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Fitz
05-23-2004, 08:11 PM
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.

getsumbaby
05-23-2004, 08:15 PM
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
05-23-2004, 08:27 PM
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
05-23-2004, 08:39 PM
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
05-23-2004, 09:25 PM
http://www.jlaudio.com/tutorials/ports/images/Fb.gif
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
05-25-2004, 04:55 PM
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
05-26-2004, 01:56 AM
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
05-26-2004, 02:50 AM
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
05-26-2004, 02:55 AM
it's the truck, extended cab.. but don't i want to have a high frequency box for spl?

dbornotdb
05-26-2004, 03:28 AM
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. :omg: Use a 4" port 2 3/8" long.

Fitz
05-26-2004, 03:39 AM
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
05-26-2004, 03:42 AM
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
05-26-2004, 03:45 AM
And I forgot to add that is 4 cuft per sub, after dispacment. :readytogo

Fitz
05-26-2004, 03:49 AM
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
05-26-2004, 04:00 AM
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.

dbornotdb
05-26-2004, 04:08 AM
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.. ??


Do you know what it is tuned to? What about the port size and length? Probally played it to hard below the tuning frequency.

hunter57255
05-26-2004, 03:38 PM
i have a box i built with wood and i was wondering what i should put in to make it have more louder sound to it please help could put foam or and what would make it louder. Email is mattpalm@yahoo.com

Thnaks

Fitz
05-26-2004, 07:48 PM
i have no idea what it's tuned to.. i could prolly figure it out.. but i don't have any time now. that's prolly what i did, oh well. thanks though for all your help.

Fitz
05-28-2004, 01:53 PM
What's the best material to make a port out of? MDF, pvc, or what?

dbornotdb
05-28-2004, 05:36 PM
If you want to be easy, use PVC for round ports. And for slotted ports I use MDF.

Fitz
05-29-2004, 12:16 AM
Thanks for the tuning stuff. For the dude asking about what he should put in his box.. try polyfill. It's pretty cheap.. my mom actually uses it when she quilts. Don't use too much though (don't know how much, ask an expert), but it'll make the box act like it's bigger.

Fitz
06-06-2004, 01:18 PM
i was also thinking about fiberglassing this box (would be a huge experiment, but sweet if it worked out), when you fiberglass it.. do you still keep the sub in mdf and fg the mdf, or do you just make the entire box out of fiberglass? That question might sound stupid, but i'm curious, and still not very knowledgeable when it comes to making boxes. Also, how would i make a port plug for such a box (mdf or fiberglass..)

On a funnier note, my friend (who's a shop kid) wants to put a system in his dodge 3/4 ext. cab. He said he could make his own box (i offered to make it for him), so i asked him if he knew how. He said yes, so I asked him about ported/sealed and how to tune it. He looked at me and said "Of course you port it, otherwise the sub will explode from not enough air." After laughing for a few seconds, I explained to him what porting/sealing an enclosure does, and what tuning is (he had no idea about tuning). I told him to go with sealed, because he doesn't want a whole lot of bump and we wants lots of SQ. I told him to wait for me to go with him to buy something, and I told him I'd help him with the box.. maybe experiment with fiberglassing (i really want to try that, it looks so awesome).

dbornotdb
06-06-2004, 02:26 PM
I keep the sub in MDF to support the weight. It can be done in 'glass, but it would take alot of layers.

Fitz
06-07-2004, 02:26 PM
what about making a port plug? and would a plug make that box suitable for daily drive?