Liutaio Mottola Stringed Instrument Design

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Lutherie Myth/Science:
You Can Believe Your Ears

When evaluating musical instruments or design features of musical instruments the bottom line evaluation is what you can and cannot hear. If you can't hear something, for all practical purposes in this context it doesn't exist. But before considering a listening evaluation it is a good idea to know something about the limits of human perception of sound. There exist sounds and sonic differences so subtle that they are below the physical ability of the ear to hear them. But there are also sounds that although physically audible are rendered inaudible by qualities of the manner in which these sounds are presented and of the environment in which they are presented. And human perception of sound is highly influenced by other simultaneous sensory input and also by expectations. All of these details conspire to make the answer to the question of whether or not you can believe your ears highly dependent on just what it is you are trying to hear and the context in which you are trying to hear it. Armed with an understanding of both how we hear and ways in which our perception of what we hear can be influenced, it is possible to devise controlled listening evaluations which provide confidence that we can truly believe our ears.

Initial appearance: Thursday, April 2, 2009
Last updated: November 25, 2017

Physical Limits to Hearing

When considering a listening evaluation of, say, two different instruments, it is wise to first consider the physical limits of human hearing and to figure out from those if our evaluation makes sense to perform at all. Much research has been performed over the last century on the limits of human hearing (much of this in the context of telephony) and the limits of hearing in terms of loudness and frequency are well established. Humans can hear pure sine waves ranging in frequency from approximately 20 Hz to 20 kHz. As folks age the range tends to contract, with most of the hearing loss on the high end. Exposure to very loud sound for extended periods of time can also cause high frequency loss. So right off the bat, if your listening evaluation is intended to identify sounds outside of or even near to the extremes of this frequency range, it is not likely to be a meaningful evaluation.

There are also physical limits to human perception of sound that is very soft in volume. That there are sounds so soft that they cannot be heard should be of no surprise, and a listenng evaluation that requires the identification of very soft sounds may not be of much practical use. Of course, it is not always apparent that one may be basing ones perception of the presence (or absense) of some quantity on an ill conceived notion of the limits of human sensory perception. Consider the following experiment, which anyone near the ocean can do. Go to the ocean, hold your breath, and stick your head under water. Hear any submarines? They are out there of course, but the noise they make is below the threshold of human perception, unless they are just about close enough to run you over. This makes so much intuitve sense that it may seem like a rediculous example, but consider this one, which involves visual perception but is still instructive in considering the limits of human sensory perception. Up until a few hundred years ago, most people were pretty sure the sun revolved around the earth. It was pretty obvious - just look up into the sky and there it was, revolving around the earth. But Galeleo's telescope made it possible to see things that the naked eye could not see, and these things pretty clearly indicated that the earth actually revolved around the sun. Took a bit of time to convince all the folks who felt that, if you can't believe your own eyes, what can you believe? The takeaway lesson here though is that your own sensory input is really only as reliable as your own sensory resolution, and there could very well be important information that is only accessible through some sort of instrumentation.

A couple more things to keep in mind. Human hearing is nowhere near as sensitive at the highest and lowest frequencies in the frequency range of human hearing as it is in the middle of the range. Interestingly enough (and probably not coincidently) the "middle of the range" is the frequency band where most of the sounds of human speech are found.

The second thing is to consider the ability of people to discern differences in loudness. Human hearing is substantially logarithmic, which enables us to perceive an extremely wide range of loudness of sound. But our ability to differentiate small volume changes is really not that good. A doubling of the power of an audible signal is generally perceived as just a small but noticable increase in volume. One area of particular interest in the evaluation of musical instruments that this relates to

Psychoacoustic Limits to Hearing

References and Suggestions for Further Reading

  1. Caldersmith, G. “Why are Old Violins Superior?”
    American Lutherie #14, p. 12.

  2. Olsen, T. “An Introduction to the Stadivarian Mystique”
    American Lutherie #17, p. 6.