https://casterconnection.com/caster/4-spring-loaded-tpr-rigid-caster?gclid=CjwKCAjwmeiIBhA6EiwA-uaeFeVFXJX935zEHcOsjgr6rbQCp5nLAUjnkhuZtFqU4I7XtfI3l9AipxoC3lYQAvD_BwE
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I don’t know the weight of your speakers. My monitors are 375 pounds each (before mods). Two in the back of this type of caster for me. The front use a single adjustable spring/silicone pod. You can set top to bottom alignment, forward or backward (caster) positive or negative. There is no need for top to bottom left or right (camber) positive or negative adjustment. Then set the toe.
It won’t move, it would be dampened very well and of course decoupled. Just a slight tip to move them and back on the front pod. You could put a slider under the pod.
I’m making new bases for my monitors this is exactly how I’m doing it. Pocket mount (enclose) the rear casters to 1 1/2" butcher block (70 lbs) and a single spring/silicone pod in the front. The 60 lb SS beveled cap is a work in progress. 500 + lb is not easy to move. I had to do something..
BTW there is NO bass used in that cabinet. It’s just the monitors made from HDF. They sound like telephone poles when you knock on them. All of my monitors do.. When they are finally placed, 100 lb of sand can added in the old bass section, as an option.. STILL decoupled.. and below my weight limit on the pod and caster springs. 600 lbs
Regards