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"Mega MOFO" Dual 15" PR build

post #1 of 35
Thread Starter 
Well I'm finally re-building new subs. The compact "sealed with boost" setup I have now works very well, but I figure I should go bigger bass reflex just because I can. I jumped on CSS's APR15 sale last year ($60 ea shipped!), and got 4 of them. These are very simple to use with the included 900g washer kit and outer attachment point, one could adjust their tuning on the fly at any time.

http://www.creativesound.ca/details.php?model=APR15

I'm reusing my MOFO 152X woofers, and O Audio 500 watt amps

http://www.poweracoustik.com/pa2012/subs-MOFO-152X.html



My intended design is 6.5 ft3, with the dual PR's loaded with the full 900g mass for a 17hz tune. I'm going to down fire the active driver so I dont have to look at it (I considered repainting the blue areas), with the PR's side firing.


My actual box is probably going to be about 0.2 ft3 smaller, which shouldn't be an issue when those dimensions give 7 ft3.

WinISD model of the native alignment


And with the Oaudio's 20hz filter boost added


I'm predicting a rise below 30hz wont be a big deal due to sound perception, but I'm placing the amps out of the enclosures this time just in case I decide to change my amp setup.
post #2 of 35
Thread Starter 
Progress will likely be slow, as I'm not a very good wood worker, and am usually pretty busy. If you're a good wood worker, skip this part. I'm going to try and help other newbs out. Most of my clamps are 24" and this box is just large enough to make them useless, so I decided the glue/screw approach would work.

My method was to dry fit the panels, and adjust for squareness. I used clamps with light pressure to keep things aligned.


Once I was happy, I drilled pilot holes (3/32" bit) through the vertical pieces to prevent splitting, and to align everything. I marked to corners with letters so there would be no confusion.


I drove the screws thorugh the top/bottom panels just enough to grab the pilot holes.


Glue (PL Premium) was put on the bottom, a panel set on the screws, and then a few of the screws were drove into the piece to hold it. After both side panels were tacked, the top was set on and tacked, and all of the screws driven in tightly


This is the first set of braces, and where I'm at currently. I measured in equally from the sides and drilled holes, then screwed the braces in place. 2" x 3/4" strips of ply.
post #3 of 35
Thread Starter 
Bracing round 2 complete.



So far everything's gone smooth, I'm sure I'll figure out a way to mess up when it comes to the side panels/braces.
post #4 of 35
Thread Starter 
Yes, I'm still building these biggrin.gif The side panels are only going to be 1/2" ply, so I'm adding stiffeners

post #5 of 35
Don't sweat the duration Jay, its far better to take your time and get the result you're after than it is to rush and wish you hadn't.

Side note, Sears and HD have 90degree calmps that will hold the corners when putting two pieces together and you don't have to worry about what legnth clamps you have. They are pretty cheap too.
post #6 of 35
Are you building 4 single enclosures for the CSS woofers? What are you using for the PR's? Are you also building enclosures for the MOFO's? If so, how do you plan on implement them?
post #7 of 35
Thread Starter 
I'm building two enclosures, each with a 15" active driver (mofo) and a pair of the CSS APR's.

I'll have to look at for those corner clamps Chop. Do you have a link to the exact one you're talking about?
post #8 of 35
Quote:
Originally Posted by Jay1 View Post

I'm building two enclosures, each with a 15" active driver (mofo) and a pair of the CSS APR's.

I'll have to look at for those corner clamps Chop. Do you have a link to the exact one you're talking about?

These are the big ones, a bit more $$, but the top of the page shows some of the small inexpensive ones too.

http://www.sears.com/shc/s/p_10153_12605_00931508000P?sid=IDx01192011x000001&kispla=00931508000P&srccode=cii_17588969&cpncode=31-79493211-2
post #9 of 35
Thread Starter 
Round two of side stiffener bracing complete.

post #10 of 35
Thread Starter 
Alright, I cross braced the stiffeners, and with that, I fill like there isnt any benefit to more bracing.



I'll have to glue up the sides one cabinet at a time as I dont have enough sand bags for both.
post #11 of 35
Thread Starter 
My high tech method for gluing the sides on



Humidity's really low right now, the PL still isnt cured after 24 hours frown.gif
post #12 of 35
Thread Starter 
Here's a good shot of the bracing scheme. This is a pair of # braces tying the sides/top/bottom togethter, a + brace on the front/back walls, with a 4" cross brace connecting them. This entire scheme used a single 24"x28" piece of wood! Regular style window style braces would have used at least three 24" x 24" panels to equal this much bracing


post #13 of 35
Thread Starter 
I've got my exact cabinet dimensions now. 25.375" H x 23.75" W x 24.75" D with four of the panels being .704" thick, and two being .45" thick. After subtracting the bracing volume I'm left with 7.15 ft3! I'm figuring I'll lose another .25 -.3 ft3 for the woofer and PR's. The tuning point should be right about 16.6 hz after loading 900g on each.
post #14 of 35
Thread Starter 
Finally some progress updates eek.gif

After flush trimming all of the edges, locating dead center on all of the panels was very simple, and the reason I assembled the cabinets in this manor. I stuck with the simple build techniques, a compass and ruler to trace the cutout diameter.


Jigsaw for a quick and easy job


The PR fits!


Not sure if I'll test fit the woofer for a while, but next up is some round overs, and then finishing.... ugh
post #15 of 35
Quote:
I figure I should go bigger bass reflex just because I can.

I love this attitude! Great hobby, DIY stuff.
Subscribed.
post #16 of 35
Thread Starter 
Making a little more progress.

Normally I use bondo for all body work, but I want to try something simpler. I really like this plastic wood stuff. It isnt as good or strong as bondo, but it is easy to apply and sand, and it's a very good match for the wood if I wanted to use stain.


Also trying something else new. I rolled fiberglass resin on the cabinet, with the goals being a very smooth surface for paint, and a much more durable surface.
post #17 of 35
So how did the fiberglass resin work? I'm about to finish a cabinet too and was thinking over sealing options and thought this would be a great way to get a very smooth and hard seal to protect the cabinet.

Scott
post #18 of 35
Thread Starter 
Well I haven't gotten further then the last pic shows, so I cant really say for certain. It rolled on very easy, and fairly smooth.
post #19 of 35
What did you use to roll it on? Just a nice foam roller?
post #20 of 35
Thread Starter 
Just a regular old 3/8 nap roller. My trick to getting good results with a roller is to "de-frock" it. I'll have to take a pic when I do the second half of my cab. Basically you just take a roll of tape, pull a piece out and stick it to a table, then run the roller back and forth on the sticky side until material stops coming off the roller.
post #21 of 35
Jay, how low do you think these babies will go? Do you think that they will go lower, and play louder than a single Dayton HO18 in a vented enclosure?
I might have to do a clone build of your MegaMOFO + CSS build!
post #22 of 35
Thread Starter 
Quote:
Originally Posted by Martycool007 View Post

Jay, how low do you think these babies will go? Do you think that they will go lower, and play louder than a single Dayton HO18 in a vented enclosure?
I might have to do a clone build of your MegaMOFO + CSS build!

The box tuning point is a hair above 16hz. With my O audio 500 watt amp, which has boost on each HPF setting, I'm going to have an F3 of 15hz with the amps 20hz setting. (see post #1)

The native (no filters) box response is basically an EBS alignment, the F3 is 27hz, but get this, the F4 is 16hz. So there's a shelf in the response for that last 10hz or so. Only issue with that is you HAVE to add a high pass filter with something like a miniDSP. That of course would change the response, 15hz HPF makes 16hz the F6 point. This still will crush an HO18 below 30hz. I actually plan on switching my woofer to an Ultimax 15 with a EP4k miniDSP setup once I leave Alaska and dont have to pay shipping.

Here's a comparison showing the Mofo15 (orange), and UM15 (green) both with a 15hz HPF and 650 watts, vs an HO18 (blue) in 4ft3 sealed no filter with 650 watts


(mofo exceeds xmax by 1.5 mm)
post #23 of 35
Quote:
Originally Posted by Jay1 View Post

The box tuning point is a hair above 16hz. With my O audio 500 watt amp, which has boost on each HPF setting, I'm going to have an F3 of 15hz with the amps 20hz setting. (see post #1)

The native (no filters) box response is basically an EBS alignment, the F3 is 27hz, but get this, the F4 is 16hz. So there's a shelf in the response for that last 10hz or so. Only issue with that is you HAVE to add a high pass filter with something like a miniDSP. That of course would change the response, 15hz HPF makes 16hz the F6 point. This still will crush an HO18 below 30hz. I actually plan on switching my woofer to an Ultimax 15 with a EP4k miniDSP setup once I leave Alaska and dont have to pay shipping.

Here's a comparison showing the Mofo15 (orange), and UM15 (green) both with a 15hz HPF and 650 watts, vs an HO18 (blue) in 4ft3 sealed no filter with 650 watts


(mofo exceeds xmax by 1.5 mm)

I am not too well versed in reading graphs. Do you believe that the MOFO 15 is less capable than the UM15, or the other way around? I currently have 2 UM15's with each in a 3 cubic foot enclosures, powered by an EP4k.
What makes these 15" drivers out perform a well regarded 18" driver? Is it the high quality passive radiators? Is it the cabinet design, or what?
post #24 of 35
Thread Starter 
The UM15 is definitely better then the MOFO. The MOFO is closer to the Dayton DVC 15 performance wise. Passive radiators act extremely similar to ports, they function almost the same with a few minor differences, which is why they can both be called Bass Reflex (BR) designs. If I somehow shoved a pair of 4" x 33.5" ports inside each box, I would practically achieve the same results. The gain from the port/pr as the tuning point is approached is what allows these smaller drivers to have more output then a larger driver in a sealed box.
post #25 of 35
Thread Starter 
Here's the technique for removing the "fuzz" from a roller that I discussed above. Once the fuzz stops showing up on your tape you're good to go. This is a 3/8 nap, smooth finish, woven fabric roller



And the cabs are fully resin covered.



We'll see how long it takes me to get around to painting rolleyes.gif
post #26 of 35
Thread Starter 
I decided I'm going to hold off on the finish work until after I move, doing large paint projects in my tiny garage is just getting really tiresome. That and I have a project I really need to finish by Sept that I cant start until I get these beasts out of my garage.

I have 4 pillows stuffed in there


Plenty of clearance for the PR's


Even though I'm going to replace these woofers with UM15's I figured I might as clean up the looks while I have the driver out


Messed it up a little while demasking, but nothing that cant be touched up


Threw together a couple of quick boxes for the amps while I was at it.

post #27 of 35
Thread Starter 
Wrapping this one up until after I move. Getting it in the corner on the other side of my setup is to much of a PITA, so yeah, that's a pretty big stack biggrin.gif



Just a generic in room of a single sub. Had it near the center of the room, about 12" from one of the front corners. 1/24 octave. Might not fully represent the second PR. You can see the noise floor I have to deal in the sub bass region with as well


I'll straight up admit I really dont know how to use REW, so I'm pretty sure I didnt have things setup correctly but I was curious to see the results compared to Omnimic.


Tuning point is right at 17hz. Not really sure if DATS is even strong enough to get a good reading with a sub like this, but I verified with a signal generator and the old cone motion test. Really easy to tell with a PR.


Oh yeah, and now one of my amps is going bad mad.gif The green light is staying on at all times instead of switching red. I now know why O Aduio went out of business, amp repairs. When I originally bought these amps one was bad right off the bat, and now here we are again... Good thing I already set the subs up for an external amp.
Edited by Jay1 - 6/9/13 at 12:11am
post #28 of 35
Sorry to hear about your amp, just so you know, I have a Behringer EP4000 that I am looking to sell for a very good price. If you are interested feel free to PM me.

Otherwise, this looks to be a very capable sub! I have a couple of UM15's in two ported enclosures that I absolutely love. I wonder how the UM15's would differ between using a vented enclosure, like mine, versus using a PR, such as yours?
post #29 of 35
Thread Starter 
Turns out it's just the red standby light that isnt working on my amp anymore, everything else functions normally. Thanks for the offer on the amp, I'm going to wait until after I move to reconfigure the setup.

A PR and port function very similarly. There is a very slight loss in output with a PR vs vented, it is known and predictable. A port can have compression issues, which dont show in models, and noise issues which can happen for a variety of reasons depending on the build. A PR wont have those issues, and functions as predicted as long as your design doesn't exceed the xmax limit of the PR. Obviously a port is a much better value, and as long as you can keep the airspeed of your design low, it makes more sense.
post #30 of 35
Jay, what would be a good pair of PR's to use with a Dayton UM15? I am currently running the UM15's in a sealed enclosure but would like to experiment with passive radiators. I would really like to do some vented or PR based enclosures for my UM15's tuned down to 16hz or so!
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