As much as I dream of owning a better instrument some day, I know from experience that the wide realm of possibilities that define a cellist’s expressiveness is more the result of mastering of the principles of technique rather than the pedigree of their equipment. This has been made evident to me on the many occasions upon which my teacher has borrowed my humble student cello in order to demonstrate a new technique or to inspect my setup, and the quality of her tone retains the same “personality” and “sweetness” despite the instrument’s limitations. While a higher quality and more resonant instrument (or bow) can be a great benefit in molding your talent and understanding of the cello, there are also some basic principles of physics that when applied to the cello playing (or purchasing) can aid in your personal search for that elusive rich & dulcet timbre.
Likely by now you have heard of such things as overtones, or upper partials when describing a certain quality of sound of string, bow, or instrument, and harmonics when describing the left hand technique of producing more ephemeral pure tones. What you may not have been aware of is that all of these terms are all synonyms describing the same types of vibrations on a string. Hidden within the broad waving motion of each note are shorter and faster vibrations at specific fractional wavelengths (eg 1/2, 1/3, 1/4, 1/5, etc). It can seem somewhat bizarre that a string can be vibrating simultaneously at so many frequencies at the same time (much like Schrodingers mysteriously bi-modal Cat). Yet we know from experience that this is the case, because we can actively select each of these frequencies when we play harmonics or “false” harmonics by isolating the individual overtones (and their octaves) by damping all the other vibrations with our finger tips:
The quality of a cello’s timbre is often described by a “color” as being warm, deep, mellow, clear, sweet, bright, rich, dull, round, metallic, rumbling or even harsh. All of these terms are actually describing the strength and distribution of the overtones. Warm, deep, mellow, pure or often what is generally referred to as “core” sound is actually describing weakness of overtones and stronger fundamental vibrations (eg all of the A’s ringing on the A string, 220hz, 440hz, 880hz, etc). Rich, bright, metallic, rumbling, clear, or harsh is describing an increase in the strength of the overtones (eg all of the E’s, C’s, and G’s etc, which are also ringing on the open A string) compared to the strength of the fundamental vibrations. Perhaps you’ve already noticed that occasionally when you play the open A string with a slightly harsh sounding technique, your tuner might register an E instead of an A. This is because brighter sounds have stronger overtones, and the E is normally the strongest non-A overtone of the open A string! As you will see later, it is no mere coincidence that the E and A sound so pleasing when played in harmony.
When a cello has a more core sound, it is easier to discern the intonation for that singular note. However, when a cello is rich in overtones, it is easier to discern the relationship and intonation for the distance between notes. Having more core sound vs rich overtones is something that you can alter by equipment selection and setup and also by bowing technique and fingering choice for enharmonics. For example, playing with your bow closer to the bridge will produce stronger overtones, where as playing closer to the fingerboard will produce a more core or mellow sound. In the case of enharmonics (ie equivalent pitches played on different strings) playing the same note closer to the bridge will reduce the strength of the overtones and produce a warmer sound, as I am sure you have noticed by now, playing the Open A string produces a much brighter (overtone rich) sound than playing the same note on the D string. You can combine these techniques & setups to create various combinations of brightness and warmness. Other factors that effect the richness of the overtones are the quality of the bow, the gauge and tension of the strings, the suppleness of the bow hand/arm/shoulder, the shape of the bridge, the thickness/density/age of the wood, dryness/humidity, the quality and application of the varnish, and even the tension on the bow hair. Generally speaking, the louder you play, and the more resonant your set up, the greater the component of overtones will be. Some mutes will selectively dampen high or low frequencies, and depending on the note being played this will make the cello produce a dim rumble or a hollow squawk.
Though we do not hear them consciously as individual notes, overtones are what define our concept of harmony and dissonance. This is because the part of the temporal lobe (auditory cortex) that is connected to our inner ear is designed to detect patterns and predict their significance. For example. the simplest harmonic ratios between note frequencies are 2:3 (major 3rd), 3:4 (perfect 4th), or 4:5 (perfect 5th). Because of the simplicity of their ratios, these notes share some of their strongest overtones, which means our brain has less work to do to detect the patterns involved, and this results in the general positive and uplifting association with these Major and Perfect intervals and this is what we perceive as “harmony”. Not surprisingly, much of the earliest written music is based on the structure of these primal harmonies. Other intervals have frequency ratios that share only weaker overtones (or upper partials) which means more work for the brain to decode that patterns, such as 5:6 (minor 3rd) 8:9 (major 2nd) or 8:15 (major 7th). This extra load on our auditory cortex is more troubling to our psyche and leaves us with a feeling of discontent or unresolved tension (evidenced by the Riot of the Rite of Spring in 1913) and this what we call “dissonance”. For better or worse, our brains are remarkably adaptable when it comes to learning new patterns and our sense of harmony is somewhat malleable & plastic both individually and as a society, which is why we enjoy music now (like Jazz and Heavy Metal) that likely would have wilted Mozart’s ears.
The same is true when detecting and manipulating harmonic resonances on the cello. Simple intervals create stronger sympathetic vibrations which is useful when trying to get better intonation by paying attention the resonance (ie “ringing”). This is because the most resonant overtones are also the simplest ratios of frequencies. As a general rule, the lower numbered overtones are stronger than the higher numbered ones even on setups with strong overtones. The strength of these basic overtones is why you can actually see your strings vibrating sympathetically when you play certain notes on the cello. For weaker resonances, you will simply hear an increase in volume and texture of the sound and perhaps even feel your other strings vibrating by touching them with your finger tips. Below is a map of the first 7 overtones on the cello (not counting the fundamental resonant frequency of the cello body itself which is usually F3 or F#3). A complete map goes off the page to an infinite number of overtones, but these ones should be the most useful for checking intonation… remember, that even though the overtones are several octaves higher than the other open strings, every note is a strong overtone of the octave below it (eg G3 and G4 are strong overtones of the Open G2 string as well as the open C2 string).
What is truly amazing about this information is not only that it is useful for creating beautiful music, but that these mathematical relationships actually define what music is!! This is why music is so fundamental to the human experience, and might even be universal to any life form with a sense of sound. Or, as math-musician Vihart puts it: all sound is essentially music…