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Acoustics Exam Two Topic 4

Terms in this set (19)

Energy
A measure of the capacity to do work
Force
A measure of what is applied to make an object (a mass) accelerate
Work
A measure that a force succeeds in moving an object for a distance
Acoustic Power
The rate at which work is accomplished or the amount of work done per unit time
Sound Intensity (in terms of power)
The amount of power per unit area
Sound Intensity (in terms of work)
The amount of work done per second per unit area
Sound Intensity (in terms of energy)
The amount of energy transferred per second per unit area
Sound Pressure
The amount of force per unit area
Drawbacks of the absolute measures in application
1) Cumbersome numbers and a large dynamic range
2) Difficult to figure out what a measured quantity means to a sound
The Decibel Notation
a relative measurement, a comparison, a ratio, logarithmic
Decibel Notation for Calculating IL or SPL
log scale
Why do we use Decibel Notation?
1) Conveniently represents very large or small numbers, used to express ratios.
2) Sound level in dB is a relative measure of sound amplitude.
Formula for Calculating Intensity Level
10 log (Ix/Ir) = Unit of dB IL
Formula for Calculating Sound Pressure Level
20 log (Px/Pr) = Unit of dB SPL
Ix
The intensity of sound wave X
Ir
The intensity of a reference sound (10⁻¹² w/m²)
Px
The absolute pressure of wave x
Pr
The pressure of a reference sound (2 x 10¹ µPa)
What are the relations between dB IL and dB SPL?
1) dB IL always equals dB SPL
2) The 0 and negative values
3) Interpretation of clinical data in dB
4) An increase in intensity by a factor of 10 (↑ in IL by 10 dB)
5) An increase in pressure by a factor of 10 (↑ in pressure by 20 dB)
6) A doubled intensity = ↑ in IL by 3 dB
7) A doubled pressure = ↑ in SPL by 6 dB
8) The level of a combined sound from two independent sources with the same frequency
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