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Name: Sreerag
Status: student
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Question:
When the same musical note is played on a guitar and violin, what makes violin and guitar sounds different?



Replies:
Stringed instruments sound different for many reasons. What you hear depends on how and of what the string is made, how the string is vibrating, how long it vibrates, and how long you can hear it vibrate.

Perhaps the most important difference is in how different strings vibrate. There is a concept in string physics called "harmonics". When a string vibrates, its wavelength and frequency of vibration strongly affect the sound it makes. However, there can be additional vibrations in the string at the same time called "harmonics" that "stack on top" of the main vibration. In other words, stringed instruments are actually making multiple different vibrations, and therefore multiple sounds, at once. The combination of these different vibrations, or harmonics, give different instruments the different sound textures that you can hear.

The harmonics that a string makes depends on a lot of factors, including how the string is made, how it is made to vibrate (picked, plucked, bowed, etc.), and if it is being touched while it is vibrating. Different harmonics last for different amounts of time -- they do not all dissipate at the same rate. You cannot hear all the harmonics equally, either; an instrument with a resonating chamber (such as a violin or an acoustic guitar) will sound different than similar instruments without a resonating chamber because they make you able to hear different harmonics for different amounts of time. Along the same lines, an electric guitar sounds different than an acoustic guitar because of how harmonics are being amplified and heard. With an electric guitar the pickups sense magnetic field changes, while in an acoustic guitar the resonating chamber works directly on sound waves. How you play the instrument affects sound too. The sound an instrument makes can be divided into four parts: the attack, decay, sustain, and release, all of which are affected by string type, playing method, amplification, and resonance. Other factors such as the overall loudness (amplitude), and the time over which the overall sound changes (envelope) also influence what you hear.

For more information, and a little more physics, this is a good resource: http://www.phys.unsw.edu.au/jw/strings.html There are plenty more similar web pages out there to give you all the detail you need.

Hope this helps,

Burr Zimmerman

p.s. My brother, who is an accomplished musician and electrical engineer, contributed to this answer -- thanks, bro!


Each musical instrument emits many frequencies when it plays a certain note, that is a certain pitch.

The number of and relative intensity of these frequencies determine the characteristic sound that allows one to distinguish one instrument from another. Incidentally, the same is true of the voice, which is a very complex musical instrument. If you do a search on a topic such as "the physics of sound".

One good resource is:

http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/sound/soundtoc.html

Another is Tom Rossing's book, Physics of Sound. There are some Scientific American articles on this subject, too. A good conceptual physics source that is easy to read and will help you is: Paul Hewitt "Conceptual Physics" Addison-Wesley

Once you find a few "hits" on "the physics of sound" or "the physics of musical instruments" or "the physics of the voice" you will explanations at any degree of sophistication you choose.

Vince Calder

Dear Sreerag,

The difference you hear in musical instruments is due to overtones that they produce. A tone from an electronic tuner or a tuning fork is almost a "pure" tone. If you could look at the wave in would on an oscilloscope it would appear smooth. Instruments create sounds with something that vibrate and something that lets the sound resonate. In the case of the violin and the guitar, the strings may be made of different materials, the instruments themselves are constructed of different types of woods. In wind instruments a reed or some type of mouthpiece is employed. The size and shape of the resonating cavity also plays a part. All of these contribute to the sound "color" or timbre of the instrument.

What happens at the sound wave level is that the wave itself is no longer smooth. It has jagged edges and looks like a mountain range. (I am referring to if you could see it on the oscilloscope.) The wood vibrates along with the strings, as well as the air in the resonating cavity, causing the wave pattern to alter. The pitch remains the same; the frequency of the wave is unchanged, but the timbre of the instrument shines through. No two instruments produce exactly the same timbre. The exception would be an electronic instrument. An A on an electric keyboard would sound the same as an A produced by the same make and model of the same keyboard.

Even our voices have a distinct tone quality. That is what enables us to figure out who is speaking in another room even if we cannot see the speaker.

I hope this enlightens you a bit. Take Physics when you can for the rest of the details. Happy Science!

Mrs. Croll


Steerag,

When a note is played on a musical instrument, a sound wave travels out into the air. Eventually the wave hits your ear. The overall frequency, or rate of vibration, tells your ear which not is played. Sound waves for a low E vibrate at the same rate for all instruments. This rate of vibration is also called "fundamental frequency" and "pitch". What is different for each instrument is the pattern of little wiggles within the wave. This pattern is known as the "quality". This pattern depends greatly on the shape of the instrument and the actual source of the sound (a string, vibrating lips, a thin piece of wood, etc.).

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


Steerag,

the note played on a musical instrument is the base frequency being resonated. (In other words, the lowest frequency) Simple tones are not usually musically appealing though, so musical instruments are designed to resonate a number of harmonic frequencies. (2x the base frequency, 3x the base frequency, 4x the....) Depending on the size and shape of the resonating chamber, the strength of each of these frequencies will change, thus giving a violin a distinctly different sound from a guitar.

Another difference is the method of creating the sound. While a Violin and a Guitar both rely on strings to create their sound, drawing a bow across a violin creates a steady note, while a guitar tends to be 'plucked', creating a much stronger note that quickly begins to fade.

Ryan Belscamper



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