Sound Pressure

Definition

Sound pressure is the local pressure deviation from the ambient atmospheric pressure, caused by a sound wave. It is the force per unit area exerted by the sound wave and is a key parameter in the measurement and analysis of sound.

5 Must Know Facts For Your Next Test

1. Sound pressure is a scalar quantity, meaning it has a magnitude but no direction.
2. The SI unit of sound pressure is the pascal (Pa), which is equivalent to newtons per square meter (N/m^2).
3. Sound pressure levels are typically measured using a microphone and expressed in decibels (dB), which is a logarithmic scale.
4. The human ear can detect sound pressures ranging from the threshold of hearing (about 20 micropascals) to the threshold of pain (about 20 pascals).
5. Sound pressure is affected by factors such as the distance from the sound source, the medium through which the sound travels, and the presence of reflections or obstructions.

Review Questions

• Explain the relationship between sound pressure and sound intensity.
  • Sound pressure and sound intensity are closely related. Sound intensity is proportional to the square of the sound pressure, as described by the formula: $I = \frac{p^2}{\rho c}$, where $I$ is the sound intensity, $p$ is the sound pressure, $\rho$ is the density of the medium, and $c$ is the speed of sound in the medium. This relationship means that as the sound pressure increases, the sound intensity also increases, and vice versa.
• Describe how sound pressure is used to calculate sound level.
  • Sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value, often expressed in decibels (dB). The sound level is calculated using the formula: $L_p = 20\log_{10}\left(\frac{p}{p_0}\right)$, where $L_p$ is the sound level in decibels, $p$ is the root-mean-square (RMS) sound pressure, and $p_0$ is the reference sound pressure (typically 20 micropascals, which is the approximate threshold of human hearing).
• Analyze how factors such as distance, medium, and reflections can affect sound pressure.
  • Sound pressure is influenced by several factors. As the distance from the sound source increases, the sound pressure decreases according to the inverse square law, meaning the sound pressure is inversely proportional to the square of the distance. The medium through which the sound travels also affects the sound pressure, as different materials have different acoustic impedances, which can cause reflections, absorption, or refraction of the sound waves. The presence of reflective surfaces or obstructions in the environment can also alter the sound pressure through interference and diffraction effects, leading to constructive or destructive interference patterns.

Related terms

Sound Intensity: Sound intensity is the sound power per unit area, which is proportional to the square of the sound pressure.

Sound Level: Sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value, often expressed in decibels (dB).

Acoustic Impedance: Acoustic impedance is the ratio of the sound pressure to the particle velocity at a given point, which determines the propagation of sound waves through a medium.