Bore reconstruction based on input impedance measurement
Marthe Curtit; Fazli Yahaya; Jean-Pierre Dalmont; Joël Gilbert; Olivier Cottet

The bore profile of a wind instrument has an important influence on its acoustical characteristics. Specifically, playing frequencies are close to the resonance frequencies of the tube constituted by the bore of an instrument. Several methods were developed to obtain bore dimensions, such as pulse-reflectometry, or radiography techniques. The method investigated here is based on tube input impedance measurement, witch provides us with an alternative way to estimate the bore profile.

In collaboration with Olivier Cottet, we have applied this method in the case of a bassoon crook, at different stages of fabrication. During the crook fabrication, a sheet of metal is used to form a straight tube which internal profile is given by a mandrel of which dimensions can be measured precisely. This tube is then filled with alloy lead and curved. At this stage, taking mechanical measurements of the bore (using a calliper for example) is not possible due to its small size. The aforementioned method is then used to make those measurements, and maybe to observe some differences in the bore profile, after and before the crooks is curved.