 The map was limited to 13 diameters and 8 nodal circles, the latter divided into even semicircles (to the left) and odd semicircles (to the right).See also Skin-Act.Although the skin of an imperial bass drum allows the excitation of a considerable number of high-frequency modes, their duration in time is not normally appreciable by the listener, apart from the timbric contribution to the attack phase of the sound.