Bore graphing can be a very interesting and useful means of studying the physical characteristics of an instrument. Graphs can be designed to permit quick visual interpretation, and if one or more reference graphs are available for comparison, a person can easily make some basic observations regarding the performance qualities of an instrument. The two most basic factors illustrated by bassoon bore graphs are
The graphs can be useful in diagnosing some of the causes of problems such as tonal imbalance, excessive resistance, and upper register response difficulties, especially when they are viewed in conjunction with a study of tone holes (their placements, sizes, lengths, and shapes).
I recently measured and graphed the bore of Heckel bassoon number 5175, in an attempt to determine why this bassoon does not play with the evenness of resistance and fullness of tone typical of most Heckels. This instrument, often used by secondary bassoon students and methods class students, produces a small, stuffy sound in comparison with most of the other school instruments (of different makes). With the belief that the problem was not solely the result of air leakage, I made up a set of predictions (in advance of the bore measurements) as to the possible bore contours which could be factors in the tonal faults of this bassoon:
Upon completion of the measurement and graphing procedures, I found that my first two predictions had been accurate, but that for the bore areas from the middle of the large boot bore through the bell I had greatly underestimated the scope of the problem. The graph showed these areas to be generally smaller in bore than I had anticipated, and for some localized areas I saw that the rates of conical expansion were quite different from those I had earlier found to exist among Heckel bassoons.
The measurement and graphing procedures used were those developed in my recent dissertation on bore dimensions. [James L. Burton, "Bassoon Bore Dimensions " D.M.A. dissertation, Eastman School of Music of the University of Rochester, May 1975.] Telescoping gauges with extension handles were utilized, with diameter readings (to the nearest thousandth of an inch) taken at each inch throughout the bassoon. The graph was then produced by comparing the diameter readings to a set of hypothetical diameters in a reference cone system (in which the constant rate of expansion was figured at 14.0 thousandths of an inch per inch). The bore graph, actually a series of six segment graphs representing each of the individual body bore parts of the bassoon plus the U-tube, illustrates general largeness or smallness of the bore as well as the fluctuation of the rate of conical expansion. A rising graph line indicates a quickening of the expansion rate; a descending graph line indicates a lessening of the expansion rate.
See Figures I and 2 for comparison of Heckel 5175 to three groups of other Heckels. Figure 1 illustrates the following groups of bassoons by showing the averages of their individual graphs:
The reader will readily note certain consistent graph contours among these three graphs, and he will note that the older instruments classified as "long-bore" (on the average, about 11/16 inch longer than the "short-bore" models) have a slightly slower rate of expansion than the more recent instruments. The older bassoons therefore generally have smaller bore diameters, particularly in the three final bore parts.
Figure 2 vividly illustrates the extent to which Heckel 5175 differs from the averages of the twenty-five other Heckels. In the first two graph segments (the wing and the small side of the boot), the predicted narrow areas in the bore may be seen. In the wing, the area from nine inches to twelve inches away from the tenon end is undersized, and the graph in general is not as smooth a line as those of the best individual instruments included in the averages. For the small side of the boot, the expansion rate is dramatically lessened, as evidenced by the falling diagonal graph line, whereas the usual Heckel graph line for this segment drops only at the very beginning and again slightly during the final three inches of the segment.
The large side of the boot for this bassoon graphs in a pattern which is nearly opposite that of all three of the average graphs. The typical hump shape in the early part of this segment is missing, and in its place is a noticeable choke. This segment of the instrument is quite small in diameter.
The long joint graph contour is not at all typical of the standard pattern found in the later Heckels. It begins quite small and generally enlarges at a rate far in excess of that used for the reference line of the graph. This graph segment bears some resemblance to the graphs I have made of several Moennig and Schreiber bassoons. The bell's contour, also atypical, closely resembles that of a Kohlert which I have measured.
In view of the results of the graph comparison, two possible courses of action would seem to deserve special consideration.
Graphing bassoon bores is but one of the aspects of experimental study which performers should strive to develop for practical use. As Don Christlieb has written, "Our happy-know-nothing period is too full of unhappy seams." [Don Christlieb, "Measuring the Conical Bore of the Bassoon," Christlieb Products, 3311 Scadlock Lane, Sherman Oaks, CA 91403, 1968.] Performers must continually learn more and more about the nature of their instruments and search out inventive means for putting the information to effective use.