An apparatus includes a first piston and an opposing second piston, where the first and second pistons are configured to move inward to narrow a space therebetween and to move outward to enlarge the space therebetween. The apparatus also includes a first voice coil actuator having (i) a first voice coil connected to the first piston and (ii) a first magnet connected to the second piston. The apparatus may further include a second voice coil actuator having (i) a second voice coil connected to the second piston and (ii) a second magnet connected to the first piston. Each voice coil actuator may be configured to apply equal and opposite forces on or against the first and second pistons.