Universal power law in the noise from a crumpled elastic sheet

Using high-resolution digital recordings, we study the crackling sound that is emitted from crumpled sheets of Mylar as they are strained. These sheets possess many of the qualitative features of traditional disordered systems, including frustration and discrete memory. The sound can be resolved into discrete clicks, which are emitted during rapid changes in the rough conformation of the sheet. Observed click energies range over six orders of magnitude. The measured energy autocorrelation function for the sound is consistent with a stretched exponential C(t) similar to exp(-ct(beta)), with beta approximate to 0.35. The probability distribution of click energies has a power law regime p(E) similar to E(-alpha), where alpha approximate to 1. We find the same power law for a variety of sheet sizes and materials, suggesting that this p(E) is universal.