Understanding the Beat Phenomenon: How Equal Amplitudes Create Harmonious Tones

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I am confused by this:

Two sinusoidal tones of equal amplitude and with frequencies of 439 and 443 Hz are sounded simultaneously.

Name and describe (qualitavitively and quantitatively) what you hear.
Why is it important that the two waves have equal amplitudes for this effect to occur

 

[atyy]

Probably:
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/beat.html
I think the two sinusoids only need to have roughly equal amplitudes.

Please note the difference between beats - where the frequencies have to be close to be perceptually obvious, and "missing fundamental" effect, where the frequencies must be harmonically spaced:
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/subton.html#c2