Every time we speak, sing, or make any other kind of advanced noise with our throats, we exhale, or to put it that way, blow air through our throats. Why is this required? After all, speakers do not need any air blowing through them, they simply vibrate the air and create the vibrations (sounds) they're supposed to.

Why can't humans create (intelligible) sound just by having an organ that vibrates the air around us? Also, are there any animals that can? (None that I can think of at least). Would it be an evolutionary gain, or just rather pointless?

PS: Obvoiusly we can clap out hands and the like, but that's not what I'm talking about.

Edit: The question is not about exhaling/inhaling, but rather why we need airflow in the first place; why we cannot use a mechanism similar to that of speakers.

  • $\begingroup$ Very similar to this but not quite a duplicate because I think this is asking about why the human voice box needs airflow to make sound, and why it isn't like a speaker. $\endgroup$ – user137 Dec 9 '14 at 19:16
  • $\begingroup$ Exactly. I know we can speak while inhaling (and sometimes I do it myself), but as you said: Why do we need airflow in the first place, why cannot we use a mechanism similar to that of speakers? $\endgroup$ – Ludwik Dec 9 '14 at 19:27
  • $\begingroup$ My guess is that is that our voice box is similar to a resonator. Our vocal chords provide vibrations at multiple frequencies and by adjusting our throat and mouth we change the resonant frequency and select the frequencies that are used to make voice. A simple speaker must be driven at whatever frequency you want, and while this is simple for electronics, it's probably harder for an evolved biological system. It was relatively simple to adapt the existing trachea for sound than to develop a biological speaker. $\endgroup$ – user137 Dec 9 '14 at 19:37
  • $\begingroup$ You can speak inhaling. It just sounds different. $\endgroup$ – vajra78 Dec 9 '14 at 20:43

As part of your question, you ask if other animals can create sound without continuous airflow. Many insects (e.g. cicadas and moths) do exactly this by using tymbals. A tymbal/timbal is an external membrane organ that is controlled by muscles or wing movements, that cause the membrane to flip back and forth, creating clicks or other sounds. So in many ways it produces sound in a similar way as loudspeakers, by creating sounds using a vibrating membrane.

One example can be found in this clip, which nicely shows how the organ functions:
Moth Making Sonar Jamming Sounds (youtube)

On this page (in Swedish) you can also listen to slowed-down butterfly sounds from four species.


Here is a list of woodwind instruments. Do you know of any (non-open) reed instrument that produces a note without anyone blowing air through them? Imagine a clarinet being played on someone's lap pouring out a melody. That would be very, very remarkable indeed.

Our ability to produce sound from our throats is in theory like a reed instrument in music. Let's take the flute.

The flutist blows a rapid jet of air across the embouchure hole. In the flute, the air jet produces an oscillating (vibrating) component to the air flow. Once the air is vibrating, the energy is radiated as sound out of the end and any open holes. The column of air in the flute vibrates much more easily at some frequencies than at others (i.e. it resonates at certain frequencies). These resonances largely determine the playing frequency and thus the pitch, and the player in effect chooses the desired set of resonances by choosing a suitable combination of keys. (More on that here.)

Our vocal chords don't vibrate without the movement of air through them. They just tense and relax to different degrees. There is no sound made if you go through all the motions of saying yes but don't move any air. The moment you move even a small amount of air, you'll get a sound. Furthermore, vibration of the vocal chords is not enough for speech. The noise must go through a chamber where a particular noise will be made to change to resemble speech. Say ahhhhhh and touch the tip of your tongue to the roof of your mouth. The sound is changed significantly. Now, add your cheeks, lips, teeth, and pharynx all changing shapes and you have language.

Our voices are a wind instrument (not like an electronic speaker. For that, look to the electrolarynx). The air column moving across the vocal chords is the air jet. The vocal chords are what sets the air to vibrate. Our "mouth" (all of those I mentioned above" affect the vibrations to produce the desired sound. That's speech.

  • $\begingroup$ Would it be possible, and what would be the downsides/upsides of having a sound box functioning like a speaker, not a clarinette? Do we see any examples in the animal kingdom? $\endgroup$ – Ludwik Dec 9 '14 at 20:22
  • $\begingroup$ @Ludwik - that, to me, is a separate question. I did my best to answer it as written. ') $\endgroup$ – anongoodnurse Dec 9 '14 at 21:06
  • $\begingroup$ While appreciating your efforts, it seems to me the that I must have written badly. Re-reading my question, you're right, it does come across as a question about how our speech system works and why we need the airflow, but my intention was rather to ask why we didn't develop "speaker-like" speech boxes, and the upsides and downsides of that. On the other hand, I might ask that in a new question, if other people interpret my text the same way you did. $\endgroup$ – Ludwik Dec 9 '14 at 21:45
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    $\begingroup$ @Ludwik it is often hard to explain why something evolved one way and not another. But consider that when our far ancestors developed lungs for breathing air, they also got a windpipe with regular airflow. Transforming it into a wind instrument must have required minor changes, compared to evolving a new "speaker system" from scratch. So, we got our vocal chords because they were easy to get. $\endgroup$ – IMil Jun 4 '16 at 1:28

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