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Quirks and Quarks

Why is the sound we hear in two earbuds not twice as loud as the sound from one?

The sound we hear in two ears is not twice as loud as the sound we hear in one because each ear inhibits the sound from the other as part of the binaural hearing process.
CBC Radio ·
Listening with two ear buds is not twice as loud as one because we have binaural hearing. (Saurabh R. Patil, Creative Commons Attribution-Share Alike 3.0)

This week's question comes to us from Steve Johnston in London, Ontario. He asks:

When I listen to a podcast wearing ear buds, sometimes I listen with only one bud. When I put the second bud in, the volume appears to get louder, but not twice as loud. Why?

Dr. Ramesh Balasubramaniam is a professor of cognitive and information sciences at the University of California Merced, and is affiliated with McMaster University's Institute of Music and the Mind.

He explains that this question is a function of our binaural hearing system. We have two ears in order to help pinpoint the origin of an incoming sound. But our perception of binaural sound is less than twice the sound presented to just one ear because of inhibitory connections between the sound heard in each ear.

This means that when sound is presented to both ears, the right ear inhibits the sound to the left, and the left ear inhibits the sound to the right. This explains why the sound coming to both ear buds is less than twice the sound coming to an individual ear bud.

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