Sound Pressure 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


6. Sound Pressure Level

In a sound wave there are extremely small periodic variations in atmospheric pressure to which our ears respond in a rather complex manner. The minimum pressure fluctuation to which the ear can respond is less than one-billionth (10-9) of atmospheric pressure.

Because of the wide range of pressure stimuli, it is convenient to measure sound pressures on a logarithmic scale, called the decibel (dB) scale. Although a decibel scale is actually a means for comparing two sounds, we can define a decibel scale of sound level by comparing sounds to a reference sound with a pressure amplitude Po = 2 10-5 (N/m2) assigned a sound pressure level of 0 dB. Thus, we define sound pressure level (SPL or Lp) as:




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