Not so Rat Rocker build thread - Sean's NLA Towers

[bkeane1259]

When Wolf decided to do a Rat Rocker build theme at InDIYana 2012, it inspired me to use some of my stockpiled and now NLA drivers and other surplus parts and whip something together for the show.

Once I got started however, it turned into more of serious build and my younger son (17 years) took an immediate interest in the towers and wanted them for his room. This is the largest speaker in the house, so there's sort of a "wow" factor in it for my son.

Anyway, the original plan was to repurpose some old shelving material and make the cabinets sort of shabby-looking. I had the mill near us plane this rather thick poplar board down to 1" and rough cut it for me. They did an excellent job and the wood actually looks really good. Yes, it's an all-hardwood speaker cabinet, but it's a rat rocker, so it's ok.

I decided to go with a MTMWW design utilizing (2) 6.5" buyout subs + Aura NS35-255-4a + Vifa bc25sc15-04.

I tried modeling a 3-way XO and not only is that an impossible task for me, but it was really expensive. I have several SA240's sitting around doing nothing, so these speakers quickly became partially active. I am powering all 4 subs with one SA240. So that leaves me with designing a 2-way XO on the top portion. I went pretty much textbook with the XO. Second order at 2k for the NS35's and 2.5k third order on the BC25 with 4db of padding. The NS35 is an underrated driver IMO. It's fairly flattish from 150Hz to 4k but then it gets wonky really fast. It has a nice natural rolloff below 100Hz, but to play it safe, I added a first order 100Hz high pass filter via 2 paralleled 100uF NPE's. The BC25 is useless anywhere near 1k and it has a slight suckout (2db-ish) at 6k which I did not address. Otherwise, it's fine. I picked the XO points really just based on analyzing the respective FR graphs and using online calculators. I was able to use a ton of my surplus XO parts for this and I did a lot of component coupling to get to the values I needed for the slopes.

Since I had only heard them in my garage the week of the show, I really had no clue how they'd fare in a more normal environment. I thought I really lucked out after hearing them at the show. Even better, I was pleasantly surprised to have received positive feedback from InDIYana attendees. Wolf even bumped me out of the Rat Rocker category...hehe.

So for yucks, here's how it went down......I'm calling them "Sean's NLA Towers"

[bkeane1259]

I'm very old-school, so:



and....



and the XO schematic:

[bkeane1259]

Here's the layout. The subs will be in a ported 1.25ft^3 (after bracing, etc) chamber, with a 3 I.D. x 11" flared PE buyout port. Tuning is 33Hz and modeled F3 is 30.2Hz. The MTM portion will be sealed in about 0.35ft^3.



I'm using mostly poplar, but also some 1/2" ply for braces and the MTM shelf.



The braces:

[bkeane1259]

One of these days I am going to have a nice square joint....but not today unfortunately. Story of my life.

[bkeane1259]

Driver cutouts.



I have a template for the truncated BC25 that I made last year. It's not perfect, but it gets me very close.

[bkeane1259]

I used a 45deg chamfer bit on the woofer cutouts and a cove bit for the mids. I had to take out a fair amount of stock for the mids....







The NS35 flanges are a real PITA. There's basically NO flange at 4 points on the underside, so not only does the cutout need to be perfect, but you still have to use some sort of gasket or seal if you want an air-tight fit.

[bkeane1259]

Unclamped and ready for a lot of sanding.





Cutouts for the ports. The exit flare requires a pretty large cutout. The port diameter is 6.5".





Also installed binding posts:

[bkeane1259]

I'm making the front baffle removable. Using these threaded inserts and bolts from Meniscus.

[bkeane1259]

Don't try to flush trim 1" stock with a 1/4" bit.



This is what happens:



Out comes my friend, Mr. Bondo.

[bkeane1259]

Dayton SA240




A slight mod to the SA240. Since I want a full range signal to come out of the hi-level section of the amp for the pass-through to the MTM, I have to open up the amp and take out the factory-installed caps.

Dayton uses a first order high-pass filter on the hi-level outputs which is basically a NPE cap.





Some heat-shrink tubing on the spliced sections of wire.

[bkeane1259]

The case for the SA240:





The XO components. I pieced together a few different components to get the correct values. After what felt like putting together a jigsaw puzzle, I got everything within 0.5% of the calculated values.







Stuck the XO's in the sealed MTM chamber.

[bkeane1259]

Box stuffing/lining. Late last year I did some experimentation with open cell memory foam. Basically it works really well if you use it on the rear wall of the cabinet. There's no need to line every surface. It actually worked better just being on the rear wall. It works surprisingly well at sucking up midrange frequencies but it also seems to enhance the low end a bit. So for this build I'm putting memory foam bats on the rear wall, in both chambers. Then, in the bottom chamber, I also used Walmart mattress topper. The sealed MTM section will be filled with Roxul....not overly stuffed, but about half way stuffed, in addition to the memory foam on the rear wall.



Gasket tape to help seal the baffle:

[bkeane1259]

I took them to the show just like this (unfinished).....I have not yet decided what to do, finish-wise. My son is not in a rush for anything other than getting them installed in his bedroom. That's good for me. Also, I'd like to wait several months at least and see if anything happens to this hardwood cabinet.....creeping, splitting, etc.

[bkeane1259]

Overall, I'm extremely happy with the sound. The 6.5" subs have more than enough low, punchy bass. The 33Hz tuning seems to be perfect and they work very well in the 1.25ft^3 box. The 3" flared port has absolutely no noise whatsoever, even at high volume.

The MTM section and my XO shockingly work well. I was lucky....I'm no liar. I got a few nice comments from the folks at InDIYana....thanks for that.

Soon they will be up in my Sean's room.......He better be nice to the neighbors, because these "not-so-rat rockers" really rock.

[johnnyrichards]

Very lucky child, sir. What a fun build!

[bkeane1259]

The total cost for this project was fairly cheap. Since I used old wood, all buyout drivers and the buyout port plus lots of used XO parts and a used SA240, I was able to keep it under $250 for everything.

Fat chance getting that out of my kid though.....

[carlspeak]

Great looking build Bryan.

So, where's the measurements???

[bkeane1259]

Great looking build Bryan.

So, where's the measurements???

Ha..... Don't hold your breath for those my friend. I got these done just in time for the show and they never made it out of my garage initially. Now they are back in the garage waiting for me to haul them up to my kid's room.

No promises on any measurements.

[PWR RYD]

Cool build Bryan. Your wood working shop looks just like mine (aka the driveway)

Even with those huge reliefs you made to the back side of the baffles it still looks like those Aura drivers are gonna sufficate They must have been designed to be mounted to 1/2" partical board baffles

Do I spy some freebie yellow caps from DIY Chicago?

[dlneubec]

Bryan,

I thought you did a very nice job on them. They sounded very good. Your son will love them. I see bigger and better challenges in your near future!