Reed 5T Opinions

lewn,

True, even with perfect zenith alignment, only at the null point would the contact area of the cartridge along the line of tangency.  But, the maximum error at other points will still be relatively small, whereas, zenith error in manufacturer is much higher, typically, according to the Wallytools people, plus or minus five degrees.  Still, I am not inclined to open that can of worms with my setup.

mijostyn,

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.  There are some arms, like the Morch Anisotropic arm, that deliberately increases the horizontal mass by using outrigger weights on the vertical axis (to reduce impact on vertical mass) so that the arm resists swinging side to side when large horizontal groove movements (i.e., monophonic bass waves) are presented.  This preserves such bass information (a lot of deep bass is recorded monophonically (side to side movement) in order to reduce big changes in depth of the groove that stereophonic  recording would entail),  I've heard that arm and it DOES have impressive bass response.  Likewise, I've heard impressive bass response from air-bearing arms, like the ET-2, and the high horizontal effective mass might be the reason.  But, I do worry about whether such arms put a lot of strain on the cantilever when it has to drag the whole setup across the record--not only is the mass high, the lack of mechanical advantage of a pivot means a lot of force is needed to drag that arm linearly.  This high sideways resistance to movement also makes we wonder if that means the cantilever is never tangent to the groove.  Still, I've heard nice sound from all types of arms, so I don't know if any are inherently superior.

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.