Isn’t “bore perurbations” an oxymoron? I mean, if a person is a bore, they very rarely act perturbed. Just kidding. 
I was actually wondering what exactly a perturbed bore is. Reyburn and Burke whistles have them, and they seem to be effective in octave balancing, but I was wondering what they actually are.
Thanks.
John Mac
Hi John,
I intend to include this question on my FAQ when we get our website updated in the next month, but for now, here goes:
The idea of a perturbed bore is not a new one. I certainly didn’t invent the idea. Arthur Benade deals with the concept in his monograph on Musical instruments, and all the old masters used perturbed bores for the best of the classical recorder designs, all the wonderful old wooden flutes made in the 19th century before the Boehm System flute was developed had them, as well as the Irish Uilleann Pipes and other instruments too like the Japanese traditional end blown flute.
It is a big word for placing contractions and expansions in a bore at strategic places to affect the tuning of the bore for frequencies other than the fundamental of the bore. This can help the bore to be in tune for certain troublesome notes, and also can make it easier to overblow certain notes that are usually harsh, rendering them sweet instead. It is based on the fact that there are pressure differences along a bore when it is oscillating, and these pressure differences change for each note. By choosing just the right spot and placing just the right amount of correction there, you can make a note that is not in tune flatter or sharper. There are interactions, however, so it can get hairy at times. Anyway, the perturbations may seem new fangled and mysterious, but they are actually only the recognition of the genius of the masters of the past and a rediscovery of a small part of that art. I have studied precise bore measurments on a lot of old Recorders and flutes and learned much, and also was helped greatly by my good friend, Pipe Maker, Craig Fischer, whose genius is unmatched in this art today in my opinion.We are pygmies standing on the shoulders of giants as we make our instruments, and I am grateful to learn from them.
All the best
Mike
Mike,
Thanks for the great information! Very enlightening.
So do you actually “squeeze” the bore to make it slightly narrower in some places, and expand the bore in other places to make the diameter slightly wider? If so, yikes! Very impressive. And to think some people view whistles as simple tubes of plastic or metal with six holes drilled in them. Makes me appreciate the true whistle smiths like you.
John Mac
Mike: I know your composite whistles contain perturbed bores…I can visualize what they must look like, inside. Are any metal whistles perturbed?
Best.
Byll
That’s a good perturbing question.
On 2002-10-10 12:00, Michael Burke wrote:
(…) when we get our website updated in the next month (…)
maybe start with just updating it , like to get some training before the big summer,er, autumn, er yearly cleanup? :roll:
Just kidding. Now, seriously, could you post a sketch explaining roughly the idea ? Like one could think that conical bores, or exponential flares (clarinet like) are perturbed as well 
so what’s the difference seen in profile ?
On 2002-10-10 11:37, goesto11 wrote:
I was actually wondering what exactly a perturbed bore is.
Perturbed is PhD for ‘not the same’ 
from Latin perturbare, to throw into confusion. “per” = thoroughly/completely and “turbare” = to agitate, move, mix.
It’s akin to words like turbine or turbulent. Unperturbed = not to be shaken or confused.
Perturbations in a whistle: The airstream is “thrown into confusion” inside the bore by little bumps sticking into the bore.
And a perturbed person is one whose sanity has been thrown into confusion. Hey! What are you looking at me for?!?
Hi,
Byll, all my whistles contain at least two perturbations- usually a constriction and an expansion. My low whistles often contain as many as 5 or 6 perturbations. It does vary with the material in terms of how much correction is needed, though.
Bloomfield’s word analysis is useful in seeing that the normal functioning of the bore is “disbturbed” in a sense at special places by causing shifts in the tuning of the overtones of the note, and this results in lengthening or shortening the octave. In a sense, all bores have interruptions in them, specially above the bell note, where a tonehole latice of toneholes that have thickness and diameters that make them have impedences to the flow of the air into and out of bore a complex function. It is well known among flute makers and whistle makers that the position of a tonehole and it’s thickness will determine to some extent the length of the octave. Even whether you undercut the top or the bottom of the tonehole matters on thick toneholes, by the way.
So called conical bore flutes are not purely conical, because about 20% of the length is usually a cylinder. Conical whistles work a
bit differently, but the conical section tends to shorten the octave to an extent that is determined by the taper rate. My early experiments with conical whistles indicated that a short cylindrical section at the top was beneficial, however. It is my opinion that a purely conical or purely cylindrical flute or whistle will not be in tune for two full octaves because of the nature of the effects that each type of bore produces on the octaves. Therefore, the best models of each type of whistle has some method for correcting the normal process that flattens the notes in the upper hand as you go higher in pitch, or the whistle will not be in tune with itself.
Theobold Boehm, the brilliant goldsmith that developed the modern concert flute discovered that you can constrict the upper part of the flute into a special type of conical bore insted of the bottom, and make the flute play in tune. The conical upper bore is a parabolic curve when seen in profile. I have plotted and
curve matched it to an equation and confirmed this from Boehm’s book on the subject. The real brilliance of the system, Boehm developed was the system of keys that allowed the toneholes to be placed in the most ideal positions and make them as big as possible. It
also allowed the flute to be ventilated below the active toneholes in places that made the notes easy to play in the upper octaves, and to make the notes all strong and very pure.
I know that many traditional musicians look down on the modern silver concert flute, but it is a wonderful thing, and when played by awesome musicians like Joanie Madden or Noel Rice from Chicago, it can sound very very traditional to my ears.
Unfortunately, we whistle makers have our hands tied in having to work with 6 relatively small toneholes, or perhaps 7 for those who like whistles with the thumbhole to get a perfect C natural, no keys or register holes
and realtively low ticket prices compared to a
multithousand dollar silver concert flute, but that is what makes it a great challenge to me.
Quickly, to answer the question,the bell of horns and clarinets, etc, do affect octave tuning, and are perturbations in a technical sense. Many recorders have a bell below the bottom tonehole that is very functional in this respect. I have reamed the bottom of whistle bores to flatten the bell octave a few cents at times, also.
As to diagrams, I probably won’t publish all I know about my perturbed bores for a while. It has taken me several years to learn about them and they are unique to my designs, and a part of my living, even though anyone that is interested can discover their secrets by studying Uncle Arthur (Benade) and others.
Hope this answers some of the questions about “perts”
All the best
Mike
Michael: Thanks for taking the time to post both messages! They were very informative and interesting reading.
-Brett
Thanks, Mike. My education from you, continues…
Best.
Byll
Bull. All of you. A “perturbed bore” is what you get when you shout obscenities into the end of your whistle after a particularly bad set. You’ll be damn lucky if it doesn’t jump out and punch you in the nose!
… get it right, people!! …
Sheesh!
J.R.R. Serpent
Some components of whistles like the tuning couplers and their strategic placement has the effect of perturbation.
It amazing how these variations change the reflection in the air column and they’re different in the high octave from the low octave.
So much great stuff to read … drooll
I think it’s time whistle makers wrote and published (on the net!) tech journals or whatever you call it on their designs. Something like, uh, whatever you call it.
So we can all read these technical stuff for fun 
(drool)
Now I’m confused. One quick way to correct a cylindrical bore to make the octaves better in tune is to put a slight constriction in the end of the tube, a sort of zero-order approximation of a conical bore. So how can a FLARE in the end (I believe Fred Rose does this) accomplish the same thing? Would this just work for conical bores?
Hi Charlie,
You are not confused. You are right about a small constriction having the effect of slightly shortening the octave for the bell note and one or two of the bottom notes. Conversely, flaring the bottom a tiny bit can shorten the octave. The bell octave note is often too sharp, not too flat, so you have to go the other way. What is true is, that anything you might do has different effects on different notes. There is nothing at all magical about a conical bore. It’s main benefit is that it makes the toneholes on the lower hand closer together, which means you can make a flute that is easily played without keys. Also, since the impedence is higher in the area of a smaller bore diameter, the toneholes are also naturally smaller for a particular position on the bore. That makes covering them easier too. Cylindrical bores are a bit longer and require some compensation or the upper hand octave notes will go progressively flatter. Designs that have thick walls can be made to play pretty well in tune, but otherwise you have to do something else to compensate. Perts do that.
Mike
thanks for all the information, Mr. Burke: knowing a bit about them helps us love our instruments more.
This reminds me of 2-cycle engines. They sometimes use an expansion chamber exhaust system to increase engine performance. These expansion chambers typically have an increasing conical bore, then a cylinder, then a decreasing cone. They are tuned to a particular frequency whereas us whistlers are concerned with a range of freq’s. - Joel
On 2002-10-11 09:07, Michael Sullivan wrote:
thanks for all the information, Mr. Burke: knowing a bit about them helps us love our instruments more.
And it also boggles the mind (my mind, at least) to learn that something with such a simple sounding name ( penny whistle, tin whistle) can be such a complex instrument!!
~Larry
And here I thought this thread was about me…
Evidently, uillean pipe regulators are extremely perturbed bores, with possible suicidal tendencies.
Fascinating, insights, Michael. There is some awareness of not strictly conical bores among pipemakers, but I wonder which of them have taken as systematic and scientific an approach as you evidently have. Has there been any interest among them in sharing your knowledge where it wouldn’t raise directly commercial/competitive issues?