cubed

Port Area: 20.25in squared

Total port volume (3/4in wood for the port frame/body included): 434in cubed (434.1in cubed actually, but we'll cancel the .1 out with the volume of the woofer).

Internal volume minus port volume: 2887in cubed, or 1.67cuf

.....what's my tuning freq? My best guess is 37Hz.

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[Hertz Mafia]

1.25cubes net and tuned to 54hz

 

[BassAddictJ 5,000+ posts]

jesus. that's high......

 

[Jeffdachef 5,000+ posts]

yup its tuned that high.

 

[BOOMINGRANDPA 5,000+ posts]

yup its tuned that high.

OK what did I miss?, if it's 1.67 cf I got 40hz., so what dropped it to 1.25cf?

 

[Boomin_tahoe 5,000+ posts]

54Hz? Lol

Don't expect that sub to play decaf anytime soon!!

 

[Jeffdachef 5,000+ posts]

OK what did I miss?, if it's 1.67 cf I got 40hz., so what dropped it to 1.25cf?

The space the port and subs take up those matter bud...

 

[BOOMINGRANDPA 5,000+ posts]

The space the port and subs take up those matter bud...

Im aware but he added that up, looked like he subtracted it from final cf to arrive at 1.67..

 

[Jeffdachef 5,000+ posts]

Im aware but he added that up, looked like he subtracted it from final cf to arrive at 1.67..

wrong. He did his calculations incorrect in the first place. (13.5-1.5) x (20.5-1.5) x (12-1.5) = 2394/1728 = 1.38 cubes NET before any port or sub displacement. he just did 13.5 x 20.5 x 12 without subtracting wood thickness.

You never take people's word for granted, always do the math properly and check. Or have a proper box software that autocalculates and takes port volume into account.

 

[jatyro91 10+ year member]

wrong. He did his calculations incorrect in the first place. (13.5-1.5) x (20.5-1.5) x (12-1.5) = 2394/1728 = 1.38 cubes NET before any port or sub displacement. he just did 13.5 x 20.5 x 12 without subtracting wood thickness.
You never take people's word for granted, always do the math properly and check. Or have a proper box software that autocalculates and takes port volume into account.

It's clear as day I don't know **** about **** when it comes to car audio or box building (which is why I'm on this forum trying to learn in the first place), but for the sake of argument...he did say that 13.5x20.5x12 were the internal box specs. Wouldn't that mean the wood was already accounted for because it's the internal specs and not the outer dimensions?

 

[Jeffdachef 5,000+ posts]

It's clear as day I don't know **** about **** when it comes to car audio or box building (which is why I'm on this forum trying to learn in the first place), but for the sake of argument...he did say that 13.5x20.5x12 were the internal box specs. Wouldn't that mean the wood was already accounted for because it's the internal specs and not the outer dimensions?

i think i missed that lol. Okay then its still 1.56 cubes tuned to 41hz.