Chapter 3 – Measurement of Sound

Chapter 3 – Measurement of Sound - Chapter...

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Chapter 3 – Measurement of Sound Stimulation of sensation—the presentation of sound to evoke a subjective response to it Function relating the output to the input allows characterization of the performance of a particular system Various parameters of sound – amplitude, frequency, and phase Concepts underlying the pertinent procedural matters and the practical units of measure of sound Important to understand how the change in one parameter of the sound stimulus can affect another, purely on a physical basis 1. Amplitude Revisited and More Amplitude—the difference between the maximum instantaneous value and equilibrium Most practical measure for quantifying sound—sound pressure Peak sound pressure—the difference between the peak condensation pressure and the ambient, or atmospheric, pressure Peak-to-peak amplitude—the difference between the maximum and minimum values (peak condensation and rarefaction, for sound pressure) Effective or root-mean-square (RMS)—a measure that better reflects the overall power of the sound or vibration Question: What measure of the AC voltage yields a value equivalent to the DC voltage, such that the light bulb burns equally brightly? Answer: the RMS voltage In the case of a sinusoid, the magnitude at each instant during one half-cycle mirrors the corresponding magnitude during the opposite half-cycle—each is equal in value but of opposite sign Sinusoidal sound (pure tones) are frequently used in hearing science Computation of the RMS magnitude of a sinusoid is simple o Task: determine a single value that best reflects the area under the curves or waveforms of the two Alternating pressure changes comprising the sound represent the same overall power as that of a constantly applied pressure A pure tone with a peak-to-peak sound pressure of 3 N/m 2 has an RMS sound pressure of approximately 1 N/m 2 —these relationships only hold up for sinusoids 2. Decibel Notation A. SOUND LEVELS Decibel (dB)—the logarithm of the ratio of two quantities Ratios of like quantities are dimensionless—the dimensions of the quantities cancel one another in the process of calculating a ratio
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Measurement of acoustic intensity in decibels yilds the acoustic intensity level (IL) of the sound Measurement of sound pressure in decibels yields the sound pressure level (SPL) Most common sound measuring device—sound level meter— indicates sound magnitude in dB SPL, not necessarily units of sound pressure The greatest sound pressure that can be tolerated is greater than 10,000,000 times that of the least detectable sound pressure The smallest sound pressure detectable by the normal human listener is about 0.00002 or 2 X 10 -5 N/m 2 B. THE LOGARITHM: FRIEND OR FOE? The logarithm of a number—the common logarithm—is the
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This note was uploaded on 05/18/2011 for the course CSD 1025 taught by Professor Durrant during the Spring '11 term at Pittsburgh.

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Chapter 3 – Measurement of Sound - Chapter...

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