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Homework Help: For what frequency does the intensity have a minimum?

  1. Feb 11, 2012 #1
    Two speakers A and B are separated by 1 meter, the point P is 4 m away from speaker B. If P is a person for what frequency does he hear that the intensity have a minimum?. (The listener hear that the sound intensity reduces and increases).I don't know the distance from P to B. (They form a right-angled triangle)


    (1.0 m)^2+(4.0 m)^2 = BP^2

    BP = 4.123 m

    The distance from Poit P to B is 4.123 m

    how can I determine the wavelength ?

    The answer should be: The minimum occurs for 1.3 kHz, 4.1 kHz, 6.9 kHz,.....

    Should i use this formula ?

    f(n) = n*v/d

    The path difference is d=(4.123-4.00)= 0.123 m
  2. jcsd
  3. Feb 11, 2012 #2


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    Staff Emeritus
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    Gold Member

    For destructive interference to happen, the path difference between the sound wave from A and the sound wave from B should be an odd multiple of half the wavelength. You know what this path difference is, so you can find the wavelengths that work.
  4. Feb 12, 2012 #3
    Estimate the relationship between the maximum and minimum intensity. Assume that there is a spheric wavepropogation and the effect from the surrounding kan be neglected. The speed of sound can be set to 340 m/s. The intensity decreases with 1/r^2 ie the intensity on the wave r m from the source is I0/r^2 where I0(zero) are the intensity on 1m from the distance from the source.

    How can i found the intensity and whats aboute the max and min intensity, what value should i use for that ?
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