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Speech Science

02 Physics of Sound- Intensity

Sound INTENSITY The sound pressure of a sound wave is a function of the force with which the object is put into vibration
force the degree to which the air molecules surrounding the vibrating object are compressed
Frequency only changed by mass
Intensity changed by force
sound pressure is determined by amplitude of the sound wave (higher the wave higher the sound pressure)
2 Important Features of the dB Scale -not an absolute scale . it is a relative scale, that compares one sound to another. -it is a logarithmic scale
2 Ways to measure sound intensity Direct - sound intensity level Indirect - sound pressure level
Formula for calculating decibels dB SPL= 20 log (pressure of signal/20 microPas)
The characteristic of a log The whole number
The mantissa of a log The decimal portion
A tone is presented at a sound pressure of 500 uPa. What is the dB SPL? dB SPL= 20 log 500 uPa /20 uPa = 20 log(25) = 27.958 dB SPL = 28 dB SPL
A tone is presented at a sound pressure of 6420 uPa. What is the dB SPL? dB SPL = 20 log 6420 uPa /20 uPa = 20 log(321) = 20 (2.5065) = 50.13 dB SPL = 50 dB SPL
A tone is presented at a sound pressure of 940 uPa. What is the dB SPL? dB SPL = 20 log 940 uPa /20 uPa = 20 log(47) = 20 log(4.70X101) = 20 (1.6721) = 33.442 dB SPL = 33 dB SPL
2 tones are presented. Tone A produces 100 uPa. Tone B produces 50 uPa. Tone A is how many more dB than Tone B? relative dB = 20 log 100 uPa /50 Pa = 20 log(2.0) = 20 log(2.0X100) = 20 (0.3010) = 6.02 dB Tone A is 6 dB greater than Tone B
2 tones are presented - Tone A produces 2970 uPa. Tone B produces 150 uPa. Tone A is how many more dB than Tone B? Relative dB = 20 log 2970 uPa /150 Pa = 20 log(19.8) = 20 log(1.98X101) = 20 (1.2967) = 25.934 dB -Tone A is 26 dB greater than Tone B
Created by: aramos139



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