Sound pressure

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 unit is Pa = pascals that is N/m2. N is the force F in newtons.

Related Topics:
Pascal - Root mean square - Pressure - Atmospheric pressure - Power

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The amplitude of sound pressure from a point source decreases in the free field (direct field) proportional to the inverse of the distance r from that source. That is 1/r and really not squared!

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Sound pressure level is a decibel scale based on a reference sound pressure of 20 µPa (micropascals), calculated in dB as:

Related Topics:
Sound pressure level - Decibel

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:

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L_p=20, log_{10}left(rac{p_1}{p_0} ight)mathrm{dB}

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This is written "dB (SPL)".

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: p0: Reference sound pressure of 2 × 10-5 Pa = 20 µPa

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Sound pressure p in N/m2 or Pa is:

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:

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p = Zv = rac{J}{v} = sqrt{JZ}

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: Z: acoustic impedance, sound impedance, or characteristic impedance, in Pa·s/m

Related Topics:
Acoustic impedance - Sound impedance - Characteristic impedance

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: v: particle velocity in m/s

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: J: acoustic intensity or sound intensity, in W/m2

Related Topics:
Acoustic intensity - Sound intensity

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Sound pressure p is connected to particle displacement (or particle amplitude) ξ, in m, by:

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:

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xi = rac{v}{2 pi f} = rac{v}{omega} = rac{p}{Z omega} = rac{p}{ 2 pi f Z}

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Sound pressure p:

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:

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p = ho c omega xi = Z omega xi = { 2 pi f xi Z} = rac{a Z}{omega} = c sqrt{ ho E} = sqrt{rac{P_{ac} Z}{A}}

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normally in units of N/m2 = Pa.

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where:

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The distance law for the sound pressure p is inverse-proportional to the distance r of a punctual sound source.

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:

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p propto rac{1}{r}

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(proportional)

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:

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rac{p_1} {p_2} = rac{r_2}{r_1}

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:

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p_1 = p_{2} cdot r_{2} cdot rac{1}{r_1}

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The assumption of 1/r² with the square is here wrong. Thats only right for sound intensity.

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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.

Related Topics:
Magnitude - Strength - Amplitude - Level - Sound intensity - Sound power

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