Yes, you need non-flexible type spikes. Rigid, with no rubber or anything like that. Speakers must not be allowed to rock at all, even the smallest invisible rocking will cause sonic problems.
Best reasonable$ upgrade from spikes?
I just read an article that suggested staying away from spike shoes that incorporate rubber into their design saying it messes with the dynamics. I have had target audio spike shoes (which are of this design) under my speakers for about 6 months to protect the wood floor. So I take them away and now the bass characteristics have changed dramatically. I was shocked. Who knew? Lost the Boom but now the dynamic balance is...er, different.. Suddenly the room has stopped resonating with overpowering bass frequencies (very specific notes) but it also seems like the contrast has washed over a bit. Like everything has taken a step back. I need a bit more volume and the balance is better but I need more definition. Have been recently been upgrading my IC's and AC mains so I have lost a bit of perspective. I know these are not the problem though. Don't want to spend as much as the aurios but want to change from the supplied spikes. (speakers are Linn Ninkas) Thanks for your input.