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Question regarding sound waves in musical instruments

  1. Dec 11, 2007 #1
    My question is regarding musical instruments. Their are waves produced in wind instruments and in stringed instruments. If a wind instrument (lets say a tuba) is played directly next to a stringed instrument (lets say a guitar) will the sounds waves (in air) produced by the wind instrument cause the strings of the stringed instrument to vibrate at a similar frequency? In other words, could sound waves of a certain frequency cause a guitar string to vibrate and produce a note/tone/harmonic? If so, what is the connection to the tones produced? Will sound waves of a certain frequency (like that which produces a C note) cause a guitar string to vibrate and produce that same frequency and note? Will this note be loud enough to hear effectively?

    If anyone is familiar with an indian sitar, it has a set of strings played like a guitar with another set of strings underneath that vibrate and produce a range of tones based on the note that is plucked on the main strings. This is similar to what I described above, except strings are produced waves that vibrate other similar strings. I mentioned this as an example, in case it would help clarify what I was talking about.

    If anyone has any insight or answers to this question, I would really appreciate it. I have tried to find the answer all over, but am getting confused by unrelated material. I apologize if my question sounds confusing. Thanks so much to anyone who can help!
  2. jcsd
  3. Dec 11, 2007 #2


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    The short answer is yes, they will resonate. The extent to which this happens depends on the number of harmonics that the tones have in common. For example, if you tune the guitar to a major chord, you should be able to excite all the strings at once by blowing the appropriate "tonic" note on the wind instrument. As you have noted, this happens to a certain extent anyway with multiresonator instruments like the guitar.

    Distinguishing the sounds (i.e. hearing them separately) will be difficult because they should sound the same.
  4. Dec 11, 2007 #3


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    Guitar sounds eminate from the vibration of the bridge and body of the guitar. The strings are just a means to cause the bridge and body to vibrate. In the case of an adjacent wind instrument, the effect would be to cause the bridge, body, and strings to vibrate.
  5. Dec 11, 2007 #4
    The term

    is a bit misleading, as when you play a C note on a guitar you're producing the fundamental (the C) and a very rich set of overtones. Hence playing C on a tuba and on a guitar would produce different frequency contents.

    While you could cause any set of strings to resonate this way, your best bet would be to use an acoustic guitar, where the energy is stored in the cavity (the "body" of the guitar) and exchanged between the strings and cavity for quite a while. You will definitely be able to hear this but it would require a quiet environment and paying close attention.

    Even clapping your hands strongly enough will excite the strings on your guitar (give it a try). Your clap produces a "delta function" in time which is (ideally) uniformly distributed in frequency space, exciting all strings on your guitar (although chances are you'll only be able to hear the low E string).

    Physically Incorrect
  6. Dec 11, 2007 #5
    Thanks! That clears up a lot.

    Would the note or frequency of the waves effect which acoustic guitar strings would vibrate? Or will they all just vibrate randomly? In other words, would you be able to vibrate a specific string on a guitar (depending on its tuning) using a specific frequency sound wave?

    Hypothetically speaking, if their was a small set of strings incorporated on the inside of a wind instrument, would playing the wind instrument vibrate the strings and produce a different, unique sound? Or would the wind instrument overpower the small sound from the strings. Would the wind instrument then act as a cavity to better amplify the sound
    from the vibrating strings?

    Thanks again!!
  7. Mar 11, 2010 #6


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    If you have ever, depressed the sustain pedal on a piano and sang a note directly into the harp, you may have noticed many strings ringing. The fundamental frequency is ringing and many harmonics. Sound is a pressure wave through a medium (in this case air). Strings will resonate at multiple frequencies relative to vibrational modes. However your voice does not produce a pure tone (sine wave), it exhibits harmonic content. This is a component of its timbre. The tuba and other musical instruments also exhibit this characteristic. that is what gives an instrument its unique sound quality. So my voice singing a single note into the harp of a piano, excites the fundamental frequency plus a whole range of harmonics associated with the spectral content of my voice. The tuba playing a note, near a guitar, will induce vibrations in the strings in the very same manner.
    Quote: good posts, like wisdom, are never outdated
  8. Mar 11, 2010 #7


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    Though the bridge and body do vibrate, it is the strings that exhibit particular modes of resonance. The bridge and body have more to do with timbre (quality) of the notes. If the strings were tuned differently, say 50 cent flat, the timbre would remain the same, but intensity of the fundamental frequency and the overtone series, would be quite different.
    Last edited: Mar 12, 2010
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