A Copernican View of the Turntable System

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.

I believe that Pryso and In_shore are correct in the fact that the air-borne sound pressure levels, affect the room's fabric to different degrees depending on their materials and structural means of support.
This transforms into 'structure-borne' feedback affecting the turntable depending on it's construction and isolation.
'Sprung' decks, because of this, are more susceptible to this feedback than 'mass-loaded' ones.