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upstart writes:

People upwind can hear you hollering into a breeze, but it's hard to hear yourself:

Shouting into the wind isn't so ineffective after all.

The idiom is commonly used to describe an unsuccessful attempt to communicate. But it's not actually more difficult to shout upwind, says acoustics researcher Ville Pulkki of Aalto University in Espoo, Finland.

Sending a sound upwind, against the flow of air, makes the sound louder due to an acoustical effect called convective amplification. Sound sent downwind is quieter. So, if you're yelling upwind, a listener standing in front of you should have no problem hearing you — contrary to popular belief.

The misperception has a simple explanation, Pulkki says. "When you yell against the wind, you hear yourself worse." That's because, in this scenario, your ears are downwind of your mouth. That means your own voice sounds quieter to you.

[...] A similar effect occurs when an ambulance goes by. Most people are familiar with the sudden change of pitch of the siren's sound due to the Doppler effect (SN: 8/2/13). But the siren is also slightly louder when moving toward a stationary observer than it is when it's moving away. When you're bellowing upwind, it's not the source of sound that's moving, but the medium in which the sound travels.

Whichever way the wind blows, acoustics can explain it.

Original Submission