Hey guys, I was messing around with my guitar (classical guitar) and my amp lately. I put the treble on lowest, bass highest, reverb highest, mid highest and mid frequency lowest. When I pluck a string when my guitar is close to the amp, the amplified sound from my amp causes that string to resonate because the frequency of the amp is the same as the natural frequency of that particular string (Correct me if I'm wrong) until the maximum volume of the amp (restricted by the settings) has been reached. There are just a few curious things I noticed: 1. Only certain frequencies tend to be susceptible to this resonance feedback loop. Has that got to do with the natural frequency of the amplifier itself? When I've tried this in the past different frequencies tended to be more susceptible. Why are certain frequencies more susceptible to this feedback loop? 2. (E string tuned to D) When I plucked the D string it started to resonate but then when I plucked the E string, which was also resonating but less susceptible to the resonance feedback loop, the amplitude of the D string started to oscillate and the resultant frequency emitted started to oscillate as well. I'm guessing the amplitude of the D string is oscillating because the maximum volume has already been reached, so the amp needs to compensate by reducing the amplitude of the D frequency and then it needs to compensate for the amplitude for the E string etc. But why is the resultant frequency oscillating (from low (~D frequency) to higher frequency)? I'm guessing some kind of interference is going on, but if someone could enlighten me on this that would be great. I'm only a senior high-school student, so maybe my questions just have to do with simple physics I haven't met yet. Thanks to everyone courteous enough to reply. I'm sure there are many things I haven't explained/worded properly so please don't hesitate to ask me to clarify on this and that.