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Discussion Starter · #1 · (Edited)
I was given a Polk MM1240 12" 4-ohm auto subwoofer. I was told it worked fine. So what to do? Build a subwoofer. I started this a couple of months ago and I can tell you, it does not end well...

My biggest problem building subs is cutting braces. I do not have a lot of tools, only the bare necessities. I have a router, a jig saw, random orbital sander and a circular saw.. No table saw, no real work bench, not even a workroom, most of what I do, is outside...

I just could not cut 45 degree angles accurately. I wasted a LOT of wood trying so I decided to make a jig... Using scrap wood, I was able to create a wood jig to help me cut the braces. It's not 100% accurate, but it's pretty close. You can see the results attached.

I would line up the circular saw against the guide. The wood would be inserted between the two guides under the jig which is already glued at the proper angle. Then just cut it.
 

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Discussion Starter · #2 ·
I got the MDF cut using a Kreg circular saw jig to help make the cuts straight. After that, I drew lines on the MDF to find the center (and to help mark where the bolt holes would go). I drilled a hole for the Jasper circular guide. I then used my router to cut the holes as needed. I used two 0.75" panels for the baffle. The driver would sit on one panel and the other panel would be flush mounted...
 

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Discussion Starter · #3 · (Edited)
I glued the baffles together, the mounted the driver inside. I used playing cards as shims to center the driver and then used an ice pick to punch the center holes for the bolt holes to start the drilling. When completed, I flipped over the baffle and routed the baffle to allow more breathing room for the driver, more so since the Polk is a shallow designed sub.
 

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Discussion Starter · #4 · (Edited)
I then glued the sub-enclosure for the amplifier together and assembled the box. I bondoed the crevices (without a table saw, the cuts will always be somewhat off in dimensions. Realizing this, I always make the largest panels somewhat larger than necessary, by about 1/4". That way, I can just trim the edges with the router to match the other sides. Sometimes, if the larger panels are a tad small, I ended up with indented edges which I had to fill.

Now this is where Murphy's law kicked in. I wanted to veneer the subwoofer with maple. The problem I encountered was that a couple of the panels was made with a MDF that had a very polished feel to it on one side. After applying the wood glue, I noticed that the wood glue would not adhere to the MDF. The glue dried in a sheet and I could peel it right off like saran wrap. Bad news. I sanded the MDF with 120 grit paper. I could not get the sheen off the MDF. A friend told me that the MDF I used is treated with some sort of fire retardant and this type of MDF is not used for cabinetry. In the photos, you can see the top panel has a different look from the sides. The surface has a semi-gloss finish that feels very slick.
 

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Discussion Starter · #5 ·
Well, I decided to try and paint the sub. I used Zinsser shellac-based primer on the top to see if it adheres to the MDF. That worked. BTW, if you are going to paint with oil-based finishes, never use odor-free or water based primers. When you spray lacquers or enamel over it, it will "prune" the surface into a lot wrinkles and cracks. It will look like the dried bed in a lake in Death Valley, I kid you not. You will have to sand the box down to remove all the primer to fix it...
 

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Discussion Starter · #6 ·
I decided to test the subwoofer out. I assembled it and put it in the living room. Seems to be fine. Played music and the sub augmented the bass from my bookshelves. So far so good, so I thought.
 

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Discussion Starter · #7 ·
So now, I had to primer the sub. I finished the whole box in primer then sanded it down. For you novices, you MUST primer the MDF, or else you will notice that the MDF absorbs paint and will have horrible surfaces, full of fuzz which cannot be sanded down cleanly without happening again. The Zinsser primer seals the MDF really well. After two coats, it is done.
 

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Discussion Starter · #8 · (Edited)
Well, I now painted the box with black primer. But before I painted it, my wife wanted the edges "softer", she thought edges was too sharp and that if my grandson hit it, he could hurt himself. So I rounded them with the router. I then painted the box with the black primer... You will notice that I used the circle cutout to cover the opening to prevent paint getting inside the sub. I am so clever sometimes... but usually not.

Actually, with the black primer, it looked pretty nice, I should have just left it alone... but...
 

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Discussion Starter · #10 ·
I painted a couple of coats. I let it dry somewhat and then painted a couple of more coats and started sanding it down... big problem. The black metallic coats layered over each other. When I sanded down through one coat, it appeared as a blemish.
 

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Discussion Starter · #11 · (Edited)
So, I had to repaint the sub with black gloss enamel. I had issues with lacquers before. It takes too long to cure before you can really sand it... maybe a month or more. I now use Rustoleum Automotive Enamel. It paints pretty evenly and it is somewhat run-resistant. if you use rattle can paint, this is the one to use... I love this. If you like lacquer, use the Rustoleum Automotive Acrylic Lacquer. It dries faster than their regular lacquer.

The pics shows the sub painted. On the bottom picture, the right side is the bottom, so it is not painted with the gloss black. That is why it is dull..
 

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Discussion Starter · #12 · (Edited)
Now the end of the story.

I assembled the sub and put it together. I tested the sub in my HT setup. That's when Murphy's Law kicked in again. While the sub worked fine with audio with it's lower bass output, the sub displayed a pronounced "flapping" sound above 100dB. Not a buzzing sound, but like something is slapping against the driver. I took out the driver and checked it out. Because of its shallow design, the frame blocks me from inspecting the spider or the cone from the rear. It really sounds like the cone has separated from the spider or maybe the voice coil partially separated from the cone.

Sorry, I don't have any pictures right now of the finished box, but I am so frustrated with this build, I just could not find the time to take any pictures. I am now in a quandary on what to do... I could just buy another sub (but it's $150) and replace the bad driver.

I also have to tend to my recently built DA HF390HO 15" subwoofer which the DA 1000-watt plate amp had its power supply die.

Then my wife just backed up into my car which was parked behind hers in the driveway. She said she did not notice it when reversing...

These things are supposed to happen in threes... I certainly hope so... I cannot handle much more of this right now... Once i decide on what to do, I will repost.
 

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Have you considered using pieces of a stout dowel for bracing instead of the pains of making exact cuts from MDF?

That's a bummer on the sub driver failing. A sub must get over worked pretty hard to wear it out to the point of coming apart, to my experience. Allowing repetitive "oil-canning" (bottoming out) of a sub is another way to ensure it's demise. Perhaps you just got a defective one. Luckily Dayton and PE are really good about replacing things under warranty...
 

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Discussion Starter · #14 ·
I did consider using dowels for braces. But from what I understand, bracing the way I did actually makes the cabinet more anti-resonant. I used dowels before and this method definitely makes the sub seem more solid. Rapping the walls makes a solid knock with no resonant effects as compared to my older dowel method. The Zaph build used eight larger braces, I used 12 braces the same size but it is 1"x2" vs. the Zaph's 2"x2" braces. I think that the 12 braces cover a larger area over the eight. The eight braces had some areas which sounded more resonant than others.

I sent my DA SPA-1000 back to PE and am awaiting their response. They were looking at it yesterday. I bought it the last week of April.

One of the mods told me to double check the driver seating... Air leakage could be causing the issue. I will check into that tonight. Hopefully that would be the cause.
 

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Discussion Starter · #15 ·
Thanks to one of the moderators, I was able to resolve my driver issue... The gasket was slightly misaligned causing an air leak. After repositioning, all is well... Unfortunately, while removing the driver, it slipped and nicked the left edge pretty badly. You can see it next to the left bolt hole.

Here are the pictures of the finished sub. Sorry, but the quality is kind of poor. The sub is in a black room. I had the lights on as well as two lights aimed directly at the sub.
 

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Looks beautiful to me! I like the styling of the woofer without a grill :T
 

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Nice build Jon! The paint came out nice. I have used the same bracing technique as you and it works good. The corner braces are easy to cut from scrap and they don't have to be fit to perfect length. They distribute vibration to perpendicular members, and they force wall vibrations to occur out of phase, which isn't likely at low frequency of a sub. I made the braces long enough so they attached 3/8 of the way into the panels. This provides 3/5 ratio (golden) and also spreads out the bracing force evenly across a panel when the braces are used on all sides. The best part is how easy they are to install compared to fitting traditional crossbraces or window braces.
Rich
 
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