# Beat frequency from >2 waves?

1. Aug 30, 2009

### Dekans6

When two waves of same amplitude but differing frequencies are added together, the frequency of the amplitude modulation of the resulting wave is the difference b/w the frequencies of the two parent waves.

How about beat frequencies from the interference of more than 2 waves, say 3, 4, or 10? How do we calculate that?

Also, it hasn't been clear to me why the two waves need to have the sample amplitude for beat frequency to occur...Isn't beat frequency only a function of the differences in frequencies and not a function of amplitude?

Could someone help me clarify these two questions?

Thanks!

2. Sep 2, 2009

3. Sep 6, 2009

### Xezlec

2 sine waves add together to create 1 sine wave modulated by "beats".
3 sine waves add together to create 3 sine waves added together.

There may be some equivalent of "beats" in this case, but it wouldn't be exactly the same concept, and it would get a little fuzzy.

Beats aren't magic, it's just math. cos u + cos v = 2 cos(½(u+v)) cos(½(u−v))

Notice that formula doesn't work if you multiply one of the cosines by something. That's all there is to it. The sum of 2 sine waves with different amplitudes is just 2 sine waves with different amplitudes added together.