sound emitting chambers 39 32 a and 32 b back sides 34 a and 34 b in this embodiment back side 34 a of sound emitting chamber 32 a terminates at circumferential groove 31 followed by circumferential protrusion 33 while back side 34 b of sound emitting chamber 32 b terminates with corresponding circumferential groove 35 followed by circumferential protrusion 37 to align back sides 34 a and 34 b back side 34 a is pushed into back side 34 b until circumferential protrusion 37 of back side 34 b snaps over and around circumferential protrusion 33 of back side 34 a such that circumferential protrusion 37 of back side 34 b rests in circumferential groove 31 of back side 34 a in this locked position circumferential protrusion 33 of back side 34 a fits under and within circumferential protrusion 37 of back side 34 b such that circumferential protrusion 33 rests in the circumferential groove 35 of back side 34 b with back sides 34 a and 34 b locked in place sound emitting chambers 32 a and 32 b are further prompted to maintain their orientation and alignment an alternative linear embodiment of the alignable locking elements is shown in fig5 in which back sides 44 a and 44 b of sound emitting chambers 42 a and 42 b are seen in a different cross sectional view taken along line 4 5 u2014 4 5 of fig2 and looking in the direction of the arrows here back side 44 a of sound emitting.