Standing waves and the guitar

[scilearner]

Hello everyone ,

 

I have some questions about standing waves and guitar.

 

In a guitar why is the fundamental frequency the centre of the guitar. Why isn't it just when you play an open string.

 

How do different strings in guitar produce different sounds. Don't they have the same length hence the same frequency.

 

Even though standing waves are produced in the strings when we listen it travels in air. Does this mean the wavelength of the standing waves is different in air or is it the frequency that is different.

 

Thanks a lot!!

[DrP]

Hello everyone ,

 

I have some questions about standing waves and guitar.

 

In a guitar why is the fundamental frequency the centre of the guitar. Why isn't it just when you play an open string.

 

I think it is because the full string gives 'half' the full wave. (half a sin wave not a full one) - but I could be wrong on this one.

 

 

How do different strings in guitar produce different sounds. Don't they have the same length hence the same frequency.

 

 

 

 

This is definately due to the different thickness of each string - you get a higher pitch from the thiner strings.

[cjohnso0]

Hi scillearner,

 

I don't understand why you state that the fundamental frequency of a guitar string is at the center of the guitar? The open string (unfretted) produces the fundamental frequency when it is excited (plucked). The fundamental mode of a vibrating is such that the wavelength of the vibration is two times the length of the string. Which is why the string vibrates elliptacally, or only looks like half of a sin wave.

 

When you lightly touch the string at the 12th fret (1/2 way down the length), you are adding a node to the vibration. This added node has the effect of reducing the wavelength by half, thus doubling the frequency.

 

As DrP stated, the strings are tuned to different frequencies based on a combination of mass (material and diameter) and their tension. The frequency produced by a vibrating string is related to mass, length, and tension. You can find the actual equation all over the 'net.

 

Hopefully I'm not too far off, it's been a long time since vibrations in college, but I do get lots of guitar playing in these days.