MadSci Network: Zoology |
Kate, This is a great question. One of my favorite teachers explained the answer to me several years ago. Let me see if I can do him justice… There are really two items to address in your question. First, how the 'voicebox' differs between birds and humans, and second, why that should matter for sound volume. A bird's 'voicebox' (its syrinx) differs from a human's (our larynx). Both of these structures create sound by using air to vibrate a taut biological substance, either muscle (in humans) or an elastic membrane (in birds). The important functional difference is that the sound produced in the human larynx is very noisy, whereas the sound produced by the bird's syrinx is more pure. By noisy, I don't mean loud, I mean that there are many different frequencies being produced at once. This would be akin to plunking your whole arm down across a piano keyboard---lots of different frequencies (or pitches) being produced at once. By pure, I mean just the opposite: very few frequencies produced at once. This is more like putting one finger down on the piano keyboard. OK, why should producing many versus few frequencies simultaneously matter? Well, for a human to sing a particular pitch, we have to filter out all of those extra pitches our larynx produced. This means much of the energy we spent running air through our larynx, producing sound at numerous frequencies, is effectively wasted. A bird, on the other hand, starts with very few extra pitches at the syrinx. So, much more of the energy spent passing air through its syrinx is converted directly into sound output, rather than being filtered out; in short it's more efficient. This efficiency means that with surprisingly little energy, a small bird can produce quite a loud sound. However, it won't have the range of pitches to choose from that humans do. I have heard, and you should check with your vocal teacher on this, that humans can actually train their larynx to produce a more pure tone. Using the logic from birds above, this would yield more efficient sound production and could explain why a highly trained opera singer can be heard over an orchestra. Thanks for the question! Cheers, Jim
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