Tuning Boxes

[Fitz 10+ year member]

I'm kinda of a newb at car audio.. in fact, my first drag was today. I got slaughtered.. 134.9 in Street B. Anyway, I really need a new box. I'm running an audiobahn 1800 watt (it's at 1 ohm) to two db drive platinum twelves from a clarion dxz945 head unit. I'm looking into building my own, larger box. I just want to know how to tune a box and how different tunings affect the volume. Any input will be greatly appreciated. Thanks, Fitz.

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[getsumbaby 10+ year member]

ok - quick answer.

Ported boxes are bigger - tuning is pretty easy after you have the size box you want - and if your going for SPL tune high. Generally speaking, ported boxes play 3db louder at the ported freq (or just above it)

Ed

 

[Fitz 10+ year member]

Thanks for the reply, but I knew all of that already. I was asking what actually goes into what frequency the box is tuned at.. i.e. what's the difference between a 35 hz and a 58 hz tuned box? Sorry if i was unclear.

 

[Fitz 10+ year member]

that's what most papers (online statements a better word?) i've read about the subject have had to say about it.. i still don't know how to tune a box though.

 

[Acidburn 5,000+ posts]

Where Av is the cross-sectional area of the port (in square inches),

Lv is the length of the port (in inches)

and Vb is the enlcosure's net volume (in cubic inches). http://www.jlaudio.com/tutorials/ports/index.html

 

[Fitz 10+ year member]

awesome. thanks a lot acid burn, that will help me tons. hopefully my new box will do well in comps when i get done building it.

 

[Fitz 10+ year member]

okay, one more question before i try to build a box. well.. actually, two questions.

1. How do i figure out when bigger stops equalling louder? Or is it just trial and error?

2. What does the frequency of a box actually mean? Will a box at 58 Hz play 58 Hz the loudest or what? And why does a higher frequency work better in comps?

Answers will be greatly appreciated, thanks, Fitz

 

[dbornotdb 10+ year member]

I don't know if you have the Blazer or the s10 truck. If it is the truck, is it the regular or extended cab? If I knew this I could figure out the frequency of the inside. But not knowing that, or the space you have to work with, I came up with this...... 3 cuft after displacement. 4" port 9 5/8" long. This tunes the box to 30 hz with a 3db down point of around 24 hz. Lower in car. Also since you seem to be after SPL, this gives you a little over 7db gain at 32.5 hz. Louder in car. Hope this helps you alittle.

 

[Fitz 10+ year member]

it's the truck, extended cab.. but don't i want to have a high frequency box for spl?

 

[dbornotdb 10+ year member]

Do you want it strickly for SPL? Or do you want to be able to listen to music with it also?

 

If you want the music aspect, go with the 3 cubes. You want strickly SPL, I'll be back in a few.

 

EDIT:::: I'm back. I would do a 4 cuft box tuned to 40 hz. The incar frequency is around 47 hz, ( I used 6' for my math from cones to windshield), and this box gives you an 11.75db gain at 42 hz. //content.invisioncic.com/y282845/emoticons/omg.gif.05aa02c3095d6ce9338996654eca0863.gif Use a 4" port 2 3/8" long.

 

[Fitz 10+ year member]

when (and if) i build this box, it will be strictly for SPL.. swap it in for comps only. I'm gonna keep the one I have now, cuz it hits like hell on the street and it sounds great, even when i listen to jazz. So yeah, SPL only.

 

[Fitz 10+ year member]

first off, i'd like to say, i'm not exactly sure where you get the math for the gains.. but it's pretty sweet that you know all of this. Second, i can get more than 4 cu feet (if that matters to you in the calcs).. this would be for 2 subs (although i'm assuming you took that into consideration anyway). Also, for pure spl, would i want higher than 40 hz on the box? Sorry for all the questions.. but i'm curious and this is really interesting to me.

 

[dbornotdb 10+ year member]

And I forgot to add that is 4 cuft per sub, after dispacment. :readytogo

 

[Fitz 10+ year member]

ahhh.. that makes more sense. but i should still tune it at 40 hz, right? no higher for pure spl?

after displacement means i make the box, subtract the volume that the subs take up inside the box, and that should = 4 f^3, right?

also, would having too small of a ported box increase chance of voice coil fries/overheating? my box right now is about 3 cu feet for 2 subs.. and i'm worried that one of the reasons i burnt out my other subs was the size of the box.. ??

 

[dbornotdb 10+ year member]

first off, i'd like to say, i'm not exactly sure where you get the math for the gains.. but it's pretty sweet that you know all of this. Second, i can get more than 4 cu feet (if that matters to you in the calcs).. this would be for 2 subs (although i'm assuming you took that into consideration anyway). Also, for pure spl, would i want higher than 40 hz on the box? Sorry for all the questions.. but i'm curious and this is really interesting to me.

I'll try to explain the cabin gain frequency, I'm tired....but here goes. Sound waves in the air travel 1130 feet a sec. Sound travels slow enough in a car below some frequencys that the path length for cancelling is longer than the car. So use 4x as the limit for no cancellation. So say the cones are 6 foot from the mic, (windshield), and 4 is the cancellation number, then the speed of sound is the frequency times wavelength. F x L = 1130.

 

Lost yet? 1130/6/4 = 47hz.

 

And some subs work different in some boxes. Just cause brand X works in a 6 cuft box with 100 sq inches of port doesn't mean yours will also. I got the T/S for your sub from the db site and ran it on winISD. Knowing the cabin gain and frequency, I came up with the 4 cuft. Anything biggger or higher and the port gets really small. Need to round it real good to reduce port noise.