What really makes your guitar or bass sound they way YOU like it?

You would probably agree that there are countless things that effect tone. At the very core of any guitar or bass is the string set. Without strings, there would be no sound. The string set is where it all begins.

WARNING: This section of Professor String covers the science of guitar string tone and frequency. Many of you out there may find science to be a boring topic full of brain twister jargon and mathematics. In some respects, this is true. Consider this:

It's boring when compared to playing a killer tune on your ax and having the audience eat up every bit of it.

It's boring when compared to playing some cool riffs on a rare vintage guitar.

It's boring when compared to sitting in a jam session with a well known artist.

It's boring when compared to.......well, you get the idea. So, why bother check'n out this section??? If you skip this information, then YOU will be missing out on something most other musicians do not know about.

Natural Frequency

At the heart of every sound is a vibration. Whether it is a speaker, a drum, or a string, the vibration of these objects are the origins of sound. Sometimes the contents of an object will vibrate to make sound. An example would be blowing into a jug to make sound. The air within the jug will oscillate in a vibratory manner giving off a sound. Within each vibration is a frequency, or rate of speed that the vibration occurs. Each object has it's own speed at which it will vibrate when it is struck or strummed. This is known as and objects Natural Frequency. Not all vibrations can be heard. In order to become audible by the human ear, the vibration needs to be great enough to create oscillations of pressure. We know the oscillations of pressure to be commonly called "sound waves." Sound waves are produced by vibrations with higher amplitudes.

The Origin of Tone

Most everything has a natural frequency associated with it, including a musical instrument string. However, not everything has a "good" sounding natural frequency. There are many frequency complexities that makes something sound clear versus something that sounds like noise. Dropping a piece of scrap metal on the floor produces a complex noise sound. Blowing through a piccolo also produces a pure tone sound. The two are completely different in their quality of sound. This quality is often referred to as the timbre of sound. Much of the sound timbre has to do with the object having a single frequency in it's sound. Things that produce a cleaner frequency without odd frequency components being introduced, are said to have a pure tone, and can be musical. Objects that have a set of frequencies that produce a whole number mathematical relationship can produce a thick and very rich sound like the low B string on a 5-string bass. Yet, other things can vibrate, with and odd number of multiple frequencies, and sound like noise. These multiple frequencies are often mathematically unrelated and do not establish a whole number mathematical relationship. Again, the resulting vibration sounds like noise in this scenario.

Pretty much everything that has a repetitive, cyclical motion, will produce a frequency. If you were to flap your arms up and down, there would be a frequency associated with your motion. When you wave your hand back and forth to wave hello, there is a frequency associated with your motion. A fan blade spinning has a frequency associated with it. A vibrating guitar string has a frequency associated with it. In each one of these cases, there is a frequency that can, or cannot be heard. The basic relationship is this:

frequency = speed/wavelength

Anytime the speed of motion or size of the wave pattern changes, there will be a change in frequency. In this case, it is natural frequency we are talking about. There are many variables that can effect the natural frequency of a guitar string. As a guitarist, you are able to change the natural frequency of string anytime you press down on a fret. This shortens the vibrating portion of a string. The shorter portion produces a smaller sized wavelength that vibrates at a higher speed. If you look back at our frequency equation, this means the higher speed divided by a smaller wavelength yields a higher frequency. So, each time you progress up the frets on the fretboard, the frequency goes up. There are other variables that effect the frequency of the string, as stated earlier. On a guitar we have strings that have different tensions and mass densities. The heavier strings vibrate more slowly due to the increased mass and less tension. Higher tensions create shorter, and faster cycles of movement. Thin strings have less mass, and tend to have less inertia in their movement. This allows them to produce a faster vibration speed with a quicker decay. You will notice that a high E string fingered on the 20th fret decays much quicker than a low E string played open. In short, tension has a profound effect on the wavelength and speed of vibration. The density of the string's material will also have an effect on it's ability to carry a wave at a particular speed. Strings that are dirty and have corrosion are also effecting the natural frequency of the string. The dirt and corrosion are adding mass to a string. The added mass (dirt) makes the string vibrate slower and can act as a dampener in it's ability to carry a wave. Again, this effects speed and wavelength. Thus effecting the frequency components of a string.

Getting Volume from Natural Frequency

The natural frequency of a guitar string can be more difficult to hear without an adjoining structure to resonate with it. As a string is plucked, kinetic energy, in the form of vibration, is transferred to the string. Yet, the string itself does not have the surface area to make the vibrations highly audible. It needs to rely on other particles to vibrate and generate sound waves. In essence, a transfer and dissipation of the kinetic energy needs to occur to other objects like an acoustic guitar's soundbox. The guitar's soundbox will accept the kinetic energy from the string and start the air particle inside to vibrate. The transferred vibration will be in the same frequency of the string's natural frequency. This transferring of vibration is known as forced vibration. There will also be a pressure build up within the soundbox as the moving air particles are needing to release energy and sound waves. The pressure, in the form of sound waves, will come through the soundbox's sound hole(s). Acoustic guitars with solid tops (versus laminated) have an advantage of transferring more forced vibrational energy due to the uniformity of a solid piece of wood versus layered laminated tops. Solid body guitars do not rely upon forced vibration energy to transfer sound in the same manner as an acoustic guitar. The string's vibrational energy and natural frequency are captured with a magnetic transducer or pressure transducer.

String Resonance

In some situations you may notice a string starting to vibrate by itself when other soundwaves, of similar frequency, are present in the room. The string will start to vibrate without being plucked or strummed. The only thing connecting the string with the other soundwaves is purely air. When the particles that make up air begin to vibrate at the same at the same natural frequency as the string, they set the string into motion at it's natural frequency. This phenomenon is know as resonance. Resonance is one of the building blocks that makes up audio feedback in a system. In a setup with an acoustic guitar and a PA system, the speaker vibrates at the same natural frequency of a string on the guitar and forces it into vibrational motion. The overall effect of this system resonance creates feedback between the acoustic guitar and the PA system.

String Harmonics

When a string plays at its natural frequency, there is an associated reflected wave pattern that occurs within the string itself. A reflection occurs at the end of the string and travels back towards it's origin. As it travels back towards its origin, it will interfere with incident waves from the source in such a manner that specific points along the medium appear to be standing still. The reflected wave is continuously repeated and is often called a standing wave. Standing waves can be heard at various vibrational nodes on a guitar string. These standing wave patterns are only created along various points of the string and occur at certain frequencies. These frequencies are known as harmonic frequencies. Most guitarist refer to the harmonic frequencies as harmonics. The harmonic frequency generated by a string has a distinctive tone that sounds distinctive and "bell like" in its tone.