It was a popular tweak back in the day, to fill up bags of sand and put them inside some speaker cabinets for additional mass and rigidity. And yes, I remember a few manufacturers having " bins " as part of the design for adding sand / lead shot ( not Bozak ). Enjoy ! MrD.
Bozak concert grand speakers
What do I do with my deceased fathers bozak concert grands that have not been moved since 1972 when they were purchased? They are in Wilmington Delaware. Last used circa 2010. Their furniture is like new.