A speaker interconnection block with two voice coils to be driven with separate amplifiers, or to use one amplifier to drive the two voice coils in series or parallel without having to reinterconnect the voice coils. A user can be a static member, dynamic member or nested member of a group. Selection of one of the orders is detected. The angle measuring instrument 9 is composed of a corner contacting member 12 with links and an inductive linear position detector 13 for measuring displacement of the corner contacting member 12. The apparatus also includes a piston in mechanical communication with the bladder ; a motor, adapted to synchronize contraction and expansion of the bladder with a cardiac cycle of the subject by applying a motor force to the piston ; and a spring, adapted to apply a spring force to the piston.