Bonavia-Hunt has this to say: The 16ft. contra viola and the violin (sometimes called gambette) 4ft. are from the voicer's point of view merely octave extensions of the viola. The contra viola is more often than not a tenor C double with a bourdon bass. Sometimes the bass is composed of an 8ft. viola and bourdon or quintaten, with the idea of creating a synthetic violone. Very small-scaled double viols are not popular with the modern organist: they are too reminiscent of the free reed of the pressure harmonium. The Hindley contra viola (on the great) is a rectangular pipe, measuring at the 16ft. note 6 1/4 in. by 5 in., and this gives a mouth equivalent to the fourth mouth of a metal pipe: moreover, this is as it should be, as the 4ft. pipe and every pipe from this point upward is a metal one with a fourth mouth. The scale of the 4ft. pipe is 2-3/16in. These metal pipes are cut up as high as four-elevenths of the width and blown to the fullest capacityon 2 7/8in. pressure (without beards or bridges), in order to match the tone and power of the wooden portion of the stop (CCC to BB). The power and pungency of the bass and tenor register are but little less pronounced than the pedal violone, which is voiced on 3 3/4 in. pressure. Wedgwood mentions this stop, saying only �Unless rigid economy is essential, a Contra Viola will be found far more valuable [than a Bourdon] on the Swell.� Irwin, the only source to list it as a separate entry, says: A manual String of 16', frequently on the Choir Organ. The pedal 32', if it existed, might be called a Contra Violone. Organists particularly value this sub-unison String for its cleanness of pitch as well as that mild stringy timbre the true Viola stop always displays. Ranks vary somewhat in loudness, and are spotted metal down to CCC.
Osiris contains nineteen examples, all at 16' pitch, the earliest of which is cited below.