Sound Intensity Level
Home Up Nature of Sound Waves Simple Harmonic Motion Characteristics of Sound Spectrum and Octave Band Strength of Sound Sound Pressure Level Sound Power Level Sound Intensity Level Free Field Manipulation with Decibels


8. Sound Intensity Level

Another quality described by a decibel level is sound intensity, which is the rate of energy flow across a unit area. The reference for measuring sound intensity level is Io = 10-12 Watt/m2, and the sound intensity level (IL or Li,) is defined as :




For a free progressive wave in air (e.g., a plane wave travelling down a tube or a spherical wave travelling outward from a source), sound pressure level and sound intensity level are nearly equal () This is not true in general, however, because sound waves from many directions contribute to sound pressure at a point. When we speak of simply sound level, we nearly always mean sound pressure level, Lp, since that is what is indicated by our sound-measuring instruments.


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