Reeds are the most exciting, the most difficult, the most colorful, the most unstable, the most unusual, the most exotic, and the most sensitive voices in the pipe organ. This family is a problem for the organbuilder because reed pipes are difficult to voice and keep in tune. Many reed problems are overlooked because the sonic and musical results are so magnificent, and reeds are included in most specifications.
The reed family is broader in tone than any other in the organ. The principals, flutes, and strings do have tonal differences within each group, but come nowhere near the diversity of power and tone color available from the highly idiosyncratic reeds.
There have been attempts to classify reeds into various categories, but these are only partially successful. An initial method would be to separate them as chorus or solo reeds. The chorus reeds would be trumpets, bombardes, etc., and the solo reeds might be regals, cromornes, etc. It is already evident that this classification system fails, because so many crossovers and dual-purpose reeds fall into both groups, depending on voicing, placement, and usage.
A second method of reed classification would be by length of resonator, into full-length or short-length resonators. Again, this breaks down when we find ranks which are short in the bass but long in the treble. There is no clear-cut method of classification which will tell us all that needs to be known about the tone color, power, and intended musical function of any given reed voice. We are left to rely on our own taste and judgment to decide what reeds to install, what to name them, and how to use them.
Some basic concepts will assist us in analysis, but we must always be aware that exceptions do occur. Generally, full-length reeds (resonators which are as long as the pitch of the stop) have a fully developed fundamental tone. This is the purpose of the full-length resonator. It is certainly possible to have a blaze of high-pitched harmonics from a full-length resonator, but it is the need for a balanced or fully present fundamental which mandates the use of these resonators. Names do not help us here, since some of the traditional full-length stops (Trumpet, Oboe, Posaune, Bombarde) have also been made in short lengths.
Short-resonator reeds are generally deficient in fundamental power, and have a tonal spectrum which varies to an extreme that is wider than any other category of organ tone. There is also a second breakdown into normally short (Clarinet, Schalmey, Cromorne) and very short (Ranket, Regal, Voix Humaine) resonators. These short resonators vary widely in shape, size, and material, and many go back to ancient forms for their origins. Generally, short resonators produce a pungent sound; full-length resonators produce a broader, more majestic sound.
The inclusion of reeds in an organ usually signifies that the instrument has gained a certain size and character. A small organ may not have a reed voice, and thousands of small and medium-sized instruments have been built without them. But the builder feels uneasy when the organ comes to the point that a reed is called for and the agonizing decision must be made as to what the first or only reed will be. It would be informative to study the history of first-included reeds and to note changes over the years.
As an organ design grows in size, the number of reeds should increase, becoming 10-20% of the total number of ranks. At this point, many organbuilders wish to include as many reeds as possible, and there is never enough room or budget to do so.
The construction of reed pipes differs from the other families of tone (principals, flutes, strings) which are flues. Reeds have a vibrating tongue of metal which makes them similar to the orchestral clarinet. This metal tongue is the source of the sound in a reed pipe. It is curved by the voicer so that the wind pressure makes it vibrate, sending pulses of air into the resonator where the sound is modified and coupled to the surrounding air. It is the vibrating reed and the resonator together which combine to create the complete sound of the pipe.
The majority of organ reed voices utilize striking reeds, but there have been occasional uses of free reeds, such as those used in parlor pump organs of earlier times. Free reeds are now out of favor, though their occasional reappearance would not surprise me.
The matter of tuning is an old problem for reed pipes. Early examples of reed construction were slowly refined to give more stable tuning, but reeds are still problematic. In some large and important organs many of the reeds are tuned every week, while the flues may remain untouched for years.
The most dramatic reed is the Horizontal Trumpet. Its visual and sonic character is both theatrical and bold. Its appearance in organs in the past 40 years is surprising, since its intent and usage in Spanish organs, where it originated, was for performing battle and ceremonial music. Because the sound of reeds (unlike flues) is directional, the horizontal placement allows the full spectrum of harmonics to carry out the end of the resonator to all corners of the church.
One of the basic functions of the reeds in an organ is to provide a full, brilliant, and climactic sound for the instrument. This is difficult to achieve using only principals, flutes, and strings, where beauty of tone would have to be sacrificed for sheer power. A few well-chosen reeds can provide such power with ease, leaving the flues to speak at a reasonable and uncompromised tonal level. The full-length trumpet family with conical open resonators is the best source of these climactic and powerful sounds.
One of the interesting topics of organ design history is the character of reeds in differing nationalities and periods. The differences and changes are dramatic and show us that it is a challenge to include enough reeds of differing color and origin to cover the wide range of organ literature the organist must present. In the past 30 years, organ designers have brought back many important reed stops which had been forgotten or ignored. There are now more types of reed voices available than any one organ or any one builder can ever use. They will continue to develop as the most dramatic, colorful, difficult, sometimes out-of-tune, and indispensable voices in the organ.
This concludes a six-part review of the pipe organ families of tone. The reader will find more complete data and information about tonal matters in the various books about the pipe organ which have been published as full-scale descriptions of the instrument.