Speaker spikes-worse sound-what gives?

Yea, spiking a speaker couples it to the floor pretty effectively. Whether it's a good idea depends on what you're coupling it to, though. If you're spiking it to something solid, then it will help to stabilize the whole enclosure and can improve the sound by, in my layman's understanding, effectively adding to the inert mass of the enclosure. If, however, you couple to enclosure to a less inert surface (such as a suspended, wooden floor), you are really only expanding the resonating surfaces that can muddy or otherwise affect the sound. Spiking a speaker to a less-than-solid and inert surface is always a crap shoot. Pretty simple to diagnose, though -- if it doesn't sound right, it's probably not a great idea.

There seem to be two basic approaches when straight spiking doesn't work out. You could either seek to decouple the speaker from the uncooperative floor (air bladders, vibra pods, various flavors of isolation shelving, and countless other products or homebrews) or put something solid and massive under the speaker and couple it to that (ye old slab of granite, e.g.). Then, of course, you could always mix and match the two, such as when you hear about folks putting a slab of concrete on a bicycle innertube and then putting the speaker on that. Folks'll argue over what works best but, depending on their gear and circumstances, they're probably all right. I sincerely doubt there's any single cure-all, but I'm sure, in any case, that spikes aint it. Assuming you think it's fun to try new stuff, then anything that sounds like it's worth a go probably is. Have fun and best of luck.

Thanks everybody. I have taken off the spikes and may try some of your suggestions. Keep the ideas coming.

It is possible that the additional height that the speaker is raised off the floor by the spikes may have reduced the bass reinforcement that is normally provided by the floor. This could have reduced the bass frequencies by 3db due to the radiation into 1/2 space, instead of 3/4 space. Placing a small plate over the open space between the bottom of the speaker and the floor may restore that boundary reinforcement, and thus the bass response. It is worth a try.

The spikes generally cause the speaker to be more steady, and improves sound by reducing doppler that is caused by minor speaker rocking on an unsteady base. They can also provide a vibration evacuation path. But if the floor is very unsteady, then this may be a problem.

I agree that some experimentation is in order to find the best result in you situation. I think it is easy to place a temporary plate over the gap between floor and speaker that is created by the spikes raising the speakers off the floor. It just might do the trick for you. Boundary reinforcement is a real effect, and it can be compromised by even a couple of inches gap.

Another approach is to use set of three Aurios MIB ($100 used on Audiogon) to float each speaker on a smooth level surface of marble or granite resting on the carpet. One or two Home Depot floor tiles provide enough surface area for one speaker. Have not compared to the much less expensive Herbie's tenderfeet on laminated glass mentioned by Hdm in the lead off response to your inquiry. Aurios can only be used if the speaker wires are held up so that they do not pull on the speaker to be floated. Results with my big transmission line speakers were favorable as the bass became more clearly defined, and seemed to extend to lower frequency cleanly.