Acoustic scales and levels


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Phon; Sone; LAeqT:equivalent continous sound level, LPN:perceived noise level; LEPN: effective perceived noise level

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Acoustic scales and levels

  1. 1. Acoustic scales and levels <ul><li>Phon </li></ul><ul><li>Sone </li></ul><ul><li>L EPN : effective perceived noise level </li></ul><ul><li>L PN : perceived noise level </li></ul><ul><li>L AeqT : equivalent continous sound level </li></ul>
  2. 2. Phon <ul><li>Phon is the unit of Loudness Level (LL) </li></ul><ul><li>Defn.: SPL of 1 kHz tone that sounds equal in loudness to the sound / noise being rated </li></ul><ul><li>LL curves shown are re. 10 -12 watt/m 2 </li></ul>
  3. 4. Sone <ul><li>Sone is another unit of Loudness Level (LL) </li></ul><ul><li>Defn.: loudness of 1 kHz tone at 40 dB IL </li></ul><ul><li>Also loudness of any sound having a loudness level of 40 phons </li></ul>
  4. 6. Relationship between Phon & Sone <ul><li>If L denotes the loudness level in Sones and LL in Phons then </li></ul><ul><li>log L = 0.033 ( LL – 40 ) </li></ul><ul><li>At 1 kHz LL in Phons is numerically equal to IL in dB </li></ul><ul><li>L = 445 I 0.33 </li></ul>
  5. 7. Equivalent continuous sound level L Aeq <ul><li>The steady state dB(A) level which would produce the same A-weighted sound energy over a given period of time as a specified time-varying sound </li></ul><ul><li>A-weighting sound energy (commonly given as dBA) implies loudness measured over a wide band pass filter centered at 2.5 kHz </li></ul>
  6. 8. <ul><li>where </li></ul><ul><li>L Aeq = equivalent continuous A-weighted sound pressure level [dBA] </li></ul><ul><li>p 0 = reference pressure level = 20 µ Pa </li></ul><ul><li>p A = A-weighted pressure [Pa] </li></ul><ul><li>t 1 = start time for measurement [s] </li></ul><ul><li>t 2 = end time for measurement [s] </li></ul>
  7. 10. Perceived Noise Level L PN <ul><li>Scale measures the perceived noisiness of jet aircrafts by observers on the ground </li></ul><ul><li>Method is similar to loudness summation of complex tones using equal loudness contours: the decibel scale is converted into a series of increments measured in units of Noy </li></ul><ul><li>L PN dB = 40 + 10 log 2 (Noy) </li></ul>
  8. 12. Adopted Scales <ul><li>From the chart at the right of the graph, the Noy scale can be converted into L PN dB </li></ul><ul><li>The decibel scale at the left of the graph is for flat response. In converting decibels on the A weighting network to L PN dB, a rough method is to add 12 dB; thus 100 dBA = 112 L PN dB. </li></ul><ul><li>Most airports accept 110-112 L PN dB for daytime flights and 100 L PN dB for night flights; these limits are more generally theoretical than actual and they are still very high. </li></ul>
  9. 13. Effective Perceived Noise Level L EPN <ul><li>A complex rating used to certify aircrafts for flyover noise. Includes corrections for pure tones and for the duration of the noise </li></ul><ul><li>A modification of the L PN to take account of tone components in aircraft broad band noise, as well as its duration. It is measured in L EPN dB, and defined as the Perceived Noise Level ( L PN ) in L PN dB plus a tone correction and a duration correction </li></ul><ul><li>L EPN = L PNmax + 10 log (t 10 /20) + F (dB) </li></ul>
  10. 14. L EPN = L PNmax + 10 log (t 10 /20) + F (dB) <ul><li>L PNmax is the maximum perceived noise level during flyover in L PN dB </li></ul><ul><li>t 10 is the duration (in seconds) of the noise level within 10 dB of the peak L PN </li></ul><ul><li>F is a correction for pure tones (which are generally found to be more annoying than broad band noise without perceived tones). In practice, F is about +3 dB </li></ul>