Problem Set 1.3 Spring 2009
Decibels

(Write your answers on this sheet)

  1. Given the following equalities:
    I = p2/Za
    Za = 415 Rayls ("rails") 

    1. A computer makes a sound intensity of 10-8 w/m2, what is the pressure of this sound? (units will be N/m2 .)

       

       

    2. A motor produces a sound pressure of 5 • 10-2 N/m2. What is the intensity of the fan? (units will be w/m2.)

     

     

  2. A machine makes a sound intensity of 10-8 w/m2 . Given a reference intensity, Ir = 10-12 w/m2, determine the sound level in dB IL (intensity level).

     

     

  3. Another machine makes a sound pressure of 2 · 10-3 N/m2, Given a reference pressure, pr = 2 · 10-5 N/m2, determine the sound level in dB SPL (sound pressure level).

     

     

  4. What is the relation between intensity (I) and pressure (p)?

     

     

     

  5. What is the relation between sound intensity level (dB IL) and sound pressure level (dB SPL)?

     

     

     

  6. Use the relation I = p2/Za and the standard reference values Ir = 10-12 w/m2 and pr = 2 · 10-5 N/m2 to complete the table below:
    I/Ir p/pr dB IL dB SPL
    4:1   6.02  
    10000:1     40
      10:1 20