Sound pressure is defined as:

• A. The peak instantaneous pressure in a wave
• B. The difference between the normal atmospheric pressure and the actual pressure
• C. The energy per unit volume of the sound field
• D. The average atmospheric pressure over time

Answer: (B)

Sound pressure is the fluctuation in pressure caused by a sound wave—the difference between the actual pressure at a point and the surrounding ambient atmospheric pressure. This deviation can be positive during compression and negative during rarefaction, and it is these pressure variations that carry sound through the air. The other ideas mix in either the total or static pressure (the absolute pressure at a moment, not the fluctuation), or energy density (which relates to how much energy is in the wave, not the pressure deviation). The average atmospheric pressure over time is just a constant reference, not the fluctuating component that defines sound pressure.