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 Sound pressure
June 03, 2005
Sound pressure p (or acoustic pressure) is the measurement in pascals of the root mean square (RMS) pressure deviation (from atmospheric pressure) caused by a sound wave passing through a fixed point. The symbol for pressure is the lower case p. (The upper case P is the symbol for power. This is often misprinted.) The amplitude of sound pressure from a point source decreases in the free field (direct field) proportional to the inverse of the distance from that source. Sound pressure level is a decibel scale based on a reference sound pressure of 20 µPa (micropascals), calculated in dB as:
This is written "dB (SPL)". p0: Reference sound pressure of 2 × 10-5 Pa = 20 µPa Sound pressure p in N/m2 or Pa is:
Z: acoustic impedance, sound impedance, or characteristic impedance, in Pa·s/m v: particle velocity in m/s J: acoustic intensity or sound intensity, in W/m2 Sound pressure p is connected to particle displacement (or particle amplitude) ξ, in m, by:
Sound pressure p:
normally in units of N/m2 = Pa. where: p: sound pressure, in N/m2 = Pa f: frequency, in Hz ρ: density of air, in kg/m3 c: speed of sound, in m/s v: sound velocity, in m/s ω: angular frequency = 2π·f ξ: particle displacement (particle amplitude), in m Z: acoustic impedance (characteristic impedance) = c · ρ, in Pa·s/m a: particle acceleration, in m/s2 E or w sound energy density, in J/m Pac sound power or acoustic power, in W A area, in m2 Note: The often used term "intensity of sound pressure" is not correct. Use "magnitude", "strength", "amplitude", or "level" instead. "Sound intensity" is sound power per unit area, while "pressure" is a measure of force per unit area. Intensity is not equivalent to pressure. Sound measurements
[This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article: Sound Pressure.] Comment ListThere are no comments. |
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