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 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:

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

• Sound power
• Sound power level (SWL)
• Sound pressure
• Sound pressure level (SPL)
• Sound intensity
• Sound intensity level (SIL)
• Particle velocity
• Particle velocity level (sometimes called Sound velocity level) (SVL)
• Sound energy flux
• Acoustic impedance
• Speed of sound

External links

• Ohm's law of the acoustics - calculations
• Conversion: sound pressure to sound pressure level