Fig. 17. Diapason Pipe with Leathered Lip
The dull tone of the old Diapasons was due to the absence of the upper harmonics or partials. With the introduction of the Lutheran chorale and congregational singing it was found that the existing organs could not make themselves heard above the voices. But it was discovered empirically that by adding their harmonics artificially the organs could be brightened up and even made to overpower large bodies of singers. Hence the introduction of the Mixture stops (also called compound stops), which were compounded of several ranks of pipes. The simplest form was the Doublette sounding the 15th and 22nd (the double and treble octave) of the note struck. Other ranks added sounded the 12th, 19th, and so on, until it was possible to obtain not only the full common chord, but also some of the higher harmonics dissonant to this chord, from a single key.