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The outer ring - do the math!!!


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One of the items I have on my TT that few others do is an outer ring. The idea is fairly simple - take a metal ring of some weight (1.5 kilos in this case) and use it to hold the record flat on the TT. It is not rocket science but what is the effect?

I spent some time considering this issue. What is the ring actually doing? What difference can it make?

At its simplest if we are not holding the record flat then there are bumps and dips to pass over. If the needle is passing over these then it stands to reason that various aspects of the setup are changing constantly and these might well have an impact on the sound.

Certainly in my experience even with apparently flat records the difference is remarkable but I wanted to go a step further and do some of the math behind it.

If you think about it the overhang is obviously changing, but, so it the tracking weight - and this really could be the most important aspect of all.

As a result I produced a quick spreadsheet. Frankly I was not sure at the outset what was important and what was not so I just banged in all the parameters I could think of and then set about producing calculations which, I think, are correct but I am not 100% certain.

Sadly I cannot attach the spreadsheet to this post directly so it is in zipped form.

To help I have posted a copy in here - although obviously the formulae do not work - but it gives you the idea.

Look at the end. the changes in tracking weight for a relatively modest bump are amazing.

If it is not clear, starting from a measured tracking weight of 1.7 grams we get a variation of some 0.7 grams either way. Makes you wonder why people bother with digital scales!!!

As follows:

Cartridge movement in the vertical plane calculations

Apparent mass of arm



Mass of cartridge



Mass of cartridge fixings






Tracking weight



Disk speed



Size of bump (length)



Height/Depth of bump



Distance from centre of record



Assuming a regular hill top - even on both sides.



cm from the centre:

Needle travels:


cm in one revoltion



cm in one second

Time to climb bump



Initial velocity in vertical plane


Distance traveled






Acceleration (S=UT+1/2AT2)










Therefore ascending the bump:

Tracking weight



At the top of the bump



(and descending)


bumps in a record.zip

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You are on the right track (har, har, har). The most important contribution to the effect is the force that it takes the groove to push the stylus and the subsequent chain of cartridge body, head shell, and arm. The spec for this is compliance. If the arm, headshell, cartridge, and all is heavy (like some head shells I've seen made of marble and other dense matter), the stylus needs to be real stiff in it's mount and provide a greater resistance to the groove surface, and needs a heavier tracking weight as well.

In the case of the B&O and maybe some others, the arm, cartridge, and all are extremely light and the stylus compliance is such that it takes very little force from the groove to move the stylus; and if needed when tracking a bump, the rest of the cart and arm assembly. The styli are made to track at 1 gram and the forces (appearent change in tracking weight) experienced on bumps is much less than if it all were heavier.

For example, the compliance on my cartridge is 30x10(-6)cm/dyne (30 micrometers per Newton meter) and the total mass of the arm, cartridge, and all on mine is only about 8grams. The tip mass is .22 milligram (22 onehundred thousanths of a gram). This combo puts the resonant freq of the whole assembly down around 10Hz and the resonant frequency of the stylus up above 50KHz. Most the the very fine cartridges consider 15um/mN as a very compliant number and about as low as I have seen outside of B&O stuff.

The thing that you did not say outright but it leads from your calculations... even when the record is flat the instantaneous temperature at the point of contact is about 800 F and the pressure is a few tones per square inch. The temperature figure is just a little below the melting point of the record and it gets a bit pliable for a very breif instant of time (long enough to weld a peice of debris into the wall which cleaning can never recover). The way friction works, the temp and pressure go up fast when one presses more firmly, so the bumps of the record are certainly to be avoided. Even after flattening a warped record the damage may be permanent.

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What my calculations do not take into account is the compliance of the cantilever as things get very complicated from there on in. In essence a stiffer cantilever will cushion the falls and the rises to a lesser extent whilst with a higher compliance unit there is a risk of inducing "wobble" into the movement so that the cartridge will continue to rise and fall after the bump - subject to the shock absorption characteristics or damping.

This then gets more complex where there are multiple rises and falls to be overcome. If the cartridge is still bouncing from the last one the effects will be even greater leading eventually to total mis-tracking.

And yet it gets even worse than this with lateral play or compliance in the cantilever. As the motion of the cartridge towards the centre of the record is dictated by the side wall of the groove on the record it stands to reason that there will be an element of lateral movement induced in the cantilever. Again damping is going to be critical here as we now have potential for undesirable motion in both the vertical and horiztonal planes.

Frankly - my math is not up to the job - but once you start to examine what is really going on it is amazing that records play at all. Suffice to say that all of these effects are reduced by the outer ring (although the suction system implemented by SOTA would do a very similar job I imagine) and that is why I use it and paid a silly sum for the privilege.

It is interesting, however - and I am as guilty as anyone of this - that we vinyl junkies beat the drum of setting the proper tracking weight so loudly. One wonders how often the cartridge is anywhere near the tracking weight we so carefully set.....

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