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Turntable Resonance Fix

I've been investigating different materials of turntable mats in hopes that I can find one that will help tame a -30dB rumble centered around the 20 Hz region that I fear is affecting the rest of the audio spectrum to some degree. I'm guessing that either platter bearing noise is to blame, or possibly vibrations from the motor creeping into the tonearm. Ultimately I would like to take steps to eliminate the source of the rumble, but I fear that will involve several thousands of dollars (a different turntable). With the vast amount of experience and knowledge out there, can any of you share an example where a particular mat helped with this sort of issue? Baring that, do any of you have advice for altering or upgrading the Pro-ject turntable to eliminate this problem? 

For reference, the setup is as follows:

- Pro-ject 2Xperience turntable (stock)
- Soundsmith Aida cartridge
- PS Audio NuWave phono preamp (digital measurements were taken from the USB output of this unit)

The well-isolated and -damped audio rack sits 25 feet from the speakers. But regardless of that, measurements were taken with the speaker output at a whisper. 

I have taken screen shots of the analyzer that I will post to my profile page. 
sixfour3
sixfour3 OP
21 posts
 
@millercarbon, I have read your essay "Vibration Control and the Townshend Audio Seismic Pods," and your advice above. I believe that your approach is a good one. Two sets of Nobsound pods have been ordered. Wish me luck. But regardless of their effect on this issue, I'm looking forward to trying them out on other components as well as the turntable. Thank you for that. 

@lewm, I used Mobile1 0W-40 to re-lube the bearing. However, I did not consider using paper lens wipes. That's a good recommendation. Hopefully the microfiber cloth I did use did not impart any foreign debris into the bearing. I very well might repeat the exercise and re-measure per your recommendations. 

All this effort to push a slight rumble a little further down the scale. Mid-fi can be very frustrating. 
millercarbon's avatar
millercarbon
12,531 posts
 
Yeah, I had a Technics SL1700 I thought was dead quiet, until years later using it with my by then much improved system it was easy to hear bearing rumble. One way to tell, if it is bearing rumble it will be more audible at the outer edge because that is where the lever arm of the platter is longest, whatever wobble or vibration is coming from the center is amplified most at the outer edge.  

Even if this is the case it is better to let the turntable dissipate this energy itself on springs rather than energize the rack which then feeds this back into the turntable. 

You can also use stuff like fO.q tape, but it is not much good at low frequencies. It is great for cleaning up midrange and treble though.
lewm
14,682 posts
 
Microfiber should be fine.  If you had already re-lubed the bearing before your OP, I apologize for being redundant.  However, if you have since done the lube, did it help???
mijostyn's avatar
mijostyn
8,570 posts
 
sixfour3, Not that oil! Too thin and too many additives. Single weight non detergent oil only. Compressor oil is perfect for this use. This may be your problem or part of it. No amount of damping or isolation is going to cure a rumble problem. 20 Hz is also quite high for rumble. You sure this is not feedback? Can you hear it at all volumes?
For turntable isolation these pods are next to worthless. MinusK makes the best isolation platform. Townsend makes a platform but I have no idea how well it works. None of these will address any intrinsic turntable noise only extrinsic environmental noise.
If the turntable is rumbling this bad it is more than likely time for a new one or a new bearing or motor. Don't buy crutches for a bad turntable, buy a better turntable instead. The Thorens 1600 is a great table for the money and completely isolated. Following this would be Sota turntables like the Sapphire, the Avid Acutus then Basis and SME models. If you have the bucks the Dohmann Helix is the last word. All of these tables are completely isolated and will not pass on any environmental noise of vibration over 3 Hz. 

sixfour3 OP
21 posts
 
I've spent the afternoon cleaning, re-lubing, re-instaling and re-measuring. Thick or thin, additives or none, synthetic or conventional, none of the different oils I tried had any effect on the results. 

What I did notice during measuring, however, is that there are amplitude fluctuations that are consistent with the rotation of the platter. It's obvious to me that the bearing is the cause of the rumble. But to the untrained eye (mine) there are no visible flaws in the bearing and no contaminate in the mechanism. 

I'm going to chalk this up to a poor bearing design that has reached the end of its useful life. I'll start by replacing the bearing. Then I'll work on replacing the table. Thanks, @mijostyn, for the recommendations. 
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