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Geek Culture / sub box for car, design ideas?

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Phaelax
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Posted: 19th Apr 2011 13:25 Edited at: 19th Apr 2011 13:26
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So I finally got my table saw back from my friend and decided to build the speaker box I modeled a year ago for my car. I did some final measurements to double check and guess what? It doesn't fit anymore! My original measurements of the trunk were too large. I measured the max width and height, and apparently assumed that was fine. Well, the floor curves up on the sides, the roof drops down in the back, ehh you get the idea.

So my new space to work with is much smaller than I originally thought. And considering I'm using 2x12" woofers (10s would be much better but I already had the 12s from a previous car), it's a tight fit. So I've made a basic design, drawn to scale. The gap in the middle is where the amp slides in, baffle is at a 26 degree angle. Pic here.

So if any engineers or designers are bored and feel like helping me on a small project, I'd like some thoughts on possible designs. I'd like more than just the standard boring rectangular box you can pick up at any store.

Dimensions I have to work with are 29.5" x 13.5" x 16" (WxHxD). The speakers are 12.5" in diameter with a 10 11/16" cutout. The volume of the box per speaker needs to be between 0.85-1.5 cubic ft and I'm using 3/4" MDF board. I'm not sure where I'd like to place the amp, I just don't want it screwed to the back of the box. If you have any thoughts on the amp placement, dimensions are 10-3/16"W x 2-1/2"H x 8-1/2"D.

Now there is about an extra 4" on either side, however, the base of the trunk begins to curve up at that point; starting at about 2" from the edge and going up an additional 2-3" from there across the 4" gap.


If nobody helps, it's no big deal. Just thought a few extra minds thinking of an interesting design wouldn't hurt.

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PrimalBeans
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Posted: 19th Apr 2011 13:29
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hmm you can look up formulas on the actual volume per output of the speaker boxes.. thats important... find out the volume you have to work with and go from there... i know there are inverted configurations as well that are kind of trick for subs so check out some sites on the matter... youll find something... If you want i can model up something, just not tonight... i need sleep..

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That Guy John
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Posted: 19th Apr 2011 13:36
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Primalbeans is right, find out the optimal box volume for the subs you have. You can normally get this information from the manufacturer, if not, try a local shop and see if they will let you have a peek at there books. Most high end shops have books with all the volume and dimension specs for most popular brand speakers and subs.

Good thinking leaving space for the amp, but make sure you are leaving space for it to breathe.
Don't forget to leave a spot to mount a capaciter later on as well.

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Fallout
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Posted: 19th Apr 2011 16:15
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Take a snap of your boot for us. I've seen some wicked designs that also are practical. I personally would forgo optimum output for practical positioning and aesthetics. If you do the old spare-tyre removal trick, then I think you should mesh over the cone, so you can still put stuff on top of it.

A few examples:






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Benjamin
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Posted: 19th Apr 2011 16:29
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I don't get it, is it so people stuck in the boot can listen to music or what?



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Fallout
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Posted: 19th Apr 2011 20:40
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It's so you can share your tasteless music, with other people who don't want to listen to it and are minding their own business on the pavement or in their homes.

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Phaelax
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Posted: 20th Apr 2011 00:30
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Quote: "Primalbeans is right, find out the optimal box volume for the subs you have. You can normally get this information from the manufacturer"

Quote: " The volume of the box per speaker needs to be between 0.85-1.5 cubic ft"

That's where the numbers came from. Alpine type-S (1243D).

I don't want to do the spare tire thing because that spare has come in handy twice before so I'd like to keep it.

The current system in the car (factory) is a 300w alpine stereo, but the stock subs are rather poor. One guy mounted 8" free air subs to the rear deck. I'll need a line output converter to hook up the sound as I believe the stereo is using an optical connection, so I can't run anything to the head unit. Battery is in the trunk, so that makes things real easy. I'll go take some pics now of my trunk/boot.

I've done a custom box for my 300m before, wish I had a picture of it. At first it was easy, cause the trunk was huge. But I neglected one small detail, the trunk opening.... it was tiny. I assembled the box inside the trunk.

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Phaelax
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Posted: 20th Apr 2011 01:43
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I attached a pic of my trunk, the lines I drew kinda show the shape of it better.

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Fallout
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Posted: 20th Apr 2011 10:02 Edited at: 20th Apr 2011 10:03
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If it's a deep saloon trunk, as it appears to be, you're probably on the right lines with your slanted back box design. Push em to the back out the way into that deep recess, with the box back flush with the rear seats. If it wasn't so deep, then I'd favour creating boxes over the top of those wheel arch curved areas you've drawn, and have them facing inwards towards each other. Those curves are always annoying to put stuff on anyway, so hiding them with big fat speakers is just and holy work.

(Edit: Btw, I think if you went with the facing inwards design, you'd want to angle them up a bit to reduce negative interference from each other).

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Phaelax
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Posted: 20th Apr 2011 10:33
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I started building the box, bout half way done with construction. But I've run into a slight problem and may have to start over with fresh wood. These MDF boards have been sitting in the garage for almost 3 years and I think the weather has softened them up too much. 3/4" thick and almost every screw I put in (pre-drilled) has split the wood. I'm not using large screws at all. I didn't have this problem when I built the last one.

What I think I'm gonna do, purely for looks, is put a piece of plexi-glass in the middle with a small LED behind it to illuminate the amp hidden away inside.

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Fallout
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Posted: 20th Apr 2011 10:48
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Sounds good. Post pix when you're done! If you don't want to buy new wood, it might be worth pre-drilling the screw holes a bit, and I would use some wood glue as well for good rigidity. Good luck chap.

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Phaelax
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Posted: 20th Apr 2011 11:55
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I did pre-drill and used wood glue, so we'll see. I take a pic soon as it stops raining (if it ever does).

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Phaelax
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Posted: 29th Apr 2011 19:04
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Almost finished with the box. I sealed it last night with silicone, gotta give it a day or two before I can mount the speakers inside; fumes from the sealant can damage the speakers (and my nose I found out).

I've had to make a few alterations due to the shape of my trunk, the back corners for example you see in this pic:




You might be able to see where the wood split in several places. This box is by far the most poorly constructed design I've done, but I blame the wood. I think it sat in the garage for too many years and the edges softened up.

Two more pics here:
http://zimnox.com/box/mod/

I have some carpet from a previous box, but it's not a perfect match in the jag so I'll have to go buy some, then I can carpet the thing and hide all the flaws! I meant to have the top piece go all the way across and not gap like that. It didn't even occur to me until after I sealed the box, I'm like oh s......

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That Guy John
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Posted: 29th Apr 2011 22:51
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Ouch, yeah.
Never drill into the end of a board.
You can use nails and wood glue on the ends then use small blocks on the inside of the structure to screw threw the plane of the board into the blocks for more stability.

As sits, your sub will eventually crumble that box.

I think I remember you posting a 3d drafts before you started, am I right?
Did you find enclosure specs for your subs?

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The Wilderbeast
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Posted: 30th Apr 2011 11:42
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If it's a sub you're going to want to port it as well, otherwise there is nowhere for the air inside to go. Again, there are formulas to calculate the diameter and length of tubing.


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Fallout
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Posted: 30th Apr 2011 16:27
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I heard porting allows for a louder sound since there is less of a pressure build up, but leaving it enclosed gives a punchier response, due to pressure pulling the cone back and assisting the magnet. I think it's horses for courses.
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Slow Programmer
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Posted: 1st May 2011 03:41
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Quote: "It's so you can share your tasteless music, with other people who don't want to listen to it and are minding their own business on the pavement or in their homes."


A law was just passed in Nashville that if a police offer can hear your radio while driving with their windows up you can get a ticket for disturbing the peace.

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Phaelax
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Posted: 1st May 2011 09:10 Edited at: 1st May 2011 09:14
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A ported box will make it louder, but a sealed box is more precise in sound reproduction. The 600w is loud enough without having to port it, I don't listen to rap. The stock 8" woofers are kinda crappy for a premium audio system. Some guys have replaced them with other 8" free-air woofers. Different boxes have different advantages, but in reality I only had room for a sealed box. Ported or band-pass would be too large to work in my trunk.

Quote: "Never drill into the end of a board."

I've done it on many projects without problems before, and pre-drilling should've prevented the splitting. Like I said, I think the wood just got too soft around the edges from sitting around. The pieces I cut towards the center of the boards didn't split nearly as bad. Oh well, I can always rebuild it later or finally get the guts to try building fiberglass.

Quote: "Did you find enclosure specs for your subs?"

Range is 0.85-1.5 cubic ft for internal volume. I'm within the range, I'll calculate the volume later.




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That Guy John
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Posted: 2nd May 2011 08:16
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Looks good Phaelax, let us know how it sounds after you et it all installed.

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Phaelax
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Posted: 2nd May 2011 08:24
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It's on my list of things to do monday, if I have time. I had to buy a pricier line input converter due to the car already having a 300w system.

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