There is no such thing as vertical and horizontal mass. There is a single scalar value inertia, and there is geometry. Distributed mass can be represented by lumped mass concentrated at a single point.
Well I have never criticised an air bearing arm for that. I'm just interested in looking at the data. Of course as manufacturers don't generally publish vertical compliance data we are a bit flapping around. Walton in the 1960s recommended a horizontal compliance of 7 and vertical of 2.5! I am not sure other than the Ortofon S-120 DJ cart if anyone tries to get lower vertical compliance but if Hans analysis that vertical resonance is the major source of FM then perhaps more work in damping in that plane is required.
Bill,
I was not saying you criticized air bearing arm. It is what most people believe that such as in Micheal Fremer's review of Kuzma airline.
Jim
I was lazy and didn't type vertical effective mass and horizontal effective mass.
Jim: Ah ok. I don't believe a word Fremer says and just read him for amusement 🙂
@Lcsaszar: I believe you can just as validly operate in vector or cartesian geometry when talking about tonearms. Cartesian helps analysis below 100Hz as there should be no vertical motion at all from the music, so any that there is can be considered a bad thing and can be examined for mitigation?
@Lcsaszar: I believe you can just as validly operate in vector or cartesian geometry when talking about tonearms. Cartesian helps analysis below 100Hz as there should be no vertical motion at all from the music, so any that there is can be considered a bad thing and can be examined for mitigation?
Lateral groove modulation is mono signal. Where both channels are in phase all the time.
Vertical groove modulation is stereo signal where the signals are different, or out of phase.
I don't believe there is a 100Hz cut off where stereo stops.
Look up 'elliptical equaliser'. Whilst the crossover point varies 100Hz is as good as any point to say that, if you do an M-S conversion most of the signal is M.
The answer is quite simple.
The arm moving up and down, causes the stylus to make large movements to stay in the track, the so called scrubbing.
These movements are causing FM modulation, meaning that a tone goes to a higher pitch when going up and to a lower pitch when going down.
Arm movement relative to the LP can only happen at low frequencies and can be diminished by applying some form of damping.
Warp and eccentricity will also lead to FM modulation, also in the lower frequencies.
So your arm is in no way unique, every arm will show this effect, the amount dependable on Fres and the degree of damping.
Since our auditory system is very sensitive to FM modulation in the range from 2.5 to 10 Hz, Fres is advised to be above 10 Hz.
A higher Fres will also lead to lesser FM modulation from warped LP's as you may understand.
It was my curiosity that made me investigate whether scrubbing, causing Waving of the signal, is the most dominant contributor to FM modulation.
And I feel that the evidence is getting stronger and stronger after having analysed completely different systems.
Hans
Hans,
It does make sense to me. I ripped these two tracks without any damping at all. After that, I added vertical damping. I may try to find the track with vertical damping later on.
From your analysis, is it safe to say that lateral damping is not so important to reduce FM? In other words, I may just disregard lateral damping.
Thank you for your explanation!
Jim
It does make sense to me. I ripped these two tracks without any damping at all. After that, I added vertical damping. I may try to find the track with vertical damping later on.
From your analysis, is it safe to say that lateral damping is not so important to reduce FM? In other words, I may just disregard lateral damping.
Thank you for your explanation!
Jim
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I agree with this statement. What I wanted to point out is that mass is mass, without any vectorial attribute. However the stylus compliance can be (and actually is) different laterally vs. vertically, causing different horizontal and vertical resonance. So is damping while we are at it. Exciting frequencies are also different (record offset vs. warp), so different resonance frequencies could be an advantage. Vertical exciting frequency is higher, and since there is not much usable program material as you wrote until 100 Hz or so, arm resonance and LPF can be set higher than in lateral case.
Question: are there any data for separate horizontal and vertical compliance from pickup manufacturers?
Hans,
Something is wrong with this picture. What I’m reading is that the Fres peak in the lateral spectrum is causing FM due to the vertical ‘waving’, and the Fres peak in the vertical spectrum is causing FM due to vertical movement. This implies that the horizontal Fres movement caused vertical scrubbing. This makes no sense. I have conducted many resonance tests and have clearly observed a horizontally cut resonance track cause horizontal movement of the arm, which causes horizontal scrubbing, which causes FM due to the horizontal Fres. Invariably, friction and other nonlinearities end up exciting vertical motions which often make the cartridge look like it’s following a Lissajous pattern (especially on offset arms), but the predominant effect from a horizontal resonance test tone is horizontal. It seems that the thread has taken a turn on the road where the only thing to focus on is vertical behavior and that vertical mischief of the arm is the only thing that causes scrubbing and FM. Did I miss the turn? My compass says no.
Jim,
No, FM is not only caused by vertical movement. Horizontal movement will cause scrubbing and FM too, even in linear trackers. Horizontal mode scrubbing in LT’s is somewhat of a different animal and is an order of magnitude less than that of a pivoted arm for the same magnitude of horizontal Fres. I suspect for your LT that the ill effects of horizontal Fres are somehow resolving themselves vertically, that the actual horizontal mode scrubbing in your arm is minimal, and its associated FM contribution is down in the noise floor, being swamped by the vertical motion. However, I would not dismiss the benefits of horizontal damping, too. I would expect that if you had the right amount of vertical mode damping on your LT, it should give you stellar performance in terms of FM immunity.
Ray K
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Actually, Moment of Inertia is a Tensor and can indeed have different values in different directions. Note that 'effective mass' is moment of inertia divided by effective length squared.
The single 'effective mass' quoted in reviews is almost always based on measurement of vertical resonance, since the most pressing issue for the arm-cartridge combo to deal with is record warp (vertical motion). The horizontal resonance would matter mainly for eccentric records, even then it is not as significant a problem as riding vertical warps.
The single 'effective mass' quoted in reviews is almost always based on measurement of vertical resonance, since the most pressing issue for the arm-cartridge combo to deal with is record warp (vertical motion). The horizontal resonance would matter mainly for eccentric records, even then it is not as significant a problem as riding vertical warps.
I said that "The demodulated FM signal is almost exclusively caused by vertical waving", not that the Fres peak was causing this.
What I show is the LF content of L+R = V(hor) and L-R = V(vert).
No pushing things in a certain direction, just plain facts.
And what can be seen is a very high correlation between V(vert) and the demodulated signal, without any further focus on whatever.
What the pictures are showing is unbiased and unprocessed, the interpretation is up to you.
For that reason I don't see what can be possibly wrong with these pictures.
I agree, look at the lateral image and you will see that to optimally correlate with the demodulated signal, I have used [V(vert) + V(hor)/4], meaning that the horizontal movement is also contributing but to a much lesser degree of -12dB.
In the vertical image I could also have added both in the same ratio, but as you can see at the almost neglectable magnitude of V(hor) that this would not have changed a bit to V(vert), but from an academic point of view it would have been consistent with the lateral image.
So fully respecting your opinion I cannot change anything to the facts as they seem to appear.
Hans
Ray,
Just an idea, because I still have the feeling you are not fully convinced.
You mentioned to have invested quite some time in resonance tests, so maybe you have some file available that I can process.
We could compare the outcome and see whether we come to the same conclusions.
Hans
Sadly very little and no way of telling how they measured the compliance anyway. Based on what LD has discovered using them I have an Ortofon S-120 DJ cartridge that I am going to put into use for mono recordings. This has a second damper which has no effect in the horizontal plane (11cu) but they don't quote any vertical parameters. It's doing something right as it has exceedingly good tracking.
Possibly, as computer tools allow much easier extraction of the relevant data, we might be able to start answering some of these questions.
@al2002: I had always though effective mass was quoted for horizontal plane. I'll need to go check, but it is possible I have been getting it wrong all these years.
Attachments
It's been a long time since I looked at cartridge reviews, so I dug up some old reviews that were to hand. Looking at the review of, e.g, the Technics EPC 205 in the US magazine Audio from the '80s, it is the vertical resonance frequency that is measured - this is clearly stated - and the effective mass for the arm-cartridge combo derived.
This does not, of course, preclude other reviewers from measuring and quoting - although why they would do this in the stereo era, I don't understand - lateral resonance frequencies.
Elastomers can be complex critters. However, I expect those used in cartridge suspensions to be isotropic to first order, and to exhibit similar compliances for small displacements in both horizontal and vertical directions.
This does not, of course, preclude other reviewers from measuring and quoting - although why they would do this in the stereo era, I don't understand - lateral resonance frequencies.
Elastomers can be complex critters. However, I expect those used in cartridge suspensions to be isotropic to first order, and to exhibit similar compliances for small displacements in both horizontal and vertical directions.
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Not a mag I have ever read. Checking back recent reports they measure the resonant frequency Vertical and Lateral, but the effective mass appears to be just copied from the data sheet.
One question, how did they calculate effective mass for the combo when compliance is a movable feast for Japanese cartridges?
Agree the elastomer should be isotropic. Walton doesn't explain HOW he made cartridges with lower vertical compliance, and he may have been talking about the Decca Deram he designed, which was an odd, but very clever design.
One question, how did they calculate effective mass for the combo when compliance is a movable feast for Japanese cartridges?
Agree the elastomer should be isotropic. Walton doesn't explain HOW he made cartridges with lower vertical compliance, and he may have been talking about the Decca Deram he designed, which was an odd, but very clever design.