Why choose LOMC cartridges?

[targeteye]

From a 1955 copy of Audio Engineering "One of the advantages claimed for the moving coil type is that the coil moves in a uniform magnetic field, even though it may not be perfectly centered. Therefore, the displacement of the stylus from the exact center of the magnetic field does not introduce any distortion"

Not that I nessessarily agree but perhaps there is some validity to it?

 

[Multiplex]

I have a question....

The whole purpose of the stylus is to extract the maximum information from the groove. So this is also highly dependant on the actual quality of the analog information cut into the LP.

The lathes or cutters that create the record therefore would determine this initial physical quality. Over the history of LP production I would assume these lathes/cutters increased in quality. So, my question is, would there not be ealier LPs that would not benefit from a MC cartridge because the LP does not have the information that would take advantage of this? Later LPs perhaps might as the initial cutting was performed by better equipment?

They make mono conical LOMCs, and they even make LOMCs with 78 styli, so I dunno... Even though there are a lot of bad pressings out there, (including many recent ones,) I don't believe that older recordings are always poorer in quality. (Unless, of course, they have suffered from years worth of groove damage...) I would imagine that the best you can do is to match the playback stylus with the cutting stylus as closely as you can. If it was cut for use with 1 mil conical styli, a 1 mil conical should give the best performance. If it was cut with a fine-line type stylus, a line contact or shibata should sound best. Beyond that, a better cartridge will probably always sound better, or so I would think.

 

[Kingshead]

The quality of the vinyl also depends on where in the production run it was pressed. The top tier record stores had the earlier runs, the department stores not so much, and why they were cheaper. As the old saying goes, "You gets whats you pays for".

Martin

 

[luckydog]

From a 1955 copy of Audio Engineering "One of the advantages claimed for the moving coil type is that the coil moves in a uniform magnetic field, even though it may not be perfectly centered. Therefore, the displacement of the stylus from the exact center of the magnetic field does not introduce any distortion"

Not that I nessessarily agree but perhaps there is some validity to it?

Unfortunately, I doubt this one too ! Not the principle, which seems self-evident. But the extent to which it might apply in practice.

The issue is to what extent does field change over the range of displacement of the armature? Thing is, the armature moves a tiny tiny distance, for example for 1kHz @-12dB (0dB ref 5cm/s) perhaps armature displacement might be c 1-2um. And I suggest that over such tiny distances field change can be ignored in practice, and this is why harmonic distortion measurements don't show differences between LOMC and MM carts, as a class - other things being equal IMO. Whereas otherwise it should show up, methinks.

Just my 2p worth, as ever, but it's how I see it awprint:

 

[dlaloum]

I believed this too, but see Figure 9 in

"Optimizing the Dynamic Characteristics of a Phonograph Pickup"
AES Disk Recording Anthology, Volume 2, pp 213-220,
originally presented October 1965,
C.R. Anderson, J.H. Kogen, and R.S. Samson (all from Shure).

They simulated the tracking ability of a stylus with various amounts of compliance. (I am referring to the stiffness of the cantilever, not the suspension.) It turned out that unless it was also massless, an ideally stiff cantilever did badly, with a severe dip in tracking ability at resonance. Making the cantilever a little bit "bendy" fixed that.

Thank goodness, eh?

They did not remark on cantilever compliance's effect on frequency response.

Dave

Very interesting....!

This perhaps explains the preference of a number of top end cartridge designers for Boron over Ruby/Sapphire?

Boron is amorphous too as opposed to Ruby's Crystaline structure (most metal options including aluminium are semi-crystaline)...

I have kept wondering whether Boron or Ruby was better... AT, Ortofon and Lyra use Boron, SoundSmith uses Ruby (as has AT in the recent ANV model)...

According to those that have tried an ATN150ANV stylus in a AT150MLx body, it is a step up on the Boron.... (Subjective? Objective?)

:scratch2:

 

[dlaloum]

I have a question....

The whole purpose of the stylus is to extract the maximum information from the groove. So this is also highly dependant on the actual quality of the analog information cut into the LP.

The lathes or cutters that create the record therefore would determine this initial physical quality. Over the history of LP production I would assume these lathes/cutters increased in quality. So, my question is, would there not be ealier LPs that would not benefit from a MC cartridge because the LP does not have the information that would take advantage of this? Later LPs perhaps might as the initial cutting was performed by better equipment?

The better your needle can follow that groove, the more information you are going to extract from it.... regardless of the cartridge type.

The best cartridges get more from that groove than your average mass market cartridge... regardless of when the LP was made.

Some of the old acoustic recordings can sound quite remarkable when the signal is extracted using modern gear rather than a victrola....

 

[dlaloum]

MMs have small magnets, but some MIs have big, powerful magnets. If it weren't for cantilever in my XLM/ZLM stylus assemblies, they would probably damn near stick there if I tossed them at my fridge... And, I'll bet a Grado body would too. Maybe that's why I tend to prefer the sound of most MIs that I've heard to most MMs. Though I do tend to find Shures to be pretty decent, I don't care for AT's MMs. I have found that the MIs that I have heard tend to have a thicker, deeper, and more lush midrange.

It sounds like the performance of high-gain/high inductance coils in most MM/MIs may be their biggest shortcoming... Makes me wonder how some of the lower output MIs like the Grado Signature series would compare to the Prestige series... I have never heard one. I wonder how it would compare to the sound of LOMCs?

With their tendancy to pick up EMF and RF, I always wondered why Grado even made low output bodies. It didn't seem practical, but if what I am reading here is true, maybe they were on to something.

Try to find an old signature MCZ/TLZ/MCR body - those had lower inductance and output of 1.5mv rather than the current prestige series 4mV.

The styli (including cantilever and needle) for them are also equivalent to the current TOTL woodies....

There are a few other designs that were similar lower (as opposed to LOW) output, most of which are legendary : Signet TK9/10 Audio Technica AT23/24/25, Technics EPC100... I am sure there were others but I cannot think of any right now.

And there are the Stantering low output models...

 

[luckydog]

I believed this too, but see Figure 9 in

"Optimizing the Dynamic Characteristics of a Phonograph Pickup"
AES Disk Recording Anthology, Volume 2, pp 213-220,
originally presented October 1965,
C.R. Anderson, J.H. Kogen, and R.S. Samson (all from Shure).

They simulated the tracking ability of a stylus with various amounts of compliance. (I am referring to the stiffness of the cantilever, not the suspension.) It turned out that unless it was also massless, an ideally stiff cantilever did badly, with a severe dip in tracking ability at resonance. Making the cantilever a little bit "bendy" fixed that.

Thank goodness, eh?

They did not remark on cantilever compliance's effect on frequency response.

Dave

Good they acknowledged cantilever flex as a relevant phenomenum. I have a related model that follows on, similar to beam bending/transverse vibration stuff. Cantilever can be modelled as a transverse transmission line I find, with reasonable predictions. One aspect where I differ is that I don't find any need for vinyl elasticity, it can be negligible. But a practical corollary in all this is that certain commonly accepted ideas about what is theoretically good in cantilevers gets busted, I'm afraid. As I see it. awprint:

 

[dlaloum]

Well don't just keep us hanging then!

Explain!!

(just when I thought I had a handle on this cartridge thing... along comes LD.... )

 

[GrampaDave]

I saw at least one other paper in there that treats the cantilever as a bending beam.

"Mechanical Playback Losses and the Design of Wideband Phonograph Pickups",
Volume 2, pp 233-238,
presented October 1971,
James V. White (Department of Mechanical Engineering, Stevens Institute of Technology).

He illustrates the main bending mode and the torsional (twisting) mode. He calculates the theoretical resonance frequency for the main bending mode assuming the groove is rigid, then qualifies this by saying the groove is not perfectly rigid, therefore the resonant frequency is lowered somewhat. "To a first approximation, this support [the groove wall] can be thought of as being equivalent to a spring in parallel with a dashpot." He goes on to calculate the frequency response loss for various groove-wall Q's, but without including the cantilever bending - at that point he's treating the stylus as a point mass and a dashpot. I can't figure out why he brought up bending, since he doesn't appear to deal with it.

Another Anthology paper, which I can't locate now, shows two resonances, one being tip-groove, the other being cantilever flex. I will look for it if you need me to.

Paper after paper treats stylus-groove resonance in the context of deformation, and none say it's not so.

NOTE: I don't own the Disk Recording Anthology; I'm just borrowing it from a library. I have one renewal left, then it has to go back.

This particular printing of the Anthology has printing errors. The following pages were omitted from Volume 2: 186 187 190 191 194 195 198 199 202 203 206 207 210 211 214 215. If anyone can send me photocopies or scans of those specific pages, I will send them to the library along with the books when I return them, as an errata supplement.

Dave

 

[Ken Boyd]

I am wondering, it seems everyone has pretty much dismissed all the aspects that we thought were the reason that LOMC's should sound better. So now that all of those old myths have been disproved, can anyone here tell us just what the reason is that a LOMC is better liked over all the others. Or perhaps I should have asked what are the technical reasons, or physical attributes that make a LOMC better than the other types.

 

[GrampaDave]

My opinion: Self-stoking cycle. LOMC has more prestige -> people with money buy it -> it gets the R & D -> it's better -> more expensive -> more prestige -> people with money buy...

In other words, no interesting technical reason.

Dave

 

[nailer]

Is beryllium semi-crystalline? Is it more or less amorphous than aluminum?

 

[BayouTiger]

One thing I don't think I saw addressed is the "HOMC". Does all the goodness of the LOMC translate into the HOMC cartridges like the Blackbird or EvoIII? I'm always wondering how they get the output up from >.5mv to 2.5?

I've been wanting to try a LOMC, and have considered the Blackbird, but always thought it would be just a better version of the BPS and I like it OK, but enough to sink another $500 into one that was only slightly better but with the same characteristics.

 

[luckydog]

My opinion: Self-stoking cycle. LOMC has more prestige -> people with money buy it -> it gets the R & D -> it's better -> more expensive -> more prestige -> people with money buy...

In other words, no interesting technical reason.

Yup, that's pretty much what I conclude too.

.........Another Anthology paper, which I can't locate now, shows two resonances, one being tip-groove, the other being cantilever flex. I will look for it if you need me to.

Paper after paper treats stylus-groove resonance in the context of deformation, and none say it's not so.........

Yup, I know I'm quite possibly in a minority of 1 in not accepting vinyl deformation as significant. It was totally accepted back in the day, as you say. However, I think it's easy to see how tough it might be to tell apart from cantilever flex. Even the presence of 'two' resonant peaks is predicted by beam theory and transmission line modelling, without needing vinyl elasticity - there is a whole series of flexural 'eigen' resonances, only the first one or two of which are typically within the bandwidth of the cartridge engine. In measurements, the separation of those resonances closes matches beam/TL models IME, it seems to confirm cantilever flex as the origin IMO. So yes, I'd be very interested to see that paper if you can find it please, GD. I'm aware of other papers from back in the day which explain the 2nd resonance as 'tip resonance', but I really prefer that it is simply the 2nd resonant vibration mode of the cantilever. And then vinyl elasticity can/must be negligible, yet there will be two or more separate resonances predicted and observed (bandwidth permitting).

Just this is how I see it awprint:

 

[GrampaDave]

I will look for the papers that touch on groove resonance and get back to you.

 

[GrampaDave]

Sorry to the rest of you for the seriously off-topic excursion. I hope it's entertaining to you-all, besides LuckyDog and me.

All from Volume 2 of the AES Disk Recording Anthology except as noted. I marked the ones I consider of special interest with an asterisk.

Kelly, "The Fundamentals of Disk Reproduction", 1954, pp 20-27 see pg 23;

Barlow, "Limiting Factors in Gramophone Reproduction", 1957, pp 53-61 see pg 59;

*Kantrowitz, "High-Frequency Stylus-Groove Relationships In Phonograph Cartridge Transducers", 1962, pp 81-93 see pg 89;

White, "A Linear Theory of Phonograph Playback", 1971, pp 105-111;

*Hunt, "The Rational Design of Phonograph Pickups", 1962, pp 186-201 see pp 193-195. (But beware - the first printing garbles this paper, see Roys instead.) In this paper, Hunt refers (Ref [6]) to

*Miller, "Stylus-Groove Relations in Phonograph Records", Doctoral dissertation, Harvard University, 1950, issued as Tech Memo No. 20, Acoustics Research Laboratory, Harvard, Ref. No. PB 125454, Office of Technical Services, US Dept. of Commerce --- A brief summary of Miller's results was presented as

*Hunt, "Stylus-Groove Relations in the Phonograph Playback Process" which is not in the AES anthology but is in Roys, Disc Recording and Reproduction, as is "Rational Design" itself.

*Anderson, Kogen, Samson, "Optimizing the Dynamic Characteristics of a Phonograph Pickup", 1965, pp 213-220 see pp 218-219 but beware, other parts of the paper are garbled in the first printing.

There's more but I have to go.

 

[Ken Boyd]

My opinion: Self-stoking cycle. LOMC has more prestige -> people with money buy it -> it gets the R & D -> it's better -> more expensive -> more prestige -> people with money buy...

In other words, no interesting technical reason.

Dave

Not quite the response I was expecting.

 

[nailer]

Sorry to the rest of you for the seriously off-topic excursion. I hope it's entertaining to you-all, besides LuckyDog and me.

All from Volume 2 of the AES Disk Recording Anthology except as noted. I marked the ones I consider of special interest with an asterisk.

Kelly, "The Fundamentals of Disk Reproduction", 1954, pp 20-27 see pg 23;

Barlow, "Limiting Factors in Gramophone Reproduction", 1957, pp 53-61 see pg 59;

*Kantrowitz, "High-Frequency Stylus-Groove Relationships In Phonograph Cartridge Transducers", 1962, pp 81-93 see pg 89;

White, "A Linear Theory of Phonograph Playback", 1971, pp 105-111;

*Hunt, "The Rational Design of Phonograph Pickups", 1962, pp 186-201 see pp 193-195. (But beware - the first printing garbles this paper, see Roys instead.) In this paper, Hunt refers (Ref [6]) to

*Miller, "Stylus-Groove Relations in Phonograph Records", Doctoral dissertation, Harvard University, 1950, issued as Tech Memo No. 20, Acoustics Research Laboratory, Harvard, Ref. No. PB 125454, Office of Technical Services, US Dept. of Commerce --- A brief summary of Miller's results was presented as

*Hunt, "Stylus-Groove Relations in the Phonograph Playback Process" which is not in the AES anthology but is in Roys, Disc Recording and Reproduction, as is "Rational Design" itself.

*Anderson, Kogen, Samson, "Optimizing the Dynamic Characteristics of a Phonograph Pickup", 1965, pp 213-220 see pp 218-219 but beware, other parts of the paper are garbled in the first printing.

There's more but I have to go.

:scratch2:

 

[luckydog]

Thanks GD, will seek out those papers and digest, and PM thoughts. I have some of them already. Which reminds me I owe you an arm mass equation, which I'll dig out and PM. Actually I think considering cantilever flex is relevant to exploring LOMC/MM differences, not least because it suggests what one might look for as evidence of 'interesting technical reason', or lack of as may be awprint: