Years ago My Dad used to be a flight engineer on a C-124 Globemaster. These
aircraft had 4 large piston radial engines. I can still tell if a C-124 is
flying over head by the resonance and throb to those engines.
Another good example was the C-130 with 4 turbo fans and had a different
pitch but you can still hear the beat frequency in the engines, , the c-130 A
was the worst..
I had a 33 hour flight time trip to Okinawa as a kid (1960) on a C-121 also
know a a super constellation or super connie with the 3 tails. this was 33
hours of a very loud and cyclic harmonic noise that you could barley talk
over.
It took a couple of days to get normal hearing back.
Its funny but I and a lot of others can tell you what is flying overhead
just by the sound , C-5, B-52, Huey, F-4C, Pedro choppers.. they all have
distinctive pitch, throb and loudness.. I guess we are better at this zero
beat
than we think.
In class at Keesler AFB we would tak 2 audio frequency generators and set on
at 25k and on at 26 k and you would never hear the note but the 1000 cycle
tone would drive the instructors nuts, but it only works once..
tom N6AJR
In a message dated 1/10/2006 8:23:21 P.M. Pacific Standard Time,
ghoffman@spacetech.com writes:
One listens not to the two tones, in an effort to discriminate them, but
rather to the slow "thrummmm thrummmmm...." that repeats at very low speeds
when you get the tones close. That is, the amplitude of the thrummmm builds
and fades at the beat frequency.
You can hear this when you tune a piano, and the beating goes away when the
two strings are matched. Some of us like to tune our pianos for a little
"roll" to add a certain sound, and so you then tune the strings so the
thrummming is slightly there.
One used to hear this occasionally on older airplanes also, where two piston
engines would be slightly apart in speed. You could hear a very slow
build-up and drop off of the amplitude of the sound, until the pilot matched
speeds. Of course you don't hear that any more with modern equipment.
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