Natural frequency occurs when an object vibrates; it creates its own frequency each time it vibrates. Take for instance a guitar string tuned in A; each time this string is plucked it will vibrate at a frequency of 440 Hz. If this string is plucked and it does not have a frequency of 440 Hz then we know that the string is not in tune. One way to explain this would be to use a guitar tuned in A and have the students listen to it. Change the natural frequency of the string to 450 Hz. Play the string and ask if they have noticed a difference. Do the same thing for a frequency of 430 Hz.
When two frequencies are heard together at the same time they can be amplified or they can cancel each other out. If the waves are in consonance amplification occurs. This means that the two waves are in phase with each other. If waves are in dissonance with each other they are out of phase with each other and the waves cancel each other out.
By understanding dissonance engineers have been able to create noise canceling technology which is being used at the work place and in leisure. (Hsu Tom, 2003). (See Activity 7).