surely a rank of 8' diapasons built for a small private chapel can't be voiced to 'fill' St. Peter's Basilica

If you found someone who wanted to do it, you don't want to hear the finished result.

Skilled voicers are almost worth their weight in gold. And, one can pretty well deduce the real quality of any organ by the amount of time and effort that goes into voicing the pipes in the church. A builder who builds organs that are works of art, such as Pasi and others in his league, will take weeks, if not months, to voice every rank with excruciating care given to raising each stop to its most beautiful potential, whether played by itself or ensemble. Lesser builders will do minimum, sometimes no, voicing in the church, and their organs sound like it.

As for how many ranks should be in a given church, this is not a question to which there is a pat answer. This depends largely on what a parish expects of its organ (leaving aside the all important matter of cost). Some parishes really have little or no desire for an organ that will do more than adequately accompany hymns and ordinaries. Others desire an instrument that will not only fulfill liturgical demands nicely, but play greater or lesser amounts of that organ literature of our heritage which was written specifically to grace the liturgy in one way or another. It cannot be said truthfully that an organ which is capable of realising a given amount of 'organ literature' is a 'concert' rather than a 'liturgical' organ. This thoughtless (and groundless) tid bit is often hurled into the equation as an excuse for an organ that is, in the long run, inadequate for liturgy or 'the literature'. Anyone who utters this shibboleth betrays immediately his, or her, own incompetence even to voice an opinion on the matter at hand.

A parish should decide not whether it wants a 'liturgical' or a 'concert' organ (an utterly false and facetious distinction), but to what degree of artistry it wishes its liturgy to be led, and how it wishes its liturgy to be graced with some degree of the para-liturgical repertory. There is no certain number of stops or style of voicing which is appropriate for any given church. Only what one wishes of the instrument and what treasure one can expend in acquiring it. As several have intimated above, there are ways of forcing extra loudness from pipes, but they will yield, every one of them, sounds which are not at all pleasant, but which are artless and, often, downright ugly. This is not an avenue down which one would want to proceed.

https://youtu.be/EyQX6eQJEng

https://youtu.be/EQ6fBdfmRrE

Engage a reputable consultant (names available upon request,) Choose a builder. Allow builder to invent solution in relation to space (size and acoustical properties) and proposed budget - but never begin with money. Allow vision to emerge. Make a case. Gather resources. Commission art...which is first the "ars artefacientis" - the art of the making. The artifact (ars artefacta) will be the result of a creative process, not a shopping trip. Inherited literature will be one consideration, as will "liturgical use," but neither has ever been adequate as a prescription for traditional organ art in the Church. Rather, ritual use and its inherited "remnants" (literature) issue from the contemplation and playing of instruments that are themselves the result of a search for formal coherence and the capacity for musical expressivity.

Yeah, there are a lot of variables. This is why you have historical organs with low windpressures that still fill large rooms (open toe voicing) but have very flexible wind (that voicing makes greater demands on the wind system), and orchestral organs with high pressures, some more conventional voicing techniques, and absolutely stable wind.

As everyone above says, it's a great advertisement for a consultant if the incumbent organist in a project doesn't have a pretty decent working knowledge of how variables need to be managed in a pipe organ.

Thank you for all of the advice and commentary. This is why I come to this site whenever I have a question!

I suppose that I can give a little bit more information - but bear with me as this will take a little time.

I will be looking at an 'historic' organ that is up for sale (an Aeolian-Skinner from the time of G. D. Harrison), which has a stop list which I and my institution's organ teacher are quite happy with. It will be for our new chapel which has not yet been built. From pictures online, the chapel it is currently in looks to be about the size of our OLD chapel, although perhaps a little bigger. What is interesting, though, is that the pipes are in a loft in a little mini-transept on the north side. (The organ console is in a loft in a little mini-transept on the south side.)

Thus the organ does not speak down the main axis of the church.

I am wondering (when I get there and hear it in person) if the organ seems to fill their whole chapel quite well from its less-than-advantageous placement, if it will be a good bet for our NEW chapel - which will be bigger than our old chapel, but have the organ speaking down the main axis from a choir loft in the back of the nave.

I am also wondering (the point of my initial question) about any leeway in terms of voicing the organ so that it will be a bit louder (if need be). Maybe I am worrying about nothing, as I have played organs of about the same size (42 stops) - even smaller - which have filled bigger churches than our new chapel. Still, there seems to be a lot of guess work involved.

kpoterack, this is why a consultant is a good thing. The dearly-missed former organ at UT-Austin, one of G. Donald's masterpieces, was something like 125rks in a room the size of two or three elementary school classrooms. That said, it was very gentle. There are many examples of a relatively small organ filling a big room, too.

Advocatus,

Could you give me the names of the consultants you mentioned? thank you

OK, so answer me this:

Would it be much easier to have an organ builder build an organ from scratch and get the voicing for the space right - even if with a smaller number of stops? For example, you might have an organ of 50 stops that was made for "Church A" and just can't be revoiced to fill "Church B" (which is twice the size) without problems. However, if the builder made the pipes and did the original voicing for Church B (the bigger one) from the get-go, he might be able to do it with 30 stops?

M. Jackson Osborn, quite right. On the other hand, I just played a 45-stop American Classic organ the other day with which I could achieve some of the desired effects, but from which I couldn't create a balanced ensemble to save my life. Nor could I find solo-accompaniment options that worked for any of the music I hoped to play. And the pedal was either too loud or too soft. I was thrilled to return to my to my 12-stop Brombaugh (not what one would call neo-Baroque)...whose principals are far more broad and rich than the former, and in which every combination I can think of worked in the music. There is certainly more than one way to skin the cat in any space, but getting the formula right is more art than science.