Method
The tuba and euphonium mouthpiece may be removed and used as a musical prop during performance. Some variations of this technique include: buzzing with just the mouthpiece, using the mouthpiece as a percussion instrument, striking the instrument with the mouthpiece (lightly!), rubbing the mouthpiece against the instrument to make a clanging metal sound, and rubbing the finger against the rim to create high-pitched squeaking sounds.
The tuba and euphonium both can also be performed with alternative mouthpieces. One method is to replace the mouthpiece with a smaller-sized brass mouthpiece. When performed with the smaller mouthpiece, a high-pitched and noisy sound results. More commonly, the tuba/euphonium mouthpiece may be replaced with a single reed mouthpiece or double reed. In the first case, anything in size from a bass clarinet mouthpiece to a baritone sax mouthpiece may be placed in or over the mouthpiece receiver and played as in a reed instrument. An English horn or bassoon reed may also be placed directly in the receiver or secured into the backbore of a tuba/euphonium mouthpiece. Both methods of using reed mouthpieces results in a wide variety of sounds, from a piercing shriek down to an extremely loud pedal tone.
Necessary information
Removing and replacing the mouthpiece during performance can be done quickly, but doing so often leads to a certain amount of metal clanging sounds. If done slowly over a longer period, it is possible to have a nearly inaudible change.
There is a slight amount of variety among tuba and euphonium mouthpiece receiver sizes, so if using an alternative mouthpiece, some experimentation is likely to be required.
Although the range of sounds possible with the reed mouthpiece are extensive, it takes a lot of practice to control these sounds. This may make some performers hesitant to experiment with the technique.
The low pedal tones achievable with a single reed mouthpiece correspond to the open fundamental pitches of the respective tuba or euphonium. It is difficult to play and pinpoint specific notes above the fundamental.
Unless the performer is a dedicated contemporary music specialist, it is highly unlikely that they will have reed mouthpieces on hand (let alone the experience and technique to use them properly).
Notation
A simple text direction for the manipulation of the mouthpiece is usually enough to suffice for this technique. One particularly effective strategy for notating the various registers and types of sounds when using a single reed mouthpiece is to separate the low (fundamentals), middle (various reed/brass hybrid sounds) and high (shrieking and reed biting sounds). These can be plotted on a graphic score, or as loose symbols within the traditional score. The provided example demonstrates this technique. Additionally, the work Piernikiana by Witold Szalonek exhibits a fantastic and very detailed use of the tenor sax mouthpiece—recordings of the work can easily be found, and the author highly recommends consulting them when utilizing this technique.
Relative Difficulty
Advanced to Professional
Works to consider (bolded titles are particularly representative examples of this technique)
Piernikiana – Witold Szalonek
Tubassoon – Melvyn Poore
Muzyka na tube – Andrzej Dobrowolski
The Composer's Guide to the Tuba 