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Chapter 4 Decibal

by: Joey Ross

Chapter 4 Decibal CDO 331

Joey Ross

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About this Document

This goes over the notes for Decibal and what was discussed in class
Introduction to Audiology
Nicole M Ferguson
Class Notes
Decibal, audiology
25 ?




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This 5 page Class Notes was uploaded by Joey Ross on Saturday January 23, 2016. The Class Notes belongs to CDO 331 at Central Michigan University taught by Nicole M Ferguson in Winter 2016. Since its upload, it has received 14 views. For similar materials see Introduction to Audiology in Child Development at Central Michigan University.

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Date Created: 01/23/16
Highlighted is documented/slide notes Regular Text is addition lecture notes DAY 4 – Decibel The Decibel (dB) Most Frequently used unit of measurement of sound Two ways it is different from other measurements of physical power: o Doesn’t measure a specific physical Characteristic o The DECIBEL is a logarithmic unit that indicates the relative difference between two measurements When we increase in decibel it is non-linear How do we measure? Absolute Difference How much greater a measurement is compared to another Example: My child has grown 4 Inches Example: addition and subtraction Relative Difference How many times greater is compared to another Example: Mississippi is twice is large as West Virginia Example: Multiplication/Division Socrative Question: We use the logarithmic scale to determine how many times greater one sound is to another. T or F True YouTube Video: What is Logarithum? A number expressed as an exponent (power) that tells us how often a number (base) is multiplied by itself 10 = 10 x 10 x 10 x 10 = 10,000 Exponent = power = logarithm Base = It is a convenient way to compress the sale into an easy to handle range In hearing science, the base 10 is issued Reading Ref: Octave on a Piano Socrative Question: The exponent of the logarithm for the number 1000 is a.4 b.3 c.2 d.1 B Logarithmic vs Linear Logarithmic function Y= log X10 Linear Function Y=X the bel (B) original purpose was meauruing power loss was developed to describe power loss along cables that transmitted speech signals The bel is calculated by determining the ration of two powers and finding the log10f this ratio The decibel This is TOO much compression in bel Created Decibel *10 L= log10(P2/P1) (B)  L= 10 * lo10(P2/P1) (B) Socrative Question: We use the unit of measurement "bel" to measure sound to honor Alexander Graham Bell. T or F False: We use it to use a large range of intensity into a smaller measurement *********Important Notes about the dB Does not measure physical property It describes Sound Intensity & Sound Pressure Pressure vs. Intensity A powerful sound source will produce a powerful sound pressure Sound intensity: indicates how much sound power is transferred to the sound source to the surrounding area Pressure : How much the sound is compressed Sound intensity and sound pressure can be thought of as a two different ways to represent the strength of sound. Socrative Question: Sound pressure? A. Indicates how compressed or rarified the partials are B. Represents the strength of sound C. is the osculation of air molecules produced by a vibration and sound source D.All of the above D. All of the above Sound intensity is proportional to the square of sound pressure I = p2 Reference Point = 0 Units of measurement Pressure is measured in Pascal’s, intensity is measured in Watts/Meter 2 Example: “Better then the leading brand” dB SPL and dB IL o dB indicates the unit, which is the same for both pressure and intensity o SPL and IL indicate the reference point is Sound Pressure Level Intensity Level Socrative Question0 dB SPL and 0 dB IL signify the absence of sound. T or F False: 0 DOES NOT SIGNIFY ABSENCE OF SOUND What happens to the sound pressure level when sound pressure doubles? ***When the sound pressure doubles, the sound pressure level increase by 6 dB. Example: 5 doubled is 11, not 10 Double intensity = +3 dB Socrative QuestionDoubling the sound pressure of 20 dB SPL equals? Answer: 26 dB SPL Socrative Question: Doubling the sound intensity of 35 dB IL equals Answer: 38 dB IL Important Equation to know** The Equation for the decibel:  dB SPL = 20 Log (pressure measured/pressure reference) Example:  dB SPL = 20 Log (45 uPa /20 uPa) = 7.04 dB SPL


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