Speaker Spikes - Working Principle

Before there was ever conjecture about spikes having anything to do with resonances, the purpose of spiking a speaker was simply to stop it rocking in reaction the motion of the drive units and to keep the speaker level. Since floors are rarely flat, spikes were seen as an economical way to achieve both goals.

A lot of lay intuition going on here.

Rubber has a lower internal impedance than say wood which is lower than concrete. The highest internal impedance I think is Diamond. 

Spikes do nothing but fix the speaker to the floor. This is only useful for subwoofers which can creep. If you use three spikes the speaker can not shake.

The issue is bass particularly with flexy floors and walls. If the floor's resonance frequency is within the range of the speaker it is going to vibrate every time that frequency is produced regardless of what you put the speaker on, even if you suspended the speaker in air. Put a test record on and play a 20 Hz tone at high volume and walk around the house. Everything that can vibrate at that frequency will sing. You will hear a symphony of rattles. Walk around the outside of the house and you will even hear the siding rattling. 

Anything that changes the speakers location in space can effect bass at the listening position and can change the speaker's sonic character. A little less mid bass can make a speaker sound more detailed as an example. Changes in location will also affect where all the early reflection points are within the room which again might change the speaker's character at the listening position. 

@ellajeanelle 

1+  You isolated your turntable from the resonance frequency of the surface you have the turntable on and also everything above the resonance frequency of your suspension. All turntables should be isolated this way. Ideally the resonance frequency of such a suspension should be 2-3 Hz which depends on the spring rate and the mass of the suspended Turntable. If a suspension device is not tuned to the weight of your turntable it may be worthless. 

Most of the stuff people put under audio equipment is purely for visual effect. If it looks cool it will sound better. Your ears and eyes are connected.  You certainly do not want to put a hot amp on carpet. 

Porcupine Tree (Steven Wilson's Band) has released a video of their performance of Closure/Continuation. There is also a CD of that performance. WOW!!! Gavin Harrison is a machine and IMHO the finest R+R drummer that ever lived. 

A couple months ago I took the spikes off my Revel F52`s and put Loctite Fun-Tak strips under each corner.

The speakers are now firmly coupled to the ceramic tile floor.

I`m hearing better bass definition and a more musical midrange. 

And don’t forget how cheap spikes are to make. I replaced mine with the Isoacoustics Gaia 1’s and there was a large and immediate change. The current price is $500 for a set, a heck of a lot more than a set of spikes!

Another misconception: "depends on the spring rate and the mass": that is called a SWINGER for good reason. at resonance frequency, amplitude will be infinite. Try driving your car with spring only. 

That is were the DAMPER comes in. Now you have a system of spring, damper and mass, and can be tuned to KILL vibrations. 

This has NOTHING to do with the vibrations the emitted sound is producing ('will vibrate even if suspend the speaker in the air'). It has to do with the vibration the mass off the speaker is COUPLING to the floor (not those of the soundwave).