[neobop]

Hi Don,
That's interesting.  Weight applied at the headshell will almost add directly to eff mass, depending on location in relation to the cart.  Adding mass further down the armtube will also increase eff mass, but not in direct proportion.  Ever see arms with sliding collars to adjust mass/compliance? 

Effective mass is also a function of distance.  That's the reason weight at the end of the arm is more affective.  Adding weight to the counterweight will usually reduce eff mass because the counterweight gets closer to the pivot.

For the benefit of any here who might be members of VE, and want to remain a member, I think we should stop talking about this touchy subject of their membership (policies).  On any forum we participate by the owner's consent and often don't know the reason for dismissal.
neo

 

[Grbluen]

Gotcha. The reason why I became curious is because adding mass to the headshell would trend to affect the vertical resonance figures, but adding the mass to the pivot would not. I've been accustomed to approaching cart/arm matching in the horizontal plane. I've yet to explore the ramifications in the vertical direction. Should be interesting to say the least!

[dlaloum]

Maybe I need to read through the VE thread - but it seems to me that adding mass in line with the pivot point (along the line of motion) will if it is equally distributed around the axis of motion, affect both lateral and vertical equally...

it is only if you have asymmetrically positioned mass that things start varying between the two (lateral/vertical) - the prime examples being CW's below the pivot, sometimes with lateral "outriggers" - or even the Longhorn mods... (which are well below the axis, being down at the bottom of the cartridge, and then having outriggers)

But the closer you are to the pivot point, the less effect and you will also tend to be closer to all the axes - and therefore effect will be more likely to be equal in both lateral and vertical directions.

Am I missing something? (time to check out the VE thread...)

bye for now

David

[Grbluen]

You are correct. When I spoke of adding mass at the pivot, I really meant the pivot area.
The mass is actually in the pivot area, but below the pivot by quite a distance. I'm actually adding mass to the ' knobs ' on the azimuth stabilizing ring.

[dlaloum]

So what you are talking about is not in fact aimed at increasing effective mass, but instead increasing stability while minimising effective mass impact...?

[Grbluen]

No, the attempt was an attempt at increasing effective mass. Maybe I need to re-read that thread. My understanding was that the effective mass could be increased by adding weights in this manner. I've not actually made the measurements using the resonance tests, because I don't really have a large selection of weights.

[dlaloum]

Thread name? Link?... thanks

David

[Grbluen]

Took me awhile to find it. Threads were merged, and some posts redacted (including my own).
I think it's mentioned about halfway down the page. The poster mentions a Rega mod. for increasing effective mass.

 http://www.vinylengine.com/turntable_forum/viewtopic.php?f=18&t=63449

[dlaloum]

Cannot find that thread... found this : http://www.vinylengine.com/turntable_forum/viewtopic.php?f=32&t=58300

[Grbluen]

I'm sorry David, I didn't bother to check the link. The thread is titled SME 3009. The first post is on the 06-Nov 2013. The first post is by Jas. Split topic.

[dlaloum]

Are we talking about this sort of thing:
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1032024188&read&keyw&technics&&st0

[dlaloum]

We probably should move this to a seperate thread -

The idea is really interesting, and appears to be related to the quote from Shibata with regards to lateral effects on the cantilever... there are also comments about needing to alter the anti-skating used after this mod.

This may be one of the few mods I could do on the electro-damped JVC arm....

[Grbluen]

Sounds good!
That post from AudiogonE, was exactly what I was trying to express.
Are you going to start the new thread?

[dlaloum]

Thread started...

[Grbluen]

Neo,
I've been thinking a little more about vertical compliance. Let's assume that I don't have any problems with footfalls or record warps (actually, I don't). The only other reason that I can come up with for being concerned with the vertical compliance would be VTA/SRA. Could it be that optimizing the compliance match in the vertical plane would help to maintain the SRA?

[neobop]

Neo,
I've been thinking a little more about vertical compliance. Let's assume that I don't have any problems with footfalls or record warps (actually, I don't). The only other reason that I can come up with for being concerned with the vertical compliance would be VTA/SRA. Could it be that optimizing the compliance match in the vertical plane would help to maintain the SRA?

Good question.  I think it's a mistake to consider lateral and vertical compliance exclusively as two separate things.  A mono record is cut so that excursions, signal modulations are all lateral.  That's why a true mono cart has no coils that modulate the vertical component.  The cantilever will still have vertical movement and that output mixed with the mono signal could cause phase or possibly even frequency errors.

A stereo record groove is cut at an angle, it is not completely lateral or vertical.  Tracking is three dimensional.  It's convenient for the sake of analysis, especially with linear arms, to think of or calculate in these two separate planes, but in actual tracking they are two parts of a whole. 
Maybe you saw the Karma thread where Scotty calculated the compliance of his Maestro (15cu) with a test record and known mass/weight?  The fact that he could do this (and get it right) with vertical cu has implications well beyond SRA. 

At resonant frequency there's a peak.  Even if there's no signal at that frequency the peak has implications at multiples of that frequency.  The arm/cart is resonating and it could effect output.  That's a big part of the reason for the recommended range of resonant frequency - below the audio band and above the warp region.  Another reason is to match springiness with arm eff mass.  You don't want a high cu cart having to drag around a heavy arm.  Put an old 50cu MM on a 30g arm and the cantilever could collapse.  Transient response suffers big time.  If it tracks,  a low res frequency might be preferable to one in or near the audio band.  In that case you're guaranteed to have modulation and intermodulation distortion.

There might be ways to mitigate res freq affects like a damping trough.  That will limit the peak and spread it out over a wider band.  It's easy to overdo it though and wind up with smoothed over mush.  I personally think it's a mistake to mismatch arm and cart and use damping as a band aid. 
neo   

 

[Grbluen]

So, in a perfect world, the horizontal and vertical compliances would match identically?

[neobop]

Sometimes they do.  When they don't, they're usually close.

There are mechanical aspects of any transducer that must be considered -dealt with.  I don't know about perfect.  It's all relative.
neo

[dlaloum]

So, in a perfect world, the horizontal and vertical compliances would match identically?

Not necessarily - there was a discussion on VE a couple of years back about the Ortofon OM Serato S-120 - although it is a DJ oriented cartridge, it is interesting because it intentionally has differing compliance (and damping) in the vertical and horizontal axes...

There was some discussion of the theoretical advantages of this approach... but honestly I cannot recall the reasoning and the outcome. (although I do recall that it was applicable within the HiFi domain and not just in the DJ domain)

bye for now

David

[neobop]

We talked mostly about MM carts with dynamic compliance specs at 100Hz.  There are some great Japanese MCs from smaller companies like the Miyajima example from another thread, also at 100Hz.  I don't know if all the Japanese high end manufacturers use 100Hz.  What about Koetsu, Kisiki, Miyabi etc. ?

To determine actual 10Hz cu, the easiest thing to do is ask other users.  Other than that, VTF range will give you a clue.  If the cart tracks at 2g or less, chances are its cu is more like 15 than 6, but this isn't exactly foolproof.  Usually the idea is to determine this before you purchase a new cart so a test record won't help.  Your dealer will know what range of arms are appropriate.  Sometimes a cart mfg. will provide that. 

If anyone has specific info on this important subject, please feel free to share.
neo