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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
If I send 10khz signal to an object and I get a 9khz signal back, would the superposition yield a 1khz signal? Can I simulate this by adding or subtracting the two sine waves to give me the third?
Any references on this with respect to obtaining a doppler shifted frequency?
Registered Member #3766
Joined: Sun Mar 20 2011, 05:39AM
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Posts: 624
IamSmooth wrote ...
If I send 10khz signal to an object and I get a 9khz signal back, would the convolution yield a 1khz signal? Can I simulate this by adding or subtracting the two sine waves to give me the third?
I think so, try graphing a 10Hz and a 9Hz wave on top of each other and seeing what it looks like. Spice might prove useful for adding them together for you. I got no references.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Wouldn't you get a beat freq of 1kHz? It's like 10kHz modulated by 1kHz in a sense (difference of the freqs being 9kHz again). Mixers can add and subtract frequencies like this.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
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Adding and subtraction of waves can't generate any new frequencies, because they are linear processes. If you add two sine waves of almost the same frequency, you get what looks like a difference frequency in the envelope, but it doesn't exist: if you do a spectrum analysis you just see the two frequencies.
To generate sum and difference frequencies you must multiply the two waves together, or some other non-linear operation. This is how "mixers" in radio systems work.
If you listen to a superposition of two sine waves, you can hear the difference frequency, as anyone knows who tried tuning a guitar. But this is because your ears are non-linear detectors. They generate it themselves.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
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Sound from a source (ie loudspeaker) has a Q or directivity in acoustic terms.
A diagram of your experiment would help, where the transducers are especially.
Two different sound sources in one common space seldom add coherently and the determination of the resultant pressure level can be calculated with a graph.
As to the beat of two tones in space, as the reference said, they dont, however for practical purposes even with two sources of similar Q , but opposite direction,they will both be present in a common space , even if they are tens of decibels different in level.
Quoting Helmholtz. ...that many different trains of waves can be propagated at the same time through the same mass of air , without mutual disturbance..
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superposition of two sound waves
