"Sump Basin" Subwoofer - MacGyver style - AVS Forum
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post #1 of 56 Old 11-25-2012, 09:12 AM - Thread Starter
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Should I be thanking an '80s TV show for my new subwoofers? I suppose so. Some months back I made a mental note - whenever out shopping always be on the lookout for a vessel/container that would make a decent subwoofer. Either something attractive, or something cost-effective and easy to work with. A couple of days ago, while in Home Depot, I saw it. A 'Sump Basin' - 20 gallons of rigid-walled goodness. I figured it could substitute for a length of sonotube, perhaps it would be easier to work with. When I saw the Sump Basin (SB) what caught my eye was the provision for four bolts on a reinforced rim, plus the rigidity of the unit - this is no garbage can, it is stiff-walled. Of course the other thing that caught my eye: The price - $23.

That price is low enough to make this project come in under $300 - for all parts and supplies - for a pair of decent passive 12" subwoofers that took less than an hour each to put together and which perform perfectly from the get-go. They are not pretty, but that can be fixed.

Intrigued by the SB's potential, I biked on down to home Depot and picked up a pair of basins, a 2'x4' sheet of 3/4 birch plywood (cut in half), some fence-post toppers, bolts, felt pads and duct putty.

Before I go any further - listening to just one of the completed subs last night, my wonderful wife Danya became concerned while we were re-watching "Big Trouble in Little China" for the gazillionth time. She was afraid the bass during the 'green lightning' scene at the brothel would cause structural damage to our house. That's a first, and she's been with me for a couple of decades worth of excessive noise-making. That's using the same drivers, in the same place, at the same amp settings as before. The main thing that changed is the subwoofer's housing.

My woofer of choice lately is the Sony Xplod XS-GTX121LW. Ignore the fact you can only buy this model at Wal-Mart - it is quality, especially for the price. It has more features and is better sounding than Kicker CompVR, Polk DXi and Alpine Type E 12" subs, all of which are sold by big-box stores and all of which I've owned. My current system contains six of them... four doing full-range woofer duty on my mains and a pair working as dedicated subs. That said, this design would work with any 12"sub that feels comfortable in a sealed configuration with 2.5 cubic feet of air.




The first step in assembly - marking the holes for the bolts on the baffle:




Step two - drawing the hole for the cut-out. Sony was nice enough to package the subwoofer with a piece of cardboard that acts as a perfect template for the cutout:



I used a jigsaw to cut the hole. Quick check to make sure the sub fits:



Next step is to cut a hole and install the wire terminal as well as the sub itself. Duct putty is used as a sealant on both the subwoofer and the terminal:



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post #2 of 56 Old 11-25-2012, 09:22 AM - Thread Starter
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...continued

I decided to screw in the 'legs' before installing the driver. They are actually fence post caps:




Everything in place on the baffle:



Time to attach the baffle to the basin. I pre-drilled the holes which were marked-up earlier. The basin uses 1/4" 20 thread/inch bolts. 2" bolts were perfect for this application...


The entire inside rim of the basin is covered with a 'rope' of duct putty. Then it's a matter of aligning the baffle and bolting it down. A perfect seal was formed right away:



Here's the undecorated sub, in all it's glory:


The only structural weakness in the SB is the 'bottom of the barrel' so to speak, which in this case is the top of the finished sub. The basin's bottom is flat, of course... and that means it is susceptible to flex. Not much, but compared to the inert rigidity of the tubular portion, it's floppy. It looks terrible anyhow, so there's a chance to do something useful.My solution - cover it in duct putty and put a paving stone on top. After an hour or so, the paving stone really settles in and bonds with the basin's bottom, making it as rigid and resonance-free as could be hoped for without putting in a fair bit more effort. For my purposes, it looks fine now. I'm thinking of wrapping the basin itself with rope, for aesthetic purposes. The alternative is to go ahead and build out the box, but not have to worry about bracing, flexing, air tightness and all that. It's rock-solid so each one serves as an end table.


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post #3 of 56 Old 11-25-2012, 10:35 AM
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Very ingenious project, seems to have a worthy success.
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post #4 of 56 Old 11-25-2012, 11:24 AM - Thread Starter
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Here's a bit of trivia – every single part of this subwoofer was bought in a brick-and-mortar store and brought home on a bicycle... even the paving stone!

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post #5 of 56 Old 11-25-2012, 02:35 PM
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Nice build buddy! You going to bring this beast with you to gorilla's GTG?

 

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post #6 of 56 Old 11-25-2012, 03:21 PM - Thread Starter
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I got two of them and they match up really nicely with the Crown XTi-2002... so yeah I think so. Ugly ducklings. Listening right now, they are pounding so hard. I was thinking of cutting up an area rug and wrapping the cylinders with that.
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Nice build buddy! You going to bring this beast with you to gorilla's GTG?

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post #7 of 56 Old 11-25-2012, 08:48 PM
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Buy a small bag of cement powder and pour it on top, not sure if it would adhere to the plastic but that would stop the flex, and then just coat the whole thing in some svs tube-like carpet; nobody would be the wiser.
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post #8 of 56 Old 11-26-2012, 06:25 AM - Thread Starter
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That would totally work - I'm thinking you'd pour it inside the bucket after roughing up the surface, should definitely stick and would be totally invisible. Maybe lose a couple gallons of interior airspace, no big deal. I also considered cutting a circle from MDF and bonding that to the inside bottom for a lighter 'internal' solution. I definitely need some solution that lets me use these in a front-firing config., the paving stone trick only works for a down-firing sub. With front-firing configs, the sub could be hidden in almost any piece of furniture that would fit it - obviously including boxes. 20"x20"x24" is enough room for the whole shebang. Then I could skip the thick MDF and the internal bracing and worry about aesthetics instead.

For now, I like the paving stone. Being able to take the stone off and have the rest of the sub be light enough to move around easily is nice. One of my goals was to make it easy to swap out the whole baffle, so I can swap drivers (that are pre-mounted to the baffles) by loosening only 4 bolts. Last night was awesome for both music and movies, pushed the drivers to new limits & the enclosures were as acoustically transparent as I could hope for. The seal is so tight, I think these subs would hold a vacuum almost indefinitely, like a mason jar.

The most important thing - these enclosures and this build method will also work with 15" drivers. I'm going to have to find a GOOD pair to mount in these and see what's possible.
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Buy a small bag of cement powder and pour it on top, not sure if it would adhere to the plastic but that would stop the flex, and then just coat the whole thing in some svs tube-like carpet; nobody would be the wiser.

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post #9 of 56 Old 11-26-2012, 09:23 AM
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Good find, I like it!

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post #10 of 56 Old 11-27-2012, 06:38 AM
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Excellent enclosure for an outside sub possibly too.
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post #11 of 56 Old 11-27-2012, 06:48 AM
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Awesome. Going to HD to check these out at lunch. biggrin.gif
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post #12 of 56 Old 11-27-2012, 07:45 AM
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Excellent enclosure for an outside sub possibly too.

Ohhh! Spectacular concept.

Maybe utilize a waterproof marine sub, sink the enclosure(s) into the ground and cover them with paverstone as dub king has here. Ensure drainage would not be a problem and volia! You have a bass walkway leading to your pool!

Thanks for the inspiration guys.

 

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post #13 of 56 Old 11-27-2012, 08:06 AM - Thread Starter
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Totally, seeing how they were designed to have water gushing through them while being buried in the ground. The baffle could be made out of 3/4" or 1" polymer - the stuff used for cutting boards. http://www.thecuttingboardfactory.com/
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Excellent enclosure for an outside sub possibly too.

Lols, like the MoMo 15" I tore apart last week when I realized how much false advertising went into marketing that driver... but it most certainly was marine-certified and would be perfect for that application. If only I'd waited before taking the kitchen sheers to it!
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Ohhh! Spectacular concept.
Maybe utilize a waterproof marine sub, sink the enclosure(s) into the ground and cover them with paverstone as dub king has here. Ensure drainage would not be a problem and volia! You have a bass walkway leading to your pool!
Thanks for the inspiration guys.

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post #14 of 56 Old 11-27-2012, 08:26 AM - Thread Starter
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I just saw these Dayton Ultimax 12" drivers. Seems they could be a good match for these enclosures. One month before I can try them though. mad.gif

http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-512

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post #15 of 56 Old 11-27-2012, 08:41 AM
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Looks like same basket as Epic 12 but motor, surround, cone, and prob other stuff different.

Inductance, Vas, and prob Mms all lower which should be better assuming it has a decent Bl since sensitivity is a couple dbs lower.

Funny how specs are though, more RMS over the Epic but only about half the Peak rating......rolleyes.gif
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post #16 of 56 Old 11-27-2012, 08:51 AM - Thread Starter
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That basket does look exactly the same, but it might be a clone because the specs for mounting are slightly different? Regardless... peak ratings are meaningless to me. The RMS matches up perfectly to my Crown XTi-2002 operating at 4 ohms stereo (800 watts/channel). xmas is gonna be fun... more xmax for xmas (I'm sure that's an ancient joke around here). If it comes close to specs, it's the driver I've been looking (waiting?) for.
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Looks like same basket as Epic 12 but motor, surround, cone, and prob other stuff different.
Inductance, Vas, and prob Mms all lower which should be better assuming it has a decent Bl since sensitivity is a couple dbs lower.
Funny how specs are though, more RMS over the Epic but only about half the Peak rating......rolleyes.gif

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post #17 of 56 Old 11-27-2012, 09:43 AM
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I just saw these Dayton Ultimax 12" drivers. Seems they could be a good match for these enclosures. One month before I can try them though. mad.gif
http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-512

So when does the 18 come out? eek.gif
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post #18 of 56 Old 12-02-2012, 08:55 AM
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So when does the 18 come out? eek.gif

fingers crossed. . . . .

thats a friggan sweet build dude. . . . I operate a machine that makes paving stones so I have been tickling the idea of using some in a sub build. . . .
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post #19 of 56 Old 12-05-2012, 03:33 PM - Thread Starter
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edit - things did not go as planned. I was playing with WinISD and it became apparent how much bass I was leaving on the table with the 'dual opposed' design. My thought - better to have four large sealed subs (12" driver in 5 cubic foot cylinders). Back to Home Depot to pick up four more sump basins! Good thing they are cheap. I gotta say it: the proponents of having multiple subs spread throughout a listening space are right on the money. The 'smoothing' effect cannot be imitated by any amount of EQ, and I found that with enclosures this large, the vibration-cancelling benefits of dual opposed would be so minimal, it would be criminal to follow that route.

So it is, I have four 12" subs, each getting 500 watts of nice clean power from a Crown XTi-2002. The subs themselves cost $150 each to build, and take about 45 minutes each to put together... using parts that are locally available - same plaza actually: Wal-Mart and Home Depot. In one week I'll be taking them to a GTG and see how they fare against an LMS-5400.

"okay, here we go. I am headed to Home Depot right now. Time to purchase 2 more basins. I joined the first 2 together into a large sealed dual opposed vertical sub, not unlike what you might see from a sonotube build, except I did not need baffles. My entire subwoofer is synthetic not a speck of wood in it. an hour or so I will put together a second one with some photo and/or video documentation. It is so fast, so cheap, and the result sounds so good, I am thinking of having a piece of furniture made to hold it."

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post #20 of 56 Old 12-09-2012, 07:11 AM - Thread Starter
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Here's one of the four subs, next to the latest iteration of my mains. Each one is 5.5 cubic feet internal volume - made from two sump basins bolted to each other - with a 12" Sony XPLOD driver that is identical to the woofers in the main speakers. I stole a 12" from each main because of what I've read on the SEOS/DIY pages about the advantages of a single 12" 2-way with the horn mounted as close as possible. I went for that alignment and got two extra subs out of it. What I LOVE about the Sony subs is they are rated up to 1,000 hz so they pull double-duty. The upshot is integrating the subs is incredibly easy since the drivers are exactly the same as the speakers'. The subs become 'invisible'.

Anyhow here's my 'right front' cluster. In my 7.1 rig (phantom center) I have deployed one subwofer into each corner of the system and I have separated them into two channels to preserve stereo information.


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post #21 of 56 Old 12-09-2012, 07:22 AM - Thread Starter
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So here's the gist of it: I cut a hole in the bottom of the sump basin. The material is about 1/4" thick structural foam. Near the edge there is significant reinforcement, and mounting the driver in this fashion turns the bottom of the sump basin into an incredibly rigid baffle. I drove some oversized screws directly into the basin to act as feet. I tested the material's strength holding screws and it's really tough stuff so no special prep was needed - not even pre-drilling.





Here's some cool data points on structural foam, all of which sound good for subwoofer building:

When should the structural foam process be considered for a part?

The structural foam process should be considered when a part of substance is desired, which will need to have structural integrity.
When small to large parts are required with medium to thick wall cross-sections.
When an increase in stiffness of 3 to 4 times the strength of parts of similar weight is desired.
If there is a need for varied wall thickness within a part.
If sink-free surfaces of ribbed parts are desired.

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post #22 of 56 Old 12-09-2012, 07:50 AM
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Run some runs of duct tape around the bottom (top of sub). Let the duct tape stick up 1" to 1.5". Apply some concrete binder to the bottom of the sump and then pour concrete to top of duct tape. This will give you stiftness and a smooth top.

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post #23 of 56 Old 12-09-2012, 08:36 AM - Thread Starter
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Certainly, the time has come to attempt a permanent solution for making the top rigid. For a moment I thought it was going dual-opposed but I don' t have the budget for that approach and more importantly I feel that the single-driver subs hit harder (probably because each driver has double the internal volume to work with). The bricks do a 100% perfect job of making the 'top' rigid but at some point soon I'm thinking of wrapping these guys in black rope as a 'finish' and it could be very cool if it was a seamless coil coming off the top. I will give your idea a try this week.
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Run some runs of duct tape around the bottom (top of sub). Let the duct tape stick up 1" to 1.5". Apply some concrete binder to the bottom of the sump and then pour concrete to top of duct tape. This will give you stiftness and a smooth top.

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post #24 of 56 Old 12-10-2012, 09:35 AM
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Really cool design, looking forward to seeing them this weekend!
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post #25 of 56 Old 12-10-2012, 12:47 PM
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This weekend!!!

Mark, I gotta warn you my friend... Do NOT let Gorilla or I be a bad influence on you! Only turn it up to your comfort level. Those Sony are single 4 ohm, correct?

 

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post #26 of 56 Old 12-10-2012, 07:43 PM - Thread Starter
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Yes they are rather modest 12" subs, 4 ohm single voice coil. They have the worst published xmax I have seen outside of pro drivers - 6mm. Of course I think Sony is being perversely accurate in a world where exaggeration is the norm, I have no clue what to expect vs. the heavy hitters. Because of excursion limits, they won't compete in the teens or single digits. My best bet is to turn on the HP filter and let them rock from 20hz on up, where their musicality really shines.

We're going to make some noise!

One nice thing about Wal-Mart, I spent $7.00 on an extended warranty. If one blows, the worst that happens is I have to stand in line at customer service for 5-30 minutes.
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This weekend!!!
Mark, I gotta warn you my friend... Do NOT let Gorilla or I be a bad influence on you! Only turn it up to your comfort level. Those Sony are single 4 ohm, correct?

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post #27 of 56 Old 12-12-2012, 10:31 AM - Thread Starter
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Took me long enough but it just occurred to me, since the subs come apart in the middle - just 4 screws - I can build tops with vents in them, different tuning etc. plus I can keep a 'sealed' lid around. Off to Home Depot, I just modeled a 17 hz tune with three 40" long, 3" diameter vents. Vent mach is .04 and the point where it reverts to being same spl as sealed is 11 hz, and crucially the gain at 16hz is modeling as 8db which is obviously super. This plot is for 100 watts. Four of these with up to 500 watts (RMS) going into each one (and a HP filter of some kind) should go past reference at my SP at 16 hz once room gain is factored in etc. and that would be a first for me.


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post #28 of 56 Old 12-12-2012, 02:19 PM
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Run some runs of duct tape around the bottom...

imagic - he's right, you have to use duct tape or it isn't a true MacGyver style subwoofer. biggrin.gif

Excellent thread, true DIY ingenuity here.

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post #29 of 56 Old 12-12-2012, 03:09 PM
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When simulating vented enclosures, don't forget that unless the ports are outside of the enclosure, you have to subtract port volume from the enclosure volume. 3 40" long ports sticking out of the top could be cool though.

 

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post #30 of 56 Old 12-12-2012, 05:30 PM - Thread Starter
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I did subtract for the vent volume, that's a great heads up for anyone doing it the first time (that's me!). I credit this forum for improving my knowledge to the point where I feel total confidence now, doing a low-tuned ported sub. I am reserving the option of adding extensions for a lower tune, so the port does stick out a bit, to make that connection. Extension would be external. My inspiration is my first real subwoofers, the B+W Acoustitune, from the early 1990's It was a T-line, this is not... but it had swappable tubes for the port which was cool, and it had a graphic that just about says is all:


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When simulating vented enclosures, don't forget that unless the ports are outside of the enclosure, you have to subtract port volume from the enclosure volume. 3 40" long ports sticking out of the top could be cool though.

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