SATELLITE CONSTRUCTION
I first did the satellites, since they're the simplest and I wanted to re-acclimate myself to the subtleties of my pathological table saw. It's all butt joints except the faceplate, which has a 1/4" rabbet all around. Both drivers and terminal cup are recessed for a clean look, which I did using a router and Jasper Jig.
Here the satellites are being clamped (poor man's clamp) and glued. While this was going on, I populated the crossover boards. As we've agreed, getting silkscreened crossover boards is a total waste so let's not beat a dead horse.
After the glue dried, I filled the seams with wood putty, and let them sit for two weeks to harden. Actually, I left and didn't come back until two weeks later (damn day job) but it certainly didn't hurt the finish. Often with wood putty people will find that if they apply paint too soon after filling then over time the putty will expand and press out the seams, leaving unsightly bulges. By re-sanding after the two week curing time, I hope I've minimized this possibility. Here're the crossovers and drivers being mounted:
I'm a big fan of PC-7 epoxy, shown above. It's got a great shelf life, easy handling (thickness of peanut butter, according to the press release), and cures to an incredible hardness. The crossovers are bolted to metal standoffs which are epoxied down to the bottom panel, and all the screw threads are loktite-ed to keep from vibrating loose. When all's said and done, here are the two satellites of my system, posed tastefully beside a bottle of sherry for size comparison.
SUBWOOFER CONSTRUCTION
As the satellites moved off the table saw to the paint booth (you'll laugh in a second when you see what exactly that entails) I began the arduous task of constructing a precision multi-chamber enclosure with my table saw, which from observation while building the satellites had gained 1/32" of skew over 24" since I last used it. After cutting all the pieces from the cut list I made in SketchUp, I had to trim a few pieces to get them all to play nicely together. I ended up deepening the dado cuts a bit reasoning that I could always reinforce the joints later with a filler of sawdust and glue. Test fittings:
The piece I'm holding is a support dividing the two chambers. It's got two 10-32 T-nuts embedded which will provide anchors for the removable cover. As shown they are being glued in place with Gorilla Glue, which for all the awesomeness that is it's space-filling expansion, requires a hefty bit of positioning as provided by the clamp and screw. The transformer and driver are simply making temporary appearances so I can test clearances. The finished raw cabinet looks like this:
You can see the silver T-Nuts in the holes. While I don't expect to be taking the cover on and off frequently, machine bolts as anchors provide strength that wood screws would lose after the first few removals. Now we move on to the painting process, and you can laugh at my interpretation of a painting booth:
A note on the finish. I had always wanted to try a micro-pebble finish, but from reading literature that would require too much fancy equipment to do right. Instead, I bought a gallon of DuraTex paint, and a few cheap textured rollers. The rollers are really coarse, and at first I didn't like the finish, but in retrospect it's durable as hell and doesn't took too bad. While this was drying, I moved on to...PLATE AMPLIFIER CONSTRUCTION
I'll be honest, I like working with metal, but only when I have a full shop. I have a long chunk of extruded heatsink and some sheets of 6061 in the closet but I'll be damned if I'm going to cut all that with a hacksaw. My recourse is the mecca of all DIY project parts, I speak of course of eBay. I browsed until I found exactly what I was looking for: a surplus plate amp pulled from some crummy subwoofer. I paid $31 for it, including shipping.
I gotta admit that for a purported cheap plate amp, it's unique. Most low power plate amps use monolithic chip amps (guilty as charged) but this actually has a fully discrete class B amplifier, sure using TIP31 transistors, but it's the thought that counts. Anyway after 5 minutes this thing looks the same as anything else I touch for 5 minutes: in pieces and FUBARed.
Now comes the part that endears me so to my mother, where I take over an eating surface and cover it with live electricity and lead solder.
Note the champagne colored blowtorch in the middle of the table. It's just there to add to the "electricity poison fire" death mix and freak her out more. For all the heat-shrinking, I just used a hot air gun which provides much nicer results with less burning. Here's a close-up of the board during the final stages of testing.
The two regulators were getting hot on the crossover board (lower, parallel to the plate) so I put in my favorite kind of light-duty heatsink: two strips of aluminum flashing sandwiching the devices. And this is what the finished face of the amplifier looks like:
You'll notice that the text no longer corresponds exactly, but I did my best. The speaker level outputs are the left and right binding post pairs, with the red set for the right speaker. The volume control knob and phase control knobs still function, and the unmarked additional knob is a bass control. The line level inputs are new, but the power LED near the fuse functions as normally.The plate amp only took a minute to screw into the subwoofer cabinet, and I was done. I ran it at high volume for a day (again, to the chagrin of my mother) to break in the drivers. A neat trick is to wire the satellites out-of-phase and face them inward, so the projected sound is greatly attenuated. Playing a mono organ music CD is the best way to hit the full spectrum, and the attenuation is maximal because of the mono signal. Note the impossibly cute iPod nano sourcing the tunes.
But you didn't come for just that photo. Here is the coup de grâce, the raison d'être for this speaker system...HOW TO ENJOY YOUR JACK-IN-THE-BOX SPEAKERS
Appreciate the beauty and simplicity of only having to transport one cabinet. Once you've decided on a location to unpack...
Turn the box upside down to expose the four thumb screws holding the bottom panel.
Undo the four screws and remove the panel, exposing the inner compartment holding the satellites!
Remove the first satellite, and place it aside.
Remove the second satellite. Place the two straps for removing satellites back in the chamber, and reseal it with the thumb screws.
Enjoy!
THINGS THAT AREN'T PERFECT
- Open-loop design for the amplifier PCB. I lost $100 for the PCB and about $25 in parts, just because I didn't do a careful design review. Don't ever ever design a circuit without testing at least something first. In simpler terms, don't be so arrogant as to think you can design everything right the first time. I've had professors that talk about "back in the day" when they'd do layout non stop with grid paper and pens, all the while subsisting on hot dogs and coke, and the chip would work the first time. There's a reason why they're the big shots, and that's definitely not me, and probably not you either.
- Volume control noisy. The only dual-gang pots I could find are 100K, which when dialed to their midband position have a maximal Thevenin resistance looking into the amplifier. You can actually hear the speakers get noisier in the middle volume setting, due to the carbon resistor noise.
- Adire Audio woofer. For all the hype surrounding its XBL2 motor technology, I'm pretty unimpressed with it's performance. I'm almost positive its sensitivity is several dB below advertised. When you factor in the price, it's definitely worth it to stick with Tang-Band drivers.
Sound wise I can't say definitively yet because the woofer is still breaking in, but the satellites are eminently musical. Thanks mostly to their physical footprint the stereo imaging is exceptional, and I find the highs present without being straining, which is my primary complaint with cheap tweeters. The lows are obviously absent, but assumed very smoothly by the subwoofer. I was hesitant to choose a fixed crossover point for the satellites, but I think I lucked out in that the listened response as well as the measured response is flat in the 100Hz region, after a bit of placement tinkering and phase adjustment.
Well, on to the next project!
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