Stephen Fox



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Some Thoughts on Clarinet Body Material

Stephen Fox

Aside from religion and politics, few topics generate as much unnecessary disagreement between entrenched, extreme positions as the question of whether, how and to what extent the material of which a woodwind instrument is made affects its playing properties.  Some aspects of this large and complex subject will be discussed here, from the points of view of the instrument maker and of the musician.

In one corner, we have the simplistically “rational” view, that the body material of a woodwind “cannot possibly” have any effect on how it plays, i.e., that the body of the instrument is a totally passive container for the air inside it, and the behaviour of the instrument is 100% controlled by the dimensions of the bore and of the tone holes.  Regrettably, we can actually still read this in some textbooks on musical acoustics.

And in the other corner, we have the intellectually fuzzy “artistic” view, that the character or “soul” of an instrument lies to a large extent, if not entirely, in the material of which it is made.

Of course the reality is somewhere in between.  What we should be saying is that as a first order approximation, the body is a passive container; the various influences of the body material are higher order effects.

Physics - which could be defined as the science of constructing mathematical simulations of reality - works by first simplifying a situation down to its essentials (what we call a first order approximation), assessing how valid and useful that approximation is, then looking later at the complexity that has been previously put aside (the higher order effects), by building more sophisticated mathematical models.

Regrettably, physicists are not always very good at explaining this principle to the general public.  In their zeal to get across the essential points, they sometimes give the impression that they honestly believe that their first order approximations are reality, and anything else is a figment of people’s imaginations; or, that non-physicists are just not allowed to talk about higher order effects!

Musical acoustics is a messy and inconvenient branch of physics, in that higher order effects, which stretch or exceed our abilities to model them mathematically in a comprehensible way, are large enough that we cannot ignore them.  It is also unique among the various branches of physics in that non-scientists (i.e., musicians) very often have access to more observational data (e.g., the “feel” of how an instrument plays) than the scientists studying the subject.

All of this goes to explain why scientists and scientifically-oriented people can be guilty of oversimplifying this question, even though they should know better.

Musicians, on the other hand, are easily misled into overvaluing the influence of body material.  First there is the natural but incorrect analogy between wind instruments and string instruments.  In the latter, the vibration of the top and back is what actually generates the sound waves, so the body is actively involved in the process.  In a wind instrument, the sound generation mechanism is separate from the body tube, so the body is far more passive.

There are also some remarkably ironic coincidences that seem to connect sound with materials:  a clarinet sounds “woody” while a soprano saxophone sounds “brassy” (or, on a more subtle level, a tárogató sounds “woody” while a soprano saxophone sounds “brassy”), a Baroque flute sounds “woody” while a modern metal flute sounds “silvery”, etc.; but these differences stem from gross dimensions, not from the materials.

Then there is the comparison of beautiful sounding professional instruments with poorly built and poorly played student grade instruments which happen to be made of different materials; and the illogical but involuntary connection between visually beautiful materials and a beautiful sound.

Can we blame musicians too much for jumping to hasty conclusions about these things?  Yes, they should know better too; being a good musician requires analysis and logical thinking. 

Part of the reason for the gulf of understanding between the two sides is simply perspective.  If we ask a physicist “What makes a clarinet sound the way it does?”, he or she will tend to assume that we are asking “What makes a clarinet sound generically like a clarinet?”, rather than like, say, a saxophone; the answer is the shape and proportions of the bore and the number and proportions of the tone holes, and nothing whatsoever to do with the body material.  However, if we ask the same question to a clarinettist or a clarinet maker, it would often be interpreted in the much more specific sense of what makes one make or model of clarinet play differently from another; since the gross dimensions will be similar, the differences must lie in more subtle factors, which may legitimately include body material to some extent.

A final general point is that while most people automatically want to talk about the effects of body material on the sound of an instrument, what is actually far more important is the feel and response of an instrument to the player.  The player is many times more sensitive to differences in feel and response than a listener is to differences in sound; feel and response, not sound, are the primary bases on which a player judges an instrument.  So, blind tests of instruments made from different materials - which are often cited as “proof”, usually that the material has no effect! - will at least partly miss the point.

An illustration of this is to compare conventional cane clarinet reeds with synthetic reeds.  If a cane reed and a plastic reed are each well made and well chosen for a particular player and mouthpiece, a listener will almost certainly not be able to tell which is which (walking past the Légère Reeds booth at a trade show will demonstrate that!).  To the player, though, they feel completely different.  So, a blind test - blind to the audience, that is, it’s not possible to make it blind to the player - is valuable in demonstrating that a synthetic reed sounds like a cane reed, but it by no means proves that the material of the reed has “no effect” on how it plays!  Of course the effects of body material are much more subtle than the effects of reed material, but the point is that differences in feel and response are greater than differences in sound.

As an example of the potential effects of different body materials, a couple of years ago the author built two clarinets, side by side, to the same design, as similar dimensionally and as similarly adjusted as handmade instruments can be, one made from African blackwood, and the other from Delrin (a synthetic polymer which is denser and slightly softer than blackwood).  The expectation in advance was that the differences between them would be minor; it was quite a shock to discover how radically different they are in character, to the player and even to the listener.  The one made from blackwood feels and sounds brighter, with more incisive response; the one in Delrin feels and sounds stronger, darker and heavier, with less immediate response.  Of course, one of each is not a large enough statistical sample to prove the point authoritatively, but it is enough to get one thinking, and to put to rest the simplistic “body material can’t possibly have any effect” assumption.

So, what are the ways in which body material might affect how a woodwind instrument plays?

First of all, it is necessary to eliminate medium scale dimensional issues arising from the ways in which various materials react to the tools and processes used in manufacturing.  These are not strictly speaking inherent characteristics of the material, but they occur naturally during series production (though they can be minimised when an instrument is built or extensively modified by hand).  One example is the degree of sharpness or roundness of edges in the airstream – at the ends of the joints, at the inner and outer edges of tone holes, and with objects such as speaker tubes and thumb tubes that protrude into the bore.  This sharpness or smoothness affects the amount of turbulence in the airflow through the bore, which has a strong influence on the ease of response, strength, stability and clarity of individual notes and of the instrument in general.  Another example is rippling or random irregularities in the bore diameter or bore shape - of the order of a tenth of a millimetre or so, over lengths of a few centimetres - resulting from the moulding of plastic bodies; this seems to contribute to harshness or edginess in the sound.  This is often associated with plastic instruments, though it’s unfair to blame the plastic; it’s not the plastic itself that’s causing it, but rather the way the plastic is used in manufacturing.  A wooden instrument can behave similarly if the bore is reamed sloppily.

Possibly the strongest influence of body material, at least in instruments which are normally made of wood, comes from the texture and porosity of the surface of the bore.  Texture and porosity both cause energy losses inside the bore, though in different ways:  texture through airflow, porosity through air pressure.  The effects particularly of bore texture are easily detected by the player, and sometimes also by the listener:  the rougher the surface, the higher the playing resistance and the more “mellow” the sound, until beyond a certain point the instrument becomes excessively stuffy and dull.  This can be demonstrated by, for example, making a series of clarinet barrels with bore of various textures:  the first with a smooth plastic bore, and the others lined with sandpaper ranging from #400 down to #60 grit (particle size 0.03 up to 0.30mm).  The differences are fairly obvious to the player, perhaps marginally detectable to the listener.  A more subtle effect of bore texture is that since the damping effects of a rough surface will make the resonance frequencies of the air column less sharply peaked than a smooth surface, the cooperation between slightly misaligned (nonharmonic) resonances is actually better, and hence some notes are more clear and stable, when the bore is somewhat rough; i.e., a certain degree of bore texture will lessen the differences between “good” and “bad” notes of the scale.

Closely related to bore texture and porosity is the impact of the thermal conductivity of the body material.  Since the majority of the energy that the player puts into playing an instrument eventually ends up being absorbed by the body walls as heat, it follows that differences thermal conductivity among materials could potentially affect how easily or how heavily various instruments play.  An instrument made of wood might play slightly more easily than the same instrument made of metal, for example, by an amount that would be marginally detectable by the player (though not by the listener).

Having disposed of any effects related to macroscopic or microscopic dimensions, eventually we have no choice but to face the most complex, most difficult to analyse and possibly most interesting potential influence of body material:  vibration of the body itself. 

In case there’s any doubt, the body of a wind instrument does vibrate.  The amount varies with the type of instrument, but a sensitive player can feel it, especially with a powerful, metal-bodied instrument such as the saxophone.  And, buzzing or rattling of loose metal parts is something that any repair technician has had to deal with; if the loose parts are vibrating, the rest of the body must be also.

Discussions of body vibration are sometimes dismissed by reporting (probably correctly) that the sonic energy radiated directly from the body into the room is undetectable or negligible; but that’s not really the point.  We may not be able to hear the body vibrating, but it could still affect how sounds are generated inside the instrument.

The main influence of the vibration most likely lies in the way in which various frequencies, on various notes of the scale, are selectively absorbed by the body, and possibly also by modification of the resonance frequencies of the air column by body resonances that happen to have similar but not identical frequencies.

There is a large body of belief by makers of metal bodied instruments, surrounding the effects of different types of metal on the tone and response of the instruments, based on the density and the hardness or softness of the metal.  A gold flute is universally believed to have a darker and more powerful sound than an otherwise identical one made of silver; with saxophones, red brass is said to give a darker tone, but less incisive response, than yellow brass; and so on.  Lacquering the outside surface is believed to make both the sound and the response slightly duller.  Besides the metal itself, a further major influence comes from the posts, ribs, ferrules and keywork which are distributed unevenly and asymmetrically along and around the body of the instrument.  In addition, internal stresses in the metal, arising from the various parts being soldered together, could be significant.  These views are not based on rigorous scientific investigation, but they are supported by a long history of instrument making, by people who know very well what they are talking about in other respects, so they should not be dismissed out of hand as nothing more than muddle-headed fantasy or as marketing hype (the author of one acoustics textbook, for example, speculates that flute players simply believe a gold or platinum flute must be superior, because it’s more expensive!).

With wooden instruments, potential differences among various types of wood tend to be dominated by the effects of bore texture and porosity, and players have traditionally not had the opportunity to play dimensionally matching, professional quality instruments made of materials other than the standard types of wood.  However, there are some well established beliefs; for example, a clarinet bell with a thick, heavy lower rim is thought to produce a stronger sound on the notes at the bottom of the scale than a thinner, lighter bell with the same internal dimensions; and the wall thickness of a clarinet barrel is believed to affect both power and immediacy of response.  Again, these effects await proper quantitative investigation, but they are more than fantasy.

Having said all that, there are some notions circulating among musicians, and the people who prey on them commercially, which are ludicrous enough to make anyone want to retreat into the refuge of “body material can’t possibly have any effect”.  There used to be a technician in the U.S.A. who would “improve” a piccolo by hanging it inside the bell of a bassoon and playing long tones over it, in order to, as he said, “realign the molecules” of the body.  A depressing number of flute players actually believe that good or bad tone and intonation are permanently programmed into the body of a flute by repeated playing.  And as a clarinettist, it’s embarrassing to admit that many of one’s colleagues firmly believe that the sound of a clarinet is affected by whether the plating on the keys is silver or nickel...

This article can only hope to skim the surface of this topic, but it is hoped that it has at least provided some perspective from the practical point of view, and indicated some possible directions for future investigation.