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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
stehno
1,453 posts
 
You rocket scientists crack me up! :)

Seriously thought, inpepinnovations with your shelf suspended by cables hanging from the ceiling, how are you able to provide an exit path for the air-borne vibrations captured as well as those generated internally?

Sure no vibrations from the housing structure can intrude (hypothetically), but neither can they escape for those vibrations that WILL be captured.

-IMO
eldartford
4,262 posts
 
Stehno...Cables to the ceiling provide a rigid path to structure: it's just that the structure is rafters instead of joists. Either one could be stable or vibrating.

Airborne vibration, which I find to be my only significant problem, is absorbed by the mass of an isolated turntable/base. If the mass is high enough it won't be moved by the vibration. The isolation alternative is more practical IMHO because it does not require a floor (or ceiling) with no vibration.
inpepinnovations1e75
395 posts
 
Furthermore, Stehno, any vibrations in the rafters are attenuated through the wires, much more so than they would be through a more resonating structure such as a support on the floor or on the wall.
Eldartford's remarks concerning airborne vibrations are dead on IMHO.
BTW, vibrations are not conducted anywhere, they are absorbed and turned into heat at rates which vary according to the mass and natural resonance of the structure. Coupling in effect adds to the mass of the object coupled, which aids in the absorption of the vibrations.
theaudiotweak
2,806 posts
 
Trapped, internally generated electro-mechanical resonance as well as airborne resonance, loss of efficiency and no fast way out. As I see it..Tom
twl
3,251 posts
 
All forms of energy seek the ground state via the fastest route possible. Vibrational energy WILL seek ground, and it CAN be transferred there. Some vibrations CAN be dissipated as heat in certain materials, but that is definitely NOT the only way that vibration can be dealt with.

According to the Zener visco-elastic model, any energy which can not be visco-elastically dissipated, will be reflected or transmitted into the nearest adjoining surface. This threshold is easily reached at the vibration levels we are dealing with in the audio environment, with the materials typically used as "absorbers". Changing mass merely "tunes" the transmitted vibration frequencies. Going to very high mass increases the Coulomb's Friction to point where it will not be moved easily at the amplitudes encountered, and that is the direction that the heavy stone stands aim for. However, it is just as resistant to transmitting the energy away from the equipment, as it is into it - so airborne vibration is not dealt with at the equipment level with that type of stand.

Without question, a properly designed stand which provides a well-engineered vibration evacuation path that conforms to the laws of physics is the best route to take, because it will allow all forms of vibration to seek mechanical earth ground, no matter what the source of the vibration is. The only exception is the movement of the earth which will affect any system that is not an "active" control system.

Also, if your floor has a problem with not being stable, it is not a "fix" to compromise your racking system performance to try to compensate for an unstable floor. Fix the floor. Then let your properly designed racking system do its job.
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