Upon reading descriptions in historical sources regarding the sound of italian “organi di legno” - organs with open wooden pipes - I was taken aback: the terms and expressions were so clear and precise that the sound seemed tangible.
In fact, the ideal of sound timbre was unmistakeable: “Quando le canne sono completamente in legno, costituisce per loro la perfezione ricevere la sonorità metallica” (1698) - “When the pipes are entirely made of wood, they reach perfection when their sound is metallic” . That is, the sound of the italian Renaissance Principale.

However, it is important to note that the aim was not to simply imitate metal pipes, but it was highly desired to achieve a sound that is “suave” (1600) - “subtle, soft” and “di dolce intonazione” (1561) - “with a sweet, delicate intonation”. As written by the organ builder Hermans, in my hometown Como: “Le canne del Principale secondo sono di legno, unisono col primo, il quale serve per cantar a voce sola ovvero con instrumenti” (1650) - “The pipes of the second Principale are made of wood, unison with the first, which is used for solo voices with instruments.”

Emilio de Cavalieri speaks of wooden organs “perfettisimi per dolcezza e soavità” - “perfectly subtle and suave”, as being considered “pietra di paragone per le buone voci” - “a touchstone for great voices”.

As a physicist I pay much attention to complex transient phenomena described in expressions like “che dispichi netto” (1517) - “that speaks promptly” and “spiccassero un puoco più presto (1569) - “that sound attacked a little earlier […], “[...] tanto nelli soprani quanto nelli bassi” (1626) - “[...] both for basses and treble.”
Therefore, not only the acoustic spectrum (timbre) was important, but also the attack transient, mentioned as “bona pronunzia” - “good pronunciation”.

Finally, Antonio Barcotto invites us not to use stopped pipes because “è da sapere che tale voce è artificiosa e non naturale come quelle delle canne aperte” (1652) - “it must be known that this voice is artificial and not natural like the one of open pipes”.

Anything that has been written about wooden organs can be found realized to a great extent in Innsbruck (Silver Chapel), when playing the only surviving Renaissance organ with open wooden pipes.

There is clear evidence in all historical sources - of the internal coherence and consistency, the “organicity” of the organ!

The keyboard, in order to comply with the desired sound rich in detail, “non sia profonda né dura, [...], asay dolza a la mane” (1508) - “must be neither deep nor hard, [...], with a very soft touch.”

The bellows, which ensure the airflow, must be made of “assesselle” in modo “che detto organo non debba in alcun modo sospirare” (1585) - “thin slabs” ensuring “that said organ shall not sigh in any way”.

The historical sources also outline the material used for the case, the keyboard, the required design and many other details “per coloro che se intendano cossa sia organo” (1538) - “for those who know what an organ is all about”.

How many stops?

Costanzo Antegnati suggests to use the Principale “solo quando si vol cantare mottetti con poche voci” (1652) - only when you want to sing motets with a few voices”.

“Quando si farà i ripieni dell’organo faransi con mani e piedi, ma senza aggiunta d’altri registri [...]” (1602) - “When one plays the ripieni on the organ, one should do so with hands and feet, but without adding other stops […]”.