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Resonance

Resonance. Everything vibrates. Ex: drop a pencil, blow in a soda bottle, pluck a guitar string– all these things will vibrate. Objects tend to vibrate at a particular frequency or set of frequencies.

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Resonance

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  1. Resonance

  2. Everything vibrates. Ex: drop a pencil, blow in a soda bottle, pluck a guitar string– all these things will vibrate. • Objects tend to vibrate at a particular frequency or set of frequencies. • The frequency at which an object tends to vibrate when hit/struck/dropped/plucked/etc. is known as the natural frequencyof the object.

  3. The quality or timbre of the sound produced by a vibrating object is dependent on the natural frequencies of the sound waves produced by the object. • Some objects tend to vibrate at a single frequency and are said to produce a pure tone. • Ex: flutes.

  4. Other objects vibrate and produce more complex waves with a set of frequencies that have a whole number mathematical relationship between them. (Go back to octave p. ____) • These are said to produce rich tones.

  5. Other objects will vibrate at a set of multiple frequencies that have no simple mathematical relationship between them. • These objects are not musical at all. • The sounds they produce could be described as noise.

  6. We know that v = fλ • So f = v/λ • An alteration in speed or wavelength will result in a change in natural frequency. • A musician’s job is to control these variables.

  7. Example: Guitar • Six strings, all with different linear density, different tension and different length. • The speeds at which the waves travel through the guitar are dependent on tension and linear density. • Changing these change the natural frequency of the strings • Vibration can be shortened by pushing on one of the frets on the neck of the guitar. • Changing the length of the string like that affects wavelength, which affects nat. freq.

  8. Controlling the speed and wavelength like this allows the guitarist to control the natural frequency of the vibrating strings and create the intended musical sounds. • It’s the same with every string instrument. • Wind instruments rely on changes in the vibrating air column, since you can’t alter the speed.

  9. If you stretch a guitar string out and pluck it, the sound is weak. • When you attach it to a guitar, the guitar acts as a sound box and generates a louder noise. The entire system vibrates. • When interconnected objects are forced to vibrate it’s known as forced vibration. • The surface area of a sound box like a guitar is greater than that of the string…leads to greater amplitude and, thus, loudness.

  10. Resonance when one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion. • The result is always a large vibration. • http://www.youtube.com/watch?feature=player_embedded&v=tnS0SYF4pYE

  11. http://www.youtube.com/watch?v=cT30XOfd1yI • A high-pitched pure tone is sounded out as the plate vibrates. • The salt upon the plate begins vibrating and forms a pattern upon the plate. • All objects have a set of natural frequencies at which they vibrate; and each frequency is associated with a standing wave pattern. • The pattern formed by the salt on the plate is the standing wave pattern associated with one of the natural frequencies of the Chladniplate. • As the plate vibrates, the salt begins to vibrate and tumble about the plate until it reaches points that are not vibrating. • The salt finally comes to rest along the nodal positions.

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