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Scientists blow their own trumpet

April 16, 2002

Brass instrument makers could soon be using the latest technology to refine the manufacturing of trumpets and cornets. An improved way of taking internal measurements of musical instruments, published today in the Institute of Physics journal, Measurement Science and Technology, has been developed by scientists at the University of Edinburgh, the Open University and Smith-Watkins Brass.

In a trumpet or cornet the musical qualities of the instrument, for example the tone, response and intonation, are defined by the precise shape and measurements of the lead-pipe (pronounced `leedpipe`), the tube that leads from the mouthpiece to the main bore of the instrument. Tiny changes in the diameter of this part of the instrument can make a significant difference to the player, yet be very hard to detect physically.

Although differences in any part of the internal shape of an instrument can have an effect on the sound it produces, variations in the lead-pipe section are more noticeable. Because the internal size is already fairly small (7mm) a tiny dent of less than a millimetre can still create a significant inconsistency. The traditional method of measuring the internal diameter of a musical instrument lead-pipe relies on the use of calipers, but access to some parts of the instrument is limited.

By applying a technique called pulse reflectometry, which measures the sound reflections inside the lead-pipes, the scientists were able to detect differences as small as 0.03mm in the size of the pipes. The research was carried out using lead-pipes of different sizes currently made by Richard Smith for Smith-Watkins cornets and trumpets.

Pulse reflectometry is a non-intrusive measuring technique that was originally developed to measure earthquakes and tremors. It has also been applied in medicine to measure airways.

"This technique is especially useful for cornet lead-pipes because unlike those in trumpets they are hand bent into a curve and a defect is quite likely to happen in that region. This curve also makes it hard to detect defects with traditional measuring methods," says researcher Dr James Buick.

The research concluded that this improved technique is a vital one for the future of musical instrument development and for diagnosing defects that may occur during manufacture. "The next step will be to use the technique on whole instruments like trombones and French horns", said Dr Buick.

Institute of Physics