How does tone-arm mass impact performance?

Thanks for the feedback.

I checked out Vinyl Engine and Cartridgedb websites, and it apears that the 2M blue is a good match for the technics sl-1200.

But I have made some minor changes such as, I replaced the stock headshell wires with heavier gauge silver wire, I added a shim between the cartridge and headshell to allow for an easier azimuth adjusmtent and finally, I am planning to rewire the arm, all this will certainly result in a different effective mass from the one listed in the generic DB.

So my question now is, how can you determine the actual effective tonearm mass of your customized tonearm?

This is a question specifically for Viridian -

I was checking out this guy's 1200 MOD page - http://audio.innerurban.com/2010/06/adding-mass-to-technics-tonearm.html

What exactly is this person trying to achieve? I was reading your post about where the mass is important and it seems this guy is doing it opposite - adding it close to the pivot point. Maybe you can critique or explain what they are doing, since they are not making it clear in their blog post.

Unless your mods add more than a gram of mass to the system, it is unlikely that you've done much to effect the interaction of cartridge compliance with effective mass. There actually IS a way, two methods in fact, to measure tonearm effective mass, that I have seen in print. One or both are to be found on Vinyl Asylum. I've never done it and don't necessarily recommend that you should do it either. Not worth the considerable effort required. You can way your shim for azimuth as a separate item, to estimate what its effect might be on effective mass, if that makes you feel better. But listening to music works, too. By the way, "effective mass" really should include the mass of the cartridge, the screws, and any shims, etc.