Sound Pressure Definition

Sound pressure is defined as the difference between the instantaneous total pressure and the ambient (or mean) atmospheric pressure at a point in a medium, caused by the passage of a sound wave.

Relating Pressure Components

Sound waves cause fluctuations in the surrounding air pressure. The total pressure at any point includes the steady atmospheric pressure plus these fluctuations.

• Atmospheric Pressure (or Barometric Pressure): This is the average pressure of the atmosphere under normal conditions.
• Total Pressure: This is the instantaneous pressure, including both the atmospheric pressure and the pressure variations due to the sound wave.
• Sound Pressure (or Acoustic Pressure): This is the fluctuating part, representing the change from the average atmospheric pressure.

Calculating Sound Pressure

Mathematically, sound pressure ($p$) can be expressed as:

$ p = P_{total} - P_{atm} $

Where:

• $p$ is the sound pressure.
• $P_{total}$ is the total instantaneous pressure.
• $P_{atm}$ is the ambient atmospheric pressure (also referred to as barometric pressure in this context).

Therefore, sound pressure is specifically the variation above and below the atmospheric pressure.

Evaluating the Options

Based on the definition:

• Option 1 is incorrect because sound pressure is not the total atmospheric pressure itself.
• Option 2 correctly states that sound pressure is the difference between the total atmospheric pressure and the barometric pressure.
• Option 3 is incorrect as sound pressure is not just the barometric pressure.
• Option 4 is incorrect as sound pressure is a difference, not a sum.

The correct option accurately represents sound pressure as the deviation from the ambient atmospheric pressure.