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 Post subject: Why no overblows?
PostPosted: 23 Jul 2015, 18:56 

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Take a tin whistle, a recorder or a flute and blow harder than usual and the tone goes up and octave. Why can't this be done on an ocarina? I don't think that it can be because it has a closed end. If you raise your fingers off a hole or two while playing, you now will have an open ended instrument like a recorder, but it still won't overblow. Can anyone give me a simplified (I'm entirely self-taught, so music theory is something I don't understand too well.) reason why not?

Thanks,
Paul N.


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 Post subject: Re: Why no overblows?
PostPosted: 24 Jul 2015, 20:25 

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Actually, it can be done on an ocarina and it is regularly used on small, high pitched ocarinas to extend the range. For example, on a well-made, high quality soprano C ocarina, 4 to 7 additional half-steps in the highest range can be obtained through overblowing. On best soprano G ocarinas available, up to 4 additional half-steps is normal.


A very beautiful application of overblown notes can be heard here: http://www.youtube.com/watch?v=Bi2UJsK3hrg - notice that the highest notes played seem to be well above the normal range of the ocarina.


On larger ocarinas, like alto C, it becomes very impractical (and terribly difficult to get the pitch right) and the timbre becomes so different that it is simply unusable.


Why are ocarinas special? If you attempted to make an ocarina, you have probably noticed that finger holes can be placed arbitrarily (within certain limitations) and still have the instrument in tune. Also, as long as the instrument is fairly round and convex, its exact shape does not make a considerable difference in sound. This is completely different than on a tubular flute. The length of a tubular flute and the position of finger holes have to be accurate within a fraction of a millimetre, otherwise tuning suffers significantly and the bore of a flute defines its timbre. This striking difference between a tubular flute and an ocarina is because the resonating chamber of an ocarina works in a fundamentally different way than how the resonance works in a tubular flute.


Tubular flutes are long, narrow tubes, while ocarinas are short, stubby, bulbous vessels. There is significant difference in the spatial distribution of the air pressure within the body of either instrument. In tubular flutes (regardless whether they are open ended, like most flutes, or closed at the end, like some flutes and organ pipes) the air pressure distribution is that of superposition of a large number of standing waves. In globular flutes, like ocarinas and gemshorns, the spatial distribution of air pressure is pretty much constant (i.e. pressure only changes in time, but at a given moment, it is almost the same anywhere within the ocarina). This is called Helmholtz resonance. An interesting property is that size of the resonator chamber is typically larger than half of the wavelength of sound produced. For example, a typical alto C ocarina is often less than 20 cm long (though this varies a lot, unlike tubular flutes), but the wavelength of its lowest note (C at 523 Hz, let's ignore sub-holes for a moment) is about 65 cm.


When it comes to tubular flutes, the fundamental mode of the standing wave can be easily switched into a higher order simply by blowing a bit harder and adjusting the fingerings (providing nodes for the wave). The difference in energy needed to drive the resonator at different modes is fairly small. This is why tin whistles, recorders and flutes squeak easily and a lot of control is required to play clean notes. Inside the ocarina, however, there is no standing wave, but more or less uniform distribution of air pressure that oscillates sinusoidally in time. In order to squeak (an overblown note is nothing but a well controlled squeak which is in tune), there has to be a complete redistribution of air pressure inside an ocarina (something similar to an asymmetrical standing wave is formed - there is a spot of minimal and maximal air pressure, and a spot where air pressure doesn't change much). This works best on small, high pitched ocarinas that are made long and narrow and with exact finger hole positions.



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 Post subject: Re: Why no overblows?
PostPosted: 24 Jul 2015, 22:58 

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Hi,

Thanks, that explanation answered my questions.

Regards,
Paul N.
Tonawanda, NY


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