turntable feedback

my turntable is a pro-ject rpm5 it sits on a sound organization stand. the main speakers are B&W 703 and probably go down to between 35 and 40hz. The crossover point on my rel 305 is about the same 35-45. The feedback comes in the form of a hum that gets louder and louder as soon as it apears. With the subwoofer on I imagine it comes in at about 90 to 95 decibles of spl. I probably get another 5db by turning the subwoofer off. Oh yea the subwoofer is in the corner behind the left speaker the way rel suggests. that being said that is probably not the place to put the turntable. The other corner of the room along that wall has a door in it. Also the rel 305 does not have a subsonic filter.

This is a statement I posted on AV Guide.
It shows that if you can't do everything you can to mount the TT from a wall.....you are pushing shit uphill!

Mount the TT on a shelf firmly cantilevered from the wall.
Sound is transmitted it 2 basic ways:
AIR-BOURNE
STRUCTURE-BOURNE
90% of audiophiles mount their TTs on racks sitting on the floor.
This is a disaster for both types of transmission.
Even a concrete floor (which is not generally bouncing around like a timber-framed one) is a great transmitter of sound, so that any rack sitting on the floor is receiving BOTH types of transmission.
This is why Continuum Audio Labs create a rack for their Caliburn that costs $25,000. That's how much technology is required to overcome this basic problem of physics.
When you cantilever off a wall, you are disconnected from the floor (USA stud frame tradition can often short-circuit this advantage).
The materials to fix to the wall, project from the wall and form the shelf for support, generally act to physically 'de-couple' the shelf from the wall.
Thus all or most STRUCTURE-BORNE and AIR-BORNE sound transmission within the floors and walls are eliminated.
The only transmission to now worry about, is the AIR-BORNE transmission directly into the supporting shelf (and here is where Jon's granite shelf is NOT a good idea.
Granite rings like a bell and transmits sound deliciously throughout many audible frequencies without much absorption or dampening. Timber is a better insulator and dampener.
However it may be academic because all one has to do is DE-COUPLE the turntable from the supporting shelf to eliminate the transmission of this air-bourne absorbed sound.
Stillpoint cones with ceramic balls is a good way and there are many others.
Then the only sound transmission to worry about is the AIRBOURNE sound which the TT base and platter are able to absorb THEMSELVES.
This is where the turntable designer earns his crust with the elimination, absorption and dissipation of this air-bourne feedback setting his TT apart from the rest.
Of course the ability of the tonearm and cartridge to absorb and dissipate this same air-bourne transmission (feedback) is equally important but the frequencies are much higher and smaller.
So the moral is......do everything possible to wall-mount your turntable.

Does the subwoofer amp have a subsonic filter to keep low-end garbage (below 15-20Hz) out of your system? This is only an issue when playing LPs, not CDs.

The floor will flex the least near outside walls, particularly in a corner of 2 outside walls. Unfortunately, this si where airborne sounds will be reinforced the most. I'd say try locating it close to a corner and see what happens.

Dear Zeekzaak: If the problem comes from a floor feedback the the Storyboy advice is an alternative or look for a better isolation platform/footers. If the feedback comes from the " sound " ( subwoofer very low bass reproduction ) sometimes changing the TT place could help.

Btw, which kind of " sounds/noise " do you hear from that feedback?

Regards and enjoy the music.
Raul.

Your only solution may be ceiling suspension.

More questions. What is the crossover point on your sub? How low do your main speakers go?

Sometimes the airbladder types of isolation will help. Like Arcici or Brighstar.

What kind of Turntable is it? What kind of stand? Where is the sub located?