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Noise Problems

  1. May 9, 2006 #1
    Dear Sir or Madam

    I have some troubles regarding the noise subject. Would you mind to help me solving the following problems? Thank You.

    1. Under what condition will sound power level be lower than sound pressure level?
    2. L10, Leq, Lmax ~ How are they related to noise fluctuation and annoyance to people
    3. Why L10 cannot be used to assess night-time traffic noise?
    4. What is the relationship between L10, Leq, Lmax, for the noise from traffic, industrial fans, and piling machine?
    5. How to the parameters L10, Leq, L90, Lmin, Lmax, L10 – L90 and Lmax – Lmin change with traffic noise in the day and night time? Which of these parameters can be closely correlated to annoyance of people?
    6. Why balconies can be a more effective noise mitigation than barriers/ enclosures?
    7. Why the important of length, gaps, and absorptive material on the noise barrier performance?
    8. What measures to reduce train and industrial noise?
    9. Why the significance of low frequency noise from train and industrial machines?
    10. How acoustic wave from human speech is generated, propagated and detected by human ear?
    11. Why shaking a metal plate with large hand movement cannot generate noise but scratching it with a screwdriver can radiate loud noise?
    12. Why rows of trees 5m high and 20m wide may not block or absorb the noise but may increase the noise instead?
    13. What are the dominant frequencies of the noise emanating from electric motor unit, light rail, and locomotive? If the train noise level is 55dB(A) and 85 dB(C), which is the major noise source?
    14. Why enclosure is needed in rail when there are crossovers of rails? Do you think the floating slab can reduce the noise near crossovers?
    15. Why absorptive barrier close to the rail and floating slab should be used to reduce train noise on the viaduet. Why the negative effects of these on the operation of the train?
    16. Can the acoustic wave from the source of sound power level of 0dB be sensed by human ear?
    17. Why the noise impact from construction in terms of L10, Lmax, Leq and the period and duration when compared with industrial and traffic noise?
    18. Why barrier or enclosure may not be effective to reduce construction noise by evaluating the major noise sources?
    19. Why road resurfacing and barriers cannot reduce traffic noise near road junctions?
    20. Why Low frequency noise impact can be higher than high frequency noise impact?


  2. jcsd
  3. May 10, 2006 #2


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    Homework Helper

    Why do you think this makes no noise?
    If the metal plate flexes it makes a lot of noise.
    Even if it doesn't flex there is edge cavitation that makes a woosh noise.
    Then there are the sub audible frequencies generated, still noise.
  4. May 10, 2006 #3
    Have any idea for the other questions
  5. May 10, 2006 #4


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    Science Advisor
    Homework Helper

    Just commenting on something that appears wrong.

    Show us what you worked out.
    Ask a specific question about what you think isn't working in your solution.
    Nobody is going to do your homework for you.
  6. May 10, 2006 #5


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    Science Advisor

    I see this is your first time here. If you read the guidelines that you agreed to you will notice that we do not do your homework problems for you. If you wish to take one problem at a time and show us the work you have put forth trying to solve it, we will help.

    In regards to the number 11 that has already been brought up, a plate (an infinite plate) can be a poor radiator of sound if a couple of conditions are met. If the frequency of the bending wave in the plate is greater than what is known as the coincidence frequency (or critical frequency) then the bending wavelength and wave speed are greater than the wavelength and wave speed in the acoustic medium (i.e. air) and the plate radiates sound. If it is below the coincidence frequency then, if you go through the math, it turns out that the sound radiation has a very rapid exponential decay factor and thus does not radiate sound very well. Of course, that is with an infinite plate. A finite plate will have some sound radiation due to boundary conditions, but that can be very little.
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