Shepherd's whistle
They are also produced commercially. Simple whistles may cost less than 1 USD in bulk; expensive ones may be quite ornate. They are commonly made of plastic, aluminum, stainless steel, silver, brass, titanium, Corian, jade, buffalo horn and other materials.
Physics of whistles
The equation above indicated 146 Hz and the Nielsen equation indicated 138 Hz. Clearly, the whistle was being driven by a cavity resonance. This is an example of a whistle being driven in edge tone fashion but the result is a monopole sound field.