Dual 12s backseat conversion - possible port redesign for new subs

[wew lad 5,000+ posts]

Posted this in the subwoofers forum on accident... and since no one has moved it yet and it's not getting any help I figured I'd post here and hopefully find some help.

I have an extended cab truck, and a few years ago I had a box built to replace my backseat. You can still sit on it and the back rest is still there, here's a pic:

Currently the box is about 2.8 cubes with a cylindrical port (L = 10 1/4", d = 3 7/8"). I have two kicker CVT 2-ohm subs (shallow mount) in the box and while they sound loud, they lack the output and powerhandling of a full size subwoofer.

So, why redesign the box, or port? Mounting depth:

My intent is to remove the port, and replace the wall on that side of the box with a slotted port. I believe I can fit a 2x6.5 inch slot port without interfering with my mounting depth.

These sketchup drawings are VERY ROUGH. The measurements may be up to an inch off and I need to polish the design still. However, it should give you a good visual of the box, and my intentions.

Subs I'm considering using (with a theoretical volume of 2.8-3 cubes with polyfill added):

NVX VCW124

Sundown SA-12 D2

Alpine SWR 12D2

I'm open to suggestions, my end goal is going to be 1000w RMS per sub and to hit in the lower ~140db range (around 35hz) without sacrificing all my subs bandwidth.

If this sparks interest I'll post some winISD models I've made so far and more pictures of the box and my setup.

Click to read more...

 

[Jeffdachef 5,000+ posts]

Better Idea would be cover up the holes and do a single sub on 2000 watts in a proper sized enclosure. Sundown Zv4 12, Soundqubed HDC3/HDC4, SSA Xcon/Zcon 12 Does well in an enclosure that size but needs more port area.

 

[wew lad 5,000+ posts]

I was considering doing that with a 15, you think one 12 will make up for the loss from having one vs two speakers? I'll get 3db back with the doubling of power but that's still a net loss, would a 3 cube enclosure make up for it all with efficiency? I don't want to end up with a 6th order bandpass and have frequency range loss

of course my other option would be to have a new box built that has more volume.

as far as port area goes, how much are you talking? I can likely modify the port to be 2x6.5 and up to 20 inches or so long, or is this a bad idea considering port velocity. I was finding that the port velocity tends to be pretty high when i was modelling a few of those

 

[Jeffdachef 5,000+ posts]

I was considering doing that with a 15, you think one 12 will make up for the loss from having one vs two speakers? I'll get 3db back with the doubling of power but that's still a net loss, would a 3 cube enclosure make up for it all with efficiency? I don't want to end up with a 6th order bandpass and have frequency range loss
of course my other option would be to have a new box built that has more volume.

as far as port area goes, how much are you talking? I can likely modify the port to be 2x6.5 and up to 20 inches or so long, or is this a bad idea considering port velocity. I was finding that the port velocity tends to be pretty high when i was modelling a few of those

You do NOT have proper space for 1 15 or two 12s man. Because more subs need more port area which you are already lacking on. The motorforce and xmax from a stronger sub will be a sh*t ton louder than subs crammed in a tiny space. Thats the secret of getting loud, proper airspace and port area, ingrain that in your head, port compression kills output

You can also do two 10s in that space.

 

[wew lad 5,000+ posts]

I'm not looking for 150db competition level output from the 2 12s in the back, if the driver is modelled correctly and the port is built properly then i dont see how a sub with more power handling and excursion than these kicker CVTs would be an issue in about 3 cubes of volume.

I mean looking at the sa-12, it recommends a 1.5-2 cube enclosure @ 35hz, I'm at 1.5 cubes and you're telling me that it's not a good volume... sure a larger enclosure is better to keep the -3db point of the rolloff at a higher frequency, but i dont have that and im willing to lose some of the lower end for gains a little higher up. saying an enclosure wont work at all because it wont play THAT low, well it just doesnt make sense to me

Don't get me wrong, I know you're telling me how to get it as loud as possible, but my main concern here is getting as loud as i can with what i have, and if I can't get 2 12s in this box to sound decent ported, then I'll build a new box for the subs i decide on.

I was even considering a dayton HO 12, but i noticed they dont have as high of a xmax as other drivers

 

[wew lad 5,000+ posts]

did some more research on port area to make sure i fully understand the direction i need to take the port design, so considering ill have 2 12s in a 3 cube box ill need about 36 inches of port area to achieve what i want, if i used a square port.

considering my current design, can someone tell me what an "ideal" placement for a port this large would be without interfering with mounting depth? obviously it isnt a perfect rectangle box like you can shove in the trunk of a car, so it requires some ingenuity.

Jeff, if I can find a way to achieve the port area I need, would I be fine running something like 2 sundowns @ 35 hz?

I'm still pretty new to winISD but I've modelled a couple drivers now and here's what I came up with for 3 cubes vs 4 cubes with the sundown, it looks like I should still get pretty good gain around 40hz with a 3 cube enclosure..

 

[Jeffdachef 5,000+ posts]

did some more research on port area to make sure i fully understand the direction i need to take the port design, so considering ill have 2 12s in a 3 cube box ill need about 36 inches of port area to achieve what i want, if i used a square port.
considering my current design, can someone tell me what an "ideal" placement for a port this large would be without interfering with mounting depth? obviously it isnt a perfect rectangle box like you can shove in the trunk of a car, so it requires some ingenuity.

Jeff, if I can find a way to achieve the port area I need, would I be fine running something like 2 sundowns @ 35 hz?

I'm still pretty new to winISD but I've modelled a couple drivers now and here's what I came up with for 3 cubes vs 4 cubes with the sundown, it looks like I should still get pretty good gain around 40hz with a 3 cube enclosure..

First off, download WINISD pro alpha, its better than beta

If it is exactly 3 cubic feet, you'll just need more power, plug in power input in the signal tab and go to rear air velocity and make sure at no point you are over 100 feet per second, if you are, then you need more port area.

Check your enclosure design again with torres box calculator, there's a whole tutorial on how to use the calculator on the page. With a smaller box, its a lot harder to achieve lower tuning, Play around with the numbers and you will see why.

Torres' Box Tuning Calculator - Updated 8/18 - Subwoofers / Enclosures - SMD Forum

 

[wew lad 5,000+ posts]

Funny you mention that because I installed both winISD regular and the pro version. I was even messing with the power and port velocities, just didn't take the time to write all up in here in an effort to not flood you with information, but considering you're looking for it I'll post it all up tomorrow.

I was actually using torres box calc earlier and see exactly what you're talking about, which is why i was considering tuning a little higher. I did notice the difficulty in tuning lower in a small box, and the curves I've test modelled in winISD tell the story very clearly, and from what I gather if you want your box to have gains at lower freqs, you need volume. But, this shouldn't prevent me from getting loud at a little higher of a frequency, right?

The box is ~2.8 cubes and if i use the 25% rule when it comes to fill I can get a theoretical max volume of around 3.4 before subs and port, which leaves me at (very) roughly 3 cubes, I'll get a more exact number once the port and sub displacement are known.

My current setup has 2 12s with a measly 3 inch port, and it really doesn't sound bad considering you're supposed to have around 10-12 inches of port area per cube. with the new setup i assume the excess airflow is going to need the extra room to move and prevent turbulence, loss of smooth laminar airflow (I guess my aviation education translates in some aspects), and SPL.

So my idea, as of now, is to find somewhere I can put a 6 inch aero port in the box where ill keep it a good distance from any walls. hopefully i can figure out a way to keep the port somewhat short without port noise becoming a problem.

I'll post up some more models tomorrow.