Let's Make Music!

If you have ever listened to a live orchestra, you would know it is an amazing experience. The variety of sounds fit together in harmony to create beautiful music. But how exactly do stringed instruments form the sound and at different pitches? In this article, we explore the science of sound with a focus on stringed instruments, which include the violin, viola, cello, and bass.

Sound, as you might know, travels in waves, similar to the ones depicted below. There are various aspects to a sound wave, and I’ll explain two of them here: amplitude and frequency. The amplitude of a wave is often described as the “height” of the wave. It is measured from the centerline to the top (crest) or bottom (trough) of a wave. Changing the amplitude of a sound wave will adjust the “volume” that you hear: a greater amplitude results in a louder sound and vice versa.

The official definition of frequency is “the number of waves that pass a fixed place in a given amount of time.” If a wave is short, more waves would be able to pass through and vice versa. High-frequency waves look more tightly packed together and are perceived as high pitched while low-frequency waves look more spread out and are perceived as low pitched. Frequency is measured in hertz (Hz), which can be interpreted as vibrations or cycles per second.

If you’re into math (that’s me!), here’s an equation: frequency = speed/wavelength. This means that frequency depends on both the speed of the wave and the wavelength, which is how long a wave is. The specific distance of a wavelength is between two consecutive peaks: it could be crest to crest or trough to trough.

There are two main ways of making music on a stringed instrument. The more well-known method is using the bow and dragging it across the string or strings. For those of you who don’t play a stringed instrument, you may not know what rosin is. Rosin is a “sticky substance that comes from trees” and is used to create friction between the bow and the string. You can look up how a stringed instrument sounds without rosin on the bow versus with rosin on the bow. Without rosin, the bow simply slides across the string. With rosin, the force of the friction creates vibrations on the flexible string, creating sound. In fact, instead of one smooth motion, the bow sticks onto the string then slips then sticks then slips—this process happens many times, even in one stroke.

Surprisingly enough, even though the force is directly applied to the string, the string is not the main output of the sound. Think of the body of the instrument as a loudspeaker. The string transfers the vibrations that it has created through the bridge to the body of the instrument; due to the larger surface area, the body vibrations are larger and more easily heard. The f-holes on the body of a stringed instrument allow air in and out of the body, letting more sound travel outside the body of the instrument.

Plucking the string is another way to create sound with a stringed instrument. This method involves using your finger to pick at the string to create vibrations. The sound emission process is similar to using a bow; an obvious difference is the source of the vibrations: bow versus finger. However, this difference in source creates a slightly different sound, which is easily distinguishable.

We covered how a stringed instrument produces sound, but how does it create the different notes that we hear? To produce the different notes, stringed instrument players press their fingers onto the string, trapping it between their finger and the neck of the instrument. This essentially shortens the length of the string, which affects the wavelength. The wavelength, as discussed earlier, directly affects the frequency. A shorter string results in a higher frequency—a higher note.

The frequency also depends on how flexible or stiff the string is. A stiffer string can’t bend as much, making it harder to emit higher frequencies. The stiffness of a string can depend on the material and thickness of the string. A thicker string tends to be stiffer. There are various frequencies emitted, even when only one note is played. However, we hear a certain vibration more distinctly because it is stronger, and that vibration is the frequency we assign the note.

If you ever looked inside a grand or upright piano, you’ll notice many strings. On a grand piano, they are strung horizontally; on an upright piano, they are strung vertically. There have been disagreements on whether the piano is a stringed instrument or a percussion instrument, some claiming that it is both types. Although it has strings, the strings of a piano are struck with tiny hammers rather than plucked or strummed. Nevertheless, the process of sound emissions is the same.

As a pianist and a cellist, I was very intrigued when researching for this article. I hope you were as interested as I am and have learned something new! Keep a lookout for the next post!