Hemisphere from Electrotap
Experimental Meyer Array
or you could follow these instructions to build a cheap array out of IKEA salad bowls and surplus automotive speakers. It won't sound as "accurate" as those other speakers, but it's surprisingly good and looks pretty cool on stage.
Special thanks and apologies to Dan Truman and the researchers at CNMAT, who's scientific work directly inspired this project.
P.S. Here's another cool loudspeaker array.
P.P.S The Stanford Laptop Orchestra built some nice ones here.
P.P.P.S. This one is nice, too .
Step 1: Acquire the Materials
but All Electronics was out of them. I got these, instead:
The important considerations were an impedance of 8 ohms (which is normal for home stereo speakers) and good frequency range. (in this case 70-10k Hertz). Sound localization is more acute at higher frequencies, so response >1k Hertz is especially important. It would be better to add a sub-woofer to make up for thin bass, than to have no high end.
While at All Electronics, get some Speaker Terminals.
I used four (4) "quad" terminals, but the four-pair ones look good.
(NB: If all electronics doesn't have these anymore. Try Parts Express or Radio Shack)
The other major elements in this project are the bowls. They cost $5 at IKEA:
Insanely cheap. Get two (2) sets because you need two of the biggest bowl. They also come in white. I imagined using one of each color, so this project would look like a big fishing float. Ultimately, though, solid red seemed best.
UPDATE: These bowls are no longer sold by IKEA. Sorry.
Finally, the miscellaneous hardware. 8 speakers x 4 mounting holes = 32. My local Ace hardware provided 32 machine bolts, locking nuts, and washers. Also, pick up 8 small nuts and bolts for the terminals. Most of the speakers were fine with 1/2" bolts, but the top and bottom ones needed longer (1 1/2") ones, as you'll see later. This may vary, if your parts are different.
- weather stripping
- speaker wire ( I had some 18 gauge stuff lying around the house, the project only needs a few feet.)
- heat shrink tubing
Step 2: Assemble Your Tools
A "high-speed rotary tool" with the following bits:
- #409 cutoff wheel
- #561 Cutting Bit
Soldering Iron, Solder, and heat shrink tubing
Wire Cutters, strippers
Scissors and a Pencil
Ear plugs and Safety Glasses
I'll emphasize ear plugs here. It wouldn't do to deafen yourself in the process of building a snazzy speaker array, would it? I like to wear earplugs when I do any work with power tools. (Or when I work with stupid fools.)
And of course, working with many of these tools is inherently dangerous. Just because I did this project without injury doesn't mean you won't hurt yourself. Be careful; as the agreement says: By using Instructables, you may be exposed to Content that is offensive, indecent, objectionable or unsafe. Each user must evaluate, and bear all risks associated with, the use of any Content, including any reliance on the accuracy, completeness, or usefulness of such Content.
Step 3: Cut the Hole for the Top Speaker
Use the rotary tool and the cutting bit to remove the circle of plastic inside this foot.
Step 4: Make a Template
Step 5: Mark the Locations of the Speaker Holes
To make sure they are exactly 120 degrees apart, used a piece of heat shrink tubing (or the like) to measure the circumference of bowl. Then divide the circumference by three, and used the same tubing to mark where the center of each speaker should be.
NB: For one hemisphere I centered a speaker on the handle and measured from there. The other hemisphere has a speaker centered on the spout. That way, the speakers are offset when you put the hemispheres together. Also, make measurements from both directions to make sure there aren't any errors.
I decided to put the speakers an inch away from the rim of the bowl. That left me clearance to put the lids back on, if I wanted to. Don't put them any further away, or they will wack into the top speaker.
Use your template to trace the speaker hole onto the bowl.
Step 6: Cut and Adjust the Speaker Holes
NB: This might be a better time to do step 13.
Step 7: Take a Break
Step 8: Modify the Terminals
Step 9: Prepare Your Speaker Wire
Step 10: Solder the Wires to the Speakers
Cut some short lengths (3/4") of heat shrink tubing and thread them on one end of a speaker wire. Solder the ends to the speaker terminals, slide the tubing over the solder joints, and use a heat gun to shrink the tubing.
My speaker cable has a reddish wire and a silver wire. I connect the red wire to the positive (+) terminal and the silver wire to the negative terminal. Some wire has colored insulation, or just a stripe on one wire. Conventionally, one connects a red or striped wire to the positive terminal. If you are inconsistent about this, you might accidentally reverse the phase of some of the speakers. While this will probably have no audible effect in this system, it would be a problem in a more scientifically calibrated setup.
For all the Rules of Hacking, see:
''Handmade Electronic Music: The Art of Hardware Hacking'' by Nicolas Collins, pp. 225-6.
Step 11: Prepare the Speakers With Weather Stripping
I ran a line of open foam weather stripping around the edge of all of the side speakers. (The flange of the top speaker sits flush against the "foot" of the bowl.) The purpose is to cover the gap between the speaker flange and the bowl, and hide any messy edges.
Step 12: Attach the Speakers to the Bowl
There is going to be a fair bit of muscle and bending in this step. As you can see, both the speakers and the bowl are a bit bent by the end. That's fine, it just makes the whole thing stronger. :-)
Repeat for the three side speakers.
BTW: It's possible that by this point you accidentally poked a speaker, and dented it.
Here is an instructable on "unpoping" dented speakers.
Step 13: Attach the Terminals to the Bowl
I was imagining this speaker hanging from the handles, so I kept the terminals as close to them as seemed reasonable. Check out the photograph to see how the positions are different on each hemisphere. There are two terminals on each hemisphere. On one, the terminals are close together near the handle. On the other, they are on either side of the speaker that is centered on the handle.
Since you've already got the weather stripping, stick some to the bottom of the terminals.
Finally, fit the terminal blocks, drill holes for the small bolts, and bolt the blocks in place.
Step 14: Solder the Wires to the Terminals
Step 15: Enjoy the Sweet, Sweet Music
You're going to need a few things to use your speakers, now that you've got them.
-- Eight channels of amplification. With the money you saved on speakers, you could by a Stewart DA-70-4 for each hemisphere. Or, to keep the whole thing on the cheap, get four t-amps . Currently, I'm running some class D amplifiers I found on ebay.
-- A source of interesting sound. I am a MaxMSP user, so I've used that software with the nbody~ from the PeRColate collection to create simulated body resonances of string instruments. You can also do this all for free with Pd .
-- I use it to make electronic instruments, or electronically processed acoustic instruments, sound more "real" and blend with other instruments.