port from the chamber. Whereas internal ducted flutes have one fipple mechanism for the mouth of the player, along with several finger holes that share the one fipple mechanism, the hydraulophone has a separate mouth/mouthpiece for each finger hole. A typical park-hydraulophone for installation in public spaces has 12 mouths, whereas a concert hydraulophone typically has 45 mouths. Embouchure is controlled by way of the instrument's mouths, not the player's mouth such that the player can sing along with the hydraulophone (i.e. a player can sing and play the instrument at the same time). Moreover, the instrument provides the unique capability of polyphonic embouchure, where a player can dynamically "sculpt" each note by the shape and position of each finger inserted into each of the mouths. For example, the sound is different when fingering the center of a water jet than when fingering the water jet near the periphery of the circular mouth's opening. Relationships to other instruments Woodwind The hydraulophone is similar to a woodwind instrument, but it runs on incompressible (or less compressible) fluid rather than a compressible gas like air. In this context hydraulophones are sometimes called "woodwater" instruments regardless of whether or not they are made of wood (as woodwind instruments are often not made of wood). Pipe organ Many hydraulophones include a separate water-filled pipe for each note, and have sound-production means similar to pipe organs (but with water rather than air), while maintaining the flutelike user-interface (finger embouchure holes). This form of hydraulophone is similar to an organ, but has water flowing through the pipes instead of air flowing through the pipes. Piano On a concert hydraulophone, the finger holes are arranged like the keys on a piano, i.e. there is a row of uniformly spaced holes close to the player, and a row of holes that are in groups of 2, 3, 2, 3, ..., a little further from the player. Whereas the piano and organ both have a similar kind of keyboard layout, the response ("key action") is different. Pianos tend to respond to velocity (how quickly a key is struck), whereas organs tend to respond to displacement (whether or not a key is pressed down). Hydraulophones tend to respond to the time-integral of displacement (total water flow), as well as to displacement, velocity, and to some degree jerk and jounce . Instruments that use other states of H2O The hydraulophone uses