a moving-coil cartridge is an absolute minimum requirement: even the best moving magnet will not be capable of the measuring the extra information in

[JP]

I mean to directly calculate it by for example measuring the total mass and estimating how its spread around the components, even better of course by dissecting it (would mean a lot of expensive garbage unless it is already damaged). An indirect method to estimate it through the first resonance mode frequency would presuppose that the stiffness of the suspension is know which I guess is rather not.*

*The stiffness and thus also the effective mass could be determined though by measuring the resonance frequency also with an additionally added known mass.

IIRC, this is an interesting read from back in the day: https://www.worldradiohistory.com/Archive-All-Audio/Archive-Audio/70s/Audio-1978-03.pdf#page=58. At the very least there's a chart at the end where they estimated mass from dims and materials and then calculated ETM. That alone should highlight why it's unlikely ETM numbers are mass numbers.

At HF you'd be dealing with the impedance of the suspension rather than the stiffness. Regardless, is the suspension going to change the resonant frequency rather than just damp it?

https://www.vinylengine.com/turntable_forum/viewtopic.php?f=19&t=30049 is a though-provoking thread that independently lands on the same methods as the audio article, but the interesting part is where the cantilever is modeled as a mechanical transmission line.

 

[MAB]

Most people who are into vinyl think that the lower mass of MC improves tracking because there is less inertia. Is this untrue?

According to the data JP provided, in general you are correct on effective tip mass:

Specifically, within the samples in the list, yes Technics EPC-(P)100CMK4 wins the race to lowest ETM (0.055 mg vs. 0.059 mg). MM vs. MC alone doesn't limit low ETM.

I am unclear about the correct application of ETM to trackability, except I think we also need to know the compliance.

 

[JP]

^ I'd throw anything above 0.5mg out. Even at 0.5mg we're talking some absolute dinosaurs.

 

[thewas]

IIRC, this is an interesting read from back in the day: https://www.worldradiohistory.com/Archive-All-Audio/Archive-Audio/70s/Audio-1978-03.pdf#page=58. At the very least there's a chart at the end where they estimated mass from dims and materials and then calculated ETM. That alone should highlight why it's unlikely ETM numbers are mass numbers.

Thank you, that's more of what I had in mind.

At HF you'd be dealing with the impedance of the suspension rather than the stiffness. Regardless, is the suspension going to change the resonant frequency rather than just damp it?

That's why it wouldn't make sense to measure it at high frequencies as then the damping force of the suspension dominates over its elastic force.

 

[JP]

Thank you, that's more of what I had in mind.


That's why it wouldn't make sense to measure it at high frequencies as then the damping force of the suspension dominates over its elastic force.

Except that we're talking about cantilever resonance, which is going to be north of 10kHz. For the 0.055mg Technics we're talking around 70kHz.

 

[krabapple]

So much nonsense. WTF is "The Quietus"? Sounds fucking ridiculous without looking.....

Online hipster* pop culture mag dating from the oughts. Definitely not a place to go for audio science.


( *would have sworn it was from Brooklyn, but it's actually from England. Which is arguably worse, in terms of the potential for serious-faced nonsense about sound)

 

[beeface]

The Quietus is great, but they're better off sticking to music, not audio equipment

 

[thewas]

Except that we're talking about cantilever resonance, which is going to be north of 10kHz. For the 0.055mg Technics we're talking around 70kHz.

No, to calculate the effective mass / rotational inertia of the needle system we are talking about the first solid mode of the movement in the suspension which will be much lower, the one you are talking about is the first bending eigenmode.

 

[JP]

No, to calculate the effective mass / rotational inertia of the needle system we are talking about the first solid mode of the movement in the suspension which will be much lower, the one you are talking about is the first bending eigenmode.

Show me - give an example.

 

[thewas]

Show me - give an example.

What example, this is basic physics.
https://physics.stackexchange.com/q...thod-for-measuring-the-moment-of-inertia-work

 

[JP]

What example, this is basic physics.
https://physics.stackexchange.com/q...thod-for-measuring-the-moment-of-inertia-work

That explains some of the disconnect. We're measuring within the working constraints of the given system. To reiterate more specifically in regard to the information provided, the resonance that was used to calculate ETM was the resonance due to the ETM against the compliance of the vinyl. Perhaps this treatment compiled from original work at the time will help convey how it was approached from the engineering perspective: https://pspatialaudio.com/analogy.htm.

 

[thewas]

What do you mean with ETM?

 

[SIY]

What do you mean with ETM?

Effective tip mass.

 

[thewas]

That explains some of the disconnect. We're measuring within the working constraints of the given system. To reiterate more specifically in regard to the information provided, the resonance that was used to calculate ETM was the resonance due to the ETM against the compliance of the vinyl. Perhaps this treatment compiled from original work at the time will help convey how it was approached from the engineering perspective: https://pspatialaudio.com/analogy.htm.

Yes, that would be the indirect method from the compliance, I was talking also about the direct determination of the effective mass, like here https://pspatialaudio.com/effective_mass.htm

 

[JP]

Yes, that would be the indirect method from the compliance, I was talking also about the direct determination of the effective mass, like here https://pspatialaudio.com/effective_mass.htm

I understand that. Great for tonearms, but rather impractical for cantilever assemblies. Also keep in mind that while it's an indirect method to measure ETM, it's a direct method to measure the primary issue low ETM was solving for.

 

[RayKay]

I was originally taken in by the title of this thread, i.e., the old MM/MC argument. But what I find more interesting is the discussion that centers on how to determine Effective Tip mass or ETM. If I understand correctly, @thewas you advocate the direct method which is by dissecting the actual individual parts and summing their contributions, and @JP you advocate the indirect method which is by measuring the resonance “due to the ETM against the compliance of the vinyl”. I think both of you are correct, and I will explain. Please allow me to preface with a heuristic example.

Let’s say we have two identical stylus assemblies – same magnets (MM) or same coils (MC), same cantilevers, same suspensions, same damping, and (important!) identical mass diamonds that are mounted the same way. The only difference between the two is that one diamond is conical and the other diamond is some micro-line cut that has a greater contact surface area than the conical. OK so far?

By using the direct method, both assemblies would have the same ETM as measured and calculated in a lab.

By using the indirect method, the larger contact area of the micro-line stylus assembly would be expected to yield a mass-to-vinyl-compliance resonance frequency that is higher than with the conical. This would infer that the micro-line assembly has an ETM that is lower than the conical assembly, but we know from the direct method that it does not.

Being a retired engineer, I intuitively feel better with the direct method. The outcome is clear. A directly determined ETM number can stand on its own, and can be verified by an independent third party lab. Trouble is, I suspect that the instrumentation and expertise needed to directly measure the actual individual tiny parts of a stylus assembly is few and far between.

On the other hand, I feel persuaded that the result from the indirect method is more useful, practical, and more accessible to the average experimenter. But this can only true if a standardized test record is used. The formulation of the test record vinyl, the elasticity, damping characteristics, etc., etc., can affect the outcome. A standardized test record would ideally control all those variables. The indirect method might yield a useful number, but it’s not necessarily a true indication of the actual ETM. An analogy might be the difference between your local weatherman announcing the actual temperature on the thermometer and then announcing what the “feels like” temperature is, which factors in humidity and moisture evaporation on your skin.

IMO, it would be helpful to adopt a new initialism for indirect method “ETM”. Instead of “ETM”, how about calling it Effective Tip Mass Frequency or “ETMF”, or something else. It might even make sense to make it a unitless value. This of course only relates to resonance “due to the ETM against the compliance of the vinyl”, which I take it is desirable to be above 20K. In the 1978 Audio article Shure engineers relate ETM and ability to maintain groove contact (trackability) at various stylus velocities, and factoring in groove modulation amplitude within the audio frequency range.

Ray K

 

[JP]

I wasn’t advocating, I was just speaking within the context of how it was done.

If you read the VE link above you’ll find that the vinyl compliance theory never fully explained what was observed. This is where LD proposed a mechanical transmission line theory - that’s it’s not the vinyl yielding, rather the cantilever bending.

 

[EJ3]

I know very little about the science of vinyl. Can you explain why MM's are not inferior to MC's when it comes to tracking accuracy? Most people who are into vinyl think that the lower mass of MC improves tracking because there is less inertia. Is this untrue?

I do not know if this will help (I hope that it does but one never knows):

Magnetism and Electricity​

Working in the early part of the nineteenth century, Ørsted noticed that, when electricity flowed in a wire, it created a magnetic field which could be detected by a small magnetic compass. Later, it was discovered that, if the wire was wound into a coil, it greatly increased the magnetic effect.
Michael Faraday (left) reasoned that if electricity could cause magnetism, then it ought to be possible to transform magnetism into electricity. So he wound a coil of wire and experimented with a magnet to see if he could detect any current induced into the coil of wire.
He noticed that, only when he moved the magnet near the coil, did a current flow in the coil of wire. If the magnet was held still, no current was induced. That’s the crucial point: electricity will create magnetism but only changing magnetism will make electricity¹.
James Clerk Maxwell formalized Faraday's discovery into what is now called Faraday's law which is written like this,

where E is the electromotive force, ΦB is the magnetic flux, and k is a negative constant which also incorporates the number of turns in the coil. The d(x)/dt part just means, the rate of change with time.
So E (the electromotive force, or voltage) generated in the coil relies on three things: the strength of the magnetic flux (ΦB); the speed (velocity) with which the flux changes (d(ΦB)/dt); and the construction of the coil, especially the number of turns of wire in the coil (k).

 

[thewas]

That law shows how voltage is induced in a changing magnetic field which is the principle of how most cartridges work, but doesn't help more to determine the effective mass.

 

[Frank Dernie]

I don't think there have been very many truly scientific inquiries into the "science" of vinyl. Everything was commercial products and the engineering that led to them. Lots and lots of trade secrets and methods. Unfortunately the vinyl "renaissance" is even more rife with this kind of bool sheet than it was the first time around.

I worked for Garrard in the 1970s.
There was plenty of science engineering being done then and plenty of knowledge about how it all worked and its strengths and limitations.

For example they had a laser doppler vibration measuring rig (I think doppler is correct, it was the first I had ever seen) in the basement on a big block of suspended concrete to avoid the earth's vibration. One of the record player prototypes had a top deck mode with the arm mount area near an anti-node which meant the cartridge body could be excited and, since the transducing elements don't "know" whether it is the stylus of "stator" that is vibrating this could give spurious output. By clever interpretation of the deck-plate modes the engineer in charge of this rig worked out where a hole could be punced in the pressed steel plate to move the anti-node away from the arm mount - result much better performance for negligible cost in an item that would retail at around £15 back then.

What changed was the onset of subjective reviewing, probably perpetrated by Jean Hiraga, this admitted technically ignorant reviewers into the place and they were unable to separate the propaganda and marketing from engineering fact and probably by the mid 80s almost everything to do with playing records was forgotten or ignored.

It is actually still stupidly full of steady state reasoning being applied to dynamic systems which is just wrong - for example claiming the more rigid a pickup arm is the better it traces the groove, easy for a techniclly illiterate individual to believe but completely wrong.

If anything it is even worse now with the re-birth and ludicrously priced styling excercises.

I left the HiFi business to go Formula 1 racing full time in 1976 and I haven't read any technical papers about record players which give more insight into the engineering of them than was already extant then. Read contemporary B&K papers, we used their test records and measuring equipment, the science was well understood even if engineering targets with such a wide frequency range were hard to achieve.

It has got worse, if anything, facts ignored or not understood, reasoning false and so on. It would be very depressing if LPs were still the main source of recordings for music lovers.