1)we will need two sound notes of equal or slightly different frequency.
2)they must travel in same direction
3) by traveling in same direction they must interfere at some point and produce waxing and waning in intensity of combined note
4) the beat frequency should always be equal to the difference in frequencies of the two interfering waves
5)finally this should take place at regular intervals of time
beat frequency, n=n1~n2.
The number of beats occurring per second is the beat frequency.
I hope this helps!!