Copy the page URI to the clipboard
Sharp, David
(1996).
Abstract
The bore profile and input impedance of a musical wind instrument provide valuable information about its acoustical properties. The time domain technique of acoustic pulse reflectometry can be used to measure the input impulse response of a tubular object, such as a wind instrument, from which both its bore profile and input impedance
can be calculated.
In this thesis, after a discussion of the theory of acoustic pulse reflectometry, the operation of a practical reflectometer is described and measurements of input impulse response, bore profile and input impedance are investigated.
In general, the experimentally measured input impulse response of a tubular object contains a DC offset which must be removed for accurate bore reconstruction. A new, faster method of determining the DC offset is introduced which doesn’t require prior knowledge of the object’s dimensions.
The bore profile of a test object, calculated by applying a lossy reconstruction algorithm to its input impulse response (after removal of the DC offset), is found to agree with directly measured radii to within 0.05mm. Various brass instrument reconstructions of similar accuracy are presented.
An input impedance curve, calculated from the input impulse response of the test object, is found to have peak frequencies which agree with those of a theoretical curve to within 0.7% (a considerably better agreement than when a standard frequency domain measurement technique is used). Impedance curves of various brass instruments
are presented.
Bore reconstructions are used to confirm the presence, and in certain cases, the positions of leaks in instruments. For the special case of a leaking cylinder, the impedance curve is successfully used to calculate the size of the leak.
Finally, a method is investigated which allows the practical reflectometer to measure longer objects than previously possible.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)
