Combining voice and alphorn
The human voice is able to produce all the sounds of the chromatic scale or the ones of the natural harmonic row. It would have been easy to combine voice and alphorn from the beginning of the tradition. In fact it's possible that herdsmen in former times did sing and play together. But there are no traces of this musical practice. There is not one description, there are no scores and there is no tradition in which alphorn playing was mixed with singing.
One exception could be found in Lucerne: The "Alpenlied auf Rigi-Scheideck" (Alpsong on the Rigi mountain) for men's choir and alpine horn ad libitum, written in 1835 by Franz Xaver Schnyder von Wartensee.
In the 1970s, when the alpine horn became an instrument of experimental folk-music, the Bernese actress Christine Lauterburg started to yodel and to accompany their singing by sounds on Büchel.
After her experiences the jazz trumpetist Hans Kennel, who also plays alphorn and Büchel, worked with the four yodeling sisters Schönbächler and presented them in 2002 together with hammered dulcimer and percussion at the festival "Alpentöne" in Altdorf, Canton Uri.
In the 1990s the ensemble "Stimmhorn" (voicehorn) was founded. The overtone singer Christian Zehnder and the wind instrumentist Balthasar Streiff became well-known by their programs which they published regularly on a CD. Streiff created new musical instruments as for example the double alpine horn (two horns with one common mouthpiece), the "alpophon" (combination of saxophone and alphorn) and a milking machine converted into a wind instrument.