Dispersive properties of a linear dispersive delay line are retained in a spiral configuration by constraining the radius of curvature depending on a desired propagation mode. The method includes controlling a storage of the first compressed data in a second storage medium at a faster writing data rate than the predetermined read-out data rate, controlling a reading-out of second compressed data of a second compressed format from the second storage medium, and controlling a decompression of the second compressed data to produce decompressed data. This controller will supply near-uniform, continuous airflow to the engine. Fastener base are respectively formed on outward sides of the enveloping frames for movably receiving head strap.