Fluepipe1 - Page: 11 of 15
This led to the next stage. How would one go about increasing the output capability of a whistle beyond that of traditional steam whistle designs. When increasing the scale of a whistle much beyond that of traditional designs, something unexpected happens-you no longer get the predicted 12 dB increase when doubling the scale, but a much more modest increase of only 6 dB or so. Something needed to be done to overcome this rather serious limitation to output and operating efficiency. The obvious solution was to increase the radiating area of a whistle beyond that of any traditional cylindrical design.

This led to my designing the toroidal whistle. Think of a toroidal whistle as a large phased array of up to 30 or so high output steam whistles all sounding the same frequency. The difference is that it is all done within a single ring shaped chamber rather than a number of separate cylindrical or "pie slice" shaped chambers. This not only insures phase coherency, so that the entire periphery of the whistle radiates in phase, but also minimizes wasted air or steam to power the whistle. If you think about it, there would be much more slot area to drive 30 separate cylindrical whistles than a single large whistle of equivalent radiating area.

Due to the large radiating area of the toroid, the acoustical output is multiplied by the increase in radiating surface over that of a conventional cylindrical whistle design. Because of this, a whistle is now able to compete with the extreme output requirements of the largest of warning sirens. This all looked good on paper, so when the prototype was tested I achieved my predicted output of 125 dB at 100 ft (155 dB at 1 meter).

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