A mold assembly including a plurality of mold components configured to form a mold cavity having a desired shape, at least one of the mold components having a notch configured to form a set-back flange in a masonry block formed in the mold cavity, the notch having a depth. The face member 16 is made up of a plurality of metallic plates 20, 21 which are superimposed over an entire surface thereof. A voice coil is connected to the terminal lug at the front surface of the frame. In one embodiment, at least a rope seal is disposed between adjacent coil loops of a portion of the helix coil for enhancing heat transfer to the helix coil. As is the case with monochrome image halftoning, both techniques are tunable, allowing for large clusters in printers with high dot-gain characteristics, and small clusters in printers with low dot-gain characteristics. Moreover, low-pass filters for intercepting passage of a frequency equivalent to the magnetization frequency difference are deployed in signal processing circuits respectively.