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Native American Flute Bore Diameters

This page looks at an important design parameter of flutes: the diameter of the flute bore or sound chamber.

If you're just looking for what bore size to use for a given key of flute, then you might want to check out the FAQ page for Crafting Flutes — it has a single table with recommended bore sizes. However, if you'd like more in-depth information, read on.

Published Recommendations

Bore diameter recommendations are available in three published sources: [Stanford 2008], page 11, [Wolf 2001], page 19, and [Wolf 2004]. Note that the information from [Wolf 2004] was obtained from a document posted by Mike Prairie on Yahoo/NFW, document: Ideal Lengths and Bore Diameters.pdf, posted in 2004.

The composite column is an aggregate of all available recommendations shown.

Bore Diameters Recommendations from Published Sources
Range Key Composite Stanford 2008 Wolf 2001 Wolf 2004
High / Alto E5 0.375″     38
D#5 / Eb5 0.500″     12
D5 0.500″ 12 12 12
C#5 / Db5 0.583″ 12 58 58
C5 0.604″ 12″ or 58 58 58
Mid-Range /
Medium /
Tenor
B4 0.667″ 58 34 58
A#4 / Bb4 0.708″58 34 34
A4 0.750″ 34 34 34
G#4 / Ab4 0.750″ 34 34 34
G4 0.771″ 34″ or 78 34 34
F#4 / Gb4 0.875″ 78 78 78
F4 0.875″ 78 78 78
E4 1.000″ 1″ 1″ 1″
D#4 / Eb4 1.083″ 1″ 1 18 1 18
D4 1.104″ 1″ or 1 18 1 18 1 18
C#4 / Db4 1.208″ 1 18 1 14 1 14
C4 1.208″ 1 18 1 14 1 14
Low /
Baritone
B3 1.333″ 1 14 1 14 1 12
A#3 / Bb3 1.333″ 1 14 1 14 1 12
A3 1.333″ 1 14 1 14 1 12

Effects of bore size

Generally speaking, for a given key flute, increasing or decreasing the bore size has some predictable effects. Straying too far from the recommended bore sizes can wreck havoc with your flute design.

For a given key flute, using smaller bore diameters tends to:

  • Increase the length of the sound chamber needed.
  • Allow for higher registers to be reached by the instrument, increasing the overall range of notes that can be played by the instrument.
  • Cause the flute to produce higher overtone frequencies in their first register, producing a timbre that many listeners say is “brighter”.
  • Cause the instrument to tend to overblow into the second register more easily.

For a given key flute, using larger bore diameters tends to:

  • Decrease the length of the sound chamber needed.
  • Limit how many notes can be played in the higher registers. On flutes with a very “fat” sound chamber, it might not be possible to reach any notes in the second register.
  • Limit the overtone frequencies produced by the flute in their first register, producing a timbre that many listeners say is “duller”, “muted”, or more “traditional”.
  • Make the instrument far less likely to overblow into the second register.

Measurements of real-world flutes

To compare real-world flutes with the published recommendations, I measured the bore diameters of the Native American flutes in my collection and plotted them against the composite recommendations.

I measured a total of 61 Native American flutes in my collection. In cases where I have multiple flutes of the same design (such as a Butch Hall Little Horse or a Northern Sprit A minor), I only measured one flute. Flutes with an inconsistant bore diameter, such as bamboo flutes with a natural bore, were not included in this survey.

Bore diameter measurements at the foot end

Bore diameter measurements at the foot end Larger image

The bore height and bore width of each flute was measured at the foot-end of the flute using a precision micrometer, as shown in the diagram above. Flutes where the bore diameter could not be measured accurately, such as flutes which flange out or in at the foot end, were excluded from the survey.

The two bore measurements were typically different, either slightly or substantially in many cases. This might have been due to the presence of the glue seam, lack of routing out the halves of a split-construction bore to a precise depth, or an intentional design choice. Measurement error may have also contributed to the difference. The average differnce between the two bore measurements was 1.6% and the maximum was 13.6%.

The cross-sectional area of the flute bore was calculated from the bore height and bore width, with the assumtion that the measurements represented the longest and shortest dimensions of an ellipse (area = pi × bore height × bore width). The diameter of a circle with that same cross-sectional area was then calculated and used for the chart and the regression analysis to plot trend lines.

This survey includes 61 measured flutes, plotted on the chart below.

Two trend lines are included, showing exponential curves that best fit the data based on a regression analysis as calculated by the LOGEST() function in Microsoft Excel 2010. The blue circles and blue trend line plot the published recommendations. The red diamonds and red trend line plot the flutes that I measured.

Four flutes in the survey were specificially designed as “extended range” instruments by their makers. These flutes were designed with a longer, narrower bore than typical Native American flutes. These four flutes are charted below as a open red triangle and their bore measurements are not included in the trend line.

Native American Flute Bore Diameters - published recommendations and a survey of measured flutes

Native American Flute Bore Diameters - published recommendations and a survey of measured flutes Larger image

Notice that the two sets of data — the published recommendations and the mesurements of actual flutes — agee quite well. There is a slight preference among flute makers to use slightly larger bores on the higher flutes and slightly smaller bores on the very lowest flutes. This might be due to the difficulty with working extremely small or large bore instruments.

Based on the trend line for the measured flutes (excluding “extended range” flutes), we can add a larger range of keys to the table of published recommendations.

The bore diameters in the table below are shown as a decimal number, together with the diameter of the nearest round-nose router bit (in steps of 18″ or 2mm). The nearest suggested router bit is followed by a depth to bore each half of the flute bore in order to achieve the same cross-sectional area as the decimal bore diameter. While you would typically bore to a depth of half the diameter of the router bit (marked as “round”), in order to attain the suggested decimal bore diameter, you might need to bore less than typical (marked as “shallow”) or more than typical (marked as “deep”).

For example, look at the row for a mid-range G4 flute:

  • If you choose to use the composite of the published recommendations, the average bore diameter is 0.771″. The nearest router bit is a 34″ diameter bit, but rather than boring to a depth of 0.375″ you would bore to a slightly deeper 0.396″ to achieve an eliptical bore of the same cross-sectional area.
  • If you choose to use the results of the flute measurement survey, the average bore diameter is 0.858″. The nearest router bit is a 78″ diameter bit, but rather than boring to a depth of 0.4375″ you would bore to a slightly shallower 0.421″ to achieve an eliptical bore of the same cross-sectional area.
  • If you use metric bits and measurements, the average bore diameter is 21.79mm. The nearest router bit is a 22mm diameter bit, but rather than boring to a depth of 11mm you would bore to a slightly shallower 10.80mm to achieve an eliptical bore of the same cross-sectional area.
Bore Diameters
Range Key Composite of
Published
Recommendations
Measured Flutes
inches mm
diameter nearest bit
@ plunge depth
diameter nearest bit
@ plunge depth
diameter nearest bit
@ plunge depth
Very High /
Soprano
F#6 / Gb5     0.302″ 14″@0.182″ (deep) 7.67mm 8mm@3.67mm (shallow)
F6     0.316″ 38″@0.133″ (shallow) 8.02mm 8mm@4.02mm (deep)
E6     0.330″ 38″@0.146″ (shallow) 8.39mm 8mm@4.40mm (deep)
D#6 / Eb6     0.346″ 38″@0.159″ (shallow) 8.78mm 8mm@4.82mm (deep)
D6     0.362″ 38″@0.175″ (shallow) 9.19mm 10mm@4.23mm (shallow)
C#6 / Db6     0.379″ 38″@0.191″ (deep) 9.62mm 10mm@4.63mm (shallow)
C6     0.396″ 38″@0.209″ (deep) 10.07mm 10mm@5.07mm (deep)
High /
Alto
B5     0.415″ 38″@0.229″ (deep) 10.54mm 10mm@5.55mm (deep)
A#4 / Bb5     0.434″ 38″@0.251″ (deep) 11.03mm 12mm@5.06mm (shallow)
A5     0.454″ 12″@0.206″ (shallow) 11.54mm 12mm@5.55mm (shallow)
G#5 / Ab5     0.475″ 12″@0.226″ (shallow) 12.07mm 12mm@6.07mm (deep)
G5     0.497″ 12″@0.247″ (shallow) 12.63mm 12mm@6.65mm (deep)
F#5 / Gb5     0.521″ 12″@0.271″ (deep) 13.22mm 14mm@6.24mm (shallow)
F5     0.545″ 12″@0.297″ (deep) 13.84mm 14mm@6.84mm (shallow)
E5 0.375″ 38″@0.188″ (round) 0.570″ 58″@0.260″ (shallow) 14.48mm 14mm@7.49mm (deep)
D#5 / Eb5 0.500″ 12″@0.250″ (round) 0.597″ 58″@0.285″ (shallow) 15.15mm 16mm@7.18mm (shallow)
D5 0.500″ 12″@0.250″ (round) 0.624″ 58″@0.312″ (shallow) 15.86mm 16mm@7.86mm (shallow)
C#5 / Db5 0.583″ 58″@0.272″ (shallow) 0.653″ 58″@0.341″ (deep) 16.59mm 16mm@8.61mm (deep)
C5 0.604″ 58″@0.292″ (shallow) 0.684″ 58″@0.374″ (deep) 17.37mm 18mm@8.38mm (shallow)
Mid-Range /
Medium /
Tenor
B4 0.667″ 58″@0.356″ (deep) 0.715″ 34″@0.341″ (shallow) 18.17mm 18mm@9.17mm (deep)
A#4 / Bb4 0.708″ 34″@0.334″ (shallow) 0.749″ 34″@0.374″ (shallow) 19.02mm 20mm@9.04mm (shallow)
A4 0.750″ 34″@0.375″ (round) 0.784″ 34″@0.409″ (deep) 19.90mm 20mm@9.90mm (shallow)
G#4 / Ab4 0.750″ 34″@0.375″ (round) 0.820″ 78″@0.384″ (shallow) 20.83mm 20mm@10.84mm (deep)
G4 0.771″ 34″@0.396″ (deep) 0.858″ 78″@0.421″ (shallow) 21.79mm 22mm@10.80mm (shallow)
F#4 / Gb4 0.875″ 78″@0.438″ (round) 0.898″ 78″@0.461″ (deep) 22.81mm 22mm@11.82mm (deep)
F4 0.875″ 78″@0.438″ (round) 0.940″ 1″@0.442″ (shallow) 23.87mm 24mm@11.87mm (shallow)
E4 1.000″ 1″@0.500″ (round) 0.983″ 1″@0.483″ (shallow) 24.98mm 24mm@13.00mm (deep)
D#4 / Eb4 1.083″ 1 18″@0.522″ (shallow) 1.029″ 1″@0.529″ (deep) 26.14mm 26mm@13.14mm (deep)
D4 1.104″ 1 18″@0.542″ (shallow) 1.077″ 1 18″@0.515″ (shallow) 27.35mm 28mm@13.36mm (shallow)
C#4 / Db4 1.208″ 1 14″@0.584″ (shallow) 1.127″ 1 18″@0.564″ (deep) 28.62mm 28mm@14.63mm (deep)
C4 1.208″ 1 14″@0.584″ (shallow) 1.179″ 1 18″@0.618″ (deep) 29.96mm 30mm@14.96mm (shallow)
Low /
Baritone
B3 1.333″ 1 38″@0.646″ (shallow) 1.234″ 1 14″@0.609″ (shallow) 31.35mm 32mm@15.35mm (shallow)
A#3 / Bb3 1.333″ 1 38″@0.646″ (shallow) 1.292″ 1 14″@0.667″ (deep) 32.80mm 32mm@16.81mm (deep)
A3 1.333″ 1 38″@0.646″ (shallow) 1.352″ 1 38″@0.664″ (shallow) 34.33mm 34mm@17.33mm (deep)
G#3 / Ab3     1.414″ 1 38″@0.727″ (deep) 35.93mm 36mm@17.93mm (shallow)
G3     1.480″ 1 12″@0.730″ (shallow) 37.60mm 38mm@18.60mm (shallow)
F#3 / Gb3     1.549″ 1 12″@0.800″ (deep) 39.34mm 40mm@19.35mm (shallow)
F3     1.621″ 1 58″@0.808″ (shallow) 41.17mm 42mm@20.18mm (shallow)
E3     1.696″ 1 34″@0.822″ (shallow) 43.08mm 44mm@21.09mm (shallow)

Effective Bore Diameter

What if you would like to create a flute with a specific bore diameter, but you only have a limited set of router bits? This chart provided by Mike Prairie can help you determine which router bit to use and how deep to route each of the halves of the flute blank:

Attaining an Effective Diameter from a given router bit size by control of the milling depth

Attaining an Effective Diameter from a given router bit size
by control of the milling depth
by Mike Prairie, January 1, 2007 Larger image

To use this graph:

  1. Determine the effective bore diameter you wish to attain and locate it on the vertical axis on the left side of the graph.
  2. Read across the graph to the right and choose one of the curve, colored, intersecting lines. Each line represents a standard size for a bull-nose router bit. Choosing the curved line that has the nearest diamond will result in a bore that is as close to round as possible.
  3. From the intersection point, read straight down to the horizontal axis, which gives the corresponding depth to mill each half of the flute blank.
  4. If your intersection point is to the left of the diamond for that curved line, your bore will be somewhat “squashed”. If your intersection point is to the right of the diamond for that curved line, your bore will be somewhat “tall”.

Some examples:

  • If you want a 1″ bore, locate 1″ on the left vertical scale and read across to the intersecting brown curved line (the 1″ drill bit curve). The intersection is at a vertical triangle. Reading down from that intersection point takes you to 0.500 — the appropriate milling depth for each half of the flute blank using a 1″ bull-nosed router bit.
  • If you want a 1516″ bore, locate 1516″ on the left vertical scale — half way between 0.875 and 1. Read across to the same brown curved line for the 1″ drill bit curve, which is well to the left of the brown diamond. Reading down from that intersection point takes you to about 0.457 — the appropriate milling depth for each half of the flute blank using a 1″ bull-nosed router bit to attain an effective bore diameter of 1516″. This will result in a somewhat “squashed” sound chamber.
  • If you want a 1 116″ bore, locate 1 116″ on the left vertical scale — half way between 1 and 1.125. Read across to the same brown curved line for the 1″ drill bit curve, which is well to the right of the brown diamond. Reading down from that intersection point takes you to about 0.547 — the appropriate milling depth for each half of the flute blank using a 1″ bull-nosed router bit to attain an effective bore diameter of 1 116″. This will result in a somewhat “tall” sound chamber.

 

 
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To cite this page on Wikipedia: <ref name="Goss_2017_bore_diameter"> {{cite web |last=Goss |first=Clint |title=Native American Flute Bore Diameters |url=http://www.Flutopedia.com/bore_diameter.htm |date=3 February 2017 |website=Flutopedia |access-date=<YOUR RETRIEVAL DATE> }}</ref>