SOUND LEVEL MEASUREMENT
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 projectsofme Active In SP Posts: 1,124 Joined: Jun 2010 02-10-2010, 01:12 PM   sound level measurement.pptx (Size: 1.22 MB / Downloads: 120) This article is presented by: ABDUL JABBAR MUHAMMAD MOHSIN ALI INTRODUCTION Sound waves in air are longitudinal waves. The disturbance that propagates in air is a change in the local air pressure (or equivalently density) above or below the average pressure a region of higher air pressure in the wave is called a condensation, while a region of lower air pressure is called a rarefaction The speed of sound in air depends on several factors, including the air temperature and pressure. At room temperature and standard atmospheric pressure, the speed of sound is 343 m/s. Note that the atoms in the air do not move with the velocity v of the sound wave … they just vibrate back and forth as the wave passes INTENSITY I the intensity I of a sound wave is defined to be the power P (work/time) carried by the wave divided by the surface area A through which the wave passes the SI unit of intensity is therefore W/m2 CALCULATING DECIBELS The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity (usually power) relative to a specified or implied reference level. Its logarithmic nature allows very large or very small ratios to be represented by a convenient number, in a similar manner to scientific notation. Being essentially a ratio, it is a dimensionless unit. Decibels are useful for a wide variety of measurements in acoustics, physics, electronics and other disciplines. Generally for every factor of 10 change in intensity or dB, there is a factor of 2 change in loudness dB=10log10 (Is/Io) Is= The intensity of the sound Io= Hearing threshold 1x10-12 W/m2