Simple Explanation

The distance from a sound source where the direct sound and reflected (reverberant) sound are equally loud.

Concise Technical Definition

The point in a room or space where the sound pressure level (SPL) of the direct sound from the source equals that of the reverberant sound field.

Layman-Friendly Analogy

Like being halfway between someone speaking and the echo of their voice in a large hall—where both reach you at the same loudness.

Industry Usage Summary

Important in room acoustics, microphone placement, and sound reinforcement design. Engineers use critical distance to optimize intelligibility in public address systems and recording setups.

Engineering Shortcut

Direct SPL = Reverberant SPL → you've reached critical distance (varies with room size and absorption).

Full Technical Explanation

Critical distance (Dc) is a function of room acoustics and the directivity of the source. It marks the location at which the energy from reflected sound becomes equal to that from the direct source. Beyond Dc, reverberant sound dominates. Calculated using source directivity and room’s average absorption characteristics.