Dual 15" "Mofo" build - AVS Forum
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post #1 of 54 Old 09-08-2011, 02:46 PM - Thread Starter
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I'm about to start building a pair of ported 7.2 ft3 19hz tuned 15"s. Just got my woofers in today! I have everything but the amp, which is looking like an NU3000 DSP after some reassurance of its actual power output (600W @ 4ohm!) My situation is very different from most of you, as I like in Alaska, and shipping from PE is absurd. After looking into many drivers none here have considered, I settled on a Power Acoustik MOFO 152X. This was only $150 shipped from Amazon. While this is no world beater, it is an extremely well built 15mm Xmax 15", that models well in sealed and vented enclosures.

Edit: Plan was changed to a pair of 2.8 ft3 sealed boxes using O Audio 500W plate amps. Final pics on 2nd page.






Close up of the aluminum heat sink/cone stiffener


600 watts with 20hz HPF, excursion only hits 13.5mm

Will update with box construction over the coming weeks.
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post #2 of 54 Old 09-08-2011, 06:15 PM
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Good luck.
This wasn't the best brand back in the day. But subwoofer technology has come so far since 20 years ago. Nowadays most mfg's just copy each other. So it's probably pretty hard to screw up a subwoofer anymore. I'm sure it'll do just fine.

"The boom is dead, long live the bass"
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post #3 of 54 Old 09-08-2011, 06:33 PM - Thread Starter
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Quote:
Originally Posted by CZ Eddie View Post

Good luck.
This wasn't the best brand back in the day. But subwoofer technology has come so far since 20 years ago. Nowadays most mfg's just copy each other. So it's probably pretty hard to screw up a subwoofer anymore. I'm sure it'll do just fine.

Yes, I am definitely taking a risk, but the price makes it worth the risk for me. I could see problems being more likely if I had 1500 watts being driven in a 1.5 ft3 sealed box like a car guy might try.


I would like to add that this will be replacing a single sealed original shiva mk2 with 240 watts
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post #4 of 54 Old 09-08-2011, 06:51 PM
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Kick ass! I ran one in 5.1 cubes tuned to 19Hz.. in car! It was spectacular! I expected it to be terrible... car audio spl burper with a 4" coil, huge brute magnet, and a maelstrom-X 21" like flat/fat/wide surround. I ran a Type R in the same enclosure and the MOFO sounded much much better and didnt need a break every 2 minutes. I love the aluminum cap and fins. Those things are built like tanks yet sound great!
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post #5 of 54 Old 09-08-2011, 06:52 PM
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looks like they sixed the Sd wasting surround issue too... the 15" I ran had a cone that was the same as 10"ers, the rest was all surround.
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post #6 of 54 Old 09-08-2011, 07:25 PM - Thread Starter
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Thanks for the encouragement KW. It looks like the new MOFOs are a complete redesign
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post #7 of 54 Old 09-09-2011, 12:47 AM
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Yep, the one I ran had tripple slug and the top and bottom plate were completely different, the bottom part of the basket was a lot different too... looks like now there is perimiter venting.
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post #8 of 54 Old 10-23-2011, 10:52 PM - Thread Starter
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Alright, I finally have begun working on this build. Due to lack of time, I decided to go with a pair of sealed boxes. I also got a pair of O Audio 500W plate amps in order to simplify things even more.



One sub cut out.




This is my jig for making long accurate cuts with a circular saw. My crappy Hitachi table saw is only good with pieces under 2'.




Should line up ok, even though the Lowe's plywood is bowed...




2nd sub cut. Hopefully I can make lots of progress in the next couple days, as I'm heading out of town for a few weeks.
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post #9 of 54 Old 10-25-2011, 12:27 AM - Thread Starter
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Made some decent progress today. I'm definitely a novice woodworker, but I'll try and and give some good detail.




Hole marked for woofer cutout.




A 1/8" hole needs to be drilled through your piece and into a backer board for the jasper jig guide pin.




Every things pretty tight, a tap from a mallet helps. Had to use vice grips to get the pin out the first few passes.




Definitely do a dry run to make sure the path is clear.




Started on the outside at my woofer flange depth, then worked in to the woofer cutout diameter.




Baffles done!




Amp cutout marked. I "chain drilled" the corners to allow my jig saw blade to fit for the start of each cut.




It fits!




Started gluing things up, I'll figure out my bracing once both sides are glued on. Hopefully I get a chance to do more tomorrow, as I'm out of town on Wednesday for a while.
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post #10 of 54 Old 10-26-2011, 05:00 PM - Thread Starter
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This is as far as I'm going to get before heading out tonight. Got half the bracing in on one cab, the other cab is at the same point without bracing. How long do you guys normally leave PL premium clamped up? Bottle says 24hrs, but that seems excessively long.

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post #11 of 54 Old 10-26-2011, 05:03 PM
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I normally clamp it, shoot some brad nails into it, then unclamp.
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post #12 of 54 Old 10-26-2011, 05:12 PM - Thread Starter
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I don't have a real nail gun, my POS can hardly shoot through 1/4" plywood.
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post #13 of 54 Old 10-28-2011, 04:55 AM
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Where do they begin the rolloff.....some dsp would be nice with the alignment now being sealed.
What response are you looking for...
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post #14 of 54 Old 10-28-2011, 06:37 AM
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How do you know that the inuke3000 puts out 600 watts per ch @ 4 ohms? Since you know this do you know what it puts out at 8 ohms as well?
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post #15 of 54 Old 10-28-2011, 09:51 AM - Thread Starter
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With an 80hz highpass the f3 models as 32hz.

As for the inuke, there was a thread a couple months ago with a link to a German mag that measured its output
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post #16 of 54 Old 10-28-2011, 02:17 PM
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Quote:
Originally Posted by Jay1 View Post

With an 80hz highpass the f3 models as 32hz.

As for the inuke, there was a thread a couple months ago with a link to a German mag that measured its output

How bout a couple pics of the room, or just the size of the room.....

Will you be using an L/T to extend FR... How low if so...
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post #17 of 54 Old 10-28-2011, 03:40 PM - Thread Starter
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The room's a 22' x 22' x 8' sealed basement, with concrete walls. I'm not worried about picking up room gain. In a couple years when I move back to the lower 48 and buy a house I can build the large ported boxes I originally intended, but for now this really will be more then enough.

This is the predicted response, i will have 2 of these

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post #18 of 54 Old 10-28-2011, 07:31 PM
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I have no idea what im lookin at without the freq
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post #19 of 54 Old 10-28-2011, 11:20 PM
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"I have no idea what im lookin at without the freq"

standard log plot. the wide range is from 10hz to 20hz. the second one to the right is 100-200hz.

Listen. It's All Good.
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post #20 of 54 Old 12-22-2011, 04:16 PM - Thread Starter
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Alright, I forgot I had this thread going Progress was definitely slow, as the plywood is incredibly crappy. I pretty much just gave up trying to get the finish perfect and this is going to be as good as it gets, I've been sitting on these too long and I still have 5 speakers to build

Box's were finished up last night, tons of bondo to fill in peeling/voided/chipped plywood. I could have spent another month doing this...




Three coats of primer down. Going let my garage air out and the primer cure up, not the easiest thing to do when its 20 degrees but at least the garage is heated.




Next, going to lightly scuff these and hit'em with flat black.
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post #21 of 54 Old 12-22-2011, 04:23 PM
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awesome awesome. hope there is a lot of EQ/LT as well... hope power is enough... either way should be a good turnout no matter what
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post #22 of 54 Old 12-22-2011, 05:16 PM
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Looking good!!

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post #23 of 54 Old 12-22-2011, 06:47 PM
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Check out the thread on the Oaudio 500w HPF for details on how to model the four choices. They each have a different Fc and Q and there is a lot of boost you need to account for. If nothing looks good you can change resistors just like in the regular 500w BASH amp.

http://www.avsforum.com/avs-vb/showt...ghlight=oaudio
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post #24 of 54 Old 12-22-2011, 07:19 PM
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To address your primer cure comment:
That specific primer in the picture is a hot solvent based primer (acetone, xylene, toluene, laq thinner, etc). When using this specific Krylon product you have a couple windows in which you need to work. Within one hour you can continue to recoat the primer or top coat with a hot solvent top coat (ie Krylon flat black in the picture). Otherwise you MUST wait 24 hours before top coating. I commonly see/hear complaints from customers who do not operate within those windows and encounter wrinkling/lifting problems as a result. What happens when dealing with the above mentioned solvents is they have a an almost "melting" characteristic to them. They are hot enough to re-wet the surface and cause lifting, wrinkling, solvent entrapment, blistering, etc. At that point you will need to solvent wipe and strip to the original substrate and start your project over.
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post #25 of 54 Old 12-22-2011, 09:47 PM - Thread Starter
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Quote:
Originally Posted by tgse3 View Post

To address your primer cure comment:
That specific primer in the picture is a hot solvent based primer (acetone, xylene, toluene, laq thinner, etc). When using this specific Krylon product you have a couple windows in which you need to work. Within one hour you can continue to recoat the primer or top coat with a hot solvent top coat (ie Krylon flat black in the picture). Otherwise you MUST wait 24 hours before top coating. I commonly see/hear complaints from customers who do not operate within those windows and encounter wrinkling/lifting problems as a result. What happens when dealing with the above mentioned solvents is they have a an almost "melting" characteristic to them. They are hot enough to re-wet the surface and cause lifting, wrinkling, solvent entrapment, blistering, etc. At that point you will need to solvent wipe and strip to the original substrate and start your project over.

Good info on the Krylon products. I was planning on waiting until sometime tomorrow before scuffing/painting. The 3 primer coats were done back-to back-to back as the flash off was rapid. The wide spray tips on these make them my favorite spray cans.


Quote:
Originally Posted by top_down View Post

Check out the thread on the Oaudio 500w HPF for details on how to model the four choices. They each have a different Fc and Q and there is a lot of boost you need to account for. If nothing looks good you can change resistors just like in the regular 500w BASH amp.

http://www.avsforum.com/avs-vb/showt...ghlight=oaudio

Thanks! I'll have to look into that.
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post #26 of 54 Old 12-22-2011, 10:05 PM
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Quote:
Originally Posted by Jay1 View Post

Good info on the Krylon products. I was planning on waiting until sometime tomorrow before scuffing/painting. The 3 primer coats were done back-to back-to back as the flash off was rapid. The wide spray tips on these make them my favorite spray cans.

In my opinion there is no reason to use any other spray can on the market. They have great hiding, even spray pattern, great distribution channels, variable tip angles, limitless color options, quick drying, sand-able, good tech support, etc. I have used various other brands and it is a night and day difference for my money.

Just be careful tomorrow not to get on it too soon. You're right it flashes almost immediately and feels dry, but I assure you it will wrinkle if it's not cured out.
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post #27 of 54 Old 12-23-2011, 01:04 PM
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With the sealed cabinet and the 25hz filter on the Oaudio amp you get a little better extension, with an F3 of around 29hz. But you're pushing it big time on the Xmax and amplifier load (VA). If you like it loud you will probably have to add at least -2db of PEQ around 25hz to protect the driver (and amp from clipping) and that will push your F3 back up.

I wouldn't try the other 3 filters at all, from what I see in WinISD they all cause problems unless you baby it. (I don't know about you but I don't have that kind of will power)

Now I'm no expert, but from where I sit if you are willing to do a little rework and add two 4" x ~28" long flared ports (18hz tune) to each cabinet and change some resistors in the amp you can get an F3 of 18hz and run the amp at near full output. The difference in output at 20hz is remarkable (10db if I am modeling things right). I realize this means reworking some of your bracing, but I think this is worth doing if this is for home theater.

If you decide to go ported, the filter you really want is Fc=18.7hz and Q=1. What you have at the 25hz setting is Fc=23hz and Q=1.42. On the Oaudio amp you need to change two resistors to get the lower Fc and Q - it's described on the Oaudio website in one of the 500w downloads. It's not the easiest thing to do if you don't solder a lot, as the leads are clinched and the clearance between lead and hole is tight.

If you aren't comfortable soldering, you can use the 25hz setting as it is and add -2db of PEQ at 28hz and get pretty close, the F3 would be at 19hz. Still much better low end than with a sealed sub.

Thanks for tipping me off on this driver - I would have never given it a second look before.
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post #28 of 54 Old 12-23-2011, 01:35 PM - Thread Starter
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Quote:
Originally Posted by top_down View Post

With the sealed cabinet and the 25hz filter on the Oaudio amp you get a little better extension, with an F3 of around 29hz. But you're pushing it big time on the Xmax and amplifier load (VA). If you like it loud you will probably have to add at least -2db of PEQ around 25hz to protect the driver (and amp from clipping) and that will push your F3 back up.

I wouldn't try the other 3 filters at all, from what I see in WinISD they all cause problems unless you baby it. (I don't know about you but I don't have that kind of will power)

Now I'm no expert, but from where I sit if you are willing to do a little rework and add two 4" x ~28" long flared ports (18hz tune) to each cabinet and change some resistors in the amp you can get an F3 of 18hz and run the amp at near full output. The difference in output at 20hz is remarkable (10db if I am modeling things right). I realize this means reworking some of your bracing, but I think this is worth doing if this is for home theater.

If you decide to go ported, the filter you really want is Fc=18.7hz and Q=1. What you have at the 25hz setting is Fc=23hz and Q=1.42. On the Oaudio amp you need to change two resistors to get the lower Fc and Q - it's described on the Oaudio website in one of the 500w downloads. It's not the easiest thing to do if you don't solder a lot, as the leads are clinched and the clearance between lead and hole is tight.

If you aren't comfortable soldering, you can use the 25hz setting as it is and add -2db of PEQ at 28hz and get pretty close, the F3 would be at 19hz. Still much better low end than with a sealed sub.

Thanks for tipping me off on this driver - I would have never given it a second look before.

It's too late in the game for me to modify the design, I've already taken a month longer then I wanted. The 25hz looks acceptable, I wish I would have known so much boost was applied on the low filters... Don't remember if I said anywhere else in this thread, box volume is 2.8ft3 after bracing/driver accounted for.

I had to research numerous "unknown" drivers in order to avoid paying $90 shipping for a $150 driver. Hopefully it does what it's supposed to do!
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post #29 of 54 Old 12-23-2011, 04:37 PM
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Sorry, I didn't figure out the 2.8cf thing - obvious now that you mention it!

Anyway, you're still good with the 25hz filter and about a 2db cut at 25hz. The boost helps you out in the 25-45 range so it's not all bad. You can try to go without the cut (or use it someplace else to cure a peak) but in WinISD it looks like without it you'll start to exceed Xmax at around 300w.

Good luck!
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post #30 of 54 Old 12-23-2011, 06:29 PM - Thread Starter
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Alright, got 2 coats of black down, gonna wait a day then stuff and wire these boys up!

I like to use scotchbrite pads to scuff paint, it will knock off any particles that stuck while priming without fear of burning through, and give you a proper "dulled" surface to adhere your next layer to without leaving any sanding lines.

I painted the bottom even though it wasn't necessary. Gave it a minute to flash off, then stood them up on the feet I previously installed prior to priming.
LL
LL
LL
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