Keep in mind that when an air horn is not operating and has no fluid pressure flowing through it, the interior of the power chamber housing is completely air tight, as the diaphragm disc creates a full air tight seal against the nozzle surface. Referring to the cut-away blueprint diagram of a conventional air horn power chamber on the right, when a constant stream of pressurized fluid enters through the small inlet at the bottom, the pressure in the power chamber increases as it is air tight internally. The pressure continues rising in Chamber 'A' until the air pressure overcomes the spring tension of the Diaphragm. Once this occurs, the Diaphragm is deflected back, and in such, is no longer sealed against the nozzle. From this, the interior of the power chamber is now no longer air tight, as the Diaphragm has deflected off the nozzle. As a result, the pressurized fluid now escapes out of the horn bell. Because the pressurized Fluid exits through the horn bell at a much faster rate than the fluid enters into the power chamber through the base air inlet, the air pressure in the power chamber drops rapidly. As such, the Diaphragm re-seats itself against the nozzle surface. This entire process is one cycle of the Diaphragm operating. In reality, this operation process occurs much faster in accordance to the frequency produced by the horn. The constant back and forth oscillation of the Diaphragm creates sound waves, which are then amplified by the large flared horn bell. The length, thickness and diameter of the horn bell contribute to the frequency of the note produced by the horn.