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At what vol level do you get rumble / flutter?

Hi everyone. I hope my Pro-ject Xpression has not started the dreaded rumble / wow / flutter problem. I recently tried a heavier MC Ortofon on my table and after switching it in and out (professionally done), my table will make the woofers rumble / wow / flutter as soon as my normal cartridge (Ortofon MC-3 turbo, HO MC) hits the record with the volume at about twice as high as my normal listening position, which is not party cranking levels, but twice as high is and that is where I see the rumble. Would you say this is normal for Pro-ject and similar tables? Will a Rega RP3 act similarly? Rest of system is posted and it is less noticeable with the rumble filter on. From what I remember, my table did not do this before the cartridge swap. Luckily, it is still under warranty.

TIA
sbrownnw

Showing 2 responses by tonywinsc

tonywinsc
583 posts
 
If you can see the woofers pumping, then I would say that they are probably cycling at 0.5 Hz to 2 Hz. Note that 33 1/3 rpm is 0.56 cycles per second. So record runout, as I like to call it, ie. the eccentricity of the record grooves to the spindle could be generating a 0.56 Hz cycle. Some cartridges may mechanically filter out this low frequency side to side motion and perhaps some don't. Just a thought...
tonywinsc
583 posts
 
Point of order. Effective mass of the tonearm is really the moment of inertia of the tonearm. The moment of inertia is calculated using I=mr^2. That means if you switch the mass of the counterweight and do not move it then the moment of inertia will change proportionally. If you must move the counterweight in or out, the moment of inertia is going to change by the square of the distance.
The angular momentum is I times rotational speed or like mv in linear terms. Angular momentum affects how quickly the tonearm moves or reacts to force changes. The force changes come from the stylus to record and through the suspension system of the cartridge
That means the natural frequency of the tonearm cartridge system is dependent upon its inertia, or effective mass divided by the spring rate of the cartridge and then the square root of that.
Long story short, change in counterweight mass as well as moving the counterweight in or out will change the Fn of the system. A lighter cartridge reduces mass and also allows you to move the counterweight in. So effective mass of the tonearm/cartridte goes down. If the spring rate of the lighter cartridge is lower (higher compliance) then the overall system natural frequency may remain nearly the same.
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