Two loudspeakers face each other, vibrate in phase, and produce identical 440Hz tones. A listener walks from one speaker toward the other at a constant speed and hears the loudness change (loud-soft-lound) at a frequency of 3.0 Hz. The speed of scound is 343m/s What is the walking speed?
Ok, where do I start?
I can find the wavelength with 440Hz, and speed of sound.
I'm guessing V=d/t? to find the walking speed. Help!
Or I could use the doppler effect? but the thing is, is the observer moving away or toward and I don't have the observed freq. The thing is that the observer is moving away from one and moving toward another one...!!
don't know how to do it but thought i'd help by ruling out the doplar effect. what do they mean by the frequency with which it changes? is it measured as the time from one peak in volume to another? i think you're going to have to find the two positions (perpendicular to the plane between the speakers) at which the volume peaks
Hmm, I might be able to find the distance betwen the two antinodes, it does say it goes from loud-soft-lound. So antinode-node-antinode, and antinode is where it peaks. But find the wavelength between them doesn't get me anywhere?
i think if you find the distance between the antinodes then you know it takes 3 seconds to walk that distance (that's how i understand the frequency of the volume change)
I think you mean 1/3 = time, 3 hz is freq. Ok, the wavelength is equal to ~0.79m. Since the distance isn't really one lambda, but lambda/2, so the distance travelled is ~0.390m. Yes, now I can use the V=d/t. 0.390m/0.3333s. V=1.17m/s. I think this makes sense.
i think the distance may actually be 1 lamba rather than a half because it is from an anti-node to an anti-node or the distance between equivalent points on a wave
Are you sure? The antinodes are the highest point of a wave right, if we were to measure from node to node, the points of no vibration then it'll be one lambda?
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I think this makes sense.
