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
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.
eldartford
4,262 posts
 
inpepinnovations@aol.com...I guess your system is like a rigid rack except that you are coupled to the ceiling instead of the floor. If you are in a one floor building, this will avoid problems with people walking around your listening room. If you lived in an apartment house you would be at the mercy of the folks upstairs. Isolation would be provided if you replaced the wires with bungee cords, but that would introduce many new and interesting problems!

It was always said that Atlas pressurization was for structural reasons. The design is about 50 years old so I can't imagine that there is anything classified about it.
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.
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