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How do the two ears help people locate the direction of a sound?

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The human ability to locate sound, known as spatial localization, relies on the brain comparing signals from both ears to detect minute differences in how a sound arrives.12

For sounds in the horizontal plane, the brain utilizes two primary mechanisms:

Low-frequency sounds: The brain identifies the phase difference between the sound waves reaching each ear. Because these wavelengths are long, the brain can effectively compare the timing of the wave cycles.12
High-frequency sounds: Because high-frequency wavelengths are short, the brain instead relies on differences in intensity (loudness). The head acts as a barrier, creating a "sound shadow" that makes the sound appear louder in the ear closer to the source.12

These comparisons are processed primarily at the brainstem and midbrain levels, specifically within the superior olivary complex, where neural pathways from both ears first converge. While horizontal localization is highly precise, vertical localization is generally more difficult for humans. Additionally, the brain can use these bilateral inputs to filter out background noise, a phenomenon known as the "cocktail party effect," which allows listeners to focus on a single sound source in a crowded environment.21