Teaching Physics with the Physics Suite

Edward F. Redish

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Arranging the patio speakers

I have set up my two stereo speakers on my back patio as shown in the top view diagram in the figure at the right. I am worried that at certain positions I will lose frequencies as a result of interference. The coordinate grid on the edge of the picture has its large tick marks separated by 1 meter. For ease of calculation, make the following assumptions:

  • Assume that the relevant objects lie on integer or half-integer grid points of the coordinate system.
  • Take the speed of sound to be 343 m/s.
  • Ignore the reflection of sound from the house, trees ,etc
  • The speakers are in phase.

  1. What will happen if I am sitting in the middle of the bench?
  2. If I am sitting in the lawn chair on the left, what will be the lowest frequency I will lose to destructive interference?
  3. Can I restore the frequency lost in part (a) by switching the leads to one of the speakers, thereby reversing the phase of that source?
  4. With the leads reversed, what will happen to the sound for a person sitting at the center of the bench?

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Page last modified October 31, 2002: O34