Is More Resonance Always a Good Thing?

As I sit here watching yet another winter storm unleash its snowy furry, I decided to peruse some online brass pedagogy forums. After reading countless posts about how to increase resonance in one’s sound, it occurred to me that many of the people posting comments on the forum unfortunately do not have an accurate understanding of what acoustic or mechanical resonance actually is. This reminded me of many times when I have heard people misuse the term over the years.

Resonance is an extremely important concept for those of us who play acoustic instruments or sing. It affects instrument design, performance practice, and the pedagogy of sound production. Musical attitudes in Western countries about resonance have shifted very dramatically over the past three hundred years. We are now almost universally taught that it is an essential part of tone production, and that more of it is always better than less of it. I would like to take this opportunity to argue that this may not always be the case.

To begin, we need a working definition of resonance. Resonance is a way in which a physical system accumulates energy impulses over time at a very specific frequency. Each part of that definition is critical to understanding both the benefits and drawbacks of acoustic resonance. Resonance is not a tone quality. Many of us think we can hear resonance in someone’s sound, but that is not really how things work. I’ve heard people describe it as achieving the maximum result using minimum effort. They are describing efficiency, which is a very important and related concept. However, this is also not an accurate description of resonance.

I actually first encountered the concept of resonance as a physics student when studying simple harmonic motion. To illustrate mechanical resonance, we were told to imagine a child sitting at rest on a swing. By periodically giving the child a very small push, one can get them moving back and forth. If the pushes are well timed to the natural oscillation rate of the swing, it only takes a small amount of effort to get the child swinging a great deal. However, if the pushes are not well timed it takes a great deal more effort to get the child moving because the pushes will cancel each other another out to either a greater or lesser extent.

The swing example is a great way to think about many different types of resonant systems. It absorbs energy easily if it is delivered to it at the correct frequency. While a small input of energy eventually results in a large output, it takes a period of time to get the swing going. If a system were perfectly resonant, it could absorb an infinite amount of energy no matter how weak those well timed impulses were. However, real physical systems lose some energy due to heat and friction.

The degree of resonance of a particular system is commonly measured by something called its “Q factor.” The Q factor measures the ratio between the amplitude of the resonator’s oscillations and the amplitude of the excitation impulse. This yields something physicists commonly call an “impedance curve.” Impedance measures how much a mechanical system resists motion when subjected to a force. An impedance curve plots how a resonator responds to many different impulse frequencies.

A resonator with a high Q factor has a very narrow yet deep valley on its impedance curve near its resonant frequency. This means that it very willingly absorbs energy at this frequency, but it resists energy at other frequencies. The higher the Q factor, the deeper the valley tends to be. However, resonators with extremely high Q factors also have very narrow valleys. In other words, the range of frequencies the resonator will willingly absorb is quite small.

So what does all of this mean for musicians? From about three hundred years ago until the present, instrument manufacturers have been striving to design instruments with higher and higher Q factors near their resonant frequencies. If musicians learn to play correctly on these instruments, they can achieve a great deal of sound without much effort. However, there are two main sacrifices which are made in the process: response and flexibility.

Highly resonant instruments respond less well. That is, it takes longer to get the sound going. Articulation is sacrificed more and more in exchange for that ever elusive “big sound.” This is not a matter of one’s playing deficiency, but rather is fundamental to how resonance actually works. In addition, highly resonant instruments require a very precise placement of that excitation impulse frequency. In other words, pitch must be placed very precisely to get a highly resonant instrument to speak. This by definition makes them less flexible in terms of moving from one pitch to the next.

For any given fingering/position on a wind instrument there are an infinite number of resonant frequencies. Higher frequency resonances tend to have lower Q factors than lower ones. In trying to increase the Q factor through the range of a wind instrument, that instrument becomes capable of producing a much bigger sound with a small amount of effort. It plays very “open.” Unfortunately, it also takes more time to get that big sound going and is more picky with placing the pitch. A highly resonant instrument makes it significantly easier for its player to miss a note or squeak and significantly more difficult to facilitate rapid articulations.

For strings and piano, resonant frequencies of a vibrating string also occur at harmonics of a common fundamental frequency. For bowed strings, exciting the correct pitch depends a great deal on bow pressure, bow placement, and bow speed. A highly resonant instrument can produce a very large sound, but is also much more fickle with producing that sound. Any imprecision with the bow can result in some degree of a “screech.” In addition, such an instrument causes the string to take longer to fully sound, making articulation more difficult to control and facilitate.

For the piano, increased resonance gives a more muffled articulation and requires a very precise hammer placement and speed. A highly resonant piano requires a heavier action in order for the hammers to reach the necessary velocities to properly excite the more tightly wound string. This makes the instrument more cumbersome and sluggish to play. However, such a piano is capable of a huge sound which can easily project over a large orchestra and fill the largest of concert halls.

Singers cannot adjust the vocal tract with which they are born. However, by learning to precisely control vowels and formants they can dramatically increase their Q factors. Unfortunately, the same laws of nature apply to the voice as with instruments. The greater the resonance, the less flexible and articulate the voice can possibly be. Only certain vowels work at the loudest of dynamics. It takes longer to get that large sound, so consonance must be modified such that it does not excessively interrupt the sound production. The vocal tract is almost perfectly adapted for human speech, where it produces its largest range of articulations and vowels. The more signing becomes a resonance maximization game, the less flexible the voice tends to be in terms of articulation and flexibility.

So finally, is more resonance always a good thing? It obviously depends on intended musical goals. Over the last three hundred years, performing musicians in Western countries have strived to increase the resonance of their instruments and voices to more easily fill larger concert halls. Larger halls meant larger audiences, more ticket sales, and more financial sustainability. This trend was ultimately brought about by the logistical demands of live music.

However, in the 20th century the new concert hall became the recording studio. Today, recorded music dominates the musical landscape. There are many reasons for this, some of which are controversial. Live performances often strive to imitate the best recordings, not the other way around. In a world dominated by recorded music, how important is maximizing acoustic resonance? Would we be better off striving for clarity of articulation and ease of tonal and dynamic flexibility? Even in live performances, amplification has become the expected norm for many genres of music. It is simply not possible for almost any un-amplified acoustic instrument to fill a venue such as Yankee Stadium.

There is no doubt about it, career ending playing/singing injuries have exploded in the 20th century and were rarely written about in the past. These more resonant instruments were not designed to make playing at lower dynamic levels easier. They were designed to make playing at even louder dynamic levels possible, increasing dynamic expectations. Today’s forte was yesterday’s fortissimo. It created an arms race that resulted in a lot of forcing and eventually injuries, even with these newer instruments.

I’m not necessary saying that resonance is a bad thing. I’m just calling into question how much of it is actually necessary anymore, and whether or not all the sacrifices to have just a little bit more of it actually worth it. I think some instrument manufacturers have begun moving in the opposite direction to an extent. I wonder if perhaps some happy balance between the two aesthetics could be reached.

Is it really unrealistic for musicians to use slightly different equipment for different aesthetic goals? I find myself switching mouthpieces more often these days to achieve different results more easily. Do all grand pianos need to be manufactured to be able to project over a modern orchestral fortissimo? Do all singers need to always be able to fill a modern opera hall?

Achieving a high degree of resonance is a wonderful goal for all singers and performers of acoustic instruments. I just want to call into question whether or not it is always the more important goal. Perhaps sometimes less resonance is better.

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