A Copernican View of the Turntable System

Halcro,
What does it mean if the feedback increases as volume increases. If airborne feedback is the ONLY problem, one would figure the effects to increase. Personally, I am not convinced that airborne feedback affecting my rack, and then feeding 'structural feedback' through an isolation system (designed to combat structural feedback) to my turntable is a more insidious problem than the same airborne feedback affecting the record, tonearm, or dustcover itself.

In testing now...

my thoughts on airborne feedback. i believe it to be real, but difficult to identify. what i did to minimize it was to minimize the surface areas that could absorb airborne vibrations/waves. i did this by building a "nude" rack. i eliminated side panels and shelves and rest my equipment on the frame itself. i also incorporate alto extremo feet to absorb and isolate.
for the equipment, such as tables, that would not fit onto a nude rack, i made isolation platforms for them, filled with dense steel shot. that way, any airborne waves would have a hard time moving the heavy weight.
i have to update the pics in my gallery (actually, i thought that i had done that!!).
don

Chris, I can offer an experience to help answer your question.

My turntable is placed on a 60" shelf, fitted within an alcove on a side wall of the listening room. The shelf is 18" deep and the walls forming the sides of the alcove extend a few inches beyond the shelf. For some time I had the tt at the far right end of the shelf. This placed the arm/cartridge close to the corner of the alcove. One day I was dusting the table/arm (using a camel hair brush) while I had a CD playing. I happened to lean over the platter while some fairly strong bass was being played. I was amazed with the amount of bass energy heard with my head close to that corner.

Realizing the probable harm from my cartridge working in that environment, I relocated the tt to the left end of the shelf. This resulted in the arm/cartridge being slightly left of center along the shelf and away from the corners. When I then played an LP with only average bass content (probably a jazz quartet) I heard improved overall clarity.

This shelf is 3/4" ply and attached to the walls on three sides and has an added brace along the fourth side. It appears to be rigid but if I place my fingers lightly on the surface while playing music with much bass energy I can feel some structure-borne vibrations. For this reason, I use a 2" deep sand box between my tt and the shelf.

So, for whatever degree of structure-borne vibrations that reach my arm/cartridge, and they would logically be greater at the mid-point of the shelf than the corner (less bracing), the change to reduce air-borne vibrations resulted in an overall sonic improvement.

I thought that this J. Carr is the smartest guy among us.
But he is as crazy as the rest of us:'Surrounding the turntable ( but not contacting it) would be a double -wall acoustic shild '(08-24-11). How about asking the Russians
for the permission to install our TT in the Mir?

Regards,

In my current home, room and speaker interactions are a source of some real problems. When the gain is turned up i believe this excites the built material of the walls ,ceiling ,suspended floor causing many problems.

With my sources 13 feet away from the closes speaker i decouple my stand from the floor the best i can for now and then decouple the turntable from the stand, it's a job still under construction.

Our previous home listening room was so much friendlier and a real joy to listen music in, concrete slab on grade timber framed home with open vault ceilings.
The living / listening room simply had excellent acoustics.

One experiment listening for feedback problems in our previous home by placing an lp on the platter then resting the stylus on a stationary lp ,turning the gain up full i would be hesitant to try in our new home yet.

This may sound all bad however using a Placette active preamp with a Hell of a nice headphone section and Sony R-10 headphones immediately solved all my room related problems, I think.