1. Home
  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, 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.
eldartford
4,262 posts
 
inpepinnovations@aol.com..You are right about the CO2, (a careless afterthought on my part) but wrong about internal pressurization stiffening up a structure. There are many examples. I picked the bike example because it somewhat resembles the tubes we are talking about. Blimps, Atlas ICBMs, and children's inflatable toys are others that come to mind. Heliocopter rotor blades are pressurized, but this is mostly done so that the pressure can be monitored for evidence of cracks.
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.
geoffkait's avatar
geoffkait
14,147 posts
 
Of course it would benefit "proper" frame stiffness to design the frame correctly in first place - w/ sufficient skin thickness and diameter of tube based on specific requirements, plus use of stength members. Many variables invloved...is it possible the best sounding structure is actually no structure?
eldartford
4,262 posts
 
inpepinnovations@aol.com...Sure, chopper rotor blades flex: that's why cracks are such a concern.

The Atlas ICBM structure is aluminum, not vinyl. It is kept pressurized at all times.

Yes, depending on the wall thickness of the tube, fairly high pressure would be necessary. But the stiffening effect will come into play long before risk of tube explosion.

Actually, I am not a big fan of super rigid TT mounts. I prefer isolation. If you are lucky enough to have a completely non-vibrating floor, I guess that coupling would work just as well. (But who is that lucky?)
More to discover