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basic acoustics a k darpe department of mechanical engineering

2. Basic Acoustics. Quantification of SoundSound Pressure, Pressure level (dB scale)Sound Intensity, Sound PowerCombination of sound sourcesSound Frequency Simple sound sourcesDirectivity . 3. Sound Quantification. Provides definite quantities that describe and rate soundPermit precise, scientific analysis of annoying sound (objective means for comparison)Help estimate Damage to Hearing Powerful diagnostic tool for noise reduction program: Airports, Factories, Homes, Recording studios,1143

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basic acoustics a k darpe department of mechanical engineering

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    3. 3 Sound Quantification Provides definite quantities that describe and rate sound Permit precise, scientific analysis of annoying sound (objective means for comparison) Help estimate Damage to Hearing Powerful diagnostic tool for noise reduction program: Airports, Factories, Homes, Recording studios, Highways, etc.

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    6. 6 Power / Intensity / Pressure

    7. 7 Power / Intensity / Pressure ???

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    18. 18 Levels A unit of a logarithmic scale of power or intensity called the power level or intensity level. The decibel is defined as one tenth of a bel One bel represents a difference in level between two intensities (one of the two is ten times greater than the other) Thus, the intensity level is the comparison of one intensity to another and may be expressed: Intensity level = 10 log10 (I1 /Iref) (dB)

    19. 19 Why log ratio? Logarithmic scale compresses the high amplitudes and expands the low ones The other reason: Equal relative modifications of the strength of a physical stimulus lead to equal absolute changes in the salience of the sensory events (Weber-Fechner Law) and can be approximated by a logarithmic characteristics (Ear responds logarithmically to stimulus)

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    28. 28 Effect of multiple sound sources

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    30. 30 Correlated and uncorrelated sources

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    43. 43 Directivity of Sound Source

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    45. 45 Directivity Factor & Directivity Index

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    50. 50 Measurement of Power in Reverberant Room

    51. 51 Semi-reverberant field technique When sound field is neither free nor completely diffuse. Use calibrated sound source with known power spectrum. Then use Lp = Lp’r - Lp’r + Lp

    52. 52 Semi-reverberant field technique To take care of nearby reflecting surfaces and background noise, Measure at number of locations on measuring surface Lpd = Lp – 10log10(d/r)2 Then use L?? Lpd + 10log10 (2?d2)

    53. 53 What we learnt Sound Pressure, Intensity and Power dB levels Multiple Sound Sources Types of Sound Sources Directivity

    54. 54 Thanks !!

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