Subsonics with Grado & Rega Arm

Hi There

The table is a spring suspended Logic DM101 similar to a Linn. It rests on the cement floor on cement blocks with inverted cones underneath.

I've checked tracking force, cartridge alignment and table levelling many times.

When I say subsonics I mean woofer bounce to the point it's ridiculous I get it on every LP I play.

I'd also like to point out I've had the same problem with the Platinum and Sonata on this table/arm and other tables so I know it isn't my cartridge.

I know it isn't vibrations because the woofers go nuts even on silent passages even on relatively flat LPs with record clamp.

So I'm down to looking at the arm and it's compatibilty with the wooden Grados. Some people say the Rega/Grado combo is great and other get subsonics big time.

I love the Grado sound and don't want to change cartridges so I'm looking for a more compatible tonearm but don't know what.

The revised description you've provided is a bit different problem than your original post suggested. Woofer-flexing due to infrasonic signals can, as you imply, be caused by warped records, and may also be caused by a cartridge/tonearm mismatch that causes the tonearm resonance to fall below 8-9 Hz. Since neither of these seem to be the cause of your problem, I'm inclined to think that you have some sort of low-frequency feedback loop somewhere in the amplification chain, but that's outside my technical expertise. You might try dropping a note to our resident tech guru, Sean, and see what he says. You might also try replacing the spring suspension in your turntable with the same kind of Sorbothane pucks that cured the acoustic feedback problems I experienced with VPI turntable.

I do not know about the Logic tt, but on some Rega turntables, hum from the motor is picked up by Grado cartridges. If that is what you are hearing, a sheet of mu-metal from the Magnetic Shield corporation will solve that problem. It seems unlikely that the arm is the problem.

I don't get hum it's definetly subsonic vibration which is why I'm inquiring about tonearms that are compatable with the wooden grados and perform as good or better than my modded RB300

I got around to looking at your post again, and a detail that I missed in your comments jumped out at me. You state that your turntable is on a cement floor, on top of cement blocks. It is possible that this location is exposing the turntable to a lot of airborne low frequency acoustic resonance, particularly if the turntable is also located close to a wall. Intersections where the floor and wall(s) or ceiling and wall(s) intersect create a lot of bass reinforcement, which is why subwoofers are often placed in the corners of rooms (where there are 3 intersecting surfaces).

You might try mounting your turntable on either a good isolation rack, or a turntable shelf mounted to the wall, and see if that helps to reduce the infrasonic overload.