2. misc-audio
  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

Showing 6 responses by inpepinnovations1e75

inpepinnovations1e75
395 posts
 
Eldartford,

Of course pressurisation stiffens structures that are inherently non-rigid, vinyl and other plastics. Metal tubes are much more rigid and pressurising them to make them more rigid would be impractical, i.e. pressure would have to be higher than the capability of the tube to hold.

BTW, that is the only reason that helicopter blades are pressurised, to detect cracks - see how much those suckers flex?

maybe we could pressurise the interiour of vinyl discs to increase their rigidity and affect their resonance also. (tongue firmly in cheek).

Salut, BoP.
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.
inpepinnovations1e75
395 posts
 
TWL, that is a fancy way of stating the Law of Entropy. Most of the time the "easiest" way for the energy to be dissipated is through absorption as heat. When the vibrations are being so-called transmitted through a structure that simply means that they are being allowed to set the structure into vibration so that ultimately the "receiver" mass absorbs it. The source of first vibrating member continues to vibrate and the amplitude has not been diminished at all by conducting out the vibration. Mass (either through direct application to the offending structure or rigid coupling to a large mass)is best way to absorb vibrations.
inpepinnovations1e75
395 posts
 
Should we pressurise the tubes with air or nitrogen? I am sure that the choice of gas will affect the sound also! Seriously, pressurising the tubes won't change the rigidity of the structure, but will add to the mass (slightly) due to the added gas.
inpepinnovations1e75
395 posts
 
Eldartford, that is why I also don't couple to the floor with a rigid stand. I suspend (isolate) the turntable from the ceiling with 4 small gauge wires holding a MDF shelf. No footfall worries nor vibration through the building structure, since the wires do not respond to nor conduct those frequencies.
I make no claims that this set-up is better than stands, coupled or isolated, but it is as good sounding as any other system that I have heard (albeit it has been a long time since I have heard another TT set-up).
BTW, again, the Atlas ICBM structure is pressurised for other reasons than structural rigidity and if I told you that reason, I would have to kill you after! :-)

Salut, Bob P.
inpepinnovations1e75
395 posts
 
Eldartford, a little knowledge is a dangerous thing. I don't know about bicyclists using pressurized tube frames, but I bet you that if they are, they are using helium as the gas and that is what is making the frame lighter, through bouyancy. Again, seriously, one doesn't "pre-stress" tubes with gas pressure. Also, CO2 would not be a good gas to pressurise the tube, since the pressure necesary to have any effect on the structural stiffness of the tube would cause the CO2 to solidify, even at room temperature! BTW, make sure that you completely dry the inside of the tube before introducing the CO2. CO2 and water make a nice corrosive atmosphere. At least it is not an explosive atmosphere.

salut, Bob P.
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