So when playing an acoustic guitar, how much do worn guitar strings affect your tone? A lot. Don’t believe me? Go to a pawn shop, pick up a guitar that looks like it has been sitting there a while, and give it a strum. What you’ll notice is that the guitar sounds muddy, quiet and just plain doesn’t sound good. Now, go to a music shop that has a lot of inventory and find a guitar that has just been taken out of the box. Tune the strings for the first time and give that guitar a strum. It is going to sound a lot brighter, have more clarity and generally sound sweeter. So why is it that the old set sounds so much worse? Well it is due to a number of reasons really.
The first reason is that over time strings get dirty. The way they are constructed, with a wound wire surrounding a core, allows dirt and grime to get trapped in between the winds on the wire. This dirt dampens the string vibration, if only slightly, but it creates an audible difference in tone. So where does the dirt come from? Well, the dirt is present on your hands, on your guitar case and if you count dust, even in the air. There are some ways you can cut down on the amount of dirt that gets trapped in your strings. Specifically, you can wash your hands before you play. You can also use a quality string cleaner. Another way to avoid dirt in your strings is to stick with a set of coated strings, which you can find more information about here on this site.
The second reason is that strings corrode, which is a fancy way of saying that they rust. From a technical standpoint, rust is the oxidation of iron, which is found in steel as well as other materials that are used to make your guitar strings. One of the biggest accelerators of the rusting process on a guitar string is water. That’s right, I said water! Now, I know that you don’t bring your guitar into the bathtub with you or use it in the pool during the summer. However, there is moisture in the air all around you which is more commonly referred to as humidity. Even when your guitar just sits there and you aren’t playing it, it is exposed to this moisture, which slowly helps rust form on the surface of the strings. Like dirt, rust will dampen string vibrations enough to change the sound. Additionally, although not related specifically to tone, it makes the strings rough and uncomfortable to play.
The final reason is that the metal in the strings fatigues due to the repeated stress of tuning and playing over time. Fatigue results in the string stretching, or in severe cases even breaking over time. Over time this will thin the string, if only slightly, resulting in the string requiring a higher tension to achieve the same note. Higher tension in turn continues to introduce fatigue, and so the process perpetuates itself. Fatigued strings are going to end up having weaker volume and a less appealing sound.
So that’s it. That is some of the science in basic terms behind why guitar strings sound worse over time.