3hz Flow Modulators(subs)
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Introduction
Don’t ask why.Ask why
not
http://srforums.prosoundweb.com/index.php/t/10128/0
See the patent for diagram and more explanation
What is it ?
“The sources were a
“flow modulator”, what I would call a class A valve in that it is half open at
“no signal”. A voice coil motor moved the valve, either opening further or
closing off the valve relative to the no signal condition.
The sources on the towers were made by LTV-Ling, the former industrial branch
of Altec Lansing and now a defense contractor. I could not find my data sheets
or the exact unit on line but I did find a similar source made by Wyle Labs.”
Why
“This simulator system needed to produce 132 dB from 5 kHz, down to 3 HZ, outdoors, 2 meters from the wall of an old house next to the air base outside Atlanta. This output required the equivalent displacement of a piston 12 feet wide and 8 feet high, moving 18inches peak to peak at 3 Hz.”
Who
“My solution was to
use a “push pull” valve and lower the pressure to about ¼ psi.
Given the job it had to do, it required an air source moving about 50 cu mtrs
per second and this required a special 3 phase service to be run to the site
for the 12, 5HP fans.
This flow modulator had vastly more air flow volume and a much lower pressure,
combined with the class”A” push pull valve, increased the signal to noise by
about 100 (20 dB) compared to the high pressure versions.
For such a valve to be used in the home which is a contained space, it is worth
considering that an air pressure of only 1/100 PSI is 132 dB SPL or 1.6 pounds
per square foot applied to your walls ceiling and floors.
At the old house in Atlanta, with 132 dB available (on one wall) and using
a slow sine sweep with the TEF machine, I was able to find the fundamental
resonance of the test wall. In the middle where the window was, the pressure
could move it in and out about a foot and a half peak to peak at 4.5 Hz.
No one of our group was able to stay in the house during this (in fear) and
later when a loud CRUNCH came from somewhere below the floor, we stopped
teasing the old house.
I’ll never forget the feeling of standing between the house and the system with
the “pickle” button that made the “N” signal. It was the kind of KAAABOOM, very
satisfying to do in rapid succession until you saturate and have to get away.
The actual use of the system the customer had in mind involved observing dishes
and household stuff as well as test subjects when it went off with no warning.
Best Regards,
Tom Danley
Danley Sound Labs”
