I tried Herbie's Black Hole and though it did seem to improve the sound, it eventually lost it's adherance and came partially off, jamming my CD player after repeated use. Haven't used it since and that was many years ago.
All the best,
Nonoise
Herbie’s Super Black Holes
How did I live without them? Finally, the veil has been lifted and I can hear the full, rich sound of which I once only dreamed. If only the joy I’m feeling wasn’t being matched, if not overpowered, by my weeping about all the shallow, empty years I endured before St. Herbert set me on the true path.