Another factor not mentioned by any of the posters is that instruments tend to come in families, or choirs, and often are tuned usually a fourth or fifth apart, in order for them to play reasonably closely spaced chords. Think for a moment of the incredibly rich sound of a top-to-bottom orchestral brass chord with trumpets blazing on top and tubas way down below. Or the same with the families of strings, saxophones, clarinets, etc. Scott Morrison