By David Osborn

An Introduction to Pan Flute Acoustics
The individual pipes that comprise the Pan Flute are fundamentally different from the pipes that form the bodies of most other flutes in that their air columns are all closed at the bottom end, whereas the air columns of most other flutes are open at their bottom ends.  The player blows into the top end, or somewhere near it, in various ways in most other flutes, and the vibrations of the air column only need to travel one way – downwards – before projecting out of the bottom end, whereas in a Pan Flute Pipe, the vibrations or reverberations of the air column must make a two way round trip – down to the bottom end, which is stopped, and back up to the player’s end, where the sound exits and projects.  Because the sound reverberations have to make this round trip and go twice as far as they would in an open-ended pipe or air column, it only takes about half the length of air column to produce the same pitch.  In other words, if we take the low “G” pipe on a standard size Alto Pan Flute, its air column length is about 21 cm., whereas an open ended air column would have to be about twice that length – that is, about 42 cm. – to produce that same pitch of a “G” above middle “C”. 

These basic laws and proportions regarding air column length and pitch produced vis-à-vis their equivalents on open-ended pipes work best with the low “G” pipe of an Alto Pan Flute.  Below this, as the air column widths get gradually narrower in proportion to the air column length, the length of pipe needed to produce a certain pitch lengthens in excess of the basic proportions and correspondences between closed and open pipes.  Conversely, above the low “G” pipe on an Alto Pan Flute, the length of air column necessary to produce a certain pitch shortens to a shorter length than the standard projected 1:2 proportions as the air column gradually gets wider in proportion to its length.  This is actually nothing surprising, because even in open ended air columns, an air column that is narrower in proportion to its length will need a longer length to produce a certain pitch in comparison to an air column that is wider in relation to its length.  When we finally get into the pipes of the upper octave or register, then the air column width plays an even greater role than the air column length in determining the pipe’s pitch.  Another thing that we notice is that, in the upper register of the Pan Flute, the degree to which a pipe’s pitch can be raised or lowered by merely altering the blowing angle – that is, “lipping up” or “lipping down”  - increases dramatically.  This is analogous to blowing on a bottle that is nearly full (short air column, greater pitch variability with blowing angle alteration) versus blowing on a bottle that is empty (long air column, lesser pitch variability with blowing angle alteration).

In terms of timbre and overtone structure, the most peculiar and characteristic thing about the closed ended air columns that are Pan Flute pipes is that they do not overblow on the octave or second partial, but rather on the octave-and-a-fifth, or third partial.  To me, this property of closed ended air columns is basically idiosyncratic, and lacks a good explanation – at least, I have not yet found one.  The ability to overblow to produce the third partial (the second, or octave is missing) only extends so far, up until about the middle “b” of the Alto Pan Flute’s range, since a requisite narrowness of the air column in relation to its width is necessary for overblowing to be possible.  Here again, this also parallels open ended air columns – the wider the air column gets in relation to its length, the more difficult overblowing will be.  Although overblowing to produce overtones or partials is indeed part of the Pan Flute’s repertory of techniques, it is not used that often. 

And so, overblowing and registers is not a usual part of the repertory of playing techniques for the Pan Flute, and pipes are usually played to produce their fundamental note or pitch.  Even though there is generally no overblowing to produce different registers in playing the Pan Flute, certain subtle shifts of tone quality do occur throughout the instrument’s range, in phases that are roughly one octave each in their overall span.  What I have observed and distilled from my many years of playing the Pan Flute is that the note “D” is the pivotal note in each octave around which critical shifts of timbre or tone quality happen.  It is also interesting to note that this pitch of “D” is also a key one in world flutes, as the standard size or key of many different world flutes happens to be in “D”, with examples being the Shakuhachi, the Pennywhistle and the Irish and Baroque Flutes, to name a few.  These natural or spontaneously occurring “registers” on the Pan Flute, and their respective timbres or tone qualities can be characterized as follows:

“D” above middle “C” to the “D” an octave higher: warm and mellow

Second “D” above middle “C” to the third “D” above:  sweet

Third “D” above middle “C: to the fourth “D” above: clear, bright and piercing

Above the fourth “D” above Middle “C”: strident and bleating. 

Below the first “D” above middle “C”, the sound is breathy and bellowing.

The first overtone or partial that is produced by overblowing, the octave-and-a-fifth, or twelfth, above the fundamental pitch, can also tell the Pan Flute maker a lot about the basic bore camber and acoustical fitness of a prospective Pan Flute Pipe.  If the overtone produced by overblowing is a full octave and a fifth above the fundamental pitch when the pipe is stopped at its bottom end and overblown, then the prospective pipe is good, and can be used as is.  If the overtone produced by overblowing falls short or somewhat flat of the full octave and a fifth, then the pipe is defective, especially in the camber of its inner bore.  In the words of Pan Flute maker Professor Georgescu:  If the fifth is good, the pipe is good.  At no point along the length of its inner bore should a prospective Pan Flute pipe be narrower than it is at its very top or blowing end; in other words, its bore should either be perfectly cylindrical in its overall camber, or it should be slightly narrower at its top or blowing end, but never wider.  This is the cardinal or Golden Rule of pipe bore camber for the Pan Flute. 

To verify whether a prospective Pan Flute pipe is properly cambered in its bore, it helps to use a set of calipers to precisely measure the relative bore diameters of a pipe at its upper and lower ends, in addition to the tuning of its octave and a fifth partial.  In most species of bamboo, a pipe’s inner bore diameter will usually be narrower at the top end of the internode than at its bottom end, and this top end up orientation is the one that should be used.  However, in some species of bamboo, most famously Black Bamboo (Phyllostachys nigra), the bore diameter can be narrower at the bottom end of the pipe or internode than at the top.  If this should be the case, there are two basic choices open to the Pan Flute maker: either widen the pipe bore at its bottom end with rasps and/or reamers; or turn the pipe or internode upside down to put its narrower end at the top.  When dealing with Black Bamboo, I generally prefer the first option.

There are some Pan Flute makers who routinely ream out the inside of a bamboo pipe’s bore, with the objective of removing the soft, pithy innermost layer of the bamboo, which they see as dampening or inhibiting the overall sonority of the pipe.  Although there may be some truth to this, the inherent risk involved in reaming out this pithy inner layer is that the inner bore may not be reamed out in a perfectly uniform or cylindrical fashion, but the bore may have some irregularities, such as ruts and/or ridges, or it might be “hourglassed”, or wind up narrower in the middle than at its top and/or bottom ends.  Such an “hourglassed” bore camber produces a tone quality that is undesirable, or what Romanian Pan Flute makers call sticlos, or “glassy”.  Not only does a pipe bore that is narrower at its middle or bottom end than it is at the top produce this undesirable glassy tone quality, as well as a fifth that falls flat, but it will also be unstable in the basic pitch or of the note it produces, which is also undesirable.  So, when weighing the pros and cons of reaming out your pipes versus not reaming them, the cardinal question you should ask yourself is whether or not you have the technical and/or mechanical capability to do a good, clean job of it, or to do it uniformly and correctly; if not, it is best to leave the inner bore of the bamboo pipe in its natural state. 

As a general conclusion to this basic introduction to Pan Flute acoustics, I would like to point out one basic principle, which may be common sense and something that goes without saying for many:  The Pan Flute is not, and cannot, be made according to purely acoustical considerations alone; making a great Pan Flute involves a blending or compromise between acoustical considerations on the one hand versus the practical or ergonomic considerations of fitting the instrument to the player on the other.  Perhaps the best illustration of this need for fusion, balance and compromise between these two sets of considerations lies in the pipes of the Pan Flute’s upper register:  If the acoustical dimensions or proportions of air column width to length were the same or directly proportional to those of the lower pipes, which are acoustically closer to the ideal proportions, then they would be so small or narrow in their bore diameters that it would be virtually impossible to blow into them, given the size of our lips and embouchure.  And so, for practical or ergonomic considerations, the basic ratios of air column width to length vary throughout the instrument’s range, from bottom to top, in a uniformly graduated or calibrated fashion.  This also produces a corresponding calibrated graduation in a pipe’s overall tone quality, dynamics and playing response from bottom to top, and getting used to these graduated differences is part and parcel of learning how to play the instrument properly. 

The Basic Acoustical Parameters of Pan Flute Pipes
A prospective pipe to be used in a Pan Flute can be assessed or evaluated along the lines of several different acoustical dimensions or parameters, such are bore width, wall thickness, etc…, each of which will have its own impact on the overall sound of the pipe.  Although these first two parameters that I explicitly mentioned above are generally the most basic and important, other parameters that I will discuss below also have their influence or impact on the sound produced.  In building a Pan Flute and selecting its pipes, which is a process that is somewhat like putting together a jigsaw puzzle, the cardinal rule or guideline to follow is that the pipes selected should all be as consistently similar to one another as they can be, with the main variable being a graduated calibration of overall pipe size and width, from widest and longest at the bottom to shortest and narrowest at the top.  Having such a smooth line, or consistent bore diameter calibration schema, is very important for optimum playability and “action” on the Pan Flute, being analogous to how the strings of a guitar are laid out over the frets of the fingerboard for a smooth, consistent action throughout the instrument’s entire range. 

And so, without further ado, I present you with a discussion of the basic pipe parameters below, presenting to you my findings as the cumulative distillation of many years of practical experience in the field of Pan Flute making:
Bore Diameter:  Of all the acoustical dimensions or parameters of a Pan Flute pipe, the overall width or diameter of a pipe’s bore in relation to the air column length could well be the most important.  Although considerations of pipe bore diameters are relative and not absolute, with the bottom line being the kind of sound and response a player wants from his or her instrument, there are certain general guidelines that can be observed.  For my general purposes in this discussion, what I call a wide bore diameter is one that is significantly wider (by a half millimeter or more) than the pipe bore diameters that I have found to be optimal, which I will give out below.  Conversely, by a narrow bore, I mean one that is significantly narrower, again by the same margin, than the optimal ones that I will give out below. 

In the lower register, a wide pipe bore will give a sound that is warm and broad, but with the possibility of more breathiness and/or lack of focus or definition; conversely, a narrow bore in this register will produce a sound that is crisper and more focused or defined, but if the bore is too narrow, the sound will be too soft or weak, as well as thin and reedy, which is not desirable.  In the middle register, a wide pipe bore will give a sound that is similarly warm, robust and full bodied, and one that is more bendable by lipping up or down on the pipe – too wide, and the pitch will be unstable; conversely, a narrow bore in this register will produce a sound that has more crispness, focus and definition, but if it is too narrow, the pipe may bleat or squeak too easily.  In the upper register, a wide pipe bore will produce a louder, more powerful sound, but if the bore is too wide, the pitch will be unstable, or require too much “pucker power” to sustain, and the handling and response of the pipes will be difficult or problematic; conversely, narrow pipe bores will be easier to handle, and have less stridency and instability of pitch and handling, but if the pipe bores are too narrow, they will be difficult to access except by the smallest and most delicate of lips.

Wall Thickness: 
After pipe bore width or diameter, wall thickness is probably the next most important parameter in determining a pipe’s overall tone quality and response.  In addition, wall thickness also impacts on the process of slatting and fitting the pipes, and the final spacing of the pipes and overall span of the instrument.  In a nutshell, pipes with thinner walls will have less inherent stability of tone and pitch with changes of blowing dynamics, but will have a brighter and lighter tone quality in general; they will also be easier and take less work to slat and fit, and will tend to produce instruments with a narrower and more manageable overall span.  Conversely, pipes with thicker walls will have more inherent stability of tone and pitch with changes of blowing dynamics, but will have a darker and richer sound and tone quality in general; they will, however, be more difficult and laborious to slat and fit, and more difficult to fit into a compact and manageable overall span.  In addition, the dimension or parameter of wall thickness does not operate in a vacuum or in isolation; most notably, it interacts with bore width or diameter quite intimately.  To sum it all up: What is a pipe’s overall proportion or ratio of air (bore diameter or width) to meat (wall thickness)?  In my experience, the general guidelines I follow for pipe wall thickness is 3.0 to 3.5 mm. at the bottom, graduating to 2.0 to 2.5 mm. at the top.    

In the lower register, thicker pipe walls will produce a sound that is similarly thick, dark and rich, as well as of greater volume or dynamic potential; conversely, thinner pipe walls here will produce a lighter, airier sound, and one with a weaker or flimsier volume and dynamic potential – as well as a tendency to squeak or bleat easily if blown on too hard.  In the middle register, thicker pipe walls will produce a sound that is darker and richer, and, most importantly, greater stability of tone and pitch; conversely, thinner pipe walls will produce a tone that is bright and sweet, but one with less stability of tone and pitch with different blowing dynamics.  In the high register, thicker pipe walls will produce a sound and pitch that is incredibly rich, “meaty” and stable, but the down side will be that they will be more difficult and laborious to slat.  As I said earlier, there is a delicate and intricate interplay of bore diameter and wall thickness, or “air” to “meat” in a pipe’s sound, and to elaborate on all the possible combinations and conjugations of these two factors would be too consuming of page space – so I will leave it to you to figure this interplay out for yourself through your own Pan Flute making experience.

Pipe Length: 
A comment that I frequently hear when I tell people about my handmade Pan Flutes is that it must have really been hard to cut the pipes to exactly the right length to produce the desired pitch for each pipe.  Actually, nothing could be further from the truth; pipe length is one of the least exacting aspects of Pan Flute making.  Just as long as a pipe is cut to longer than the minimum length it needs to be to produce its designated note or pitch, it can then be tuned up to pitch by the addition or insertion of tuning material of various types – wooden stoppers, epoxy or other kinds of putty, and finally beeswax.  Unbeknown to casual observers, the pipes of a Pan Flute’s upper register are more than halfway full of tuning material – otherwise, they would be too short to grasp properly with the non-dominant hand.  With this in mind, we can see that the exact lengths to which one cuts the pipes of a Pan Flute is as much a matter of manual utility, design and aesthetics as it is a matter of acoustics or pitch.  As long as you pay attention to the general guidelines for pipe bore diameter and length that I give below, you will be fine, and have nothing to fear. 

In a Pan Flute’s lower register, the “tuning margins” for the pipes are the narrowest; and so, cutting the pipes to their proper length is the most exacting and demanding here.  In the middle register, pipe length is the most exacting at its bottom end, although not excessively so, as there is still a comfortable tuning margin there; the right aesthetic curve is probably a greater consideration than the precise length of the pipes in the middle register.  In the upper register, the tuning margin is huge, and the pipes are more than halfway filled with tuning material; the key consideration here is mainly ergonomic – to make the upper pipes long enough to grasp freely and comfortably with your non-dominant hand.  On the short end, I would go no shorter than 6 cm.; on the long end, no longer than 8 cm., with 7 cm. being a happy medium between the two.  The only exception to this general rule for the upper register is when building a bass Pan Flute; here, nine or ten centimeters at the top end is best.

Cross-Sectional Profile: 
By the cross-sectional profile of a pipe, what I am talking about is whether the overall cross-sectional shape of the bore is perfectly round versus oblong in any way.  The pipe that is perfectly round or cylindrical in its cross-sectional profile is often touted as the ideal, but it is seldom achieved in real life.  In reality, most Pan Flute pipes fall considerably short of this perfect ideal - nor is this perfectly round cross-sectional ideal necessarily so great or desirable.  In the real world, if you divide the cross section of a pipe into four quarters, splitting it along two perpendicular axes, one of those axes is probably going to be shorter than the other, sometimes even markedly so.  The prevailing general practice is to have the axis that yields the shortest cross sectional bore diameter be the front / back or audience / player’s side of the pipe’s cross-sectional profile, with the axis that is perpendicular to it being the axis along which the bore diameter is the widest, with this second axis having a lateral or side-to-side orientation.  In the pipe dimension guidelines that follow, the specified bore diameters are the bore diameters along the narrowest cross-sectional axis, which is the front-to-back axis.    

Ergonomically, this prevailing orientation presents a broader surface of the blowing edge to the player’s breath stream, making for greater ease and response in playing.  A pipe whose bore cross-section is more or less, but not perfectly, round will have a difference of bore diameter between these two perpendicular axes as being a half a millimeter or less.  By the time we get to a full millimeter’s difference or more, the pipe is markedly oblong laterally in its cross-sectional profile.  In my experience, having a basic conformity between the pipes of a certain instrument in terms of their cross-sectional profile is usually the best way to go; either a Pan Flute has pipes that are all more or less round in their cross-sectional profile, or they are all laterally wide or oblong in their cross-sectional profile.  Differences in cross-sectional profile also produce subtle differences in tone quality and playing response; one thing I have noticed with pipes that are wide or oblong in their cross-sectional profile is that this makes the accidentals, or sharps and flats, which are produced by altering the blowing angle, much easier to play.  The down side of wide pipes is that the instrument’s overall span will often be wider when the Pan Flute is finally assembled.                               

Bore Camber: 
Bore camber is defined as the bore profile resulting from the relative sameness or differences between bore diameters at different points along a pipe’s length.  It comes last because it is one of the subtler parameters to consider, but it is not least by any means.  As I said earlier, the Pan Flute maker should try, if at all possible to have the bore cambers of all his pipes either be perfectly cylindrical, of equal bore diameter throughout the pipe’s length, or slightly narrower at the pipe’s top end than it is anywhere else along the pipe’s entire length.  Only then will a pipe yield a stable and pleasing tone quality and/or pitch.  Having ruts or ridges anywhere along the inner bore of the pipe, or hourglassing, which is having the bore diameter being narrower in its midsection than it is at either end, are both to be strictly avoided if one is interested in obtaining an optimal and consistent tone quality, pitch and playing response.  Rasping, reaming or otherwise engineering a pipe’s inner bore diameter is permissible just as long as undue ridges, ruts or hourglassing is not created in the process; the reaming must be clean and consistent throughout the pipe’s bore.

That’s it – these are the five cardinal parameters to consider when designing a pipe’s dimensions and specifications.  Once you have gained an understanding of the basic principles at work here, you can then proceed to the more specific and concrete guidelines for pipe dimensions outlined below. 

General Guidelines for Pipe Dimensions
What follows are general guidelines for pipe dimensions, focusing chiefly on pipe length and inner bore diameter, which are the two most important dimensions to consider in selecting pipes for a Pan Flute.  Guidelines and specifications regarding pipe length will be more specific and detailed for the lower pipes, since their tuning margin, as explained above, is narrower.  Typically, for these lower pipes, there will be two different lengths – the “downhill” length versus the “uphill” length.  For a Pan Flute with its low pipes on the player’s right hand side, the longer or “downhill” length will be on the right side of the pipe, and conversely, on the left hand side of the pipe for left-handed instruments.  For the middle and upper register pipes, the pipe length specifications will be more approximate and flexible, again for reasons explained above.  The bore diameter specifications given are for the narrowest or front-to-back cross-sectional axis of the pipe; bore-wise, pipe diameters are selected according to their measurements along this crucial front-to back axis, which delineates the distance between the player’s lips and the blowing edge, somewhat like the relative string heights above the frets in a guitar delineates its overall playing action.  It must also be remembered that these bore diameter recommendations are relative and not absolute.  They are what I have personally found to work best for me, but your experience may be different, and you may wind up preferring wider or narrower bore diameters than those I have recommended, even by a half millimeter or more. 

(‘G’ below middle ‘C’ – low ‘G’ of a Bass Pan Flute) – Length: 48 – 44 cm.;  Bore: 21 mm. 

(‘A’ below middle ‘C’) – Length: 44 – 40 cm.;  Bore: 20 mm.

(‘B’ below middle ‘C’) – Length: 40 – 36 cm.;  Bore: 19 mm.

(middle ‘C’) – Length: 36 – 33 cm.;  Bore: 18.5 – 18.25 cm.

(‘D’ above middle ‘C’) – Length: 33 – 30 cm.;  Bore: 17.5 cm.

(‘E’ above middle ‘C’) – Length: 30 – 27.5 cm.;  Bore: 17 mm.

(‘F#’ above middle ‘C’) – Length: 27.5 – 25 cm.;  Bore: 16.5 cm. 

(‘G’ above middle ‘C’) – Length: 25 – 22.5 cm.;  Bore: 16.0 mm.

(‘A’ above middle ‘C’)  - Length: 22.5 – 20 cm.;  Bore: 15.5 mm.

(‘B’ above middle ‘C’) – Length: 20 – 18 cm.;  Bore: 15.0 mm. 

(‘C’ above middle ‘C’) – Length: 18 – 16.5 cm.;  Bore: 14.5 mm.

(2nd ‘D’ above middle ‘C’) – Length: 16.5 – 15.0 cm.;  Bore: 14.0 mm.

(2nd ‘E’ above middle ‘C’) – Length: 15.0 – 13.5 cm.;  Bore: 13.5 mm. 

(2nd ‘F#’ above middle ‘C’) – Length: 13.5 – 12.5 cm.;  Bore: 13.0 mm. 

(2nd ‘G’ above middle ‘C’) – Length: 12.5 – 11.5 cm.;  Bore: 12.5 mm.

(2nd ‘A’ above middle ‘C’) – Length: 11.5 – 10.75 cm.;  Bore: 12.0 mm.

(2nd ‘B’ above middle ‘C’) – Length: 10.75 – 10.0 cm.;  Bore: 11.5 mm.

(2nd ‘C’ above middle ‘C’) – Length: 10.0 cm. – 9.5 cm.;  Bore: 11.0 mm.

(3rd ‘D’ above middle ‘C’) – Length: 9.5 – 9.0 cm.;  Bore: 10.5 mm.

(3rd ‘E’ above middle ‘C’) – Length: 9.0 – 8.5 cm.;  Bore: 10.1-2 mm.

(3rd ‘F#’ above middle ‘C’) – Length: 8.5 – 8.0 cm.;  Bore: 9.75 mm. 

(3rd ‘G’ above middle ‘C’) – Length: 8.0 – 7.75 cm.;  Bore: 9.5 mm. 

(3rd ‘A’ above middle ‘C’) – Length: 7.75 cm. – 7.5 cm.;  Bore: 9.25 mm.

(3rd ‘B’ above middle ‘C’) – Length:  7.5 – 7.25 cm.;  Bore: 9.0 mm. 

(4th ‘C’ above middle ‘C’) – Length: 7.25 – 7.0 cm.;  Bore: 8.75 mm.

(4th ‘D’ above middle ‘C’) – Length: 7.0 cm.;  Bore: 8.5 mm.

(4th ‘E’ above middle ‘C’) – Length: 7.0 cm.;  Bore: 8.25 mm.

(4th ‘F#’ above middle ‘C’) – Length: 7.0 cm.;  Bore: 8.0 mm. 

(4th ‘G’ above middle ‘C’) – Length: 7.0 cm.;  Bore: 8.0 mm. (or slightly narrower)

The pipe lengths I have given in this chart should allow some “wiggle room” for sculpting a pleasing curve at the bottoms of the pipes after assembly – but to be on the safe side, it’s always a good idea to cut a little bit outside the line, and never inside it.  Another thing to keep in mind regarding pipe lengths is that the length of pipe necessary to produce a given pitch on a Pan Flute pipe will lengthen slightly, or even more, if you make the bore diameter narrower than that given in the above guidelines; and, the more you make the bore narrower, the more the necessary minimum length to produce the given pitch increases.  Conversely, the more you widen the bore diameter of the pipe in excess of the above guidelines, the shorter the necessary minimum length to produce the desired pitch becomes.  This acoustical principle can have practical or ergonomic applications as well:  For example, if a maximum pipe length of 48 cm. for the lowest “GG” pipe on a Bass Pan Flute that you’re making is a bit too long to fit in your suitcase or carrying case, then widening the bore diameter by a millimeter or more might enable you to shorten that lowest pipe just enough to get it to fit.  But, if you are going to widen the bore of the bottom pipe, the bore diameters of the pipes above it must be adjusted in order to create a smooth line or schema of calibrations in bore diameters as you go up the scale.  Remember: a smooth “line” or schema of bore diameter calibrations in a Pan Flute is analogous to a well adjusted guitar fingerboard for a smooth and easy playing action.

Meta-Dimension I: Total Instrument Span
It’s easier to play and “get around on” a Pan Flute with a narrower, more compact span than it is to get around on an instrument with a wider, more unwieldy span.  In the words of Damian Luca:  Why get used to a longer trip (between pipes) when you can get used to a shorter trip?  More compactness in an instrument’s span is a kind of labor saving device that makes playing easier and more efficient.  Making a more compact instrument is more work initially, in that the slats have to be cut to greater depths, but that initial hard work pays off in more ease of playing later on.  Of course, there are limits to how far you can push the whole idea of compactness; for example, if you slat the pipes too deeply in the upper register or octave, they may wind up being so compact and close together that it may be hard to squeeze your mouth and embouchure tight enough to hit the desired pipe without also hitting its neighbor(s).  On the other hand, compactness and a greater slatting depth is really advantageous in the pipes of the lower octave or register, since the pipes themselves are big and wide enough so that excessive compactness is not an issue – but excessive wideness is. 

However, Zamfir gives a cardinal rule regarding slatting depth:  The slats should never be cut so deeply that the distance between the edges of adjacent pipe bores is thinner than the wall thickness of either one of the pipes that are joined together.  Say that you are joining the low “G” and “A” pipes of an Alto Pan Flute together, and both of these pipes have a wall thickness of 3.5 mm., for example.  The total distance between the edges of the bores of these two adjoining pipes at their closest point should never be less than 3.5 mm.  If this distance between the bore edges of these adjoining pipes becomes significantly less than 3.5 mm., then Zamfir says that the sound of one pipe when it is played will “bleed” into the other. 

All this being said, there are certain general guidelines for total instrument span regarding the Pan Flute.  Again, these are not absolutes, but merely that which is preferred or desirable.  The total span of a 22 pipe Alto Pan Flute (G to g”) is best kept within one foot or 30 cm. of total width, from the center of the bottom “G” pipe to the center of the top g” pipe, where the pipes directly interface with the player’s lips.  29 or 29.5 cm., they say, is even better.  For a 22 pipe Tenor Pan Flute, (DD to d’) a good total span would be about 32 cm.  For a 25 pipe Extended Tenor Pan Flute (DD to g”) a good total span would be 35 cm.  For a Bass Pan Flute, just slat the pipes to their maximum allowable depth.  Again, these are not absolute guidelines, but just general preferences – don’t kill yourself if the total span of the Pan Flute you build should be a half a centimeter or so over these specifications!  In the final fitting stage of the pipe slatting process, which could also be called the pre-assembly stage, you can see what kind of span the instrument you’re building will have by doing some measurements while the pipes lie on the Pan Flute mold.  Please keep in mind that the cumulative width of the glue involved in the assembly process usually comes out to an additional 2 to 3 millimeters. 

Meta-Dimension II: Slatting Depth and Pipe Spacing
The Pan Flute is an instrument that dates back to classical Greek antiquity, and so, my feeling is that, in making a Pan Flute, one should strive to make an instrument with pleasing, classical proportions.  Other people may say that I am being too rigidly perfectionist and “anal” here, and certainly, it is possible to build a good Pan Flute, perhaps even a great one, without strictly adhering to the classical pipe spacing proportions that I will give below.  My whole concept of the ideal classical pipe spacing proportions for a Pan Flute revolve around what I call the “Keystone Pipe”, or the pipe that is exactly in the center of the instrument’s span or arch – or darn close to it.  And if the Keystone Pipe is not exactly in the dead center of the instrument’s span or arch, I favor having a few extra millimeters on the top half instead of the bottom half.  The following is a little chart or table of Pan Flute sizes and their Keystone Pipes:

Alto Pan Flute
(Standard size, G to g”) – b pipe

22 Pipe Tenor Pan Flute
(DD to d’) – F# pipe

25 Pipe Extended Tenor Pan Flute
(DD to g”) – g pipe

22 Pipe Bass Pan Flute
(GG to g’) – B pipe or A pipe

Please notice that, in 22 pipe instruments, with the possible exception of the Bass Pan Flute, the Keystone Pipe is the tenth pipe from the bottom.  If you are building other 22 pipe instruments in other keys and/or ranges, try making their Keystone Pipe the tenth pipe from the bottom as well. 

As a general rule, the slatting depths between adjoining pipes should be as regular and uniform as possible, to make for well-regulated distances between the pipes.  If slatting depths between the pipes are irregular or erratic, that instrument will be difficult to get accustomed to.  In slatting the Pan Flutes I make, I use two basic types of slatting schemas or policies: graduated slatting and uniform slatting.  I prefer graduated slatting for the high pitched instruments, the Alto Pan

Flute or higher, whereas I prefer uniform slatting for my lower pitched instruments, Tenor or lower.  I will briefly describe these slatting schemes or policies below:

Graduated Slatting: 
The slatting is deepest for the bottom-most five pipes (G through D on an Alto Pan Flute), with the interspace between the adjoining pipe bores at their narrowest point being no wider than the pipe wall thickness.  Then, the further I get above the low D pipe, the shallower the slatting depth becomes, until, by the time I get to the upper octave or register, there is a full 4.5 mm. interspace between the bores of the adjoining pipes at their narrowest point, in contrast to the wall thickness, which is only about 2.5 mm. at that point.  Graduated slatting works best for the higher pitched Pan Flutes because it gives more space to the small, high pitched pipes up in the upper octave or register. 

Uniform Slatting: 
The interspace between adjoining pipe bores at their narrowest point is uniform throughout, from bottom to top, being somewhere around 3.5 to 4.0 millimeters.  Uniform slatting works best on the lower pitched Pan Flutes, Tenor or lower, because the uppermost pipes are not that small or narrow in their outer diameter. 

One final pipe spacing ratio that I have found works more often than not is what I call the 7 / 8 ratio: The total span between the midpoints of the top seven pipes in the lower octave is equal to the total span between all 8 pipes of the octave above.  For example, in an Alto Pan Flute, the total span between the midpoints (lip contact points) of the A to g pipes is equal to the total span between all eight pipes of the octave above, which would be g to g’.  And the same rule applies for the octave above: a to g’ = g’ to g”.  I will leave it totally up to you as to whether you choose to go “super anal” with this 7 / 8 rule, but if you’re a diehard perfectionist – go for it!

Special Tips for Building Different Sizes of Pan Flutes
A Pan Flute is traditionally made from bamboo, a natural, not synthesized or manufactured, material.  Working with bamboo as nature grew it, we must select from the many pieces of bamboo that make up our collection or “stash” pieces that come closest to the exact specifications we are looking for.  If you are using lathed wooden pipes, on the other hand, you can machine them to the exact specifications you desire, up to the maximum degree of precision allowed by the machinery and hardware at your disposal.  Machined or lathed wooden pipes will have exactly the bore diameter you machine them to have, and the bore will be perfectly round in its cross-sectional profile.  When working with bamboo, as a product of Nature, on the other hand, we must allow for and accommodate subtle natural deviations from the theoretical ideal – and some of these natural deviations can actually be a good thing, giving the pipe and its sound more individuality and character than would be obtainable from a manufactured product.  The following special tips are given with the bamboo Pan Flute builder in mind. 

Alto Pan Flute (G to g”) –
The Alto Pan Flute is the standard treble or high pitched Pan Flute these days, and the notes / pipes of the upper half of the instrument really have to shine, and be eminently clear, strong, in tune and playable.  If the bore diameters of these pipes are too wide, these higher notes will suffer, and will lack the above desired qualities and virtues.  At the same time, since the lower notes / pipes are also played quite a bit, and are also important, they must also have the necessary or requisite strength and tone quality as well.  What many builders of Alto Pan Flutes will do, especially if they are making an instrument for someone with the requisite small mouth and delicate lips to handle it, is to make an instrument whose bore diameters are consistently about ½ millimeter narrower than the standard diameter calibrations given above.  This is also advisable if you are using wide or oblong pipes, whose bore diameter along their lateral axis is significantly wider than the front-to-back axis; in such cases, the maker may use pipes whose front-to back axis bore diameter measurements are even a full millimeter narrower than the recommended bore diameters given above, especially if the bore diameters of the pipes along their lateral axis are a whole millimeter or more wider than the front-to-back axis.  Another thing that often works well when making Alto Pan Flutes is to make the bottom two pipes, A and G, just a little bit narrower than the recommended bore diameters; this makes for a deep, hollow tone, which is desirable, provided the basic tonal strength and quality exist. 

Tenor Pan Flute (DD to d’) –
The Tenor Pan Flute is the best Pan Flute for playing “easy listening music” – soulful songs and mellow ballads, and it features the more sweet and mellow tones of the bottom and middle registers.  Most important among these are the three lowest pipes – DD, EE and FF# - which don’t exist on the Alto Pan Flute.  In contrast to the Alto Pan Flute, which features the higher notes, the Tenor Pan Flute features the lower notes, so, whereas it was a good idea to make the bore diameters of the pipes a half a millimeter narrower than the standard recommendations for the Alto, in making the Tenor, going a half a millimeter wider, especially in the pipes of the bottom two octaves, often works very well in assuring that a full bodied, mellow tone will be produced.  Even if you choose not to “go wide” by any significant amount, you must select pipes for the bottom register, especially for the crucial bottom three pipes mentioned above, that are strong, solid and beautiful in their overall tonal strength and quality.  The whole instrument is only as good as its foundation, which are those bottom three pipes.  Uniform slatting, or close to it, is the best slatting policy to use for the Tenor Pan Flute. 

Extended Tenor Pan Flute (DD to g”) – This is the full gamut, 25 pipe instrument that includes not only the bottom three pipes of the Tenor – DD, EE and FF# - but also the top three pipes of the Alto Pan Flute – e’, f#’, and g”.  Because this size of Pan Flute features both the low notes of the Tenor and the high notes of the Alto, the best pipe selection policy to follow here is to select pipes that are “right on the money”, or exactly on the basic recommended pipe bore diameters that I have given above.  You may decide to make the bottom pipes a little wider than the standard bore diameters, and to also make the top pipes a little narrower than the standard bore diameters, but if you choose to do so, please keep in mind that you must make subtler bore diameter adjustments throughout the middle range in order to create a “smooth line” of pipe bore diameter calibrations from bottom to top. 

Bass Pan Flute (GG to g’) – The Bass Pan Flute is a full octave lower than the Alto Pan Flute, and is the main bass instrument used by most Pan Flutists today.  More than any of the above sizes of Pan Flutes, the Bass Pan Flute features the low notes.  So, not only is it a good idea to make the pipe bore diameters a half a millimeter wider than standard, which can be applied consistently throughout the instrument’s entire range, But the bottom pipes, especially the bottom two to five pipes, can be made even a whole millimeter wider than standard.  Of course, adjustments must be made to the bore diameters of the middle pipes to create a smooth line of pipe bore calibrations throughout the instrument’s entire range.  A possible added benefit of making the lowest pipes of a Bass Pan Flute especially wide is that it may be possible to make the lowest pipes a little shorter than the standard recommended lengths, enabling the instrument to fit into a smaller suitcase or carrying case.  Because the Bass Pan Flute is so big, it can also be quite heavy, especially if the wall thicknesses of the pipes are thick; so, to “lighten the load” a bit, pipe wall thicknesses can be made a little bit thinner throughout the range of the entire instrument.  If the bore diameters on the lowest pipes are not too narrow, you don’t need to worry about a thin, reedy sound down at the bottom; it will be good and mellow.  Another big challenge when making a Bass Pan Flute is that the lower pipes – at least the bottom five pipes or so – are likely to have nodes, which must not only be reamed out very smoothly on the inside, but also smoothed away on the outside when skinning the pipes and slatting them.  Use uniform slatting throughout the entire range of the instrument.

Conclusion: Some Pithy Aphorisms for Pan Flute Makers
A Pan Flute can only be as good as the raw material or bamboo out which it is made; therefore, use only the best materials. 

The Pan Flute is a precision instrument; if you want to make a great Pan Flute, you must be very precise and exacting in the specifications for your pipes, and in the crafting and assembly of the final instrument. 

When making a Pan Flute, it’s not that hard to just throw something together that plays, but if you really want to make a quality instrument, that’s not so easy, and requires serious effort. 

A Pan Flute maker can never have a collection or assortment of bamboo material that is too large; not only do you need a very small diameter for the top pipes, and very wide diameters for the bottom pipes; you also need every possible gradation and increment in between.

A Pan Flute is like a chain of pipes, and a chain is only as strong as its weakest link.  Therefore, care must be taken to make sure that each and every pipe of a Pan Flute is equally strong, both in the quality of its material and in the quality of its sound.    

Take special care when selecting the pipes you will use in an instrument, to make sure that they really “belong” and fit together like a hand and glove; once you assemble the pipes, the core instrument is already made, and cannot be changed. 

The art of making a Pan Flute lies in the expert utilization of raw materials to realize your artistic vision for the instrument you want to create.  Although flexibility is desirable and has its place, supreme satisfaction comes when the Pan Flute maker sees his original artistic vision through to completion in the final instrument.