lift one of these 80 lb bags of concrete mix at home depot,
https://www.homedepot.com/p/Quikrete-80-lb-Concrete-Mix-110180/100318511
....................................3 wheels for speakers. no wobble and more weight/wheel than 4.
80lb speaker: 26 lbs/3 wheels rather than 20 lbs/4 wheels
anti-tilt rear corner blocks (slightly shorter than the wheel height) do not touch floor when stationary, but contact floor if speaker starts to tilt during movement.
softer wheels for hard floors; harder wheels for carpet
2 front corner wheels, stable left to right
1 rear center wheel, unstable in rear when moving
2 anti-tilt corner blocks in rear
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quickie finds, just to illustrate ideas
wood finish, 14 x 14
simply relocate a rear wheel and add two rear anti-tilt corner blocks
https://www.wayfair.com/outdoor/pdp/innova-hearth-and-home-square-caddy-innv1246.html
perhaps try these, see if you actually benefit from adjusting toe-in. If not, remove them.
listen on spikes; listen on 3 wheels, any difference? I seriously doubt it.
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furniture dolly, 11.5 x 22.5
cut to size, make finished wood cover to conceal it
https://www.homedepot.com/p/Stalwart-440-lbs-Wheeled-Furniture-Dolly-M550109/302662176
cut to size, reattach wheels, add two anti-tip blocks, then have local woodworker make a cover that simply drops over it, finished wood, laminate, paint, ....
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IF, after preferred placement is found, only adjusting toe-in, never pushing them rearwards, you might think about leaving the factory spikes, put them on a properly sized base plate that can be rotated.
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btw, 4 wheels can certainly work, you get a bit less weight per wheel, might not matter, and you simply need to solve any wobble that might occur, not hard, but I have bad back and knees, so I go for 3 wheels. You want the drivers to move, not the speaker, so 3 wheels is definitely preferred.