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Assess your understanding of Industrial Nosie
  1. The total sound pressure level due to two uncorrelated sound sources with sound pressure levels of 73 dB and 75 dB is:
    (a) 148.0 dB      (b) 78.4 dB      (c) 77.1 dB      (d) 76.7 dB


  2. Three mutually incoherent noise sources produce intensities of 93, 89 and 85 dB respectively at a given observation point when operated one at a time. The intensity when three sources operate simultaneously is:
    (a) 94.9 dB      (b) 103.6 dB      (c) 100.2 dB      (d) 98.8 dB
    If the strength of the first (ie. 93 dB) source is reduced by 5 dB the intensity will become:
    (a) 101.3 dB      (b) 97.5 dB      (c) 92.4 dB      (d) 96.3 dB


  3. The output from a sound level meter is 350 mV rms for a sound level input of 94 dB and an attenuator setting of 90 dB. If the attenuator setting is changed to 100 dB the calibration factor in mV/Pa will be:
    (a) 110 mV/Pa      (b) 220 mV/Pa      (c) 330 mV/Pa      (d) 440 mV/Pa


  4. An isotropic sound source with a sound power level of 120 dB is in a room having a Room Constant, R = 46 m2. If the machine is moved into a free-space acoustic environment, the reduction in sound pressure level measured at 3 metre distance will be:
    (a) 5.2 dB      (b) 7.8 dB      (c) 8.8 dB      (d) 10.3 dB


  5. If the average absorption coefficient is 0.2, the reverberation time of a room 7m x 5m x 4m high is:
    (a) 1.24 Sec.      (b) 0.98 Sec.      (c) 1.66 Sec.      (d) 0.67 Sec.


  6. Sound pressure levels in the 400, 500 and 630 Hz 1/3 octave bands were measured and found to be 83, 79 and 86 dB respectively. The sound pressure in the equivalent octave band is:
    (a) 88.3 dB      (b) 99.7 dB      (c) 94.3 dB      (d) 102.5 dB


  7. The sound pressure level measured at the operator position of a small lathe is 101 dB with the lathe working and 97 dB with the lathe switched off. The sound pressure level at the operator's position due to the lathe only would be:
    (a) 100.2 dB      (b) 98.8 dB      (c) 96.2 dB      (d) 93.6 dB


  8. A machinist is exposed to an LAeq value of 82 dB(A) over an 8 hour working day. During the evening he attends a discotheque and is exposed to a further LAeq value of 79 dB(A) over 3 hours. His combined exposure level for the 11 hour period is:
    (a) 86.4 dB(A)      (b) 83.4 dB(A)      (c) 80.1 dB(A)      (d) 81.4 dB(A)


  9. The following A-weighted sound pressure levels were obtained at 10 second intervals from a visual inspection of a sound level meter: 67, 65, 62, 75, 63 and 63 dB(A). Estimate LAeq.
    (a) 72.7 dB(A)      (b) 79.8 dB(A)      (c) 68.8 dB(A)      (d) 65.5 dB(A)


  10. A machine with a sound power level of 126 dB is operated in a small room having a Room Constant of 12 m2. Assuming the machine acts as an isotropic sound source, the sound pressure level in the reverberant field will be:
    (a) 116.5 dB      (b) 121.2 dB      (c) 103.9 dB      (d) 97.0 dB
    How close must one be to the machine for this value to increase by 1 dB?
    (a) 1.7 m      (b) 0.29 m      (c) 3.0 m      (d) 0.98 m