[MeganM (OP)]

Cynthia's grandson wants to know:

How come our voice boxes are “all built the same”, but our voices all sound different?

Any ideas?

[Colin2B]

If you look at similar musical instruments eg violin, viola, ‘cello etc you can see that differences in string length and body size make a big difference to the sound. Also, listen to the variation a player can get from different uses of the bow.
This is the same with humans, but there are a lot of variables. Many different resonant chambers in head, throat and body, size of tongue, larynx etc. Added to this, all the elements are under the autonomic control of the brain and nervous system, lots more variables.

[alancalverd]

Because they aren't built the same!

Vocal cords develop at different rates and aren't quite symmetrical, and the resonant cavities are all different lengths (which determines fundamental frequency) and shapes (overtones). Think of the difference between an oboe and a cor anglais - adding a small chamber in place of the flared bell produces quite different overtones.

Unlike musical instruments, apparent size isn't everything! I've sung with skinny little guys who produce a rich bass, and high tenors who look more comfortable in a rugby shirt than a dinner jacket. A lot of it is to do with muscle training: most people's voices rise under stress, and I certainly need to consciously relax for the low notes.

[Bored chemist]

In spite of considerable variation in physiology, must of us sound sufficiently similar that we can understand eachother.

[evan_au]

Mouse vocal chords are very tiny, and produce high frequencies - up to 70kHz.

Imagine the surprise of researchers who, after working with mice for many decades, suddenly discovered that mice could laugh...

[alancalverd]

In spite of considerable variation in physiology, must of us sound sufficiently similar that we can understand eachother.

It turns out that the essential information in speech is contained within a band around 3 - 5 kHz. With aircraft VHF channels now restricted to 8.33 kHz bandwidth, speech is still adequately intelligible, with enough clues to usually assign age and sex to the voice, but it sure ain't music!