Build Your Own Delorean

A guide to constructing your own six-channel hemispherical speaker
with built-in amplification

compiled by Scott Smallwood, Lawrence McIntyre, Dan Trueman, and Perry Cook

View History of hemis at Princeton

Parts List

These are the parts we used and their prices as of Jan 2008. Obviously these prices may change at any moment.

Multichannel audio interface
[ ESI U46XL ] $198
Six 4" coaxial speaker drivers
[ Polk db401 ] $58 / pair
Three Charlize T-Amp boards [*]
[ http://diyparadise.com/charlize.html ] $156 ea = $468
A 6-position potentiometer (conductive plastic, 3/4" shaft with 3/8" bushing and 3/8" shaft protruding. 50K log taper, 6 gang: from potentiometers.com, the part number is L26190)
[ http://www.potentiometers.com ] $58
A coaxial power jack (5.5 x 2.1 mm)
[ Kobiconn MJ21-EX ] $1.75
A 6-pin XLR jack
[ Neutrik NC6FP-1 ] $9.94
A 6-pin XLR plug (for cable)
[ Neutrik NC6MRX ] $13.04
Six RCA plugs, or 1/4 phone, depending on interface (for cable)
[ Neutrik NYS373 ] $1.89
A Knob
[ Radio Shack 274-424 ] $2.50
A 12-volt 4 Amp power supply (5.5 x 2.1 mm barrel)
[ PST-AC1240 ] $26.80
1-inch length 8-32 machine screws.
1/2-inch 6-32 machine screws w/ truss heads (6)
6-32 hex nuts (6)
3/8-inch 4-40 machine screws, w/ flat head (4)
Thermal adhesive
Removable threadlocker adhesive
Thermal insulation foam tape
Polyester Fiberfill
Several colors of 22 AWG stranded hookup wire
1/8" shrink tubing

[*] The Charlize amp boards are available from the folks at DIY Paradise and Calv Acoustic Labs at http://diyparadise.com/charlize.html. The version we are using includes blocking capacitors for removing DC offset, which also rolls off frequencies below 80 Hz, since these speakers do not represent low frequencies effectively (we use subs for that). There is also a higher-powered four-channel version available (see their website). There are also other manufacturers using the Tripath class-T amp (T-amp); this one uses the TA2020 chip and rates about about 10-20 W per channel. For more on the T-amp, see T-Amp FAQ.

This comes to about $837.92, not including small parts (screws, wire, tape, etc). This also does not include material costs for the body/shell of the speaker.

Finally, if you really want to all ALL OUT, check out the custom cases we had designed by the folks at Platt, for $150. Contact them directly for info about how to order one!

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Step 1: Building the Aluminum Shell

Building this speaker first involves creating the shell. There are many different ways to build a speaker shell. The one we describe here involves cutting sheets of aluminum and welding them together, so it may not be for the faint of heart. However, if suitable metal-shop skills and equipment are available, these instructions will get you there. Ours was built by Lawrence McIntyre in the Princeton University SEAS Machine Shop

1a.) Cut out main body, cut large holes in all panels and half holes in half panels. Drill and tap 8/32 holes in all panels excluding the half panels for speaker mounts.

[ pdf ]

1b.) Bend up all panels 110 degrees. Weld at half panel joint. Sand joint smooth.

1c.) Cut out, drill and tap bottom plate. Weld to main body. Sanding is not necessary on the bottom plate.

[ pdf ]

1d.) Cut out top plate. Cut out large holes and drill and tap 8/32 holes for speaker mounts. Weld to main body. Sand smooth with radius.

[ pdf ]

1e.) Fabricate drill jig to drill and tap 8/32 holes in the half panels.

1f.) Apply finish

There are obviously other options available for creating your own shell. Electrotap sells the larger 6-channel hemi we were using for several years, which could potentially be retrofitted with built-in internal amps. See also the Low Cost Spherical Speaker Array instructable, and the salad-bowl speakers of the Stanford Laptop Orchestra (SLOrk).

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Step 2: The Guts

Once you have built the shell, it's time to build and mount the guts, which includes the amplifiers, jacks, and volume pot, and all of the wiring involved on connecting everything together. You will need the following:

Three Charlize T-Amp boards [1]
A 6-position potentiometer [2]
A coaxial power jack (Kobiconn MJ21-EX)
Several colors of 22 AWG stranded hookup wire
1/8" shrink tubing
Foam tape

2a.) Solder a common 12-inch ground wire to all the potentiometer grounding terminals, as shown:

2b.) Solder six 36-inch long colored wires to each of the pot's lower terminals, and one 36-inch long black wire to the ground. Twist them together into a harness of cable.

2c.) Now solder six 8-inch long wires, using the same color scheme as the cable harness above, to the middle, right-most terminal of each pot position. Twist these together into three pairs, as shown:

2d.) Solder three pairs of the wires above to three different Charlize boards. Whatever you chose for channels 1 and 2, for example, white-purple/purple, will be soldered to the left and right input terminals of a Charlize board. Do the same for channel pair 3 and 4, and pair 5 and 6.

2e.) Using red and black wire, solder the power terminals of each Charlize board together and connect them to the coax jack; and include the ground common ground wire of the pot in this power ground.

2f.) On each Charlize board, solder an 8-inch pair of wires to the left and right output terminals of the board. Use the same color scheme to identify channels. For example, the white-green/green input wires for channels 1 and 2 would result in a left output with white-green/black, and the right output with green/black.

A completed set of guts.

Guts wiring overview. [ pdf version ]

An important final step before mounting the guts inside the shell is to TEST each amp channel to make sure it works. Simply plug the amps into a 12V power supply and run test leads to each input on the pot from a line audio source (CD player, iPod, etc) and connect a speaker temporarily to the corresponding output. If they all work, go on to the next stage.

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Step 3: Install the Guts

This is a delicate and often frustrating operation that involves mounting the amps and all of their appendages into the center of the shell. Here it is very important to make sure the shell has the proper holes drilled (see Step 1). Here is what you will need:

The guts you've assembled in Step 2 above
A cool knob (we got ours from Radio Shack)
1/2-inch 6-32 machine screws w/ truss heads (6)
3/8-inch 4-40 machine screws, w/ flat head (4)
Thermal adhesive
Removable threadlocker adhesive
A 6-pin XLR jack (Neutrik NC6FP-1)
Thermal insulation foam tape

3a.) Mount short pieces of foam on each end of the back of the Charlize boards. Then use nylon cable ties to fasten the three Charlize boards together into the shape of a triangle. NOTE: You will probably have to leave one corner unbound until you get the whole contraption into the shell! Otherwise you may have trouble fitting it through the speaker hole.

3b.) Stuff the boards into the shell through one of the speaker holes, and fasten the final side together to finish the triangle. Position it in the center. Mount the volume pot through the top hole in the hemi, as shown:

3c.) Mount the coax power jack as shown:

3d.) Paint the bottom of each of the TRIAD amp chips with thermal adhesive. Then position the board cluster in the center of the inside of the hemi so that the six circular holes on the bottom will line up with the half-moon indentations on the TRIAD amp chip of each board, as shown. Use 6-32 machine screws and nuts, and be careful not to over-tighten! Use threadlocker on the screws and nuts. NOTE: Be careful to orient the three amps towards the speaker holes whose speakers they will power, if possible.

3e.) Thread the long cable harness tailing off of the volume pot through the jack mounting hole. Solder the leads to pins 1-6 for channels 1-6, and solder the ground lead to the grounding terminal on the jack. Mount the jack using 4-40 machine screws. Remember to use threadlocker! NOTE: Make sure that the tab on the jack is facing the right edge of the speaker.

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Step 4: Install the Speakers

For this step you will need:

Your favorite 4" coaxial drivers (6). We like the Polk db401.
1-inch length 8-32 machine screws.
Foam tape.
Polyester Fiberfill

4a.) Mount some foam around the openings for the speakers, enough so that any flat metal or plastic part of the speaker flange will not rattle.

4b.) Pull out the appropriate pair of leads for each speaker, solder it up, and carefully mount the speaker. Use threadlocker!

4c.) Before installing the sixth and last speaker (top), first fill the inside of the speaker with acoustic fiber. Put in a lot of fiber -- but don't over-stuff. Make sure that wiring and boards are not pressed-upon too much.

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Step 5: Testing the Speakers

Once the speakers are all in place, mounted, and ready to go, it's time to test your speaker. This can be done in many ways, and should involve testing each speaker independently and together with the others.

We have devised several test patches for Max/MSP and ChucK which you can download here:

hemitests.zip

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The Connecting Adapters

The six-pin XLR input jack is quite non-standard, so there aren't any adapters available commercially. You will have to build your own, or you can order them custom from HAVE, Inc if you are ordering several (send them the pdf below - they will have seen it before).

The six pins represent the hot signal from six independent line inputs. They share a common ground, which should be connected to the connector plug's ground casing. The diagrams below show how 2 different adapters should be made. One is as described, and the other is a "mono" adapter, which essentially splits the signal six ways.

Speaker Cable MULTI. [ pdf version ]

Speaker Cable MONO. [ pdf version ]

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