Tension is the amount of force that must be put onto the string to bring it up to pitch. Generally speaking:
- The tension rating on a string is based on a scale length decided upon by the manufacturer. If the same string is put on two guitars. One with 650mm scale length and the other with 660 scale length, and it is considered medium tension on the 650 scale (as measured by the string maker), then it will require more tension to bring it to the same pitch when put on the 660 scale. It will become more like high tension when put on a longer scale length. So, be sure to consider the scale length of your guitar when considering tension (650 mm is usually the standard that most string makers use to decide tension ratings, D’Addario uses 648 mm).
- The higher the tension the thicker the string.
- The thicker the string the more mellow the sound.
- The harder the material the brighter the sound (carbon trebles would be brighter than regular nylon for example).
- The lighter the tension the easier to fret, but the more propensity toward buzzing (it really depends on the set up of the guitar).
- More tension does not mean louder. Higher tension strings may vibrate with more intensity, which may play a small part in increasing loudness. But the guitar itself, specifically the sustain of the guitar, will have much more to do with loudness. A case can even be made that an extra-hard tension string could put so much stress on the top of the guitar that the top becomes restricted which actually decreases loudness.
- Before using extra-hard tension strings, always check with the manufacturer of your guitar to be sure the guitar can handle them. Many luthiers do not recommend extra-hard tension strings for their instruments.