Loudness and backpressure

Whistle
1

What makes a whistle louder? Is it the bore size, the size of the window, the size of the lip (blade)…?

Also, what creates backpressure? Maybe a smaller or longer wind passageway?

Is there any relation betwen loudness and backpressure? I ask because I don’t have many whistles to try and feel the relations/differences.

2

Hello, Feadin, and welcome!

From my own attempts to make whistles in the garage, I do think there is a relationship between bore size, window size, windway size, and fingerhole size and sound volume. My experience is that, up to a point, larger tends to mean louder (when talking about the same whistle key).

I would guess that the single biggest variable for backpressure is the size of the windway, but other things can affect that, too. A rough windway can cause backpressure (and lousy sound), a tapering windway will do the same.

Some whistlemakers also use “wings” on the fipple block that keeps the width of the windway constant under the window. Mack Hoover said that this doesn’t create backpressure on its own, but it gives the whistlemaker more ability to control backpressure.

Mark

3

Hi Mark!

Thank you for your answer!
What are these wings that you mention? I would like to know more about that… I’m planning to start building another whistle but I want to do a little more research first. The last one has a pretty small windway, really short too, with very little backpressure. Has a big window too, and is pretty loud so I believe there’s a connection betwen window size and loudness.

4

The Greatest determining factor to whistle loudness is the velocity of the airstream as it exits the windway, (QED) E = 1/2mv2. The “E” energy/amplitude of the sound is increased if the “v” wind velocity increases. A narrow windway exit improves backpressure, but also promotes spit clogging. Tapering bores help with backpressure and improve acoustics

Secondary factors are…

  1. The size of the voicing window.(larger = louder)
  2. The diameter of the bore (larger = louder)
  3. The diameter of the toneholes (larger = louder)

There are other factors, but these are the major players.

5

Feadin,

Wandering Whistler talks about them in his review of a Hoover Whitecap, and you can see them in a couple of the pictures he posted. They aren’t unique to Hoovers, it is something that several whistlemakers use.

Mark