My bandmate discovered this product when he was at Sweetwater in Indiana. It is a board with acoustical foam underneath that you set your speaker cabinet on. He A/B'd a bass amp with and without the Gramma and said the difference in sound was rather remarkable. He said it removes the "boominess" one confronts with hollow stages and certain halls without taking away from the overall lows. Anybody here use or have tried this product? Is it worth the $50?