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Discussion Starter #1 (Edited)
I originally posted this over at AVS (http://www.avsforum.com/avs-vb/showthread.php?t=1161766). This was my first attempt at a DIY sub. I have been looking at the M&K subs for a long time now but as I'm still in college I don't have that much money to blow on a sub so I chose to go the DIY route. I originally had a Sony SA-WX700 which is also a Push-Pull sub. Basically this was an attempt to take the sound from that and go bigger and better.

This is the build thread for my Peerless Push-Pull (Non-Isobaric) sub. The original design thread was here:
http://www.avsforum.com/avs-vb/showthread.php?t=1147609







First off, let me start by saying this was my first real wood working project. This was the first time I’d ever done any finishing work, including painting. I mean I built a catapult for a school science fair in junior high but that was going on 10 years ago and that was all hand sawed. This was my first experience personally using a circular saw and a router.

That being said I am really happy with the way it turned out, the finish is nowhere near perfect but everything else turned out great. It seems to perform very well, granted I’ve never actually heard any high end subs, Bose doesn’t count nor should it. I’ve heard some Klipsch, Polk and Infinity at the big box stores but that’s about it.

Starting out my father just bought a router so I had that to use on the project. I was also able to borrow a circular saw. I bought one of these:
http://www.sears.com/shc/s/p_10153_12605_00966423000P?keyword=bora+clamp
to make a makeshift table saw and one of these:
http://www.sears.com/shc/s/p_10153_12605_00967173000P?keyword=drill+guide
to use as a makeshift drill press. The Bora clamp really came in handy when using the circular saw, the router and the jig saw. Along with those and a couple orders from PE and a few orders from McMaster Carr this is what I ended up with:



After cutting all the pieces I started out making the window braces. I tried the hole saw in the corners method and that really sucked. I tried going slow as suggested here and no matter what I did the teeth kept getting gunked up and burned the wood.



I went back to Home Depot looking for something better and came across a Forstner bit. Man is that thing nice, it turned a three minute job into a 30 second job. I did 48 holes with that thing, 8 of which were through 1-1/4” MDF and it is still sharp. It turned the MDF into confetti and no burning what so ever regardless of drill speed.



I then used the Bora clamp and a jigsaw to cut between the holes. These were the final products:


I had decided from the beginning to make the walls thick. I decided to clamp and glue 1/2 inch MDF to 3/4, this would also allow me to flush mount the Peerless 830952 drivers. I cut the hole in the 1/2” bigger than the hole in the 3/4” and this is how the front and inner speaker baffles turned out:



After that I decided to cut groves in the front and rear walls of the box to put the braces in, made assembly easier.






I decided to use EZ-Lok threaded inserts instead of T-nuts. I read about the problems with the T-nuts and I saw the thread discussing how to glue them to the wood so they wouldn’t back out when removing the drivers. Because of that I decided to give these a shot and I think they worked out really well. These wouldn’t hold a Maelstrom but they do make them with different lengths. In this shot you can see the threaded inserts around the lower speaker baffle and around the edge where the removable bottom goes:



Assembled:


Prepped for paint with 3/8” round overs all around except for the bottom edge where I used an 1/8”:





Now this being my first time working with MDF I did not know the end grain was going to be such a problem. I put wood filler on the exposed ends and sanded them down even but in doing so in some places the end grain reappeared. These spots became a nightmare when trying to put primer on them. I tried to build the primer up as much as possible on these areas but sadly they did end up showing through with the final finish. I used Rustoleum textured black paint which I hoped would help hide some of the flaws. Luckily the bad spots are not horribly noticeable.















Old v.s. New (Sony SA-WX700 v.s. Peerless Push-Pull)


It isn’t in its final position in these pictures, it was in the living room for testing. It is now in my 1100 cubic foot bedroom hooked to my Denon 2808-CI and is more than enough bass for me. Hopefully I can get a hold of a Behringer ECM8000 so I can quantify the results.

Question: Does anyone else have experience with push-pull subwoofers like those of M&K? There is a high pitched squeaking I think may be coming from the sub when pushed hard. Either it’s something else in the room or both this new sub and my old Sony made the same sound. I just wondered if it was possibly a sound coming from the exposed driver as I know Michael Hurd mentioned I could have a problem with motor noise and I wanted to know if that’s what I’m hearing.

Thanks again for your help Penn, tlag, Mr. Hurd, and Mayhem13. :)
 

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Discussion Starter #5
There are 2x 12" Peerless 830952 in this cabinet, which has now been replaced by the Peerless 835017.
http://www.madisound.com/catalog/product_info.php?products_id=8636

I don't have plans exactly, I drew it up in CAD using Unigraphics as you can see here:
http://www.avsforum.com/avs-vb/showthread.php?t=1147609

You can see I didn't make the wall joints nearly as complicated as I had them drawn, just glued together a piece of 0.5" MDF and 0.75" MDF of equal size. This was mainly so I could flush mount the two drivers and then I just decided to do it for every wall.

I knew the external box dimensions, 17"x20"x32" (WxDxH), and I kept a calculator handy so I could figure out the dimensions of the internal pieces as I went along by subtracting the external wall thicknesses.

I can tell you that all of the walls are doubled up with 0.5" on top of 0.75" MDF, as is the baffle for the second speaker firing into the enclosure from the bottom. This second (internal) baffle is 6" above the bottom of the front piece, 7.25" from the bottom of the entire enclosure. The holes near the bottom (vents) on the front and back pieces are 4"x12.5". The internal window braces are 0.5" MDF and spaced evenly through the internal volume. After the walls are all together and the top and bottom pieces were the only things left I cut a piece of 0.5" MDF 17"x20" and glued it to the bottom of the walls to make the "trap door" and allow access to the second driver as you can see in the photos.

I was aiming for 88.5 liters and I think it ended up somewhere around 90 liters. The Oaudio plate amp is great for this sub, I could easily bottom out the drivers before the amp clips so it has some head room.
I have been very happy with the sound quality, there is no stuffing inside of it and I'm not sure if that would make the sound any better. It is great for music and handles movies just fine.

Feel free to ask any other questions you have and I'll do my best to answer them in a timely manner.
 

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Discussion Starter #7
For the internal window braces I just left an inch around all the edges, (the grooves in the front and back were 0.25" so 1.25" on the front and back edges) then the cross in the middle, those beams are one inch wide. I cut the holes in the corners with a 1.25" forstner bit and cut in between them with a jig saw.
 

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Elite Shackster
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Did you use thinner MDF for the bracing? I ask as I started my own push pull build tonight and your input would be valuable.
 

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Elite Shackster
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Ive gone with 1/2" for the brace as well. Ive done OK with my build this last couple nights, and I'm going to post up my thread tomorrow to see what you everyone thinks. How does yours sound in pure SQ terms?
 

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Discussion Starter #11
I really like the sound quality of the sub. As I said, it sounds great with music and it has enough output for movies in my small bedroom at home. The only thing I have considered changing is the possibility of adding some polyfill to the inside of the enclosure and see if there is any difference in sound. However there is a problem with this as the bottom of my enclosure has the cone of a driver in it.

I saw your build with the AV15-X drivers, nice work. I'm considering doing something similar in the future, possibly dual opposed AV15-X's, kind of like Mark Seaton's Submersive. That's a more expensive project though. Currently I'm working on a ported Tempest-X2 build in 7ft^3.
 

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Just stumbling on this post in 2017, it's like traveling through time. I just thought I'd offer an option for finishing MDF. I went to school for Industrial Design, and we had to make several scale models and MDF is often a material of choice. What we do to allow us to finish such a material with something like spray paint (MDF readily soaks up moisture through an unprepared surface) is you actually apply a few coats of Polyurethane to seal it, sanding in between. This also circumvents the need to add wood filler, as the poly will fill in the imperfections and sanding will smooth it all out. For any large issues, you can use Bondo between primer coats like you would with a car.
 
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