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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
stehno
1,453 posts
 
I'd like to take a stab at your question. But I am not an expert by any means.

Keep in mind that the goal is not only to keep vibrations from the floor from entering the rack, but more importantly the goal is to provide an expedient exit path for all air-borne vibrations that the components and rack have already captured.

When properly done, a concrete floor is said to be an excellent conduit for transfering vibrations away from your rack. I did not think this to be so, but one expert in this area, (who may have more knowledge on this subject than any other) made this statement. Much to my surprise as I assumed a wood sub-flooring system was the preferred foundation.

For others to better assist, you might consider listing all of your equipment and accessories.

As for the rack, you are using MDF shelving which is not a very good material for this applicaton. You also are using vibration dampening sand in your hollow tubes. Perhaps, solid rods would work better?

You also may be using inferior engineered spikes, cones, or points. In addition, you do not mention using any spikes, cones, or points of any kind under each component or speakers.

In other words, you have to properly execute the vibration handling methodology you choose.

I'm not saying you haven't, but as with everything else, there is a right way and wrong way to accomplish this goal.

If, per chance, one has improperly executed this strategy, then one cannot expect miracles where the points makes contact with the concrete.

-IMO
eldartford
4,262 posts
 
Although I am skeptical about the need for exceptional vibration isolation/suppression for well-designed audio equipment, I can offer a few thoughts about vibration isolation.

In my business (testing of missile inertial guidance systems) for some tests vibration must be minimized. Our test stations, where the GS is mounted, are set on top of 3000 pound granite slabs, which are resting on pilings that are driven about 60 feet into the ground. These "piers" are isolated from the building.

Over the years we have learned that this type of construction is almost always effective, but occasionally is not. There is no way to tell before you build the pier. You build it, and then you test it. At our facility we have a room with five of these piers in a row. Four of them are fine, but one has so much vibration that sensitive optical measurements can't be done. I'm told that this type of pier can pick up ground vibration from trains passing a mile away.

Accordingly, I surmise that while a concrete slab is usually vibration-free, this cannot be guaranteed.
twl
3,251 posts
 
I agree with both of the above.

It's not just any concrete floor/spiked metal rack. It's your floor and your spiked metal rack. They have an interaction with your component which is not properly engineered. The first thing that I would do is get the sand out of it.In a coupled system, deadening the ringing is not the goal. Letting it vibrate is the goal. If it is truly well coupled and properly designed, the ringing is passing the vibrations to mechanical earth ground. Then try steel or hardwood shelves instead of MDF. And make sure that your CD player is on good audiopoints, so that the rack isn't defeated by the lack of good coupling at the start.

There is one other possibility, which we can't assess if we don't know what your CD player is. That possibility is that the CD player/cables combo may have a naturally overbearing bright sound, and that the rubber de-couplers actually created a condition that allowed colorations to be introduced that sounded more apparent in the bass.

I realize that may sound funny, but we all know that sometimes when an upgrade is made, it reveals shortcomings in some other part of the system. Perhaps the rack is functioning well, and thus revealed some other problems. I can't say for sure that this is the case, but it may be. Maybe now you are hearing what your CD player/cable combo is really doing.

If you want to fill the stand with something, use the Micro Bearing Fill from Sistrum. This is designed to enhance the performance of a tubular rack that is coupled, and not fight against it like sand does.

Those are my initial thoughts on the subject.
Post removed 
viggen
838 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.
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