Ok guys, I discovered this cool method to fine tune your acoustic guitar accurately in the absence of tuners and such. Your guitar may not be in the standard E tuning, but it surely will be tuned once you are done.
Ok, first a little something about beats. No, I'm not talking about drum beats... these are the beats that you'll find in any XII standard physics text book. By definition, it is the alternate waxing and waning of intensity of sound when two waves of nearly equal amplitudes and frequencies traveling in opposite directions in a medium interfere. The frequency of beats (i.e. no. of beats per second) is equal to the difference in the frequencies of the interfering waves. Make any sense? Wait, it will soon....
Now, to employ this method to tune you guitar, you must have a good ear, and you should be very sensitive to the vibrations made by your guitar.
First, tune your guitar by any conventional method using your ear, with help of a keyboard, or a software like guitar pro 4(which I use). Though you would get a fairly good tuning, it is near impossible to get the exact perfect tuning. This is where beats come in.
You must be knowing that the frequency of an open string matches with the frequency of the string above it when a certain fret is pressed.
The fifth fret of the 2nd string has the same frequency as that of the open 1st string.
The fourth fret of the 3rd string has the same frequency as that of the open 2nd string.
The fifth fret of the 4th string has the same frequency as that of the open 3rd string.
The fifth fret of the 5th string has the same frequency as that of the open 4th string.
The fifth fret of the 6th string has the same frequency as that of the open 5th string.
Press the fifth fret of your 6th string and strike the 6th and the 5th strings together. If there is a slight difference in their frequencies, you should be able to make out the alternate waxing and waning of sound, i.e. the intensity of sound would reach a peak, then it would go down to a minimum alternately. Itís a bit difficult to explain, it is something like as if someone was changing the volume of your guitar continuously between a maximum and a minimum. These are called beats. If you do get beats, it means that your guitar is imperfectly tuned, but only slightly.
Detecting beats could be troublesome. You should be in an absolutely quite room. Also hold your guitar close to yourself, so that you can feel the alternating vibrations.
Now comes the difficult part. How do we know whether the 5th string is at a lower frequency than the correct one or at a higher frequency? It can be done by two methods. The first is trial and error. First, tighten your 5th string a little. If the number of beats per second increases, it means you should loosen it. If the number of beats decreases, it means you should tighten it further till you hear no more beats. Remember to tighten/loosen your string only slightly.
The second method is that if you have an excellent ear, you would be able to make out the difference yourself, and then tightening or loosening the string as required. Saves a lot of trouble.
Now repeat this procedure with the rest of the strings, and you have a perfectly tuned guitar!
However, it is a bit difficult to detect beats in the thin strings (the 1st and 2nd strings). It is relatively much easier in the fat strings.
This method takes some practice. However, it is quite a good method to achieve perfect tuning for you acoustic.