THE FLUTE HEADJOINT is perhaps the single most important factor in determining the flute’s tone quality and responsiveness, given a skilled player with a mechanically adequate flute. I own about 20 headjoints, some of them professionally made, but most left over from my days as an amateur flute headjoint maker in the early 1980’s. Recently, I made an interesting discovery about how bad or indifferent headjoints (of which I have many!) can be quite remarkably transformed into good or excellent ones. Even many headjoints that are good to start with can be noticeably improved. I call this “Acoustic Knife- Edge Design Element for Improving Flute Headjoints.” THE KNIFE-EDGE DESIGN ELEMENT is shown schematically in Figure 1. Basically, it is just a way to controllably alter the profile of the “strike edge,” a critical feature of the embouchure hole. (The strike edge is the portion of the embouchure hole toward which the player’s air stream is directed; it divides the air stream into a portion which goes into the embouchure hole and a portion which goes over the embouchure hole.) I used the following procedure to construct and install knife-edges: Starting with a piece of 3M ScotchTM MagicTM Tape (normally 2 mils (0.002”) thick, 3/4” wide, 1” long), I cut out a rectangle having a width of about 6 mm and a length of about 20 mm, as shown in Figure 2(A), being careful to leave the original straight edge (future knife-edge) intact. This cutout piece of tape forms the “knife-edge assembly.” Its exact dimensions are not critical; it should be small enough to fit entirely on the lip plate, and big enough to provide a good contact area with the lip plate surface. I like to cut the knife-edge assembly to size from a larger piece of tape (instead of tearing it off the roll) because it gives me better control over the knife-edge dimensions and fewer fingerprints. However, if you have narrow tape and a good dispenser, you may be able to get your knife-edge assembly straight off the roll without any cutting. I then press-fit the knife-edge assembly into the headjoint lip plate, positioned as in Figure 2 (B), with an even overhang over the embouchure hole of about 0.3 to 1 mm. The optimum overhang differed for each flute headjoint, and was determined empirically. As might be expected, the best adhesion is obtained with clean, dry lip plates and fingerprint-free tapes. WHILE MY INITIAL EXPERIMENTS have focused on home installation of temporary knife-edges made from ScotchTM MagicTM Tape, one can also experiment with knife edges of other thicknesses, materials (different tapes, etc.), shapes (straight, curved, etc.), and degrees of permanence. More permanent knife-edges could easily be made from metal, and perhaps could be offered as a factory-installable option for mass-market student model flutes. It should also be noted that the knife- edge design element might also be applied to headjoints for other members of the flute family (e.g., piccolo, alto flute, etc.). A WORD OF CAUTION: Members of the Editorial Board of The Flutist Quarterly have expressed concern that application and removal of tape knife-edges might damage the finish on wood or plastic piccolo headjoints, or peel off poorly adherent coatings on metal-plated headjoints. In addition, there was concern that the sulfur content of rubber electrical tape might damage silver or silver-plated headjoints. While I myself have experienced no difficulty in removing ScotchTM MagicTM Tape from my metal flute headjoints, you should keep these concern in mind and proceed at your own risk.
IN MY FIRST EXPERIMENTS, I tested MagicTM Tape knife-edges on several homemade and professional model flute headjoints classified by me as “being in need of improvement.” The homemade headjoints were solid nickel-silver or silver-plated nickel-silver, and the professional headjoints were solid silver. For these headjoints, the addition of an optimally-positioned knife-edge always resulted in a noticeably warmer and more focused sound. The improvement was most dramatic on flute headjoints having overly large embouchure holes or slightly rounded strike edges. Usually, the optimum knife-edge overhang was smaller for better quality headjoints. I NEXT TESTED knife-edges on homemade and professional model flute headjoints classified as “good” or “excellent.” Improvements to these higher quality headjoints were more difficult to quantify, in part because there is no one single paradigm for the “best” flute sound. For example, some players may prefer a headjoint designed for a distinctive sound or tone color, while others prefer a more neutral headjoint which produces different colors more easily by changes in embouchure. The headjoint best suiting my “tonal ideal” is a Cooper- style headjoint I selected for its warm sound, fast response, and good focus (Brannen Bros., 1986). Knife-edge additions on most of my good and excellent headjoints gave them a sound more like this Cooper-style headjoint. However, the Cooper-style headjoint was not improved by the knife edge addition, but rather became slightly stuffy and fuzzier. USUALLY, too large a knife-edge overhang results in a fuzzier, stuffier tone, but even with the optimum overhang I sometimes sense an additional “thinness” in the hight register. I suspect that this thinness is not intrinsic to the knife-edge design, but rather a result of excessive tape knife-edge vibration induced by the higher velocity air stream used to play the upper octave notes. This explanation would predict less high register thinning with knife-edges constructed from more rigid materials, and is consistent with my results with a heavier duty 3M ScotchTM  Filament tape. These knife-edges gave a more robust, freer high register, but at the sacrifice of some lower register warmth. THESE TAPE KNIFE-EDGES have a finite and somewhat unpredictable lifetime. A suddenly fuzzier tone in a headjoint that has previously been working well with a tape knife-edge is a warning sign that the knife-edge may be starting to life off or peel from the lip plate. This means that it is time to remove the old knife-edge and install a new one. While this is easily done at home, it is not something you would want to be dealing with during a performance. If your tap knife-edge experiments are giving you a new sound that you want to keep reliably and / or permanently, it may be time to think seriously about getting a new, professionally-made headjoint. Don’t expect too much. Knife-edge addition may not improve every headjoint, especially those that are excellent to begin with. Also, a beginner is likely to sound like a beginner on even the best headjoint. WHY DOES THE KNIFE-EDGE WORK the way it does? I don’t exactly know. Headjoint embouchure design is still more of an art than a science. “First principles” scientific answers are lacking even for basic questions about embouchure hole dimensions. Why are different sound produced on oval embouchure holes compared to rounded rectangular ones? Why are different sound produced by different chimney heights and different degrees of undercutting? All of these questions have the same general answer. A change in embouchure hole design changes the air flow pattern in the vicinity of the embouchure hole, and alters the details of how this air flow starts oscillating to make the sound waves you hear as a flute tone. REMEMBER: While trying this experiment, have fun? At best, you will get yourself an improved flute headjoint. At the least, you will have amused yourself while acquiring some instructive hand-on experience with flute headjoint acoustics. Katherine L. Saenger is a Research Staff Member at the IBM TJ Watson Research Center in Yorktown Heights, New York, where her current (non-flute) research is is the area of electronic materials. She is a substitute flutist with the Putnam Symphony Orchestra, a community orchestra based in Carmel, NY.
An Experiment in Flute Headjoint Acoustics by KATHERINE L. SAENGER
It’s easy! You can make and install a knife-edge for your flute headjoint using materials and tools usually on hand at home (estimated time: less than five minutes).
This article originally appeared in the Vol. XXII, No. 1 (fall 1996) issue of The Flutist Quarterly, the member magazine for the National Flute Association, and is reprinted here with permission.
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