I has thinking that there might be sources of sound that can be regenerative and more efficient than others. I also thought that even a small amounts of energy can be increased by using circuits like voltage doubler over and over until you reach a goal voltage..
I have considered using crystals as a primary source for energy generation. Consider a turning fork. It is not large, nor loud, yet it can shatter glass. I am sure with the primary tone and it's harmonics, some acustic engineering and channeling it's point of critical mass or it's most...