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?

You really can't. Don't worry, the range of acceptable resonant frequencies is fairly wide, you have not materially changed the effective mass unless your shim is quite heavy. You will still be in the right ballpark. Do your mods and enjoy!

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.

Well, it's only been six years. My experience is that the primary resonance of the moving system rarely falls in the audio band. Sure it can cause problems but it is pretty forgiving of minor mismatches.

What colors the sound far more are the secondary, bell like, resonances that fall within the audio range. Gently tap your tonearm with a pencil with the volume control at a quiet level. Start near the pivot point and tap several times moving out to the headshell. At one point the ringing is far more pronounced, and this point is usually a third of the way from the pivot. In the past we used to damp this resonant point with a ring of Blue Tak being sure not to over damp the arm - a subjective decision.

I think that the gent is both adding mass and damping the arm tube at the same time. For that matter he's using lead tape which may also deter RFI in that part of the arm. So there's more going on here than just mass tuning. Why not give it a try if you're a tweeker as it's completely reversible. Good luck.

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.