Reed 5T Opinions

Larry, Reports from my friend who has taken up a formal study of zenith error tend to agree with yours, to the effect that cartridge manufacturing errors are paramount in determining the error.

Also, I agree with your point about inertial mass of linear trackers (air bearing or otherwise). Some reputable engineers evidently think that high inertia in the horizontal plane is desirable for best bass frequency reproduction. Not only do we see some pivoted arms like the Moerch with outrigger weights at the horizontal pivot but also we have the Dynavector tonearms which very deliberately also strive for high horizontal effective mass. I have mentioned this at least once before, but one rationale for that goal arises if you consider that bass frequencies, increasingly as f goes down, are generated by increasingly horizontal motion of the stylus tip. Since these frequencies generate a lot of energy at the stylus/cantilever, the high inertial mass would be seen to stabilize the pivot relative to the stylus tip, so that the tail does not wag the dog (from side to side). Fremer often repeats his bias view that horizontal and vertical effective mass ought to be nearly equal, and, right or wrong, his opinions have had an effect on others’ perceptions. I suppose he learned his opinion at the feet of one or another tonearm designer who feels the two should be about equal. But I have never heard or read a good argument for it.

@larryi 

The dramatic difference in the inertial mass of air-bearing arms in the horizontal and vertical planes may be a problem or it may be a benefit. 

It's a benefit according to Bruce Thigpen.

By having differential effective mass in the horizontal and vertical plains you have 2 much lower amplitude resonant frequencies instead of 1 large one. If you have both resonant frequencies at the same point the amplitude is compounded along with the deleterious effects on tracking.

Bruce also makes the point that the ET2 does not pivot at low frequencies, whereas servo arms and low surface area air bearing arms will pivot at low frequencies - they are not rigid at low frequencies.

For discussion on high effective mass, it would be interesting to take a look at the following paper by Kuzma on their new Safir tonearm with a 60g effective mass. In contrast to the common believe that cartridge / tonearm resonance frequency should ideally be in the 8-12hz range, Kuzma stated it would do no harm for the resonance frequency to get down to 3hz. 

https://www.kuzma.si/media/uploads/files/SAFIR%209%20Technical%20aspects%20220409(1).pdf

@thekong 

An interesting white paper.

The ET2 horizontal effective mass can be as low as 25g less the decoupled counterweight compared to the 80g Kuzma Airline.

Kuzma ignores tracking and focus's only on resonance. I always thought the target of 8-10hz was partially based on keeping it above footfall on sprung floors which is typically around 4hz.

If you examine the Shure white papers on tracking, they have found that the fundamental resonance, if not dealt with properly, causes a scrubbing motion from the cantilever/stylus assembly. This causes tracking issues and of course distortion in the bottom and its harmonics that will distort up into the audible regions. I assume this is why they came up with the stabiliser brush.

Kuzma makes no comment on the impact of high mass on tracking at low frequencies, and there is no measurement indicated in the white paper.

Even Bruce Thigpen of ET states that on eccentric records, arms with high horizontal mass will be less accurate than lower mass arms.

Bruce Thigpen has measured wow and flutter on pivoted arms versus air bearing linear tracking and can demonstrate the linear tracker has lower wow and flutter.

His argument, supported by measurement is that there is typically more wow and flutter from a pivoted arm than from the TT itself.

@lewm , yes you did. Sorry about that. 

@dover , yes, I am talking about any air bearing arm. The problem is that the vertical effective mass of these arms is much lower than the horizontal effective mass. The cantilever, the suspended part, has to move the tonearm in two directions, up/down and side to side. Up/down the cantilever only has to move (suspend) the wand, bearing housing, counter balance, headshell and cartridge. The masses farthest away from the fulcrum have the most significance. In the horizontal plane there is no fulcrum. The masses of everything mentioned above plus the mass of the air carriage count in full force as they all have to move the same distance as the stylus. It does not matter if there is no friction. If you tune the system so that the vertical resonance point is within reason the horizontal resonance point is going to be very low, 2-3 Hz. What happens is the cantilever starts moving towards the spindle and it takes a bit for the tonearm to respond. Once it starts moving the cantilever has to stop the arm, the arm overshoots and the cycle repeats. Under every circumstance I have looked at you can actually see this happening. The cantilever shifts back and forth. Even if you can not see it the stylus is oscillating from one groove to the other. You can attenuate this by adding a horizontal damping trough which some arms do but then the right channel groove wall has more work to do moving the arm through the damping fluid, the opposite of skating. There is no good way to make this work. Straight line trackers that move a more or less standard arm along in a mechanized carriage is theoretically a better way to do this if the mechanism can be kept quiet and reliable , The B+O table is an example. The Reed arms and the Schroder LT side step both problems by moving the bearing housing of the arms along a specific trajectory. The 5T does this in a motorized fashion again bringing up the noise and reliability issues. The 5A and the Schroder LT animate the bearing housing by capturing the force generated by friction in the groove. The same force that generates skating in offset arms. I have not had the chance to listen to any of these arms yet but I have enough confidence in Frank Schroder that I would buy an LT on the bet that it works as designed. Unfortunately at this point I do not have a table it will fit on...yet. I am of the belief that the major benefit of an arm like this is not it's reduction in tracking error but the absence of significant skating. I am all for low friction bearings but even with no friction you still have to deal with mass and inertia in a system with a spring loaded suspension no different than your car. Also, what on god's green earth makes you think the counter balance of the ET arm is decoupled? It has mass does it not? It moves at the same speed and distance the rest of the arm moves, right? Sorry dover but, it counts just as much as everything else and when you get a really good pivoted arm you will realize this. You you are determined to have as little tracking error as you can there are some excellent choices out there now.

@thekong , do your self a favor and add some lead weight to your arm until you get the combined resonance down to three Hz and let us all know what happens. Better yet make a You Tube for us! Give us a little forewarning so we can get the popcorn ready. Frank Kuzma is a very interesting fellow. You might notice that he makes one of everything. He makes mass loaded tables and suspended tables. He even makes suspended turntables that are not really suspended. He makes unipivot arms, gimbal arms, 4 point arms and air bearing arms. He definitely has moments of genius but he will make whatever people think they want to buy so, he makes one of everything and is committed to not much.