How does tone-arm mass impact performance?

The relationship between the arm and the suspension of the cartridge can be modeled like a spring. The springier, more compliant, the suspension, the less mass is desired in the arm to bring the total resonance of the system to the optimal point. Likewise, if the suspension is stiffer, more mass is required in the arm to keep the total system resonance at an appropriate frequency.

Interestingly, the weight of the arm is not of importance. What is importance is the effective mass, which takes into account the distance that the mass is from the pivot point. An extra gram at the headshell increases effective mass much more than a gram near the pivot point.

If the resonance of the system is too high it can be excited by low freqency tones within the music. If it is too low, warps will cause the resonance to be excited.

In your example, yes a one ton arm and one ton counterweight could play a record, provided that the compliance of the cartridge was suffienciently low. This is kind of theoretical though.

Commercial arms vary from somewhere around 6-7 grams effective mass all of the way up to 30 grams or so. Most medium mass arms, like the Rega, Audioquest/Jelco, Technics, etc. fall into the 9-10 gram range.

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.