Question

why should the no beats must be les than 10​

Answer 1

Answer:

So if the relative frequency of two sounds ie (f1~f2 ) is more than 10Hz then the time period between the beats would be more than 0.1 seconds .

We as humans can't have the ability to differentiate two sounds or beats whose time intervel is less than 0.1 seconds so we won't be able to hear them but we will hear the resultent of those beats as a single beat.

I hope it's help you...

Answer 2

Explanation:

If the beats occur more often than roughly 20 or 30 times per second, we no longer hear them as beats: our ears are not fast enough to respond to events that quickly. (Nor are our eyes: we cannot recognise a light that is flashing 30 times per second.)

Consider, for example, what happens when we play two tones with frequencies 400 Hz (approximately the note G4) and 500 Hz (approximately the note B4). The resultant waveform will look rather like a wave of 450 Hz whose amplitude varies at a rate of 100 times per second. But that is not what we hear: we hear the chord G4 plus B4 .