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55956RE: Understanding NAFlutomat Design tool

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  • moosewinds_mike
    Dec 1, 2013
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      Randy,


      Here is my recommendation:


      Measure from the foot end.  There is too much variability in the TSH/bird design to use the TSH as a reference point.  The folks who measure from the sound hole are either the transverse flute community (who have a relatively "standard" embouchure from which to work) or maybe those who have a standard sound hole design for which their formula works.


      Don't worry about the total bore length--which means don't worry about the 3/4" backset (space between the plug & the TSH).  That comes into play when you worry about keeping notes in tune in the second octave, or if you used it in your bore length measurement and ended up putting the top hole too close to the TSH (which creates "nodal interference"--keeping the top hole about 1/3 the distance from TSH to the foot should take care of that).


      Now, for where your "foot" lies.  There are a couple ways of visualizing what is going on.  For instance, if you close the direction hole an play, you will get something like a G# that is flat by about 20 cents or so.  You can figure out the acoustic length of that note from the MIDI note numbers.  A is number 69 and G# is number 68, etc., and 20 cents is 0.20 (there are 100 cents between G# and A), so


      G# - 20 cents = 68 - 0.2 = 67.8 = MIDI


      The next thing you do is find the frequency of that note


      f(G#-20) = 6.875*2^((3+67.8)/12) = 410.5 Hz


      The next thing you do is find the acoustic length of that note


      L(G#-20) = 13552/(2*410.5) = 16.51 inches


      where 13552 in/sec is the speed of sound in air at 72 degrees F.  Likewise, the A (440 Hz) is 15.40 inches.  The difference is 1.11 inches, or about 1+1/8 inches.  So in your case, you can measure north 1+1/8 inches from the physical end of your flute, and that is where the end would be if you had a fundamental A with a bore without a direction hole.  Using that mark as the foot end, you can use the hole calculator of your choice to lay out the holes.


      Mike




      ---In nativeflutewoodworking@yahoogroups.com, <rdbat1@...> wrote:

      I have at least three ways of measuring finger hole distances. One is in an instruction booklet by Raymond Wells, another is the rule of thirds, and also the NAFlutomat design tool. All come up with finger holes in slightly different places. Thing is the NAF site measures from the south end of the flute, while the rule of thirds divides the distance of the bore, and the Ray Wells book measures from the north end of the air split. After my latest disaster placing finger holes I want to make sure I do it right. To add to the mix I have a direction hole too. It started as two direction holes, but now that I have put on a new finger board I only need one direction hole to get the A I want.
      So my question is about where to measure from to place finger holes.
      My fundamental note is A4. 3/4" bore, 3/16 thick walls at the finger hole area. Entire bore length is 13 3/4" but the TSH is only 13" from the south end of the flute. The direction hole is 3/8 across and the center of it is 1 13/16"  from the south end. So the north end of the direction hole is 2" from the end.
      So if I want to use rule of thirds do I measure from the direction hole or the end of the flute? Do I include that extra 3/4" in my measurement of bore when I measure for the NAFlutomat or do I measure from the TSH? It seemed like I had to make things a bit shorter to make the right note using NAF on this flute and now I wonder if it is because I should have been measuring the full length of the bore instead of from the TSH.
      So where should I be measuring for the bore length? TSH to direction hole? TSH to end of flute? Full length of bore?
      I am so confused at the moment. I sure get why I want to take notes as I go. It will make future flutes so much easier!.
      Any help would be so appreciated here.
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