[Wayner]

I think this topic is the most understood, and perhaps (to a point) over-rated topic in the vinyl world. Perhaps it's time to get some discussion going on with it. Maybe some will have examples of great cartridge/arm combos and other horrible stories when things go wrong.

 

The chart above is a nice one that I found. The vertical numbers (to the left) are resonance frequency, the horizontal numbers (underneath) is tonearm/cartridge mass. The curved lines are cartridge compliance ratings in increments of 10 from 10 to 50.

The thing you need to know is the effective mass of the tonearm. This is where there will be lots of controversy, but as I was "learned", it is the weight of the arm, with the counterweight off,  with the VTF set to max ZERO (edited for correctness, thanks Bob), (thus neutralizing any effect of a dial-in VTF. This can be done with the cartridge installed and would be the total arm/cartridge mass. The entire assembly is then weighed on a digital scale (do not rest the entire weight on the stylus, as you probably will destroy it). Put stylus guard down or remove the cartridge and weigh it separately, and the value will be your arm/cartridge weight.


So, if we have a tonearm/cartridge mass that is 25 grams, and we are looking for something in the middle of the accepted resonance frequency (10 hz), we then can see that a cartridge with a compliance rating of 10 would be the best choice.

All right, lets get this thing going.......

Wayner

[chester_audio]

I think it is important to the the discussion of tonearm/cart pairing to understand that this parameter only regards the actions at the cartridge end. The capability of the arm to truly control the cartridge has much more to do with the quality of the bearing(s). This is part of the reason why the arm/cart resonance formula is just a guide. It can help tell if you're way off, but there are many examples of pairings that work very well even though the numbers might make one suspicious.

I hope I explained myself well enough to be of help to someone.

[Minn Mark]

has much more to do with the quality of the bearing(s).

So..is this a reason for the popularity of uni-pivot arms?

Wayner, can you or someone explain the dotted lines on the graph, that is, the reason(s)  for upper and lower limits for reasonance freq?

Mark

[BobRex]

Minn, the dotted lines demark the "ideal resonant frequency".  Go above the top line and you are into the area where the combination will resonate with record warps.  Below the bottom line and you are into bearing rumble.

Wayne, given that the majority of tonearms aren't dynamically balanced (spring loaded), I'm not quite following your logic.  I'm good with the first part, where you remove the counterweight.  That will work with 99% of the arms.  But I think you have the second part backwards.  Every dynamic arm I've ever played with (SME, Lustre, FR) had a zero position which deactivated the spring.  This was typically the Min position.  The Max position would maximize the tracking force and would result in a false (too high) mass reading.  When measuring for arm mass, I don't think you want the spring's influence in the picture.

[Wayner]

Yes, Bob, I did not explain that correct. The thinking is to remove any spring "counterweight" effect to the arm, which would give you a false reading on the true weight of the arm, via the weight dial (like on a Rega RB300) for example.

Wayner

[chester_audio]

Minn Mark,

I'm not sure I understand your question. Speaking in general terms, the psi seen at the pivot of a unipivot makes it damn near impossible to have any chatter. Uni's can suffer from instability and there are many examples of such. Yes, the bearing of a unipivot is still very important.

[BaMorin]

It is a fairly good graph, but either the compliance of my cart is mis-marked, or the EF mass of my arm is mis-marked.  My cart is listed @20cu.......my arm is listed @ 11gr. the weight of my cart, attaching screws and lead wires come in @ 7.2 grs. according to the chart, I should be in the slightly below 8hz range. My Shure test album, at 8hz is rock steady. at 10 hz i get some jiggle, at 12hz it is back to rock steady. What isn't in the chart is Vertical and Horizontal friction numbers of the bearings. Which is probably affecting the base "assumed" numbers.  As far as arms go, Linn arms have a fairly high friction coefficient at the bearings listed as < 50mg.  I've seen numbers on other non-unipivot arm of  <5 mgs.  A unipivot would have near zero measurable friction numbers.  The friction numbers have to affect moment of inertia due to what is known as "moment of motion" from static to kinetic. And, inertia is really what the EF mass rating of the arm is.

[BobRex]

Here's a classic example of compliance mis-match and what can go wrong. 

Back in the late '70s and early '80s a competing store (actually a big box warehouse - SILO for those of you in the Philly region) used to sell Technics tables with Sonus carts.  The Sonus was a high compliance cart and never really mated well with the Technics arms.  Without fail, the cantelever would collapse within six months, and the customer would be back in for a new stylus.  After a couple of rounds, the number depending upon the patience of the customer, the customers would come to us complaining about the failed carts.  We'd explain the problem, even show them on either the Signet analyzer or the Ortophon computer, and then sell them a more suitable cart.  Problem solved and we got a customer for life.

[Wayner]

Well, I think the reason why I started this thread was to bring to the surface, some of these issues. The whole concept has many folks confused, and I thought a group discussion might clear up some issues.

I don't think that there is one gospel set of data that will solve any of these types of mismatch problems, but I think the intention is to get into the ballpark with the compatibility issues.

If anything, it may prevent someone from making a gross error matching a cartridge with a tonearm.

[TheChairGuy]

Silo!  I remember them well from 1981-82 (Lancaster Avenue in Bryn Mawr, PA)

John

[*Scotty*]

Wayner,I may have misread the instructions,but it looks like weighing the counter-weight separately and then adding its mass to rest of the parts involved was left out of the instructions.
 The resonant frequency has to be calculated from the this total,the counter-weight cannot be left out of the sum of the total mass in the oscillating system.
Scotty

[Wayner]

The counterweight is on the other side of the bearings and has no effect on total mass.

Wayner

[BaMorin]

The counterweight is on the other side of the bearings and has no effect on total mass.

Wayner

That is correct, but it does affect inertia.  And I believe that formula is never listed in relation of CU and arm mass.

[hotrod]

 Keep in mind that Romy may be slightly off his rocker,but I can't help to agree with some of his findings and suspisions when it comes to how manufactures come up with their compliance data.
 My Denon DL-S1 on a 12'' Jelco(26g) using the HFN test record come up with a resonance of around 8-9Hz where according to the data tables it should be around 5Hz.
 To add fuel to the fire of Grado users,here is a good read.http://www.goodsoundclub.com/Forums/ShowPost.aspx?postID=1868#1868

[dlaloum]

I agree - the total mass is actually looking at inertial effect, and the total effective mass includes the counterweight.

LuckyDog on VinylEngine published a very usefull spreadsheet in which he embedded the mathematics required.... you weigh the headshell (if removable) the arm without counterweight, and then the counterweight and the cartridge.

http://www.luckydog.demon.co.uk/images/EMC.xls

Plug the values in, and the calculator provides a reasonable estimate of effective total (ie inertial) mass.

There was also a thread on a lenco site that went into all the maths involved, from which I pulled the formulae and built a spreadsheet .... but LD's spreadsheet was easier to use and the results were very similar.

When looking at audible variations (as opposed to theoretical discussion and signal tone measurements) - we are listening to the tone arm as a vibrational system.

This involves the arm tube, the headshell, the counterweight (all individual components that may or may not have their own vibrational issues and possibly damping) - also the little rubber ring between a standard headshell and the arm does have an impact on the sound - for the same reason... ie it is another vibrational factor.

With tonearm / compliance matching, we look to minimise the resonance, and position it where it does the least harm (10Hz).... but it is still present, and so are its harmonics, and of course the associated IMD across the frequency spectrum.

So controlling this vibration, the harmonics and the IMD is part of this picture.

There is a very good article in the Boston Audio Society Newsletter (B.A.S. Speaker) Vol 3. No 4 - January 1975 where Leigh Phoenix wrote an extensive (and mathematically complex...) article on tonearm damping. - part of the outcome of which was the now relatively common arm paddle with oil trough mechanisms....

Also http://www.aes.org/e-lib/browse.cfm?elib=3295 an early AES paper by Lipshitz...

The important summary bit being:
"A model of the pickup arm-cartridge system is considered which includes both stylus assembly and arm pivot damping. The impulse response of this system is considered when the stylus is subjected to a sine-squared displacement. This enables the evaluation of the behavior of the system when excited by both infrasonic (that is, warp) and audio impulses. It is shown that no signal choice of parameters can provide ideal behavior at all frequencies of interest, but that the best compromise involves both arm and stylus damping. This shows up a clear deficiency in most current high-quality record-playing systems, in which no arm damping is used. Equations are furnished to enable further analysis in any specific case."

I would also refer people to the (legendary) Technics EPA100 tonearm brochure

http://downloads.nakedresource.com/ve_download_centre/index.php?technics/technics_epa100_brochure.pdf

Of interest is the information with regards to damping allowing the tonearm to match a wide range of cartridge compliances...

There is other information out there... but to summarise what i have dug up over the last 4 months during which I have been reading up on this...

1) Arm Mass/ Compliance determines the resonant frequency, and practical considerations (rotational speed, likely warp frequency, footfall sound frequency) lead to an optimal resonant frequency of around 10Hz
2) Damping in its various forms is a requirement for good results.
3) Depending on the damping mechanisms used (and the frequencies within which they are effective) the cartridge/arm resonance may(!) become relatively irrelevant...

Contrary to some theories / myths - a totally friction free arm is NOT optimal, as there is then no mechanism for damping. So some relatively simple undamped (or internally/minimally damped) designs achieve very good results by having bearings designed to provide a small amount of friction -ie: damping (difficulty being achieving friction without stiction... but there we wander into engineering solutions).

Also related to this issue (and coming back again to damping) - counterweights with complex (or simple!) Vibration control/absorbing mechanisms... (rubber layers, varying materials, or for a very sophisticated example read the EPA100 brochure I Linked above) - Headshells which use various vibration absorbing mechanisms (magnesium construction, elastomer absorbing layers as used in AT LS12 and others), Tonearms that have internal damping - or are moded with material around the outside, and of course various oil damped and electro magnetically damped designs.

When I run a frequency sweep through my system, and analyse it with an RTA (FFT) - as it goes through the low frequencies a range of harmonics can very clearly be seen extending right up the midrange...

At some point I intend to experiment with different settings for the arm damping (electrically damped servo arm on my JVC QL-Y5F) as well as various headshell and other treatments to see whether some of these "parasitic" vibrations can be controlled....
But right now I am still working on understanding cartridge loading / frequency / phase behaviour... so I will come back to some of these other aspects a little (months?) later.

bye for now

David

P.S. Low and High compliance designs require different solutions as the Low compliance tend to push a lot of energy into the arm - so a lot more damping is required at various frequencies and of various types. - But the arm has a higher mass "budget" - so it is easier to do!
The High compliance designs work best with low(er) mass arms - so also a lower damping mass budget - but they also feed less energy (vibration) back into the arm....

[dlaloum]

Keep in mind that Romy may be slightly off his rocker,but I can't help to agree with some of his findings and suspisions when it comes to how manufactures come up with their compliance data.
 My Denon DL-S1 on a 12'' Jelco(26g) using the HFN test record come up with a resonance of around 8-9Hz where according to the data tables it should be around 5Hz.
 To add fuel to the fire of Grado users,here is a good read.http://www.goodsoundclub.com/Forums/ShowPost.aspx?postID=1868#1868

Hi Hotrod,

another thing to watch out for... the Cu measurement we are talking about is @10Hz.... most japanese manufacturers quote compliance @100Hz.

My personal rule of thumb is that you need to multiply the value by between 1.5 and 2 to get an estimate of the value for 10Hz from the 100Hz value. (this is just a rule of thumb - and some cartridges simply don't match this model.... but it seems to fit a lot of the time)
Basically compliance at 10Hz will be higher than at 100Hz - but the exact relationship is complex.

This might be the cause of your discrepancy...

bye for now
David

P.S. - my "rules of thumb" for compliance conversion (as imperfect as they are..) are:
to convert Static compliance to dynamic compliance @10Hz - halve the value
To convert dynamic @100 to dynamic @10 - multiply by 1.75

[Wayner]

The counterweight actually impedes inertia. Mass in motion tends to remain in motion, mass at rest, tends to remain at rest. The counterweight keeps the tonearm from following the stylus motion by nulling the movement. While it does have implications on vertical movement, and side to side movement with non-concentric LPs, (off-center hole), I think it's effect may be minimal, since it is on the other side of the bearings.

Wayner

[dlaloum]

You are making my point for me - thank you

Mass at rest tends to remain at rest (yes that is called inertia)

And the issue with effective mass is in fact inertia.

The fact that the CW is on the other end of the balance point does not change it's impact on inertia.... but don't take my word for it.... there are plenty of physics texts that cover this topic!

The physicists of the VinylEngine community went into this in awfully mathematically geeky depth on the tonearm mass thread out there....

Just because something is balanced does not mean it is easy to shift (overcome the inertia)

With a high compliance stylus, after it hits a warp the arm goes up and back down.... and the high compliance springing does not have the "strength" to stop the motion - it has to fight the inertia generated by both sides of the balance point. (hence repeated reports of ultra high compliance styli - ADC XLM - collapsing...)

Total effective mass - is "effective" because it is in fact talking about inertia....

bye for now

David

[TheChairGuy]

A warm hello to any newbies that have stopped by in this topic at an increasingly busy Vinyl Circle.

WARNING: This topic is mostly for experienced vinyl users only.

If your eyes are glazed over by the above banter of physics and engineering concept about cartridge compliance - pay it little mind

Yes, it's good stuff to know, but if you choose not to....you can still get remarkably good sonics from a vinyl front end system.  Talk to your dealer, brick n mortar if you are lucky enough to have one near you or online, and ask them for cartridges available that match your tonearm & deck.

Or, ask us here at the Vinyl Circle your specific question - there's lots of seasoned hands ready and willing to help 24/7.  Unlike digital technologies, analog ones tend to have a degree of tinkering in the mechanical realm to make things 'perfect'.  But, perfect is NOT required to get really soul-stirring sound from vinyl

Those of us that have been tinkering with phono cartridges for 30+ years find compliance issues interesting as we are boring down on some of the finer details of getting vinyl sound reproduction....but if you're a newbie, please mostly disregard until you have a comfort level with your new'ish vinyl front end.

Our unrepentant love for vinyl cannot continue without new enthusiasts.  Once you get your turntable dialed in with 90% of the details right, you'll know why most of us describe vinyl as the highest resolution source - and then feel free to get involved in conversations like this to further your knowledge to unlock more from the medium.

John / Facilitator / The Vinyl Circle

[dlaloum]

Thanks John

Excellent point/aside....

I especially like the bit where we are "Boring"....

And would like to add to your point, I purchased my first TT (of my own that is..) around 81/82, and until last year, never tinkered or messed with it (or my subsequent TT) at all - just listened to music.

Now that I am being a bit of a bore.... or is it that I was a bit bored... I started getting involved in trying to "perfect" the system......

The first part was listening to music - the second may improve that listening, but is fundamentally a different and seperate hobby....

bye for now

David