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Old 09-09-2010, 06:53 PM   #9
Registered User
Join Date: May 2009
Location: Crestview, Florida
Posts: 743
My Ride: 2006 330CiC/ZHP
Talking Part 1 - Sub box and amps

Here's a build log on the sub. I am using the KISS principle here, in order to keep it short and sweet.

Cut my MDF...I always use MDF. Best for speakers, easiest to work with. Clogs a shop-vac in a heartbeat, though!
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Cut my holes for the drivers, cut holes in brace, ran dadoes into my sides.
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Busted out the woofers, Elemental Designs 8" variety.
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Mounted in (painted) baffles with wood screws in every hole, after putting silicone bead on back side.
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Glued and screwed baffles and brace to one side using gorilla glue and coarse thread drywall screws.
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Attached other side, same way.
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Ran all wires. Soldered all connections. Attached bottom.

WIRING DETAILS (if interested):
The woofer pairs at each end are ran in series = First wire (the positive wire) from hole in box (eventually from amp) to positive terminal on speaker "A"; a second wire connecting negative terminal on speaker "A" to positive terminal on speaker "B"; a third wire from negative terminal on speaker "B" to hole in box (eventually back to amp).
Repeat for other side.
The two positives from the woofer pairs (and similarly the two negatives) will eventually be connected TOGETHER, or in parallel, at (or prior to) the amp. Since each woofer is 2-ohms, this wiring setup makes each woofer pair 4-ohms with the series connection. Then as both pairs are connected together in parallel, the load goes back down to 2-ohms at the amp, so the amp will see a 2-ohm load.
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[NOTE: Normally, when building any speaker, I will silicone all internal seams to prevent air leakage. This time I really couldn't due to the way the box was constructed. By using very tight tolerances and dado joints, I feel confident that this box will never leak, despite the missing silicone.
If you use silicone when building a box as mentioned above, be absolutely sure to wait a few hours before closing the box up, otherwise the silicone gassing-out will be trapped inside the speaker box forever, causing eventual damage to your drivers.]

Ran my two sets of positive and negative wires that will go to amp through two very tight holes in box back-side, sealed with silicone (liberally!) on both sides. I could have used a terminal cup, but there are 3 reasons I didn't:
1. Except for you guys, no one will ever see the back.
2. Terminal cup has greater chance of leaking air than my holes.
3. Amp is physically, permanently attached to the box, so there will never be a need to disconnect the wires from the box. They are one "unit", so to speak.
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Loosely stuffed internal chamber with high quality fiber fill. This chamber gets filled, the two constant-pressure chambers that are between the woofers do not get any acoustical stuffing.
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This double compound isobaric configuration serves my purposes to the tee! I wanted a small box (don't we all!), and this allowed me to cut my internal volume by half. The woofers are not your typical automotive long-throw high X-max super woofers; they are standard woofers that have a low Fs, medium magnets, and medium power handling. So by using this configuration, each woofer will only have to throw 50% as much as it normally would (essentially doubling that spec), and can now also handle twice the power. Additionally by doing it twice, two sets, I get the benefit of a 3dB volume increase! All in all, a perfect solution; for me.
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Covered all except for bottom and back in matching carpet (old school, I know ). Mounted amps and crossovers. These will all face front. All future wiring will be hidden behind box.
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There is also a set of 6" pieces of wood stacked 2.25" thick (if I remember correctly) and attached to the "passenger-side" of the box on the back, no pic. This makes up the difference in the distance in depth on left side versus right side.

Here's the single 8" HK woofer in the vert with the luggage compartment maximized. For those that don't know, it's a way to get more luggage in the trunk if needed, but once you do this the top has to stay up. I had to design the box to fit with it NOT maximized, of course!
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And not maximized, normal ops. This is where my design had to fit.
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There was an small issue I had to contend with in the design. I needed to be able to get to the spare tire in case of a flat. My solution was to psuedo-suspend the woofer just above the spare tire cover. I cut an angled groove along the bottom of the box, and then pounded copper tubing in the groove, to protect the wood from wear. (That's cardboard you see protecting the woofers in the pic)
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Then I ran aircraft cable through the tubing and locked the box to the trunk. This holds the box tight, and doesn't allow it to move at all. But there's still that space underneath...
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In place with top-down capability. (Ignore the wiring in the pic, some of that's just temporary)
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To further support the box and provide a better overall look, I built and carpet-covered a support piece. This piece slides under the box, not physically attached, but cant move either. If I get a flat, I simply pull this piece out, then very carefully manuever the spare tire cover out of the car. Box never needs to be removed.
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In place.
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[NOTE: The entire unit, subs+amps+crossovers+carpet+everything = 48 pounds. Not too bad...centered along the width of the car, and not in the very back. Now my front to rear weight distro is 49.09-to-50.01!]

Well, that's it for now.
Waiting on my LOC and time to do the doors, rears, wiring, etc.

Last edited by radarcontact; 10-18-2010 at 08:06 PM. Reason: Clean up text, delete picture placeholder text, etc.
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