Craig Brougher writes in MMDigest 990320:

> I am wondering, regarding this topic, if anyone has checked something
> else regarding resonances that just seem so obvious to me.

Well, as a pipe organ builder who runs their own pipe shop, I would like
to make a feeble attempt to speak to this if I may.

> First of all, you cannot change a round pipe into a square one or
> vice-versa, nor a wooden pipe into a metal one.  You can build a
> diapason in either type, same scale and voiced similarly, perform a
> spectrum analysis.

There are occasions and reasons why one would prefer to use metal over
wood.  Typically, "stringy" and Diapason/Principal tones, which is the
backbone of pipe organ-type sounds, are done with metal pipes.

Again, we have choices in metallurgy, ranging from dead-soft
(although hammered) lead, up to nearly pure tin content, and many
variations in-between.

There is a formulation by which one can create a similarly-scaled pipe
out of wood as a metal counterpart, which reads:

  Square-root of area of wood pipe, divided by 2, multiplied by 2,
  is equal to the diameter of a metal pipe.

> My criteria is different, and, I think, more noticeable than small
> harmonic differences between similar scales.  First of all, the speed
> at which a pipe speaks plus its first intonation -- between the two
> different materials -- is what is so different, to my ear.

If the pipes are properly made, and the same kind of wind chest is used
for comparison purposes, it shouldn't matter.  Wooden pipes can be made
to speak every bit as fast as metal pipes, irrespective of whether they
are stoppered or open.

> But the promptness and initial "honk" of a pipe is very distinctive,
> to me.  Every pipe changes tone during the initial thrust of air.
> The manner in which it straightens out in the pipe is, to my ear,
> the single most distinctive difference of that rank.

This phenomenon is called "chiff" or "enunciation" in the speech of
the pipes.  Again. if both wood and metal pipes are properly built and
voiced, there should be no real difference.  Either type of pipe can be
built to "bark" or "chiff" at the onset of speech, or not, depending
upon the degree of nicking or feathering that takes place between the
lower lip and languid.

> The second thing is the "breathiness" (or in some cases, stringiness)
> of a wood pipe, versus a metal one.

Usually, this is the sign that the windway and the languid is too
large.  (The windway is the distance between the lower lip or cap,
in the case of a wooden pipe.  Not to be confused with a stopper!)
Minimize this and much of the breathiness goes away.  Again, this is
true for both metal and wood pipes.

> There is absolutely no way a builder of pipes can create the sound
> of the sharp languid and upper leaf of a metal pipe in wood, nor
> would he want to.

Actually, there is, and we do it.  Sometimes, we take older wooden
pipes with very high cut-ups (the height of the upper lip above the
languid) and apply metal plates to them to lower them without sawing
them apart.  As you can imagine, the "chiff" of these pipes is quite
pronounced.

> I would think that when air strikes a thick, soft leaf material,
> it's going to be split with more distance from the two streams than
> were it a metal leaf. So its oscillation would have a bit wider
> "bandwidth." In pipes that don't oscillate like that, the impedance
> of the thicker leaf in wood would be greater,

It doesn't work quite that way.  It is more a matter of the type of
material out of which the pipe is made, since it's the vibration of the
air column one is hearing, and not the sound of the wind splitting on
the upper lip.

> The angle of the bevel also creates a change in diameter at the
> same point, whereas in a metal pipe, it usually doesn't.

All the angle of the bevel of the languid does is to direct the
wind sheet coming up through the flue (space between the lower lip or
cap and languid) either further in or out of the pipe.  With wooden
pipes, some have flat languids while the cap is angled, and in the
so-called "German" style of construction, the languid is angled, while
the cap is flat.

> The third thing I have noticed is the interplay between wood pipes,
> I think because of the flat wooden sides which are close to each
> other.  Metal pipes don't seem to intervibrate when they play, but
> wooden pipes definitely do.  You can even feel their next-door
> neighbors vibrating in response, but you can't feel a metal round
> pipe next to the playing pipe doing that.

I disagree.  It depends upon the intensity of tone of the pipes, not
the kind of material they are made out of, because the walls of metal
pipes definitely _do_ vibrate!

> And the fourth thing is the way I listen to a wooden pipe cut off.
> It does it with a "whu" or a "whoof" very quick sort-of tone.  It's
> never perfectly clean and crisp.  I am sure that all these things
> can be seen on an analyzer, but are probably discounted or tuned out.

This would be more a function of the kind of valve mechanism the pipes
are planted on, because (at least on my instruments), the wooden pipes
certainly stop as "smartly" as metal ones do.  Now, in the case of reed
pipes, where the tone is made by an impinging piece of brass against a
shallot, then there would be a slight delay in the cessation of tone,
until the brass reed tongue stops vibrating.

> So I think what I am noticing about wooden pipes are their peripheral
> sounds which do not equate directly to harmonic content, but which
> describe the pipe better than anything else.  It's the same way we
> recognize voices over the telephone.  Two voices may sound the same,
> but the S's and the Z's, the P's and T's and K 's are different,
> to me.  So all it usually takes is a sentence, and I've got them.

While I understand what you are trying to say, and it's true that the
use of the types of materials for pipe construction definitely plays a
part in the end-result, it _is_ very possible for a skilled voicer to
make a metal stop sound like a wooden one, and vise-versa.  That makes
the material choice somewhat less important than would otherwise be the
case.

> I wonder if pipes could not be understood and categorized that way,
> too?  Someone who understands the characteristics of speech might
> be interested in taking a stab at it from a completely different
> perspective (?).

Well, I did, and I hope this clarified, rather than muddied the waters!

Faithfully,

Richard Schneider, Schneider Pipe Organs, Inc.
Kenney, IL   61749-0137
(217) 944-2454 VOX   (217) 944-2527 FAX