The Hope-Jones leathered Tibias have already effected a revolution in the tonal structure of large organs. They produce a much greater percentage of foundation tone than the best Diapasons and are finding their way into most modern organs of size. They appear under various names, such as Tibia Plena, Tibia Clausa, Gross Flöte, Flute Fundamentale and Philomela.
"The word Tibia has consistently been adapted to the nomenclature of organ stops on the Continent (of Europe) for some centuries. The word Tibia is now used in this country to denote a quality of tone of an intensely massive, full and clear character, first realized by Mr. Hope-Jones, though faintly foreshadowed by Bishop in his Clarabella. It is produced from pipes of a very large scale, yielding a volume of foundation tone, accompanied by the minimum of harmonic development. Even from a purely superficial point of view, the tone of the Tibia family is most attractive; but, further, its value in welding together the constituent tones of the organ and coping with modern reed-work is inestimable." [6]
"The Tibia Plena was invented by Mr. Hope-Jones, and first introduced by him into the organ at St. John's, Birkenhead, England, about 1887. It is a wood Flute of very large scale, with the mouth on the narrow side of the pipe. The block is sunk, and the lip, which is of considerable thickness, is usually coated with a thin strip of leather to impart to the tone the requisite smoothness and finish. It is voiced on any wind pressure from 4-inch upwards. The Tibia Plena is the most powerful and weighty of all the Tibia tribe of stops. It is, therefore, invaluable in large instruments. * * * The Tibia Profunda and Tibia Profundissima are 16-ft. and 33-ft. Pedal extensions of the Tibia Plena." [7]
"The Tibia Clausa is a wood Gedackt of very large scale (in other words, a stopped pipe), furnished with leather lips. It was invented by Mr. Hope-Jones. The tone is powerful and beautifully pure and liquid. The prevailing fault of the modern Swell organ is, perhaps, the inadequacy of the Flute work. * * * It was the recognition of this shortcoming which led to the invention of the Tibia Clausa." [8]
The Tibia Dura is another of Mr. Hope-Jones' inventions. It is an open wood pipe of peculiar shape, wider at the top than the bottom, and described by Wedgwood as of "bright, hard, and searching" tone.