Irwin describes this stop as follows: A very liquid, penetrating form of the 8' Tibia Clausa, made from stopped wooden pipes of even larger scale and thicker and smoother walls than the Tibia Clausa, which itself is a solo stop. Solo Flute 4' is sometimes given to pipes of the same rank, and Solo Piccolo 2' may also be used for the same rank if these stops are unified, and they uaually are in a theater organ. The Solo Tibia Clausa may be heard from the fourth manuals of many of the big theater organs and the many recordings made from them. Strony writes: Some builders used this term to denote the larger of two Tibia Clausas. Often, the Solo Tibia Clausa is on higher wind pressure; or perhaps it's voiced a bit fuller, OR it may just be that it's in the solo chamber!
Solo Tibia Clausa; Emery Theatre, Cincinnati, Ohio, USA; Wurlitzer.