Sound

• Sound is a longitudinal wave.

• speed of sound

  • (e.g. in air at 20\,^\circ\mathrm{C} is $343m/s$, in water is $1482m/s$)

• acoustic waves

measurements

• sound intensity: $I=\frac{P}{A}$
  • SI unit: $W/{\mathrm{m}}^2$
  • $P$ is the sound power (in $\mathrm{W}$) and $A$ is the area through which the sound power flows (in ${\mathrm{m}}^2$)
  • $\mathbf{I}=p\mathbf{v}$
  • also called: acoustic intensity,
  • sound intensity level (SIL): $\beta =10{\log }_{10}\left(\frac{I}{I_0}\right)\mathrm{dB}$
    • $I$ is the sound intensity
    • $I_0=1pW/{\mathrm{m}}^2=10^{-12}W/{\mathrm{m}}^2$ is the standard reference
• sound power
  • sound power level (SWL): $L_W=10{\log }_{10}\left(\frac{P}{P_0}\right)\mathrm{dB}$
    • $P$ is the sound power
    • $P_0=1\mathrm{pW}=10^{-12}\mathrm{W}$ is the standard reference
• sound pressure
  • sound pressure level (SPL): $L_p=20{\log }_{10}\left(\frac{p}{p_0}\right)\mathrm{dB}$
    • $p_0=20\mu \text{Pa}=2\times 10^{-5}\text{ Pa}$ (threshold of human hearing at $1\mathrm{kHz}$)