I have returned to re-read this thread after so much time has elapsed. The comments have been right on point. Thank you. It is the return system which has caused the problem. I have a dedicated 2.5 ton hvac system with hydroair heat directly below the green marble shelf. The returns which draw air across the amps produce 50db at 25hz.
The initial attempt to baffle them in the return boxes, each of which has it's own 12" round duct to the blower unit reduced the volume but did not eliminate it.
I have been advised to have the ducts interrupted by making a horizontal turn, then a downward turn, then a horizontal turn, then an upward turn and tie on back to the system. Each leg to be treated similarly and each duct lined with hospital grade accoustical liner and wrapped with fiberglass insulation.
Your thoughts please?
Bill E
The initial attempt to baffle them in the return boxes, each of which has it's own 12" round duct to the blower unit reduced the volume but did not eliminate it.
I have been advised to have the ducts interrupted by making a horizontal turn, then a downward turn, then a horizontal turn, then an upward turn and tie on back to the system. Each leg to be treated similarly and each duct lined with hospital grade accoustical liner and wrapped with fiberglass insulation.
Your thoughts please?
Bill E