When one exhales air by twisting the lips appropriately, one does not create enough sound. But when the same amount of air with the same pressure is blown in a flute or whistle, a relatively audible sound is produced.

Is it because in a flute or whistle the air is used to vibrate the air inside the instrument and when blowing directly into air the pressure of the exhaled air doesn't create any vibrations?


closed as unclear what you're asking by CuriousOne, tpg2114, user36790, Gert, Norbert Schuch Feb 26 '16 at 15:01

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    $\begingroup$ I can whistle just fine... it's probably as loud, if not louder than as a small flute and I have met plenty of people who can whistle with quite a volume. $\endgroup$ – CuriousOne Feb 25 '16 at 5:20
  • $\begingroup$ @CuriousOne i was not referring to whistling , i was referring to blowing air simply (without any interference by the tounge) $\endgroup$ – Faiz Iqbal Feb 25 '16 at 5:38
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    $\begingroup$ I am not using my tongue to whistle. It's completely out of the way. Lips only. Why do you think that the tongue would be needed, anyway? All that's needed is a resonating volume and sufficient air flow to create turbulence. $\endgroup$ – CuriousOne Feb 25 '16 at 6:27
  • $\begingroup$ @CuriousOne i tought that the tip of tounge vibrates $\endgroup$ – Faiz Iqbal Feb 25 '16 at 6:37
  • $\begingroup$ Not for me. Try as I may, I can't whistle with tongue and I don't think the tongue plays a role, except to direct the airflow. $\endgroup$ – CuriousOne Feb 25 '16 at 6:48

Steady laminar flow between two fluid layers is often inherently unstable [Rayleigh 1894, The Theory of Sound]. When the boundary is sharp and the difference in speed is significant, this instability can create audible noise. This is the core mechanism of sound production in both whistling with the lips and some instruments like the flute and flue organ pipes.

The other feature of these sounds is resonance from a cavity and sometimes a feedback of the resonance to the driving oscillation. In instruments, the feedback is enhanced by a sharp mechanical edge in the flow stream (an edge in the mechanical windway in pipes and recorders, and the opposite edge of the mouthpiece hole in a flute), so that the oscillation alternates to opposing sides of the edge.

It's interesting that in some configurations of whistling one can transition from no sound to sound by: 1) blowing harder (enhancing the speed difference between the outgoing and stationary air); or 2) introducing a knife edge perpendicular to the airflow (reducing the width of the boundary between the two flow regions).

To answer your exact question: steady flow in air can produce a sound. Whether it does depends on the boundary between the flowing and stationary air (and because it's unstable, whether you now call this "steady" is a bit a question of semantics).

  • $\begingroup$ so you are saying the sound is all because of the shape we have madeof our lips during whistling . right ? $\endgroup$ – Faiz Iqbal Feb 26 '16 at 3:55
  • $\begingroup$ also could you please elaborate the first paragraph of your answer specifically how the reasons you mentioned produce a vibration in the air $\endgroup$ – Faiz Iqbal Feb 26 '16 at 3:59
  • $\begingroup$ It's a combination of the shape of the lips and the speed of the air and possibly other factors, like the tension in the lips, etc. Whatever ends up contributing to the nature of the boundary between the moving and stationary air. $\endgroup$ – tom10 Feb 26 '16 at 4:20
  • $\begingroup$ may you please provide a simple but in depth link where i can study everything about how this flute and whistle produce sound (im a high school chap) $\endgroup$ – Faiz Iqbal Feb 26 '16 at 4:22
  • $\begingroup$ The reasons for the instability are harder to describe briefly, and can take on many different forms from analogies to equations. It's probably better to seek out an explanation that you like. I would say, that to within a reference frame transformation the problem is symmetric at the boundary so either the boundary is going to do nothing, bend with positive feedback in one direction, or oscillate directions due to negative feedback. It happens that the physics of the dynamics leads to the latter. $\endgroup$ – tom10 Feb 26 '16 at 4:26

You are in fact asking why a sound is produced by a specific musical instrument but not when you blow air with your mouth. Sound is produced by vibrations in a media, here air. When you blow no vibrations ( obviously there are some that cause a little sound of blowing to be heard) are caused as for you to here a sound. Instead, a musical instrument is build with such a geometry as for sound to be produced; even more sound that we may call music.

I hope this covers your question. You can dig up a lot of thinks in the web for musical instruments and how they work and there also exist many books on the subject.


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