What is Beat Frequency?
Beat frequency is a phenomenon observed when two sound waves (or other waves) of slightly different frequencies interfere with each other. This interference causes the amplitude of the resultant wave to periodically increase and decrease, creating a noticeable pulsation in loudness or intensity, known as "beats."
How Beats Are Formed
When two waves with frequencies f1 and f2 (where f1 is close to f2) arrive at the same point, their superposition results in a new wave. This combined wave oscillates at the average frequency of the two original waves, but its amplitude varies. The peaks of this amplitude variation occur when the waves constructively interfere, and the troughs occur during destructive interference.
Hearing Beats with Musical Instruments: A Practical Example
A common example of beat frequency is heard when two musical instruments, like guitars or pianos, are slightly out of tune. If one string plays a note at 440 Hz and another at 442 Hz, a listener will hear a pulsating sound, getting louder and softer twice per second. This "beat" helps musicians tune their instruments until the beats disappear, indicating the frequencies match perfectly.
Applications of Beat Frequency
Beyond musical tuning, beat frequency has practical applications in various fields. It's used in sensitive measurement devices, such as optical interferometers for precise distance measurements, and in radio communication for heterodyning, which shifts a signal to a different frequency for easier processing. It also plays a role in ultrasound imaging and radar systems.