The Organ and its acoustics

[KB7DQH]

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The Organ and its Acoustics
by Glenn White, acoustician
The organ, as every organist knows, requires a room with proper acoustics to be a completely
satisfactory musical instrument. The instrument itself, voiced and tuned, cannot generate the exciting
sounds that a sympathetic acoustical environment provides.
What acoustical requirements enhance the sound of an organ? First, the room must be large enough to
accept the organ's sound and blend it together, then cloak it in an aura of reverberant energy, which is
more a characteristic of the room than of the organ. The reverberant sound must not be too loud
compared to the direct organ sound, which would detract from the clarity of the musical line, and it
should have a non-directional quality which seems to come from everywhere. The listener needs the
impression of being immersed in a field of sound within a diffuse reverberant blanket, but with a true
sense of directionality for the direct sounds from the instrument itself.
The quality of subjective directionality combined with diffusion is sometimes called "envelopment,"
and can be elusive and difficult to achieve. Envelopment, simply, is achieved by suppression of echoes or
discrete strong sound reflections, while providing reflecting surfaces that assure the listener hears
sounds arriving from the sides of the room rather than from the ceiling or straight ahead.
Sounds reflected from the ceiling should be diffuse, with no discrete reflections to any location in the
room. The room must have no "right tri-corners," which send strong discrete reflected sounds in
unwanted directions. The reflected and reverberant sounds must contain the correct blend of high and
low frequency energy to complement the sound produced by the organ without placing any false
emphasis in any musical register.
When Lola Wolf asked me to design this room's acoustics, I was exhilarated to work on a project that
was yet unbuilt. Then, recalling frustrating experiences with some architects, I asked what conditions
and requirements would be imposed.
"How big is the room to be?" Lola answered, "You tell me how big it should be." I asked what kind of
interior finish she had in mind. "She said, "You tell me what it should have." As we conversed, I realized
I was about to live an acoustician's dream – a commission with no restrictions or preconceived ideas.
Adding to the delight, Dale Kowalchuck, the contractor, made the most complex shapes without
question, and with no technical difficulty at all.
What determined the size and shape of this room? Starting with the size and shape of Martin Pasi's
already designed organ case, I chose the square root of three as an appropriate irrational ratio to use as
an integrating design factor. An irrational ratio is no common integral factors, root 3 being close to
1.7320508 ... Other irrational ratios have been used in art and architecture for centuries, but the house
and lot seemed, to my eye, to incorporate a ratio of about root 3. (Not wanting to appear weird at the
time, I did not confirm this with measurements.)
After selecting the ratio, it became a fairly simple matter of scaling from the dimensions of the organ
itself to arrive at the height, width, and depth of the room, balcony height and depth, etc. The fun began
when we designed the wall and ceiling shapes. The walls are convex to achieve proper diffusion, but no
so much as to prevent lateral reflections. Root 3 again came into play for the fadii of curvature, which are nearly – but not quite – equal to each other. The inward, upward tilting of the walls is imperative for
proper envelopment. The amount of tilt was a compromise, being a little less than a root 3 ratio to the
curvature radius and width at the ceiling to preserve architectural integrity.
The walls look simple and, I hope, elegant, but they are very complex in design and structure. The
surface density is six pounds per square foot to get the correct bass reverberation. The curves have many
strategically placed stiffeners inside which prevent too much wall vibration. The ceiling provides
complete diffusion to prevent echoes or reflections that would call the listener's attention to the ceiling.
There are many small design details that are not very evident but assure that no echoes or false tonal
responses creep in.
I would like to thank Lola ... for giving me the rare and exciting opportunity to design a recital hall from
scratch, and Martin Pasi for recommending me to then. I have seldom if ever worked with a more
harmonious and dedicated group of people.
In the words of a long forgotten Roman punster, NE IMPEDIATUR MUSICA.

Eric
KB7DQH

[flared_ophicleide]

An unconventional, but ideal, room design for an organ.

After thinking on the relationship between the organ and a churches' sanctuary, assuming that the design and the result of the construction of the latter are suitable, I've concluded that if this assumption is not met, then you have only part of a musical instrument (the organ itself).

I've always been big-big-big on acoustics.

[ComptonNewbie]

Interesting comparison to the Cinema organs I'm more used to seeing.  As they are completely enclosed and on much higher pressures, the whole accoustic can be far more 'driven'.  This means much of the reverberation can be achieved inside the organ chambers, with less reliance on the auditorium outside of them.  The degree of carpets, soft furnishings etc is some venues would presumably kill all possibility of a reasonable result with a more classically constructed instrument.


Simon.

[David Pinnegar]

Hi!

Simon's point is very real.

An instrument which is worth referring to as "the source" is that of St Maximin in France. It is in a building of perfect and reverberant acoustic and is very powerful even despite its design to be pumped by hand - or rather by treading on levers operating the bellows. Its power comes from the resonance of its box: behind the facade pipes, the ranks of pipes occupy hardly more than a yard but there are at least two or three yards behind of empty space backed by a stone wall with pine floor at soundboard level and pine ceiling at probably 16ft level. So the pipes speak at the front of a resonant box, a bit like the effect of introducing a speaker unit into its enclosure.

Best wishes

David P