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Let's say there's a humanoid species that are essencialy humans but tiny, around 13cm tall. As their vocal chords are smaller they would have high pitched voices, but could that effect be minimized in a biologically possible way?

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    $\begingroup$ I have a pair of earbuds a few millimeters across and they can reproduce Bach's Toccata and Fugue in D minor beautifully... $\endgroup$ – AlexP Dec 21 '19 at 19:26
  • $\begingroup$ @AlexP, small speakers use partials to fool your brain into thinking that it's hearing longer wavelengths that aren't physically possible for that speaker to make, Turns out our brains are quite willing to be fooled in this way. Tiny humans can seem to have low voices by using the same trick, but would need a rather more complex larynx to do so. $\endgroup$ – user535733 Dec 21 '19 at 21:04
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    $\begingroup$ @user535733: "Small speakers use partials to fool the brain": No they don't, except in quite specialized applications, for example, in the tiny loudspeakers of a mobile phone. In general applications it's more of a bother than it's worth. And specifically for earbuds, there is no need; small speakers can make low pitch sounds, they just cannot make them loud; earbuds don't have to be loud, because they are already very close to the eardrums. (There is no relationship between the size of the speaker and the wavelength; tiny speakers simply cannot move enough air to make loud bass.) $\endgroup$ – AlexP Dec 21 '19 at 21:52
  • $\begingroup$ It is not inevitable: they might loose the ability to make sounds entirely. Evolution is haphazard like that. $\endgroup$ – SRM Dec 22 '19 at 1:18
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    $\begingroup$ Tiny humans with deep voices....I wonder what they’re compensating for...? $\endgroup$ – Jim Dec 22 '19 at 18:02
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Bullfrog says "NO WAY!"

bullfrogs

https://www.youtube.com/watch?v=wbXItUDliuo

Bullfrogs win mates with their low pitched masculine calls. This guy is likely less than 13 cm. I suspect (but do not know) that the trick is his resonant apparatus - that throat sac offers a larger surface than human vocal cords and consequently the ability to generate deep notes. Some frog sounds are considerably lower pitched than human voices.

Your small people could have large throat sacs that they inflate while singing the tenor and bass parts. It would be an intriguing look as well and one I am not sure I have run across.

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    $\begingroup$ This is really interesting. This guy is up to 15 cm max, but the voice in this recording is as low as 215 Hz. Which is 1.58 m wavelength. Seems that this guy breaks the laws of physics :-) $\endgroup$ – TMS Dec 22 '19 at 14:34
  • $\begingroup$ It's worth noting that the principal issue in producing deep notes is getting the sound into the air - getting a small membrane to vibrate at a low frequency is just a matter of tuning the parameters; getting the membrane to push enough air around to actually transmit the sound is the hard part - but bullfrogs seem to be pretty dang loud for their size, especially if you have a whole chorus of them hanging around. $\endgroup$ – Milo Brandt Dec 22 '19 at 21:49
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These humanoids could possess a disproportionate throat region to accommodate longer vocal chords that vibrate at a lower frequency. They may have a sort of throat pouch like many animals that require the ability to make booming calls.

Is it possible for them to have a voice that is as deep as regular humans? Probably not. 13cm is pretty small (the world's smallest living woman, Jyoti Amge, stands at 64cm). In theory, a 13cm human could have throat anatomy that accommodates longer vocal chords and disproportionately large lungs, but if these features were increasingly disproportionate it would start to interfere with other requirements of the body, but it could certainly be disproportionate enough to limit the squeakiness of their voices. I assume you only want their voices to be deep enough to not sound like chipmonks. You also have to ask why this would happen and that could be a feature of whatever story you are writing too.

Runaway sexual selection could, for example, end with one sex (for a mammal this would usually be the males but not universally) having disproportionately deep voices as an audible way to make themselves sound bigger and more dominant.

EDIT: What Willik said.

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  • $\begingroup$ Sexual selection serves as a likely candidate for most bravado. It’s a lot safer to shout loudly and show bright feathers than head but each other all day like elephant seals. $\endgroup$ – Darius Arcturus Dec 21 '19 at 22:05
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They could have syrinxes in addition to larynges. This would permit them a much greater vocal range, and hence disproportionately low voices for their sizes. (Their voices would still be higher than a full-sized, anatomically-correct human's, though.)

To get an even lower range, they could have a structure that they vibrated directly, like a speaker. Human-sized muscles can't vibrate fast enough to get much beyond the very lower part of the human hearing range, but (wild speculation!!) perhaps smaller muscles could vibrate fast enough to give a range overlapping slightly with the syrinx range?

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