# Physics of Sound 301 Spring 2005

HOMEWORK ASSIGNMENT #3
Due Friday Feb 11, 2005

RMW refers to the textbook The Science of Sound, 3rd Edition, by T.D. Rossing, F.R. Moore, & P.A. Wheeler

Use 343 m/s for the speed of sound.
• RMW, page 58, exercise 2.
• Suppose you listen to sound from two loudspeakers at a distance of 6 m from one and 4.8 m from the other. What are several wavelengths and the corresponding frequencies for which you will experience constructive interference? What are several wavelengths (and frequencies) for which the interference is destructive?
• Speakers A and B are vibrating in phase. They are directly facing each other, are 7.80 m apart, and are playing a 73.0 Hz tone. On the line between the speakers there are three points where constructive interference occurs. What are the distances of these three points from speaker A?
• A musician standing close beside a railroad track hears the whistle blowing while a train passes her. She reports that the pitch dropped by the musical interval called a major third. As we shall learn later, this means the received frequency must have been about 12% higher as the train approached (and 12% lower as it receded) than the frequency that would have been heard with the train at rest. How fast was the train going?
• You wish to ensure that the diffraction angles for the mid and high frequency cones on a loudspeaker are the same. Find two values for the diameters of these cones that will satisfy this requirement. Assume that the cones emit sound with frequencies of 500 Hz (mid frequency range) and 5000 Hz (high freq. range). (Note that there are many possible solutions to this problem - try to find values that are reasonable.)