Simple Explanation

When two similar sounds arrive very close together in time, we only hear one—and it sounds like it’s coming from the direction of the first one.

Concise Technical Definition

A psychoacoustic phenomenon where two identical sounds arriving within ~40 milliseconds (ms) are perceived as a single sound, localized to the source that arrived first.

Layman-Friendly Analogy

Like someone clapping twice really fast—it sounds like just one clap, and you turn toward whoever clapped first.

Industry Usage Summary

Important in stereo imaging, speaker placement, and sound reinforcement; ensures that localization is based on timing rather than volume when reflections are present.

Engineering Shortcut

First-arriving sound defines localization if delay < ~35 ms.

Full Technical Explanation

The Haas Effect, also called the precedence effect, is a psychoacoustic principle where two identical or similar sounds are heard as one if they arrive within about 1 ms–40 ms of each other. The sound is localized to the source that arrives first. This effect is crucial for spatial perception and stereo imaging, especially in environments with reflections or multiple sound sources (e.g., live sound systems or stereo monitors). If the time delay between the two signals exceeds ~35 ms–40 ms, the brain begins to distinguish them as separate sounds. The Haas Effect explains why early reflections don’t typically interfere with localization and why sound reinforcement systems prioritize time alignment of speaker arrays.