I should have known that in writing about the various types of pipe organ tone I would eventually have to tackle the string family, so despised and so loved, so accepted and rejected, so ridiculed and praised that this writer asks your indulgence while trying to find my way through this difficult family.
In a sense, the strings are really small scaled principals, but tonally they are no match for the commanding principal chorus sound, and many organists would be surprised to find that there is little difference between the appearance of a string and that of a principal.
Some consider strings a decadent Romantic invention, their presence in the organ evidence of bad taste, showing ignorance of the organ literature. However, there are many examples which exist in very old organs. It is an accident of recent organ history that they were discounted and downgraded as acceptable organ voices in the period 1960-80. Some large organs were built at this time without them, or with a token single rank in one division. This feeling is still with us, and will continue for some time as the organ world wrestles with the concept of subjectivity of sound and design.
An important document relating to strings is the rebuilding scheme which J.S. Bach prepared for the organ at Mühlhausen. Bach was very specific about the Viola da Gamba 8' which he wanted on the Great, which would then work with the Salizional 4' on the Rückpositiv. How many of us today would include such strings on the Great and Positive for the purpose of playing Bach, much less advocate or teach "playing Bach on the strings"? You can now see the difficult job of discussing strings in a historical context since our traditional concept of registration has not included these voices for older music, and, indeed, strings have been practically forbidden as well as ridiculed for such use. We have much to learn.
If Bach (and others even earlier) used strings, how can we proceed to discuss these voices in a way which will be open and understandable? I think the clue lies not in our current milieu, which is somewhat suspicious of strings, but in some future time when we understand them and have a sufficient openness to use them without fear or criticism in performance.
What are the tonal details of the string family, and how are they included in the pipe organ? String sound is harmonically rich, even pungent, and generated by open pipes of small scale (long and thin). The volume of sound ranges from near inaudibility in dulcianas, to medium intensity in salicionals, to unbelievably loud in theater organ solo strings. In fact, the Dulciana is really an echo Principal; the same harmonic structure only softer, but that has nothing to do with its use or acceptance in the organ, since the sound is perceived by most as just a very soft purr which has no connection with its more powerful brother, the Diapason or Principal. The majority of pipe organ strings are considerably louder and stringier than the Dulciana, and most organists will recognize the Gamba, Salicional, Viola, Gemshorn (tapered), Cello, Violin, etc., as the most common members of the string family.
Since the invention of the swell box, it has been popular to place the strings under expression. Perhaps it is this placement which has contributed to their ill repute, and excessive pumping of the swell shoe while playing the strings was one crutch which the untrained organist used to excess. In competent hands, such expression is wonderful and evocative: in the hands of those with little musical taste it can be depressing and embarrassing. Still, the enclosed divisions have become the home for the majority of string voices, where they may be found at 16', 8', and 4' pitch.
It is no longer typical to find a separate string division or a fully developed string chorus. Such chorus ideas have not completely vanished, but most contemporary pipe organs of small size will have string voices only at 8' pitch.
One of the most easily recognizable effects in the pipe organ is the sound of the string and celeste together. As the most subjective voice in the organ, this effect has received the bulk of academic criticism in recent decades. The celeste is tuned sharp (or flat) to the string, and this piling up of phase interruptions from the two out-of-tune ranks produces the wonderful wash of sound which is such a contrast to the precise pitch and perfect intervals of other organ voices. This effect goes back to the 16th century and has existed in many forms ever since. Many names are used for this combination, depending on the type of ranks employed. The Unda Maris is a Dulciana Celeste. The Schwebung is a generic celeste for string or principal ranks. The Voix Celeste implies a keen or "stringy" string. Since the celeste is tuned off-pitch with the rest of the organ, it must be used with care and knowledge, and the organ tuner usually can gauge the proficiency of an organist by how it is set up on an organ's combination action. Likewise, the proficiency of an organ tuner may be shown by how the celeste is tuned.
Recently, there has been a renewed interest in strings and the voicing techniques necessary to produce these sounds which were nearly lost in the Baroque revival. For the organbuilder and voicer, strings represent the antithesis of the philosophies promulgated in that revival. Strings need many nicks, closed toes, and, frequently, roller beards to bring out their true string character. Such techniques were ridiculed and dismissed in the organ reform movement, and it has been difficult for the builder who wanted to include string voices to go to the voicing extremes to get these sounds. Now, with the freedom to voice which our postmodernist era gives us, strings may again be used in the organ without the all-pervading disgust which once greeted such use. Still, none of us is so broad-minded that we would welcome or use every possible organ voice without restraint or judgment, but strings do put us to the test and we usually temper our use of them for one reason or another.
Strings are the least used and most controversial of our tonal families. They should not be ignored simply because of passing fads or arrogance. Their misuse by the untrained will still disappoint us, but sublime moments from great artists tell us that strings are a vital part of organ design, and that we must give them careful thought and consideration in the continuing evolution of the King of Instruments.