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Old 07-21-2007, 09:01 AM
Richard Weisenberger Richard Weisenberger is offline
 
Join Date: Apr 2006
Location: Paducah, KY
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I would like to help you with this project. The "coarseness" sounds more like frequency beats occuring between the bells (a matter of fine tuning) rather than the general pitches themselves. By this I mean that each whistle heard separately would sound fine, but two or more of them sounded together produce the "coarse" sound that you mention. The material of which a whistle is built has very little influence on its actual sound, but more on its durability. The actual sound is a product of its design parameters.

The pitch of a whistle is not really determined by the bell length, as is widely believed, but by the Working Length, which includes a cutup to produce a radiating mouth area that is equal to the cross sectional area of the bell itself. For a typical whistle using a full 360 degree mouth this area is achieved when the bell is set at 1/4 its diameter above the bowl. The Working Length is the distance between the bowl to the inner top of the bell. The frequency is dependent on the speed of sound in the medium, which for steam is 1330 feet/second.

Since the height above the bowl is dependent on the operating pressure, the whistle will probably overblow at this setting. The operating pressure of a whistle is also dependent on the width of the slit from which the steam impinges on the upper lip of the bell. The width of this slit is dependent on the scale of the whistle or its Working Length to diameter ratio.

I invite you or anyone else interested in the design of steam whistles to join us at http://groups.yahoo.com/group/steam-whistles We have interactive spreadsheets available to all of our members that automatically calculate the optimum parameters for frequency, operating pressure and output which are based on the whistle's scale and working length. I would like to see everyone who deals with steam whistles on a regular basis take advantage of the services our group offers. The goal of our group is to bring the steam whistle back as a mainstream sound signal through a knowledge of the physics behind its sound by the members. Try us.


Quote:
Originally Posted by Alan Bates View Post
Does anyone know the origin of the Belle's whistle? She came close to losing it. Captain Paul Underwood didn't like it, claiming that it was "too coarse," by which he meant it was pitched too low. I was told to design a new one and we sold a lot of scrap manila line to pay for the project.
Her whistle is made with cast-iron bells and the lower edges are eroded and blunt. I decided to humor Captain Paul and make new bells of brass - the same sizes as the existing ones. That may have changed the timbre, but the pitch would have remained the same. Fortunately the going price for used manila lines was low. I did manage to make one bell but it was never fitted. Cap retired and the project died. I was greatly gratified for the whistle and saddened by his departure.
As far as I know the whistle came out with the boat. It could have been a product of Ree's foundries or it could have come from an earlier boat. Or neither.
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