S. No. 1 2 3 4 5 6 7 8 9 10 SPL (dB) 71 75 70 78 80 84 76 74 75 74
Understanding L$_{90}$ Calculation
The L$_{90}$ represents the sound pressure level (SPL) that is exceeded for 90% of the measurement duration. With 10 instantaneous measurements, this means we need to find the SPL value that is exceeded by 9 out of the 10 readings.
Data and Sorting
The given sound pressure level (SPL) measurements are:
| S. No. | SPL (dB) |
|---|---|
| 1 | 71 |
| 2 | 75 |
| 3 | 70 |
| 4 | 78 |
| 5 | 80 |
| 6 | 84 |
| 7 | 76 |
| 8 | 74 |
| 9 | 75 |
| 10 | 74 |
To find L$_{90}$, we first sort the SPL values in descending order:
84, 80, 78, 76, 75, 75, 74, 74, 71, 70
Determining L$_{90}$ Value
L$_{90}$ is the level exceeded for 90% of the time. In a set of 10 measurements, this corresponds to the value exceeded by 9 measurements.
Looking at the sorted list (descending order):
- The 1st highest value is 84 dB.
- The 2nd highest value is 80 dB.
- The 3rd highest value is 78 dB.
- The 4th highest value is 76 dB.
- The 5th highest value is 75 dB.
- The 6th highest value is 75 dB.
- The 7th highest value is 74 dB.
- The 8th highest value is 74 dB.
- The 9th highest value is 71 dB.
- The 10th highest value is 70 dB.
Therefore, the SPL value exceeded by 9 measurements (90% of the time) is 71 dB.
The estimated L$_{90}$ is approximately 71 dB.
Important Questions from Air and Noise Pollution - Teaching
Statement (I): The impact of Green House Gas emissions on the environment may comprise an accelerated increase in global warming as well as a significant rise in mean sea levels.
Statement (II) : Green House Gas omission is responsible for decreased landmasses, increased population densities, and food shortages.
Choose the correct statement from the following:
The equivalent noise level is significant for the following:
- Electrostatic Precipitator is used in Thermal Power Plants to remove which of the following air pollutants?
- What is Noise Induced Permanent Threshold Shifts (NIPTS) ?
If [$_env$ < [$_d$ ,where [$_env$ and [$_d$ are environmental & dry adiabatic lapse rates respectively ,which of the following types of plume emitted from a stack of a thermal power plant is observed ?
