Coiled spring type acoustical transmission lines commonly called artificial reverberation lines, which convey acoustical signals in the rotary transmission mode are well known. Examples are U.S. Pat. No. 2,982,819 issued to H. E. Meinema et al., May 2, 1961; U.S. Pat. No. 3,363,202 issued to H. E. Meinema, Jan. 9, 1968; and U.S. Pat. No. 3,106,610 issued to A. C. Young, Oct. 8, 1963.
Although the prior art is well developed there are several major deficiencies present. One significant deterrent to use of such lines in modern miniaturized equipment is the large overall packaging size necessary in the lines to obtain the necessary reverberation characteristics. Thus, the lines may take up more room than the amplifier and signal processing electronic equipment in which they are used.
Prior art attempts made to shorten lines by folding them at the center have introduced various problems in the suspension of the line and coupling of signals as shown by Meinema U.S. Pat. No. 3,363,202; U.S. Pat. No. 3,564,462 issued Feb. 16, 1971 to W. Fidi et al.; or U.S. Pat. No. 3,431,516 issued Mar. 4, 1969 to H. W. Schafft et al. Such lines require special engineering construction of the coupling networks for different delays or line characteristics. If this is not done the coupling means may introduce distortions such as high frequency attenuation. Also matching of different length or different diameter spring line segments is difficult. Thus, construction techniques are not uniform and lines may become too costly to employ. Also, such folded lines of the prior art are susceptible to shock forces applied transverse to the coil spring axis, which tends to introduce rotational motion and thus introduces noise into output signals.