Almost everybody old enough will say they have trouble hearing voice in a noisy room. That's because hearing normally declines by about one decibel for every year you age. If you imagine a squiggly line on a graph, you can appreciate why understanding speech is a very complicated exercise. Add to that the confusing din of a crowd, and it's no wonder we sometimes struggle.
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But if you have good hearing, what's the furthest distance you can hear a voice - even if you don't know what they're saying? Under ideal conditions, the range of the male human voice is about 180 metres while still being intelligible.
Sound pressure level normally halves (by six decibels) for each doubling of distance, so you might still be able to hear the speaker's voice at 360 metres even if you can't understand what they are saying.
That's outdoors, but indoors, things become more complicated because of acoustics. If you're standing close to someone, the voice you hear is dominated by a direct path from them to you. Beyond about a metre, sound becomes dominated by sounds reflected around the room, making it prone to being absorbed by soft surfaces, bounced off hard ones, and shaped in other unpredictable ways.
In a room with heavy reverberation, your ears pick up multiple copies of the sound, slightly out of sync according to how they were reflected around the room.
Add a hissing espresso machine and a chattering crowd and things are getting difficult.
That's why, when you're talking to someone with hearing loss, you need to stand close and look at them directly. It helps if they can see your face so they can lip read.
According to The Guinness of Records, there is a case recorded of a voice being heard at a distance of 17 kilometres. That was across still water at night
You can hear the "whispering wall" effect around some curved dam walls, or visit Questacon where you can communicate a surprising distance using a pair of curved dishes.
Or you could be a blue whale, pumping out very low-pitched, extremely loud sounds - as high as 188 decibels. That's easily the loudest sound made by any animal (a jet at take-off is about 120 decibels). Another blue whale could hear that more than 800 kilometres away.
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