A calliope (see below for pronunciation) is a musical instrument that produces sound by sending a gas, originally steam or more recently compressed air, through large whistles—originally locomotive whistles.
A calliope is typically very loud. Even some small calliopes are audible for miles. There is no way to vary tone or loudness. The only expression possible is the timing and duration of the notes.
The steam calliope is also known as a steam organ or steam piano. The air-driven calliope is sometimes called a calliaphone, the name given to it by its inventor, but the "Calliaphone" name is registered by the Miner Company for instruments produced under the Tangley name.
In the age of steam, the steam calliope was particularly used on riverboats and in circuses. In both cases, a steam supply was already available for other purposes. Riverboats supplied steam from their propulsion boilers. Circus calliopes were sometimes installed in steam-drive carousels, or supplied with steam from a traction engine. The traction engine could also supply electric power for lighting, and tow the calliope in the circus parade, where it traditionally came last. Other circus calliopes were self-contained, mounted on a carved, painted and gilded wagon pulled by horses, but the presence of other steam boilers in the circus meant that fuel and expertise to run the boiler were readily available. Steam instruments often had keyboards made from brass. This was in part to resist the heat and moisture of the steam, but also for the golden shine of the highly polished keys.
Calliopes can be played by a player at a keyboard or mechanically. Mechanical operation may be by a drum similar to a music box drum, or by a roll similar to that of a player piano. Some instruments have both a keyboard and a mechanism for automated operation, others only one or the other. Some calliopes can also be played via a MIDIinterface.
The whistles of a calliope are tuned to a chromatic scale, although this process is difficult and must be repeated often to maintain quality sound. Since the pitch of each note is largely affected by the temperature of the steam, accurate tuning is nearly impossible; however, the off-pitch notes (particularly in the upper register) have become somewhat of a trademark of the steam calliope. A calliope may have anywhere from 25 to 67 whistles, but 32 is traditional for a steam calliope.