Any help or advice very welcome, my Sennheiser HD25-1 seem to been seriously lacking in the bottom end. Iv compared them with others of the same model and its not just me. Not sure what to do? Try rejigging the cables abit to no avail. Iv had them for a few years, and dont really blast the volume at all. Is this a common problem, and what could one to do to fix it? Or is it even fixable?