Speaker spikes-worse sound-what gives?

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.

Your speaker was probably light in the bass to begin with. You became accustomed to the sound WITHOUT the spikes. Then when you put them in, the sound was different, that is less bass. Oftentimes, the floor acts as a bass addition, especially if the floor joists are running in the direction of the sound (read not perpendicular, which would break up the flow of the sound)allowing for more bass. The first rule of audio is, there are no rules. What works for Billy Bob, may not work for you, your tastes, and more important your environment. Place the speakers where they are acceptable to the wife, and sound the best to you. That will keep the peace and sonically give you the best result.
Spikes are intended to eliminate (ameliorate) the rocking of the speaker, as well as to minimize the amusical sound coming from the bottom of the speaker, when it sits directly on the carpet. I have experienced many occassions in which I liked the sound better, sans spikes. Don't let it worry you. Just do what works best.
Best,
Larry
PS If you want a private consultation you may email me for a more detailed explanation. I traveled the country as Director of Sales for a speaker manufacturer,and have 20 years in the industry, so my input may help. Although the group here seems to be doing a pretty good job already.

Thanks Lrsky.

Wow, I am glad I found this thread today. After moving my Tekton 6.5t monitors from the top of my low and wide wooden stereo cabinet to older sound organisation 25" metal speaker stands (usually sold to pair with Linn Tukans), I was getting a much bigger sound stage and imaging but also a level of harshness and edgyness. The sound organisation stands have some very aggressive floor spikes and after removing them, I am very happy. The edgyness and harshness is gone but the great imaging and soundstage remained. I also think I got a little more bass out of the removal. I have the stand bases weighted down and hope to fill the hollow columns very soon. The Tektons are both on spikes and also screwed into the top platform of the stands since I do not want my cat to tip them off. I was thinking of adding some blue tack / fun tack between the stand platforms and the bottom of the Tektons, but I am very very pleases with the results I have now. Who knew that the floor spikes could have such an impact?