Access Cab Sub Box build

I noticed a distinct lack of affordable options for us access cab (2012 specifically) people so I decided the best course of action was to build/install my own on a sub $200 budget.

Materials list/price breakdown:

Box:
1'x6' 3/4" mdf about $10
Screws free from my parts drawer
Oreilly's automotive carpet 36x72 roll only used about half $10
Port trim piece 3d printed free (or a few cents worth of filament, idk)
Bag of polyfill 20 oz (only used about 5oz give or take) $5
14 gauge speaker wire free (already had some lying around)
Terminal cup (had an extra one) free

Sub/amp:
Skar IX-8 D4 $40
Skar RP-350.1D $100

Install gear:
BOSS audio install kit 10 gauge $15
More 14 gauge speaker wire free
Some shoelace to tie it in place free

Grand Total: $180 plus tax (Great success!)

The box is 11"x11"x13.5" outer dimensions and about 0.63 ft^3 volume (maybe closer to 0.6 accounting for the sub). On the lower side volume wise for what Skar recommends but it sounds great to my ears. The sub hits plenty low and starts rattling my rearview mirror at a reasonable volume and about halfway up on the sub knob.

I'll include a few pics and if anyone in the Richmond, VA area is interested in one of these bad boys, let me know!

 

Looks pretty good. I’ve never used any of there stuff but people seem pretty happy with it

 

Applause for having a go at it yourself, but that hole in the top isn't doing you any favors. Port volume is not arbitrary - it's a function of the intended tuning frequency. Since the port volume here is essentially zero, all you have is a box with a hole in it - which if I had to guess is contributing to destructive interference as well as an unintended tuning frequency. That's to say it's severely compromising any efforts to achieve decent low end. You'll be much better off either finding a way to use a proper port or just sealing the enclosure.

I'd be going beyond a shoestring tied around the bottom of the enclosure for security as well. F=MA. Where's that thing going first time you have to stop quickly?

 

I did make sure the port area was exactly 13 in^2 as per Skar's recommendation (hence the trim piece). I know it's better to use a specific port tube or incorporate a baffle for more laminar airflow. But I decided having the extra volume was more important for my case. I did play around with covering the hole and it sounds noticeably worse when covered. Perhaps I should replace the shoelace with some climbing accessory cord or something haha.

 

The issue is not with the 'port' area - it's with the volume. You have almost zero port volume. This isn't a port. It's a fancy hole in the box. A port would have some length dimension in addition to height and width - based on desired tuning frequency. I can assist with modeling if you wanna try & fix the port.

You can't just 'cover' the hole and make that work either. You need to seal it if you're going to go sealed - like either replace that top panel or place another on top of it (or below) and seal it with glue. Covering it with a hand or a book or something won't cut it. A sealed enclosure can't do its job if it's leaky. It also appears it will be on the large size for a sealed enclosure, but that may be a good thing in terms of extension - as long as it's not excessive.

But hey, if you're satisfied, then that's what counts. But if you want to get the most out of this setup, there's a lot of room for improvement.

 

Good CAD skills brother!
Unsure about Port size but overall looks good.

 

I'm always up for trying to improve a design, so I'd be interested in modeling and printing a better port. If you have any ideas I'd be happy to hear them. Does something like this seem reasonable?

 

Sure, I'll model that port for ya. It'll have to wait 'till work's done, but remind me if I haven't done that by tomorrow. Have a tuning frequency in mind? IIRC Skar recommends ~40 Hz. If you do this are you going to use that same form factor you used for the flange and just extend it (print another piece)? I'll model it sealed as well as a 40 Hz tune might be close to an oversized sealed setup. Might as well make a model the way it is while I'm at it.

What are RMS power and crossover frequencies?

 

Ah ok, 40 hz then. Thanks for the offer, but you don't have to do that for me. I'm sure you've got plenty of projects to keep yourself busy. I'll do some research and see what I can build myself.

 

Getting closer. I'm guessing you subtracted from internal volume to compensate for the port - good.

Not so sure you want the slotted port option though. That's where you build the port into the enclosure itself with walls inside the enclosure as opposed to a drop-in vent (requires more overall space). That's pretty hard to do after the fact. That port would also give you 4 sq inches which is a good bit less than what the manufacturer recommends - you have 13 posted above. If you were going to extend the port to just match that printed piece that might be your easier option. You're going to be limited in tuning frequency though by length unless you can make a turn with the port. You'll need to leave a few inches between the wall of the enclosure to the port opening as well.

If it were me, I'd work up a new lid for that thing, or close the box with a piece of MDF from the inside and go sealed. But that's just me. Because it seems like fitting the port you need in there is going to compromise internal volume to the point it doesn't seem worth it to try and port because your tuning frequency will be too high. But that's seat of pants - that's why modeling is so useful. It gives you a good idea of what to expect once everything is done before you lift a finger to build anything.

I'm still going to model this because I'm curious what it looks like. Never modeled a box with a hole in it before.

Or, if you wanna have a go at it yourself, and you seem capable, WinISD is a free, feature rich program that lets you do that. Basic Car Audio Electronics (bcae1.com) is also a great car audio resource with lots of calculators and good advice.

 

Well, I was hoping to model this but it seems Skar may have fudged their TS parameters as they fail WinISD's integrity check. They also don't include Le. And after putting in the minimal parameters it auto calculated Sd as almost 2,000 square inches and SPL of like 130dB at 1W/1m (both very far from reality). I'm calling those completely unreliable. I'd just use calculators and maybe take an average of a few to find that vent length.

 

Hmm yes. I understood some of these words haha. Thanks for the advice, I'll see what I can come up with!