Tonearm massematics (aka bollocks)

Effective mass isn’t quite the same as mass, its more of a square on the distance.

Maybe. I doubt it’s a huge effect, unlike the vast difference you see with linear trackers.

Agree, but the distances is the same in both planes, no?

Might not be, you see the arms with the big heavy bell like thing over the pivot with the weight hung low, mass around the pivot very close horizontally, but could be an inch or two on the vertical.

Imagine a weight suspended from a handle via a compliant spring. You shake the handle & the weight may move a bit but won’t follow the movement of your hand. You replace the spring with a steel bar. Now you shake the handle & the weight moves following your hand. It’s the cartridge’s compliance that determines how much vibration will be transmitted into the arm. The Decca doesn’t have much compliance.

Unipivot arms don’t really react in the same way to being shaken as a gimballed arm might. Decca cartridges might well behave better in such arms.

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Yeah, fair enough I. Was thinking about it after I posted and yes, that would seem to make the V larger than the H. Opposite of what you get with air arms.

Yeah, I agree.

Do you have any stats on the effective mass of linear trackers? I’m trying to get my head around how it would work. It’s effectively clamped so the entire arm would move for the horizontal resonance, isn’t it? So it’s not a moment at all

Yeah, like on this one

Still, miniscule difference I bet.

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Its not a moment, but its still a sprung system. (cantilever is the spring)

In the case of air arms, the whole sled generally moves in the horizontal, while they have piddly short arms tubes which moves in the vertical. Certainly the Terminator is like that. Others are different, though.

Dynavector is another that would be like a linear,

Some waffle on there about it.

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Yep.

Yeah but basically different maths - just a weight on a spring, so it’s actual mass (horizontal) rather than effective mass (vertical), yeah?

The maths is the same. The numbers are different.

I suppose it’s the same maths once you introduce the concept of effective mass, yeah

Sometimes effective mass == mass, sometimes it doesn’t. Where it doesn’t, you need to work out the effective mass, which requires a bit of additional maths. :smile:

P.S. both Both H&V it’s effective mass that’s important.

Massematics FTW

I have always considered effective mass a wishy washy term anyway, not sure its used in the same way outside of tone arms. Always seen it a little pointless trying to work it out, much easier to stick on a test record and see where the arm has a fit.

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Yep. Essentially impossible to work out, easiest way is to measure compliance and resonance, then back calculate.

How much would effective mass change for the cm or so that the cartridge can slide back and forth in the headshell?