Enclosure design advice

[thethriller]

Hi all, first time poster but not first time visitor.

First off I am upgrading from a single previous gen 10" Alpine Type-R (Dual 4ohm) on an Alpine MRP-M500 (500W RMS @ 2ohm).

I built the vented box Alpine recommended in their manual and overall was VERY pleased with the setup.

Flash forward a couple years to the present and I find myself with two new SWR-12D2 and an MRX-M110 (Gifts).

Anyway, my intention is to build a new box for them with individual chambers, each separately ported, and I am concerned about all the vent/box calculators out there giving me different results. My main concern is which volume figure to use when calculating the port dimensions (gross, gross minus port?) Or what I have been assuming, gross minus woofer displacement?

Alpine's recommended enclosure is 23 x 12.5 x 14 with a slot port 1" x 12.5" x 19" long (1.71cu gross, 0.23cu port, 0.10 cu sub for a net of 1.38cu. I cannot, however, fit two of these in my trunk So creating a box with other dimensions should be done as follows?

For example: external dimensions of 18"Wide x 16"Deep x 14"Tall (1.73cu gross internal, 1.63cu after woofer), with a port on the bottom. Using the12volt.com's slot port calculator I use a 16.5" Wide x 1" Height slot port, 1.63cu Vb, and tune for 35Hz it recommends 18.9" of port length. Do I trust this? (Two of these will not fit in my trunk either, was just an example.)

I could also be talked into a single chamber box with a single port if that would be more recommended. My max available dimensions are 32" Wide, 16" Tall, roughly 20" Deep, and the front of my trunk ends at the back of my back seats which is a 60° Angle

Anyinformation would be helpful. Thanks in advance!

[Joe X]

Your amp can only source about half of the power those subs are rated for so efficiency wise I would recommend 1.5 cubes net per sub, you can fit that, in these dimensions: 15 3/4h, 32w, 19d common chamber box, to see if it will fit in it's way in I usually recommend building a cardboard dummy box. BTW welcome.

[thethriller]

Thanks for the input!

I realize the amp is going to be less power than the subs can handle but it's the right price (free) It'll also be lots more power than keeping the 500W hehe. I'm still hoping for some more detailed info on port calculations for a custom sized box, if anyone could explain a little better that would be wonderful.

That box won't have any trouble fitting, I should've maybe said hatchback instead of trunk, but with those dimensions (15.75x32x19) or (14.25x30.5x17.5 internal) I'm coming up with 4.4cubes, what kind of port am I looking at?

[Joe X]

I can give you detailed specs but I would need to know what vehicle is exactly, the 4.4 cubes you got does not account for the subs, bracing and port displacements that is why you are getting a large figure, for hatchbacks most commonly you find subs/port up, subs up / port back and sometimes subs / port back. And never mind the amp's power it will still sound pretty loud, besides you will need lighter electrical upgrades.

[bbeljefe]

If you want to play with modeling on your own, download WinISD Beta and enter the TS numbers for the drivers you have. You can play with cabinet and port sizes, tuning, etc and you can model multiple configurations and see them all together for comparison. I've been using it for about 7-8 years now with success.

As for your questions, yes... you need to deduct port and driver dimensions when modeling. You also need to deduct material thickness from your overall dimensions. Ergo, when you said you have 32X16X20 I assumed 3/4" material and used 30.5X14.5X18.5 for a total of 4.73 cubic feet. You'd also need to figure 1.5 inches for the baffle if you plan to laminate two pieces on the baffe (recommended) and deduct for any forty fives or other braces you plan to install.

As far as port dimensions go, Apline is recommending 12.5 square inches of port per woofer which is essentially the same as one 4" round port (12.56 sq in). Personally, I don't like one inch wide slot ports because in my experience with them, they can be noisy. Especially if they're not rounded well. You get a lot of turbulence at the ends of a port and when it's narrow like that, the turbulence can become quite annoying. My guess is that with a woofer that has as much xmax as the one's you have, a one inch wide port is going to be noisy. But maybe not... I love Apline's head end equipment but I've never used their speakers so I have no experience with their box recommendations.

Another thing I like about WinISD is the vent mach calculations is does. This is basically a number it gives you based on the port dimensions you choose and it tells you if the port will be noisy or not. It displays the number in red or green which indicates noisy (red) or not noisy (green). Of course, the number tells you that as well but when that red number flashes on the port screen it tends to keep you from forgetting to check. Or at least, it keeps me from forgetting. That said, I modeled your drivers in a common chambered 2.76 cu ft box tuned at 32 hz and with two 1X12.5 ports and the vent mach is .06. Lower numbers are better and the number turns red at .16 so, those ports should be fine for those drivers. But be sure and round them...

Hope that helps and if anything I said was well below your experience level forgive me... I have no idea where you're at with knowledge. :-)

[thethriller]

Thanks guys. First these are going in a 1999 Mercury Cougar which is of course a hatchback. My previous single 10" sounded best facing back, with the port then also facing back. I tried both up and facing either side and all three didn't seem as loud and had some port noise. I'll definitely check out WinISD, thanks for the heads up.

[TeamHT]

Is there a specific reason you're wanting separate chambers?

[thethriller]

No reason, nope. Well actually I had planned the chamber separator to be bracing but I can just as easily brace a single chamber box if I can figure out what volume to base the port on and a trusted port calculator, hehe.

[thethriller]

Anyone for some nerd porn? After some thinking and a few hours of doing math and drawing in SolidWorks this is the box design I've come up with, any input will be very welcome, but for tonight I am done. Tomorrow I will post detailed specs/calculations.

(P.S. I probably spent 6 or 8 hours drawing up the actual speaker and amplifier a couple weeks ago from base specs and pictures so in the 3D View they'd look pretty!)

Front of design:

Top:

Isometric:

Dimensions:

[Joe X]

That is about 3 cubes @34hz, 42 square inches of port area which on the power is ok, on 2kw would be a little low. You will need 3" of free airspace in front of the port for proper operation. If you are placing the amp on the top of the box it's recommended that you use some form of damping to install it to avoid possible long term reliability issues.