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What the scaling of Gothic and Baroque organs from Bologna and St. Maximin can teach us

September 30, 2016
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Michael McNeil was awarded twenty-seven patents over a period of forty years as a research and development engineer, and in a parallel career he designed and constructed four mechanical action pipe organs. He has written five books and two technical papers, three of which are e-publications.a

We are all familiar with organs that have an overbearing harshness. There is now a backlash under way towards an organ sound better suited to the typically dry acoustics of American churches and concert halls. The organ reform movement of the twentieth century was itself a reaction to the sounds of great builders such as Ernest M. Skinner, who knew very well how to deal with dry acoustics, but Skinner’s sound was not at all convincing when playing the compositions of Baroque masters. The twentieth century reform movement looked to the home of those Baroque masters, especially that of J. S. Bach, for guidance.

While the pipe scaling and voicing of many organs in northern Germany works extremely well in the interpretation of Bach’s music, it is not suited to the smaller, dry acoustics of American churches. An examination of two famous and successful organs will suggest ways in which we might deal with this, while maintaining a sound that does justice to the older masters.

The monumental work Gli Organi della Basilica di San Petronio in Bologna by Oscar Mischiati and Luigi Ferdinando Tagliavini (2013) contains data detailed enough to allow an analysis of the scaling and voicing of the remarkable Gothic organ constructed by Lorenzo da Prato in 1475. This book provides evidence of the originality of much of what we see and hear in the present organ. The publication in 1991 of the book by Yves Cabourdin and Pierre Cheron, L’Orgue de Jean-Esprit et Joseph Isnard dans la Basilique de la Madeleine à Saint-Maximin, gives us the most complete documentation of any organ ever attempted and the opportunity to analyze a famous French Classical design constructed in 1774 by Jean-Esprit and Joseph Isnard. These organs are very different in their design, but are so successful that they have survived centuries virtually unmolested. They can teach us something of value.

The principals are the main voice of an organ. The smoothness or stridency of a principal chorus is mostly the result of two factors: 1) the size of the acoustic, i.e., the distance of the organ from your ears, and 2) the scaling and voicing of the organ’s pipes. 

 

The acoustic 

Large rooms make a sound less strident and less powerful. There are two things going on here. First, sound power falls off with distance, so much so that if you listen to an organ from twice the distance, the organ will sound four times less powerful. But for higher frequencies, the sounds we perceive as “harsh” or “strident,” the sound falls off much faster with distance. This is because air has mass (you feel the force of this mass on your face in the wind, and it powers the sails of your boat), and only the lower frequencies (the alto down to the deep bass) travel easily through this mass of air. The higher frequencies (the soprano up through those high mixture pitches) are absorbed by air and travel much shorter distances. This type of loss starts to noticeably affect pipes at 12 pitch and it gets vastly more pronounced as the pitch rises. To show just how vast these losses are at very high pitches, a 116 pipe loses 98% of its original power when heard 500 feet away; this is the “high C” of the 2 stop on your 61-note keyboard. It is virtually inaudible at this distance, even if it screams at the console.

 

Pipe scaling

So this is all very interesting, but what’s the point? The point is that many northern German organbuilders relied on large distances to refine their choruses. They used what is termed a constant pipe scale, which simply means that all of the pipes at a single pitch have the same “scale,” or width, regardless if they are used in the foundations, the octaves, or the mixtures. For example, in such a scale the 2 pipe in the Principal at middle C will have the same width and power as the pipes at this pitch in the Octave, Superoctave, and mixtures. A pleasing sound will contain harmonics that fall off in power relative to the fundamental, but a constant scale has no fall off in power for higher-pitched stops like the mixtures. So how does a constant scale work? It works by the absorption of the high frequencies in the air over great distances. Transplant this constant scale into a small, dry acoustic, and you have a recipe for overbearing harshness. 

Some of my colleagues would now point out that we can reduce the power of mixtures by reducing their toes (which admits less wind) or reducing the flues at the mouth (which admits less wind). I would counter that there is limited leeway in the reduction of toes and flues, and a steep price is paid for such measures—the speech of the pipe is slowed—and a chorus that is well-knit and cohesive will have pipes that speak at the same speed. A good chorus can have pipes that are all relatively slow or all relatively fast, but a mix of the two will not produce a cohesive chorus, and our ears are extremely sensitive to this. 

So if we don’t want to use large reductions in toes and flues, how can we obtain a well-balanced chorus? The wisdom of da Prato in 1475 and the Isnards in 1774 shows us two alternate paths. While those builders didn’t have the technical tools we use today to analyze acoustics and organ pipes, they were obviously superb experimental engineers who used their ears to great advantage in the practice of their art.

 

The alternate paths

The comparison of organ sounds requires a specific set of data and its analysis requires a model. In 2012 the author published a detailed description of such a model in The Sound of Pipe Organs. The model is based on the physics of sound, its perception by humans, scaling and voicing parameters, and the effects of distance and atmospheric losses. A fully worked example of the model was applied in this book to the Isnard organ. In this article we will look at just the scaling of pipes and the balances of power.

Take a look at the figures. These are scaling charts used by many organbuilders. They are based on the “normal scale” devised by Töpfer in the nineteeth century. Töpfer assigned an arbitrary width to each pipe in the normal scale, and all other things being equal, pipes made to this scale produce a relatively constant power from the deep bass to the treble. The normal scale is represented by the line that runs from left to right at a value of zero (0) in the middle of the graphs. Pipes wider than the normal scale have more power, and narrower pipes have less power. 

At the bottom of the graphs we see the pitch of the pipes increasing, from 16 bass pipes to 18treble pipes. Look at the left-hand columns in the graphs; the pipes widen in units of “half tones” of scale, with very wide scales at the top and very narrow scales at the bottom. The different colored lines represent the relative widths of the pipes in the different stops in the chorus; these stops are identified in the tables at the right of each graph. 

For example, look at the middle C pipe at 2 length in Isnard’s 8 Montre in Figure 1. The pink arrow points to it in the pink line, and at 2 pitch it is -2 half tones in width. The yellow arrow in Figure 1 points to the Isnard 4 Prestant, which has a 2 pipe at tenor C, scaled three half tones narrow. 

Many trends leap off these graphs. The da Prato principal chorus in Figure 2 is very tightly clustered around a constant scale at about -7 half tones, rising to about -5 half tones at the high a of the compass. The two flutes of the da Prato organ in Figure 2 are remarkably wide-scaled relative to the principal chorus. The only member of the principal chorus in Figure 2 that is widely scaled is the 8Principale, and it has wider pipes to adjust for its highly unusual position in the back of the organ—this organ has two façades, one in the front with the 24(16) Principale, and another in the back with the 12 (8) Principale (the compass of this organ extends to low F). The pipes of the 8 Principale need to be wider and louder to compensate for their unusual placement—they speak not towards the front, but face backwards at the rear of the organ. In stark contrast, the Isnard chorus in Figure 1 is very spread out, with wide foundations and increasingly narrow upperwork.

Now having shown you the more traditional pipe diameters of the principal choruses of the da Prato and Isnard organs, I have to confess that there is a more accurate way to compare power. Pipe diameters, or widths, are the most common descriptions of organ pipes, but the power of a pipe is much better related to the width of its mouth, not the width of its resonator. Those wishing to understand this in more depth can find detailed explanations in the author’s book The Sound of Pipe Organs. The power relationships of the da Prato and Isnard choruses are much better described by the mouth widths of their pipes, seen in Figures 3 and 4. 

In Figures 3 and 4 we see something similar and very striking. The pipes noted in group 1 in both figures start to widen at 12pitch and increase dramatically by nine to eleven half tones at 18 pitch. Both builders were compensating for distance losses due to the atmosphere. A pipe at 18 pitch will drop to about 28% of its power when heard from 500 feet away. As the author has shown, such losses can be completely compensated for at this distance by widening the pipes at 18 pitch by twelve half tones; both da Prato and Isnard were scaling their pipes to be heard correctly in the large acoustical spaces in which they built these organs.

In Figures 3 and 4 we also see something very dissimilar and very striking. The pipes in the principal chorus by da Prato in Figure 3 in group 2 follow a constant scale where the upperwork is scaled roughly the same as the foundations, while Isnard in Figure 4 in group 2 chose to drastically reduce the scale of the stops in the principal chorus as they ascended in pitch; the mixtures are eight half tones narrower than the 16 foundations.

The exciting but not overbearing sonority of the Isnard chorus is clearly explained in the graph at the left by the reductions in the scales of the higher-pitched stops. But the well-balanced chorus by da Prato is explained very differently. Italian organs used a device rarely seen outside of Italy: the rack board that holds the pipes in place on the Italian wind chest is placed above the mouths of the pipes, and the pipes that are placed far to the back on the windchest are greatly muted by the effect of this rack board. The da Prato upperwork is placed towards the back, and the sound of those pipes must find its way under a rack board and around the feet of hundreds of pipes before they can project into the room. This is the secret of the Italian organ, its constant scales, and its refined chorus.

With the examples of the da Prato and the Isnard organs we see a purposeful effort to reduce the power of the high-pitched pipes relative to their foundations. This is the evidence for the assertion that a constant scale will sound overbearing in most American churches and concert halls. While the Italians used a rack board above the pipe mouths to mitigate their stridency, and Isnard used narrower scaling of upperwork, there are German traditions where neither compensation is made, and these traditions depend on vast acoustical spaces to succeed. The use of constant scales in smaller, dry American acoustics does much to feed the current backlash in organbuilding.

There are fine examples of classical organbuilding in the United States that are well scaled to their rooms. One such example is the universally liked Fisk organ at Old West Church in Boston, a building neither vast in scale nor highly reverberant. Its scaling is reportedly based on the design of J. A. Silbermann at Marmoutier, France, whose pipe scales look remarkably like those of the Isnard at St. Maximin. Designing for American acoustics is always a difficult challenge, but we can also learn from good examples. ν

 

References

Cabourdin, Yves, and Pierre Cheron. L’Orgue de Jean-Esprit et Joseph Isnard dans la Basilique de la Madeleine à Saint-Maximin. Nice: ARCAM, 1991, 208 pp, ISBN 2-906700-12-6.

McNeil, Michael. A Comparative Analysis of the Scaling and Voicing of Gothic and Baroque Organs from Bologna and St. Maximin. CC&A, Mead, 2016, 8pp. ISBN 978-0-9720386-3-8, e-book on Lulu.com. The current article is a shortened version of this publication. The e-book includes a voicing analysis and tables of measurement data.

———. The Sound of an Italian Organ. CC&A, Mead, 2014, 78 pp. ISBN 978-0-9720386-6-9, e-book on Lulu.com.

———. The Sound of Pipe Organs, CC&A, Mead, 2012, 191 pp. ISBN 978-0-9720386-5-2.

Mischiati, Oscar, and Luigi Ferdinando Tagliavini. Gli Organi della Basilica di San Petronio in Bologna. Bologna: Pàtron Editore, 2013, 577 pp.

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