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  3. 1064803157

Why Does A Concrete Floor/Spiked Metal Rack...

suck all the warmth and life out of my system?

I have been thoroughly dissatisfied with my hi-fi system for the good part of a year now and I have been unable to until recently to put my finger on the problem. In a nutshell, almost every CD I would play would sound bright and harsh and bass light. The top end and upper midrange would completely overwhelm the bottom end. I have experimented with all sorts of tweaks and in particular various isolation devices, and although I was able to achieve minor changes to the tone the overall top end brightness and lack of bass was still evident.

I was enjoying (as best as I could given the problem!) a listening session and wracking my brain (for the ten millionth time) for ideas on how to make my system work better, when it suddenly dawned on me that I had these small plastic/hard rubber? cups that might be ideal to place under the rack spikes as a last ditch attempt to solve the brightness issue. With the music still playing I carefully tilted the rack enough to slip the cups under each spike on the four corners of the rack, thus de-coupling the rack from the concrete floor. They were a perfect fit and the effect was both immediate and DRAMATIC. The system was for the first time tonally balanced, the bass response increased, the sound stage widened, the noise floor dropped, there was greater depth, increased clarity, and most importantly the brightness and harshness had completely disappeared!

I was firmly of the belief that audio racks should be coupled to the floor for stability and assist with the reduction of floor vibration eminating from the floor. My rack is a rigid design composed of tubular steel and every cavity is filled with sand in order to reduce any possible ringing. The rack is supported by four large adjustable screw in spikes which penetrate the carpet and couple the rack to the concrete floor beneath. The components are supported on MDF shelving. What I discovered this weekend is that this rack/floor interface was completely sucking the life out of the system. Upper midrange and top end frequencies were being accentuated at the expense of the lower mid range and bottom end, thus producing the fatiguing brightness and harshness.

Can anybody explain to me in laymans terms why this occurs?
unhalfbricking
elizabeth
6,726 posts
 
I would think it is a resonance problem. Your room with your stand is just messing with the electronics via some high frequency vibration. As you found out, just changing one thing in this chain will stop the problem.
You might experiment with different solutions similar to the one you have used, but may be more elegant.
I personally would try some sorbothane hemispheres in there.
Or even size 8 or 10 rubber bottle stoppers from a place like American Science and Surplus.
viggen
817 posts
 
In layman terms, the order of execution might not be correct.

In some circumstances, totally isolating the system can cause it to sound sterile. However, I am not sure this is the case since the rack/component interaction hasn't been properly described. Although, you do seem to try to kill vibration with your application of sand and mdf boards. I think this is more relevant than the rack/floor interaction.

Also, generally, in applying draining and deadening techniques to system, one wants to drain vibration from component to something that is "dead". You seem to have this backwards. And, this seem to lessen the effect your rack/floor interaction has on your system's sound.

Lastly, as the rubber cup is under the rack now, vibration is not drained as expediently as when the rack's spikes are directly touching the bare floor. This ought to slow down the velocity of vibration traveling in your rack if there is any significant vibration still moving around. I don't think this is very relevant since you got the sand and mdf applied to your rack.
unhalfbricking OP
15 posts
 
Thank you for your responses. I think TWL may be on to something with regard to removing the sand from the rack. The only changes I have made to my system in the past twelve months have been to fill the rack with sand and upgrade my amplifier from older model Plinius pre/power separates to a Plinius 8200 MKII integrated. Up until then my system sounded just fine. The interesting thing is that I did not hear my older amp on a filled rack as I had sold it prior to filling the rack, and I have not heard my new amp on an unfilled rack as I had filled the rack prior to bringing the new amp home! I believe it is time to experiment futher. I'll keep you posted.
bigkidz
1,784 posts
 
Here is my two cents worth and probably nobody will agree with me. The MDF is very good for shelving, and the sand fill is also a step in the right direction. You want to eliminate vibration from the rack and your components. The only thing that should be spiked to the floor is your speakers and adding a good solid base, spikes and weight to them is helpful. Vibration kills dynamics and details IMHO.

I have known a local designer in New Jersey who has shown me the light on this subject and proven it to me many many times so if you wnat to email me, I will pass along what I have learned so far.

Happy Listening.
unhalfbricking OP
15 posts
 
Gawd! As much as I appreciate all the help I'm now completely confused?? It took me the good part of a day to fill the stand as there are four uprights and sixteen cross supports each with only two very small filling holes, one at each end, and each hole needed to be adequately plugged to prevent the sand from leaking out. Now it will not take anywhere near as long to empty, but I do not wish to go through all that rigmarole again if emptying does not provide the desired result. Regardless of whether it is correctly set up or not, my system seems to be working, so maybe I should just leave well alone?
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