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jcarver
04-05-2012, 02:37 PM
So I'm building a box for a single 12, ported, that I'm having trouble figuring out what length to make the port. For those wondering I'm putting about 1200 w rms to the sub, its a HDC312.

Based on the instructions provided by Audioque they said to make the port length about 18" to give you 40hz if you use their formula of 16 sq inches per cu ft of box. So here's what I have to work with.

Box volume Gross: 2.98 cu ft
Displacement of sub: .15 cu ft

I used a couple of calculators but this one seems to be the nicer Car Audio - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES (http://www.carstereo.com/help/Articles.cfm?id=31)

My problem is all of the calculators I use say to put in the volume of box. Do they mean Gross or Gross-sub or Gross-sub-port displacement? This all made a huge difference. I'm wanting to tune to 38 - 40 hz and based on these different possibilities I get crazy different numbers. Oh its a slot port 14 x 2.75.

Here's some of the stuff I came up with:
slot port 14 x 2.75
Using Gross volume: 38hz= 17.62 in
40hz= 15.26 in

Using Gross less sub: 38hz= 18.89 in
40hz= 16.42

Using Gross less sub less port displacement:
38 = to long to possibly fit in my box :)
40hz= 23.25 in

Any help on this would be great. Thanks all again .... I wonder if I'll ever get this thing built lol

Buck
04-05-2012, 02:39 PM
What vehicle is it going in? I can almost guarantee you will want to tune it lower than 38-40 hz.

You are going to want 2.5 cubes net tuned anywhere from 32-36, depending on what you need to do.

And don't forget, ports can bend.

jcarver
04-05-2012, 02:49 PM
I will be bending the port. And I understand that most subs sound good at 32-36 but I want something with a little more spl and from what everyone has said the hdc's sound loudest at 40 +/- and still get pretty low. Net box for this sub should be 1.75 to 2.75 most saying 2.25 to 2.5 is best. I'm just trying to understand what "box volume" these calculators are looking for. I'm thinking gross less the sub displacement.

jeremyg1
04-05-2012, 02:57 PM
Gross = total volume

Net = volume after all displacements

Most box calculators are looking at a NET number for volume.

Buck
04-05-2012, 02:58 PM
Tell me the vehicle though. In my personal opinion, I will never tune to 38-40 hz. Never heard one I liked. Yes they will still play low, but they usually sound like doo doing so when tuned that high.

jcarver
04-05-2012, 02:58 PM
Gross = total volume

Net = volume after all displacements

Yep got that, now just need to know which to use on these calculators to help me figure out port length..........

jeremyg1
04-05-2012, 03:00 PM
Tell me the vehicle though. In my personal opinion, I will never tune to 38-40 hz. Never heard one I liked. Yes they will still play low, but they usually sound like doo doing so when tuned that high.

And you will need a subsonic filter to prevent the sub from unloading and destroying itself quickly.

jcarver
04-05-2012, 03:00 PM
Tell me the vehicle though.

2011 Scion XB. The box is taking the whole back of the car with the seats up. Subs and ports firing up.

jcarver
04-05-2012, 03:11 PM
And you will need a subsonic filter to prevent the sub from unloading and destroying itself quickly.

The one on the amp should be ok for this right? I don't want a sharp cut off. Also why would audioque recommend this if it will damage their products.

Kangaroux
04-05-2012, 03:13 PM
The one on the amp should be ok for this right? I don't want a sharp cut off. Also why would audioque recommend this if it will damage their products.

AQ assumes you know how to setup your amp and all that to prevent damage. Also, it depends what kind of music you listen to. If you listen to dance music, rock, dubstep etc. 40hz would probably be fine. For someone who listens to low frequency rap it's a different story. And yes, the subsonic filter on your amp will work.

jcarver
04-05-2012, 03:28 PM
AQ assumes you know how to setup your amp and all that to prevent damage. Also, it depends what kind of music you listen to. If you listen to dance music, rock, dubstep etc. 40hz would probably be fine. For someone who listens to low frequency rap it's a different story. And yes, the subsonic filter on your amp will work.

Thanks, I'm pretty sure 38 - 40 is right where I want this one but does anyone know what the port length calculators use for "box volume". I'm thinking they want the box less sub and they take into account what the displacement of the port they are recommending is going to be.

double 07
04-05-2012, 05:01 PM