Method
The interior space of the tuba and euphonium is a harmonically-rich series of tubes and curved surfaces, and as such it is ripe for experimentation and sonification. One way in which this is accomplished is by embedding speakers within the bell or other parts of the instruments and playing back sound through the body. This is especially effective when surface-mount transducers are utilized, since the additional resonance of the metal transmits the sound to a very high degree.
A related technique involves playing sound into the instrument from the edge of the bell and varying the sound by changing the length of the instrument via the valves.
Finally, a whole host of normally inaudible sounds are revealed when placing a microphone deep inside the bell of the tuba. Mechanical valve noise, inhalation sounds, the sound of rubbing fabric on the bows of the instrument–they all are picked up by internal mics.
Necessary information
When placing objects like a speaker or microphone into the body of the tuba or euphonium, great care needs to be taken not to damage the instrument. The author has avoided these issues by placing a modest amount of padding when needed and utilizing painter’s tape to secure objects without leaving residue on the material of the instrument.
Utilizing such an intimate technique plays a lot on the construction of an instrument, and as such this technique is partly affected by the huge variety of tuba and euphonium designs. In regular usage, however, this tends to not be a major issue.
One technique that would seem to work on principle is using a bass bow to bow the edge of the bell or other parts of the instrument. Although this may be effective in some limited circumstances, the author has never personally been able to get this technique to work properly in a reproducible fashion. If internal mics are used, this technique will yield much better results; as a purely acoustical technique, it is however of limited use (unless the theatricality of the technique is the sole criterion for its use; in that case, it may be used liberally).
Notation
The notation of sonification methods is not usually a concern, but if this technique is notated, the usual rules for clear and consistent methodology apply.
Relative Difficulty
Advanced to Professional
Works to consider (bolded titles are particularly representative examples of this technique)
Duet Elephants – Mark Trayle
The Composer's Guide to the Tuba 