Effective "effective mass" primer for dummies

I once asked the same questions here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=2981&highlight=
The answers are no simple read but they do explain most of your queries
Peter

The VTF is not really affected by vertical effective mass, as long as the record is flat. IF there is a warp or change in vertical plane during play, then the effective mass can have an effect of compressing the stylus as it rides up the warp, and increasing VTF momentarily on the warp, and then being slower to come down the back side of the warp, causing lighter VTF on the back side. Lighter effective mass is better for this warp tracking activity, as it responds faster to changes in the record surface.

Optimizing the effective mass of the tonearm for the cartridge being used (mass/resonance matching) is the primary purpose of using tonearms of certain effective mass with certain cartridge characteristics. The purpose of my HiFi mod is to improve the matching of Rega and OL arms to lower compliance cartridges than they are optimally designed to handle. It increases horizontal effective mass for keeping the cartridge centered over the groove during play, with cartridges of low compliance that would normally drive the arm into unwanted movement laterally. It does not affect the vertical effective mass, so warp tracking is not changed from the standard version. The purposes of effective mass of a tonearm are to ensure that the arm is not driven into unwanted movement and stays centered over the groove when the cartrige is being excited by the groove modulations in the record, AND to ensure that any resonance in the arm/cartridge matchup is happening at a frequency which is least damaging to the audible listening range.

In many tonearms, the designers seek to make the effective mass equal in the horizontal and vertical planes. In other tonearms, there is more effective mass in one plane than the other. These are the decisions of the designer. In an arm with equal effective mass in both the horizontal and vertical plane, there needs no differentiation in the description or specs of the effective mass. In arms with different effective masses in the vertical or horizontal plane, many times only the vertical effective mass is in the specs. Only the Dynavector 507 series arms and the OL arms make a big promotional issue out of the two planes of effective mass, that I'm aware of.

Vertical effective mass can be measured with a scale.
Or it can be calculated.
Same with horizontal.

Hi Goatwuss,
high effective masses are not bad and low ones neither. The influence of warps is not different for high and low effective masses, as long as the resonance frequency is the same.

So there must be the right dynamic compliance for a certain effective mass to attain a resonance frequency which is high enough to ensure stable tracking.

Your headshell rests right upon yr cartrdge. So the headshell- influence on the stylus suspension is higher than a part located closer to our arm- pivot. The vitual sum of all these mass-influences seen from the tip- location is called effective mass.

Basically we talk about a mass- spring- combination here. Our tonearm/ cartridge combination should work like a suitable seismic filter, which isolates the relative movements of our tip relative to our headshell. It isolates these movements from warps, modulation- rubbish coming from the groove and energy coming from the floor.

At a modulation- frequency of 8 Hz we still find rubbish and warp- energy coming from the vinyl- groove. The real silent region is from 10 to 14 Hz. So there we must locate our resonance frequency, independant of the current effective mass.

Mass is not the same thing as force. Just imagine that a planet in space may have a very high mass but perhaps could not experience any force working upon it. But try to stop it's movement with your own hands and you will not end the job alive, I fear.

But a higher effective mass is not a bad thing on it's own, as long as there is a low enough dynamic compliance to keep our resonance frequency high enough.

This effective mass can be calculated after the estimation of the current resonance frequency.

The calculation of the effective mass of an arm can be done as follows too:
Calculate the sum of all specific products (armpart- mass) x (part - to- pivot- distance)^2 of each part of the tonearm and divide this product by (effective lenght)^2.

Appr, one year ago we have read an interesting topic at this forum dealing with resonance frequency. Look for it using the search- window.

In the library of the Vinyl Engine Forum an interesting english- written danish AES- paper by P, Laadegaard can be found which I see as the best one upon this mattter published ever.
Jan.

Wow, thanks for the helpful responses!