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4' flutes


ATG
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I can't remember whether it was here or in "the other place", but in one thread there was a general agreement that it is easy to make 4' flutes sound beautiful.

I wonder, firstly, whether this is true, and secondly, why?

Speaking as an educated layman, could it be that the specific physical qualities of air/wood/metal are such that, at these pitches, there is the perfect combination of materials to allow this? Or is it that they are flutes and therefore sound beautiful by default? I can certainly say that the 4' flutes on both of my digital organs are the most realistic stops.

I would be interested to hear from the professionals or from anyone with some insight.

Regards,

ATG

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A feature of the physics of flue pipes in general (note I said 'flue' not 'flute') might be relevant.  The air sheet, arising from the flue slit and moving upwards across the mouth, oscillates back and forth across the upper lip - moving from inside to outside the pipe - while the pipe is speaking.  If the relative positions of the upper lip, the languid and the flue slit itself are such that the sheet spends the same amount of time inside the pipe as outside over each cycle of oscillation, then the even-numbered harmonics in the generated waveform will be reduced in strength compared with their strengths otherwise.  This minimum condition occurs regardless of whether the pipe is open or stopped at the top (though stopping the pipe reduces them even further).  The situation is similar to that of a square wave in electronics which has no even harmonics at all, and it sounds extremely 'hollow' in tone if heard through a loudspeaker, having some vague similarity in this respect to the 'hollowness' of most flute pipes.  The square wave has what is termed a 1:1 mark-space ratio, the same as the air sheet in a flue pipe in the situation just described.  Should the mark-space ratio be varied away from 1:1, then the even harmonics will begin to reappear (for the square wave), or regain their strengths (for the organ pipe).

The 1:1 mark-space ratio is, broadly speaking, a desirable voicing aim for most flutes, which seem to sound more attractive when their even harmonics are somewhat suppressed (though it is avoided for principals/diapasons and strings where strong even-numbered harmonics are essential components of the desired timbre).  Quite why 4 foot flutes rather than, say, 8 foot ones, should sound the most attractive I could not say, though we are now firmly in subjective territory here where adjectives such as 'attractive' and 'beautiful' (the word you used) are only in the mind of the beholder.

In a few cases, such as powerful solo flute stops with names such as Orchestral Flute or Flauto Traverso, the above might not apply.  In these instances the voicer might allow the even harmonics to become stronger to better imitate the orchestral instrument, by adjusting the relative geometry of the upper lip, the languid and the flue slit.  Such adjustments are obviously easier to make in metal pipes rather than wooden ones, where the dimensions are less amenable to adjustment.

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