Quiz about adding dense mass to a vibration isolation application!

First, I'm a believer now in decoupling everything.  But you are correct about energy having to go somewhere.  Passive components like DACs and preamps have little created vibration energy- the transformers perhaps.  Active components like speakers and CD Transport motors are creating vibrations and that energy needs to go somewhere.  My experience is that the speakers definitely need a way to drain energy and that was measurable.  My speakers perform much better sitting on the spring loaded wood platforms vs directly on springs.  They are decoupled in both cases but the speaker cabinet still rings for over a second when I hit it with a steel ball when sitting directly on springs.   The speaker cabinet has no ringing at all when sitting on the spring loaded wood platforms.  The sound difference is striking.  The clarity and detail is vastly superior with the speakers sitting on the spring loaded wood platforms.

I experimented with my preamp directly on springs, on a spring loaded wood board and spring loaded HDPE board.  In all three of these cases the preamp is well isolated.  No vibrations from the music get through to the chassis vs the preamp sitting directly on the shelf.  Based on listening, I preferred the preamp on the spring loaded HDPE board or the spring loaded wood board the best.  Between the wood and HDPE I probably could not distinguish in a blind test.  

I designed my spring loaded wood platforms for the speakers to have limited travel.   The speakers will rock if pushed on but only a small amount with no risk of tipping over.  They sway at 3 Hz and quickly come to a stop.  The preamps and DAC have little play as well.  I am able to have just one spring per footer (two springs required on the one footer near the transformer) on the preamps and DAC which leaves about 0.200" travel.

I tried putting springs on my entire stereo rack.  It weighs about 450 lbs, I estimate. It took (8) 57 lb/in springs.  It worked but I did not like my entire rack swaying.  That much weight and all of my equipment moving with just a touch was too unnerving.  I'm more comfortable with individual isolation.  This was a good 3 hours work to put the entire rack on springs and then take it back off of the springs.  The things we do for this hobby.

Ideally, you want the system resonance to be around 3 Hz.  Compressing the springs to 50% doesn't mean much.  The springs could be compressed to 90% and the isolation affect will be the same as long as the total spring rate and mass make for a (ideal) 3 Hz system resonance.  I am able to get down to 5 Hz on my components using the Nobsound springs and they are compressed to about a 0.200" gap.  So I have no room to add mass (weight on top of my components) in order to get the resonance down to 3 Hz.  Still, 5 Hz provides very effective isolation. The isolation added clarity and detail to the music.   The added detail to the music was distracting at first but now I'm used to it and I could never go back.  

My experience is very different. Vibrations affect everything to some degree. I hear quite a difference isolating my front end components as well as my amplifiers with springs. Granted my DAC and preamps use vacuum tubes but my amps are solid state. I also have experimented with different materials for the boards that the components sit on as well as having them sit directly on the Nobsound feet. I have tried granite (terrible), wood, carbon fiber and HDPE (High Density Polyethylene). Woods work well but I found the HDPE boards seemed to have a slight edge over wood under my preamps.

I have cable elevators too. Unfortunately, I could hear a difference with the cables lifted off of the floor. I made my own cable elevators on the cheap. I used electric fence ceramic isolators supported by rubber bands stretched between two dowels pressed into 4x4 wood boards. Seems to work.

I use the VibrationAnalysis app on my iPad and iPhone. The frequencies are accurate but the magnitudes are for reference only and can only be used for comparative purposes. If I were still working I would be able to compare the magnitudes with a calibrated accelerometer in the lab at work. I know that the FFT analyzer app was dead on with frequency using a calibrated tone from a B&K tone generator but I was not able to verify the magnitudes so they are reference only as well. The iPhone and app work very well and is quite sensitive. Even the lightest of footfalls from several feet away can be detected.