NOISE;
“Wrong sound at wrong place or time”. The word ‘noise’ derives from latin nausea, a sickness.
Measurements of sound
There is two other aspects of sound pertinent to sound perception.
Intensity (I) - better called sound pressure level. Intensity is rate of flow of sound energy per unit area. Thus its unit is Watt/m2. Our ear can detect a sound as little 10–12 Watt/m2 intensity at 1000 Hz, which is called the threshold of hearing. Again, sounds greater than 1 Watt/m2 are painful to the ear.
Bel. The difference in intensity level of two sound of intensities I and I0 is defined as Log10 (I/I0) Bel. Because bel is an impractically large unit, a decibel has been devised which is 0.1 bel.
Sound Decibels
Threshold of hearing 0
Whisper 20
Conversation 65
Traffic 70
Recommended maximum 85
Pain 120
Effects of noise
1); Auditory
- Fatigue appears with noise of 90 dB and greatest at 4000 hz.
- Deafness: Temporary deafness (by a large blast of sound) lasts < 24 hrs.
- Chronic exposure to noise (> 100 dB).
- Sound greater than 160 dB ruptures the Tympanic membrane.
2); Non-Auditory
- Annoyance—A 2005 study by Spanish researchers found that in urban areas households are willing to pay approximately four Euros per decibel per year for noise reduction.
- Interference with speech—Noise also makes animals communicate louder, which is called Lombard vocal response.
- Loss of efficiency and sleep, ↑ BP and ↑ HR; high noise levels can contribute to cardiovascular effects.
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