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
There are a number of whistle phenomena in which heat plays a role. The temperature in a sound wave varies, but since it is so small normally it is common to neglect its effects. When amplification can occur a small variation can grow and have important influence on the sound field created. The most well known thermal whistle is the Rijke tube. Peter Rijke placed a heated a gauze material inside a vertical tube.