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Correcting for Operating Time

If a sound source is operating during a shorter period of time tE than the duration of the reference time interval tB, then the time correction Dt is added to the calculated sound pressure level to obtain the average sound pressure level during the reference time interval.

\(D_t = 10 \lg(t_E/t_B)\)

The reference times are specified on dialog Calculation|Configuration, tab „Reference Time“, by assigning the letters D (day), E (evening), and N (night) respectively for every full hour.

Prior to this, select on tab „Evaluation Parameters“ the parameters Lde (day-evening) and Ln (night).

Evaluation parameters Lde and Ln

Adjust the reference time on the tab „Reference Time“ as illustrated below.

Input of reference times and penalties (example)

The reference times considered here are as follows:

  • for Day (7:00 -20:00 hours): 13 hours,
  • for Evening/Recreation (6:00-7:00 hours and 20:00-22:00 hours): 3 hours,
  • for Night (1 hour, activity during the loudest hour).

Set the penalty for Evening/Recreation to 6 dB (by default).

Note

The default penalty of 10 dB for night is not relevant as there is no mixed evaluation parameter assessing the night period.

The actual operation time is entered on the dialog of the point source.

  • First, select the option „Operating Time (min)“ instead of the default setting „Source in Steady-State“.

In this example, half of the reference times are entered for the day and the evening period, while for the night period a quarter is entered:

  • Day: 390 min. operating time = ½ reference time (780 min.)
  • Evening: 90 min. operating time = ½ reference time (180 min.)
  • Night: 15 min. operating time = ¼ reference time (60 min.)

Thus, the following time corrections result:

  • time correction day: DtT = 10 lg (390/780) = - 3 dB
  • time corr. evening/recruitment: DtE = 10 lg (90/180) = - 3 dB
  • time correction night: DtN = 10 lg (15/60) = - 6 dB

The A-weighted sound power levels of the point source and the receiver levels during the time periods Day/Evening and Night result in this example as:

  1. time period Day/Evening:

emitted sound power Day/Evening:

\(L_{wA}=10\lg(\frac{1}{16})*[13*10^{(100-3)/10dB} + 3*10^{(100-3+6)/10dB}]=98.9dB(A)\)

receiver level Lde:

\(L_{AT}=98.9 dB(A) - 51 dB - 0.2 dB = 47.7 dB(A)\)

  1. time period Night:

emitted sound power Night:

\(LwA(N)=100+10\lg(15/60)dB=94dB(A)\)

receiver level Ln:

\(L_{AT} = 94dB(A)-51dB-0.2dB=42.8dB(A)\)

Those levels are displayed on the receiver’s dialog in CadnaA::