from: David Goldberg <goldb...@wccnet.org>
subject: Re: [Hornlist] Playing under a ceiling fan
James Maddrey wrote:
".... the reflected frequency is higher nearer the tip of the blade."
Wrong!
The tip of the blade is revolving at the same rate as the other end.
Both ends revolve at the same frequency.
Right!
youngjim
But the tip travels faster than points nearer the center of rotation,
making the molecules it whacks travel faster.
"Travel faster" = greater (linear) velocity. Angular velocity,
frequency is the same, as you note.
Not wrong, but irrelevant.
Experiment: aim a running water hose at the center of a fan; watch how
little the water is reflected. Then aim closer to the circumference
of
the blades; the water will bounce off the fan with greater velocity.
So what? The important thing is the velocity in the direction of the
ear, which depends on the PITCH (i.e. angle relative to the plane of
rotation) of the blade, which is usually less at the tip than near the
center.
I'm assuming that "playing under a ceiling fan" refers to a helicopter
style fan in the plane if the ceiling not a a centrifgal drum type
fan, and that that "under" means "directly below", not off at some
complicating angle.
Also, I'm not sure that sound is a physical substance that bounces off
fans like water does. If it is, it will be affected by gravity and air
resistance, and should fall to the ground unless well projected. (Ah,
that's what's wrong with my playing!)
Similarly, when you play a stringed instrument the string vibrates
most in the plane of the bowing surface, so the sound particles thrown
off should be concentrated in that plane and sound louder to people in
or near that plane. I'm sure you've experienced this frequently. That,
by the way, is why jazz players pluck their basses; it spreads the
sound in all directions.
Well, I've got some homework to do now; I must brush up on the quantum
theory or sound.
Simple Simon
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