But it gets processed through the RIAA curve. Record surface noise is at all frequencies, no matter what speed of the record. The problem is best solve first mechanically with a more inert turntable. And because we're talking about sidebands of mechanical resonances, it's hard to filter it with a rumble filter or just by rolling off low and subsonic frequencies.
If you record some of that noise and do a spectrum analysis of it, you'll see that it's not one frequency. Also, in my experience, the better isolated the motor is from the whatever the arm is mounted to, the less motor noise breakthrough - also, since some of that is from cogging torque, different motors and different method of motor control will produced different frequencies of vibration, and different amplitudes. Ladegaard recommends placing the fundamental arm/cart resonance much higher than we typically do - 13-18 Hz instead of 8-10 Hz - and to use fluid damping to minimize some of this. It's a complex mix of frequencies and it's not necessarily identical from arm to arm or table to table or even record to record.
If you look at the famous 1977 AES paper by Poul Ladegaard of Bruel & Kjaer, " Audible Effects of Mechanical Resonances in Turntables," you'll see that rumble is typically a mix of tonearm resonances and arm/cart responses to surface irregularities and motor vibration breakthrough, many of which have fundamental frequencies below the audible range but which have sidebands in the audible range and which modulate signal in the audible range. Click to expand.Depends on the source of the noise.
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