The triangle is an atonal percussion instrument – one with no fixed pitch. It is made from a steel bar bent into a triangular shape. One angle of the triangle is left open to avoid an unusual pitch. When it is struck with an iron rod, there is a clear “ding” sound. It is hung from a catgut or nylon cord. To stop the sound, you press the steel bar with your fingers. If you strike the inner sides of the triangle repeatedly and rapidly, you can produce a roll or a trill effect.
Why is the triangle called a triangle? From its appearance. In general there are two kinds of triangles, the large and the small. The large has a lower, muted sound; the smaller is higher, clear and sharp. Both are played with a short metal stick. The triangle’s sound is loud and clear, and easily noticed during a performance.