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Lab 12 Dual Opposed Sealed Sub

post #1 of 16
Thread Starter 
Several months ago I purchased two Eminence Lab 12 drivers for $90 total. One of the drivers is brand new and the other was only used for some limited testing of a design idea. I decided to build a dual-opposed sealed subs for my office. I am currently using a Hsu VTF-1 MK-1 ported subs from about 2002.

The sub will be 15" wide, 21" tall, and 20" deep. Those proportions are similar to a Submersive. According to the enclosure volume calculator at HomeTheaterShack it has an internal volume of 2.173 cubic feet. The build will use 1 sheet of plywood. I used Cutlist to optimize the build for use with two 4x4 sheets if anyone wants to copy the build and can't get a whole sheet of plywood in their vehicle. I bought a piece of 3/4" 11 ply baltic birch veneer/poplar plys at Menards for $30. I had used it before and really like it. It is cheaper, yet stiffer than the Arauco ply carried by Menards. It also has nicer outer veneer. I will have 1 1/2" thick baffles so the driver can be recessed. The sub will have a Neutrik Speakon connector with the drivers wired in series for a 12 ohm load. I will paint the sub with DuraTex. The nice thing about DuraTex is that you don't need to prime the cabinet, it is easy to apply, and it is very durable. I have some speakers with DuraTex and really like it. You can get the DuraTex dyed other colors, but I am using black.

The sub will be powered by a Samson SX1200 amplifier that will be bridged. I bought the amp from MKTheater about a year ago. In bridged mode, it has 900 watts at 8 ohms. Since I am using a 12 ohm load it will probably output around 700 watts. This will be plenty for use in my office. I could make a 4 wire cable that goes into the Speakon on the sub and is branched to the two Speakons on the amp and use both channels of the amp. Each channel would then have a 6 ohm load. I get more power bridged and it is a simpler cable so I don't see any advantage to running the amp in dual mono mode. Any comments?

EQ and a Linkwitz Transform will be handled by JRiver Media Player. I've had a DCX2496 and miniDSP and JRiver is far more powerful and easier to use if the source is a PC.

The sub will be used mostly for music with an occasional movie during lunch. I also do some gaming during lunch and can route the game audio through JRiver so the EQ is still being used. I will probably shoot for a -3dB of around 25 Hz.

Tonight I will cut the plywood and hopefully cut the round openings in the baffles and braces. For the braces I will cut 3 rectangles that fit in the sub and then cut a large circle out of each rectangle. If you read any shelf deflection tests in a wood working magazine you find that a strip of plywood mounted vertically along the bottom front edge of a shelf measures to the least deflection. It is stronger than doubling the shelf. My braces are similar in that they are placed around the entire inside of the cabinet and stiffen the walls. They are only about 3" apart, too, so the cabinet becomes incredibly inert. They are easy to make - you just cut a rectangle and then a circle. It is a lot less time consuming than some of the post or dowel bracing system. It also has the most surface area support with the outer walls.




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post #2 of 16
Cool project!

I got three of those Samson's from MKtheater too.
post #3 of 16
why didn't you just build a simple LABHorn? :-)~
post #4 of 16
Thread Starter 
Quote:
Originally Posted by LTD02 View Post

why didn't you just build a simple LABHorn? :-)~

Too big for under my desk at work. Also, my coworkers would think I'm crazier than they already do.

I also looked at the Tuba 60 and Tuba 60 slim from Bill Fitzmaurice. They are also way too big.
post #5 of 16
Thread Starter 
I got all the wood cut between last night and this morning. Here I am using a straight edge with clamps to cut the wood with my circular saw.



I wanted my inner braces to be exactly the same width so the edges would be tight against walls of the subwoofer. Two of the boards were about a 1/64" too wide. I clamped two boards together with one edge flush and used a flush trim router bit to trim the top board to the bottom board's width.



When cutting the plywood into 48" long strips the correct width you end up with a small board for the last cut. To make it easier to cut I clamp another plywood strip next to it with a plywood strip on top. This makes it easy to "hang" the part I need to cut off the end of the saw horses.



To cut the width of the plywood I used my Bosch compound miter saw. It will only cut 12" width so I make a cut and then flip the board and finish the cut. I set a stop on the right side so all my cuts are the same without having to measure.



After I finished cutting I had two stacks of wood. The stack on the left is for eight 15" drivers and was cut from one sheet of plywood. The stack on the right was also cut from one sheet of plywood and is for the Lab 12 Dual Opposed build. You can see one of the MFW-15 dual opposed in the background. I have three projects going at once right now!


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post #6 of 16
Thread Starter 
After I finished cutting, my wife called me in for breakfast. She had made the whole family omelettes with avocado on top. Yum!


LL
post #7 of 16
Looking good. That ply looks very nice for the price as well!
post #8 of 16
"Too big for under my desk at work. Also, my coworkers would think I'm crazier than they already do."

:-)

but seriously, that driver in a small enclosure is going to have a pretty steep rolloff, so will more than likely need some eq.

red is my guess at the hsu mk1

yellow is my guess at what you have there.
LL
post #9 of 16
Thread Starter 
I couldn't work as long as I wanted on Saturday due to rain. I finished putting the cabinet together on Saturday. I used 1 clamp, Loctite Pl Premium adhesive, and an 18 gauge nail gun to put the cabinet together by adding just one piece at a time. After gluing, clamping, and nailing one area I can release the clamp and it stays tight. I then slide the clamp down, reclamp, and shoot a few more nails. I started with the bottom and one side, added the other side, installed the inner baffles, slid in the 3 braces, and then installed the top. The last thing I did was install the outer baffles. I had slightly oversized the width of the top and bottom and all of the outer baffles.

I only had a few hours available yesterday. I used my trim cut router bit and cut off the edges that were overhanging slightly. I then gave all edges a slight round over.





The DuraTex instructions say it doesn't adhere well to Bondo and they recommend using drywall mud to fill holes and imperfections. I had a partial bag of 45 minute mud (joint compound) and I mixed some up with water in a sour cream container. I filled in the holes and let it sit for a few minutes to dry. It was dry in about 15 minutes after I was done filling in the holes. I then sanded it down with a medium sanding sponge. You can see the size of the cabinet in relation to the MFW-15 dual opposed subs I'm refinishing with DuraTex.



This morning I painted the cabinet with the first coat of Duratex. I used a 4" sponge roller to apply it.



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post #10 of 16
Thread Starter 
For fun, I'm going to take my driver cutout and install a 14.5" port that is 3" in diameter. This will tune the sub to around 22.5 Hz per WinISD. Here is what both subs look like at maximum SPL with the Samson SA1000 amp. Dual Opposed Sealed is Yellow and Singe Ported is Red.


If I add a little EQ and high pass each sub at 21 Hz, then I get the following:


Here is the cone excursion with the EQ.


Both alignments now model very similar and have a 10 dB rolloff from 40 Hz to 20 Hz. It will be interesting to see if they measure like they model and if I can hear the difference between the two alignments.

If I like them ported, I can use the same amp and add about $50 in materials for a second ported sub. Here is dual ported vs a single dual-opposed as modeled in WinISD.

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post #11 of 16
nice job on the cab desert.

"For fun, I'm going to take my driver cutout and install a 14.5" port that is 3" in diameter."

sounds like a good experiment. not sure if you are going straight port or one with a roundover. roundovers can make a pretty big difference as far as reducing chuffing.

http://www.subwoofer-builder.com/port-flares.htm

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=268-350&FTR=precision%20port%203"%20flared%20port%20tube%20kit
post #12 of 16
Quote:
Originally Posted by desertdome View Post

For fun, I'm going to take my driver cutout and install a 14.5" port that is 3" in diameter. This will tune the sub to around 22.5 Hz per WinISD. Here is what both subs look like at maximum SPL with the Samson SA1000 amp. Dual Opposed Sealed is Yellow and Singe Ported is Red.

If I add a little EQ and high pass each sub at 21 Hz, then I get the following:

Here is the cone excursion with the EQ.

Both alignments now model very similar and have a 10 dB rolloff from 40 Hz to 20 Hz. It will be interesting to see if they measure like they model and if I can hear the difference between the two alignments.

If I like them ported, I can use the same amp and add about $50 in materials for a second ported sub. Here is dual ported vs a single dual-opposed as modeled in WinISD.

Hello desertdome,

Did you complete the build? I'm curious as to how it turned out. Thanks!
post #13 of 16
Wouldn't a 3" port chuff to high heavens with anything over 100W against a 12" sub? When I was doing some simulations I saw either 2x 3" ports or a single 4" as the minimum.
post #14 of 16
Thread Starter 
Quote:
Originally Posted by grubyhalo View Post

Hello desertdome,

Did you complete the build? I'm curious as to how it turned out. Thanks!

I completed the build and have been using it in my office as intended. It sounds great. I never did try it ported since I liked it so much sealed and I had other things to do.

I'll try to get a chance to post pictures and measurements.
post #15 of 16
Quote:
Originally Posted by desertdome View Post

I completed the build and have been using it in my office as intended. It sounds great. I never did try it ported since I liked it so much sealed and I had other things to do.

I'll try to get a chance to post pictures and measurements.

Good to know. Thank you for posting this!
post #16 of 16
Awesome project, I bet it sounds phenominal!
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