I suppose that one should have been able to predict the return of the Solo division, but its return in recent organs still caught many of us by surprise. As the organ reform movement caught on in the 1960s and '70s, the Solo division of the 19th and early 20th centuries departed the scene as one of the first casualties.
The Solo division was really a part of the "big" organs of the earlier era. When designs reached the four or five manual stage, a Solo division was almost certain to appear. The theater organ used the name "Solo" for a third or fourth manual division, but the Solo we are talking about was a division encountered in large church or concert hall instruments. The surprise is that it has returned in the 1980s as a part of church instruments of modest size. It is a tentative return, since the number of stops is small, and may be only a horizontal trumpet and a cornet. Big organs still have sizable Solo divisions, but the use of the Solo in smaller organs is a sign of design experimentation and innovation.
The Solo division in a small or medium sized organ serves a very useful and ingenious purpose. The extravagant and powerful voices of an organ usually create difficulties when they are included in the Great or Choir divisions, but when placed in their own department they relieve the other divisions from the voicing and performance compromises which would otherwise occur.
Early Solo divisions were usually a collection of interesting and colorful sounds with little relationship to the other divisions of the organ. There were, seemingly, no rules or historic precedents to guide the designs of these divisions, and they varied widely from one instrument to another. Some were highly developed up through mixtures and other upperwork, others were mostly eight foot divisions. Some contained more than 20 stops, but the norm was much less. The term Solo could mean many things; a capacity for a single note melody against an accompaniment elsewhere, a keyboard for crashing chords of power and brilliance, or a division to furnish sounds to couple to other divisions. In almost all cases, Solo implied a division of greater power, pipes of larger scale and wind pressure, more color, more subjectivity; and a tonal design of exotic and unusual nature. There were a few exceptions.
In the current revival, the Solo division takes the place of the Choir or Positive in a three manual instrument, but is usually unenclosed with its pipes in a prominent position. I predict that this idea will develop further with other voices added to create a new eclectic concept for the third manual division after the Great and Swell. Exactly what these voices will be remains undetermined at this time. Each builder will have a different approach, and many builders will not use the Solo at all in their designs. These new Solo divisions will add a dimension of greater presence, flexibility, dynamic range, broader differences in color and excitement to the organ.
In larger organs where the Solo already is a somewhat normal part of the tonal design, it will continue to be a division of color, beauty and power but with fewer of the less interesting stops of the earlier Solo divisions.
An interesting development is that modern Solo divisions have appeared early on in tracker organs where one would least expect it. This is an indication that tracker organbuilding is not locked into a predictable design theory. It may be that the newer innovations in tonal design will stem from the efforts of the tracker builders to break away from the typecasting which has unjustifiably surrounded them. Placing one or two stops on a tracker solo chest on higher pressure is far superior to having an entire Great division on high pressure just to create adequate sonic force for the organ, at the expense of heavier key pressure. The Solo need not be on higher pressure than the other divisions, however, and may acquire its prominence through proper placement.
The new Solo divisions are really a combination of tonal attributes from a 'variety of other divisions. The Bombarde, Choir, Positive, Echo and Grand-Orgue divisions of earlier times are all sources for solo ideas. As the organ world moves further into the Romantic revival and a new consideration of the organ literature of the 19th century, the pipe organ will continue to evolve new tonal ideas to provide for these needs. The reappearance of the Solo division is another indication that the pipe organ is alive and well and developing in many different ways as a vital part of the musical life of our time.