AvFan
Super Member
I have been concerned that after nearly 40 years the Technics SH-15B3 base and its feet are not isolating my SP-25/Jelco tonearm from external vibrations as well as it did when new. @marcmorin and I were discussing TT isolation and he reminded me that sandbags are the best way of minimizing recoil at the rifle range and they should be very effective at isolating turntables. He also noted that each sandbag could dissipate vibration independently of the sand in the other bags. So I set out to build a sandbox using sandbags versus filling the entire box with sand.
I carefully measured my TT base and its feet to determine the inside dimensions of the sandbox and laid it out on my kitchen counter. Mrs. AvFan pitched in and made four sandbags that use closures from hospital ice bags (Amazon). These closures are important to keep the sandbags relatively flat. I added 3 pounds of dry play sand to each bag.
Next to build the box itself. The bottom and floating plate the TT sits on are made from 3/4" birch plywood. The sides are 1/2" alder dadoed and rabbeted around the bottom plate. I primed and painted the box
The bottom has short feet with thin felt on them to protect the surface it sits on. I added a center foot to minimize any deflection of the bottom panel.
Added the four sandbags and the top plate.
The top plate has about 1/8" clearance around the inside edge. And here are some photos of the installed sandbox.
The TT feet have about 1/16" of clearance from the sides and I can reach in and turn each foot to fine level the TT. Total weight is about 17 or 18 pounds, 12 of which is the sand. The box is 3 3/4" tall and the same width and depth as the Technics base. I need to evaluate the sandbox's performance over time but I hope it will isolate my TT from vibrations induced in the cabinet it sets on plus any vibration that could be coming up through my concrete floor (e.g. spiked speakers).
I carefully measured my TT base and its feet to determine the inside dimensions of the sandbox and laid it out on my kitchen counter. Mrs. AvFan pitched in and made four sandbags that use closures from hospital ice bags (Amazon). These closures are important to keep the sandbags relatively flat. I added 3 pounds of dry play sand to each bag.
Next to build the box itself. The bottom and floating plate the TT sits on are made from 3/4" birch plywood. The sides are 1/2" alder dadoed and rabbeted around the bottom plate. I primed and painted the box
The bottom has short feet with thin felt on them to protect the surface it sits on. I added a center foot to minimize any deflection of the bottom panel.
Added the four sandbags and the top plate.
The top plate has about 1/8" clearance around the inside edge. And here are some photos of the installed sandbox.
The TT feet have about 1/16" of clearance from the sides and I can reach in and turn each foot to fine level the TT. Total weight is about 17 or 18 pounds, 12 of which is the sand. The box is 3 3/4" tall and the same width and depth as the Technics base. I need to evaluate the sandbox's performance over time but I hope it will isolate my TT from vibrations induced in the cabinet it sets on plus any vibration that could be coming up through my concrete floor (e.g. spiked speakers).