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:: Big Voice ::
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The system is
affectionately referred to as
"Big Voice", but its official designation is the
Beachmaster Announcing System.
From
the manual:
"It is a portable,
high-level, high-gain auditory system for distant
projection of sound. It is intended primarily
for use by a Beachmaster in directing landing
operations."
Get it? Beach landings... as
in World War II !
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| The system was designed
and built by Western Electric for the Navy (well
prior to becoming part of Altec
Corporation). Each of the 4 cabinets are rated
at "250 Watts", and contains 9 individual high-power
speaker drivers, with a rated output capability
of 116 dB at 30 feet! Each of the
individual drivers are equipped with 'blast valves'
to protect them from the impact of 'gun blasts'.
The diaphragms are phenolic, and replacements can
still be purchased from Altec! According to the
manual, the original amplifier was a 250 Watt, forced
air tube job. I wish I could have seen it.
So, what's it doing on the roof
of the Admin building? Well, it seems that it
was originally installed back in the '60's. War
surplus even then, it was installed as an emergency
announcement system; so that the campus President,
the Department of Public Safety, and a handful
of others could make announcements campus-wide.
Now why would anyone have wanted
to be able to make emergency announcements? In
the '60's? Here's my opinion:
- THE COMMUNISTS
ARE COMING!!!!
- THE HIPPIES
ARE RIOTING!!!!
So, somebody dug up this surplus
hardware, bolted it to the roof of Admin, built
an enormous custom amplifier to power it, and
even added a reel-to-reel tape player (...to play
music, of course! Everybody knows that
if you play classical music during a RIOT,
it will pacify the participants! I guess somebody
forgot to throw the switch after Poly Royal.)
Recently, our department was
required to move a bunch of equipment around on
the fifth floor of the Administration building.
Among the equipment was the amplifiers and switching
systems for Big Voice. Since the system had really
never been used, it was determined that we needed
to perform a complete evaluation of the system,
and a full-power test. Tom D. got the heavy work
of moving the amps and rerouting the speaker cables
from one end of the roof to the other. I got the
job of system evaluation and testing. So I hauled
my beloved Crown amp, a pink noise generator,
a UREI EQ, good ol' Radio Shack SPL meter, tools
and a mover's blanket up on the roof. |
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This is
a view of Big Voice, facing roughly due west. The
back panels of the cabinets have been removed for
access and inspection. The big coil of cables in
the foreground are the speaker wires due to be rerouted.
(200k .gif) |
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This view is west-by-northwest.
The speakers under test have the mover's blanket
over the top of them, so as not to bother the folks
below. Even with the blanket over the 3 drivers
under test, this sucker is LOUD. The amp, noise
generator, and eq are in the lower right. There's
only about six feet between the front of the speakers
and a six story fall, so SPL measurement is interesting.
(240k .gif) |
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This view is facing
north. The individual speakers are wired in groups
of 3 (vertically); that's also how I tested them,
initially. Basically, I just let them cook on band-limited
pink noise at an output of about 120 dB for about
5 minutes, measured at the mouth of the horns. Then,
with ear plugs well in place, I rolled back the
blanket, and cranked up the amp until I sustained
a level of about 120 dB at 4 feet.
(344k .gif) |
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A view of campus, with
Big Voice taking direct aim at "Fort Fisher". We
did need to have some replacement rear panels fabricated,
as the old ones were rusted through. You can see
there's only two screws holding the field-replacable
magnet and diaphragm assembly. You can also see
the soldered barrier strips for the complex series/parallel
wiring used in the cabinets.
(375k .gif) |
| After all of that,
I found NO defective drivers! The whole wretched
mess outlasted the Russkies! I installed a replacement
mixer/limiter, equalizer, the Crown Com-Tech 300
amp, and some other interface gear in the equipment
room on the floor below. Setting levels was going
to be pretty subjective, since I wasn't about
to sit in front of Big Voice and listen for clipping.
When I first keyed the push-to-talk mic, the system
fed back through the roof and wouldn't stop!. It scared the
h*ll out of me! Eventually, I set the level by
having a second person listen for adequate speech
articulation from about 1/4 mile away.
We'll probably be installing a digital message
repeater soon to eliminate any future feedback
concerns.
Here's
another Beachmaster link. (off site)
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| All comments and questions
welcome!
pwoodwor[at]calpoly[dot]edu
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