Chapter 31, Problem 22A

Suppose the speakers at an open-air rock concert are pointed forward. You move about and notice that the sounds of female vocalists can be heard in front of the stage, but very little off to the sides. By comparison you notice that bass sounds can be heard quite well both in front and off to the sides. What is your explanation?

To determine

To Explain: The sound from the speaker is heard only in front where as the sound from bass is heard well at sides as well.

Explanation of Solution

Introduction:

The bending of waves while encountering an obstacle and spreading out through a small opening is called diffraction.

Diffraction is the phenomenon that basically depends on the nature of the wavelength. Now, in the given situation, the female vocalists can be heard only in the front part because the sound of female has a high frequency which means shorter wavelength. Hence, shorter wavelength can spread around a short distance making it difficult to hear all the way back. On the other hand, bass sounds can be heard in front and off to the sides as well due to lower frequency and longer wavelength. Longer wavelength can spread out to a larger distance. Hence, diffraction is more pronounced with longer wavelengths than with shorter wavelengths.

Conclusion:

Hence, the longer wavelength results in more diffraction which is why the bass sounds can be heard in front and off to the sides as well.