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Can-Can
A
Computer Speaker in a Light Canister
(69,996
bytes)
Some time
ago, we installed some cheap overhead lighting in one room
of our house. The light fixture were "track-like"
but without the track - just three canister lights mounted
to a metal bar that's screwed into the ceiling. These were
cheap units in every sense of the word and when I removed
two of them during a room overhaul, various parts fell apart
rendering them useless as lights.
Recently,
I was contemplating mounting a full-range driver into a light
canister mounted inside an armoire. I shelved that project
for another day but decided to see what would happen if I
tried it on a smaller scale in a computer speaker for my office.
(50,851 bytes) Here are the raw parts - canister light
housing, Aura NS3-193-8A drivers from Madisound,
and a small surplus JBL multimedia amplifier from ApexJr.
 (54,061
bytes)  (71,911
bytes) The drivers arrived well packed in cardboard wrappers
with plastic standoffs to protect the rubber surrounds. The
Aura driver boasts some interesting specs
(PDF file). The 3 inch driver has a very low Fs (80 Hz)
for its size, decent power handling (20W RMS, 80W peak), is
magnetically shielded, and has a large excursion (5 mm Xmax,
20 mm peak to peak max excursion). The potential for equalizing
this driver to achieve a decently flat and wide response is
intriguing. The main drawback is the low efficiency (80 dB
1w/1m) but that's ok given the intended use as a computer
speaker.
 (68,494
bytes)  (35,283
bytes) The JBL amplifier is the same one I used on the
CeePeeDee project. I
had a spare unit collecting dust. It uses a TDA7360 amp chip
and has its own wall wart for power.
 (93,287
bytes)  (79,635
bytes) To mount the driver to the white metal housing,
I milled a ring of MDF on a drill press with a fly-cutter.
Each ring was painted black to match the driver's flange.
I cut a small notch in each ring to provide clearance for
the driver's + and - wiring tabs.
 (58,661
bytes)  (64,057
bytes)  (63,964
bytes) Each ring is glued to the canister with construction
adhesive. The excess is scrapped off the outside after it
has hardened somewhat. The driver is screwed in place with
four sheet metal screws. Driver wiring runs inside the canister
and mounting post.
No attempt
was made to "design" the enclosure. The internal
volume for the canister is about 0.38 liters, not accounting
for the driver; to small to be of use in any alignment with
these drivers. Since this is for simple computer use, I opted
to just enjoy them as they are. The holes in the rear of the
canister (to let light bulb heat exit) are left as-is.
 (65,854 bytes)
The small amplifier PCB is mounted to the center
of the light fixture assembly (where the third light canister
used to be) on a piece of wood (which acts as an insulator).
I made no attempt to house the amp in anything.
 (74,610 bytes)
With everything done, I mounted the light assembly
to a shelf over my computer monitors with two bolts.
[Updated
Jan-13-2005] How do they sound ? They're much better than
the Altec Lansing/Dell multimedia speakers they replaced.
Pointing them downward, they provide better coverage of the
sitting position than desktop speakers. I did some simple
informal A/B listening and everyone liked them better as well.
The main drawback is the lack of power on the amp and low
output voltage on the sound card. The drivers are not all
that efficient but do have loads of excursion. I fed some
60Hz hum and they were able to move some serious amounts of
air. The canisters are very stable. There's enough friction
in the joint to keep the speaker pointing in whatever direction
I want yet still allow me to move them easily and accurately.
My initial
tests showed minimal vibration in the housing. But subsequent
usage showed that the cans not only vibrated a good amount
when the volume was turned up, but the vibration was also
transfered up the supporting joint to the overhead bar. In
the office setup, the vibration continued to the plywood shelf,
then down the center supporting leg to the desktop. I could
feel the vibration with my wrist resting on my keyboard.
As luck
would have it, I had to remove the speakers from this setup
so they are now sitting about collecting dust. When I get
the chance, I'll try applying EQ to see how flat and low a
response I can get. I'll also try filling the bar with clay
to help deaden it.
13-January-2005
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(50,851 bytes)
(54,061
bytes) 
(71,911
bytes)
(68,494
bytes) 
(35,283
bytes)
(93,287
bytes)
(79,635
bytes)
(58,661
bytes)
(64,057
bytes)
(63,964
bytes)
(65,854 bytes)
(74,610 bytes)