Aluminum has a natural whiteness compared to other metals like steel. Regardless of the color, its still aluminum foil based on Fatmat's description.
I don't doubt the effectiveness of it tightening up the bass, but it's not something i would risk increased harshness for it. That is, assuming that it is true that the foil layer has this effect.
Perhaps covering up the foil with felt might absorb the higher frequencies?
Edited by mkygod - 6/10/14 at 11:23pm