Traditional Indonesian music uses an ensemble called a gamelan that is based on tuned percussion instruments somewhat like gongs. In Bali, the gongs are often grouped in pairs that are slightly out of tune with each other. When both are played at once, the beat frequency lends a distinctive vibrating quality to the music. Suppose a pair of gongs are tuned to produce notes at 151 Hz and 155 Hz. How many beats are heard if the gongs are struck together and both ring for 2.5 s?

n = 10 beats

Explanation:

Given:

- Frequency of note f1 = 151 Hz

- Frequency of note f2 = 155 Hz

- The total time they ring t = 2.5 s

Find:

How many beats are heard

Solution:

- The frequency of beat (fb) is the difference between the two frequencies of notes as follows:

                                fb = f2 - f1

                                fb = 155 - 151

                                fb = 4 Hz

- The number of beats per second is also called beat frequency:

                                n = fb*t

                                n = 4*2.5

                                n = 10 beats

it is the second option.

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