VB 1-x from Cascade Audio is the paint on or spray on thick acoustic paint that helps seal off the bad sounding stuff bleeding thru your drivers or cabinet. I like this product because it drys hard and is not a soft damping energy storing energy robbing soft material. Please keep in mind a speaker cabinet is a passive radiator. Even a sub box crossed over at 50hz has harmonics generated and passed thru the cabinet enclosure..it also is a passive radiator.
As for the horn speakers. If there are holes in the stand then there is discontinuity in the material and the stand. The sides with the holes are disconnected from the other sides. If your thought is to ground these rails to the floor which is the best for sound quality then you need to have a controlled surface material that transmits vibration in a linear fashion and time. The Brass screws completes the connection within the vertical rails. There is so much more that can be done in this manner...to drivers, enclosures, components of crossovers as well as the entire crossover mounting method it's all a continuum. Most manufacturers don't go to the level that an informed hobbyist will. Actually many of these vendors see no value or lack any understanding of some of these methods mentioned here.
As for the horn speakers. If there are holes in the stand then there is discontinuity in the material and the stand. The sides with the holes are disconnected from the other sides. If your thought is to ground these rails to the floor which is the best for sound quality then you need to have a controlled surface material that transmits vibration in a linear fashion and time. The Brass screws completes the connection within the vertical rails. There is so much more that can be done in this manner...to drivers, enclosures, components of crossovers as well as the entire crossover mounting method it's all a continuum. Most manufacturers don't go to the level that an informed hobbyist will. Actually many of these vendors see no value or lack any understanding of some of these methods mentioned here.