Arm effective mass confusion

[anubisgrau]

1200 stock arm eff.mass is 12g without headshell (according to manual)

The headshell weight is 7.5g

What is the effective mass of the arm with the headshell? How do you calculate this?

[Barry]

1200 stock arm eff.mass is 12g without headshell (according to manual)

The headshell weight is 7.5g

What is the effective mass of the arm with the headshell? How do you calculate this?

Gordan,

The effective mass of an arm is the moment of inertia of the arm, about the stylus point, divided by the square of the length between the stylus and the arm pivot point. Since the headshell is close to the stylus, a reasonable approximation (and one good enough to calculate the LF resonance frequency) is to simply add the mass of the headshell to the effective mass of the arm (without headshell); that is 7.5g + 12.0g = 19.5g.

Regards

[anubisgrau]

Gordan,

The effective mass of an arm is the moment of inertia of the arm, about the stylus point, divided by the square of the length between the stylus and the arm pivot point. Since the headshell is close to the stylus, a reasonable approximation (and one good enough to calculate the LF resonance frequency) is to simply add the mass of the headshell to the effective mass of the arm (without headshell); that is 7.5g + 12.5g = 19.5g.

Regards

Thanks - so this is a general approximation that could be used for a Technics arm? Likewise - the effective mass with a Sumiko (12g) headshell would be 24.5g?

[Barry]

Thanks - so this is a general approximation that could be used for a Technics arm? Likewise - the effective mass with a Sumiko (12g) headshell would be 24.5g?

Hi Gordan,

Yes, it applies to any arm and the effective mass of the Technics/Sumiko combination will be 24g (12g for the arm without shell + 12g for the Sumiko shell). Sorry I mis-quoted the effective arm mass (without shell) in my last reply.

Are you going to use the Denon 103?

Regards

[anubisgrau]

not in technics arm - i gave up on 1210 because i've restored my kuzma stabi 2 from the 80s and it's, pardon my opinion, a bit better sounding engine than 1210, at least with a level of mods i had applied.

so denon 103 plays in stogi - not the happiest combo, i may try to add some weight.

another deck i've just got yesterday - stabi S, stogi S, benz micro MC gold. an excellent combo for not much dosh on a s/h market!

[DSJR]

The techie arm seemed to me to be extremely low mass for such a device when I handles a "bitser" a few months back. I'd respectfully suggest the older Technics arms fitted to this deck's ancestors were higher mass...

[Rare Bird]

1200 stock arm eff.mass is 12g without headshell (according to manual)

The headshell weight is 7.5g

What is the effective mass of the arm with the headshell? How do you calculate this?

That arm should be 12g inc headshell !!

[sc_ita]

I don't think so. The eff mass of 12g does not include headshell. 12 g is the mass of tonearm alone. Otherwise, the value of 12-7.5=4.5g would be really too low for an alluminium/titanium tonearm.
Bye.
SC

[Marco]

Ciao Siro,

No, Andre is right.

The Technics arm has an effective mass of 12g including the headshell, which is 7.5g on its own.

If it were as you were indicating, the effective mass would be 19.5g, which of course it isn't.

Headshell weight is a critical part of the overall effective mass of any tonearm :)

Marco.

[sc_ita]

:mental: I read again the Tech manual, and it effectively says 12g, excluding cartridge, while nothing is said about headshell. Thus, by logic, Marco and Andre should be right. My only concern regards the result of the subtraction: 12-7.5=4.5g of effective mass, which is quite low :scratch:

Thanks,
Siro

[Marco]

Yes, but the subtraction doesn't apply in use because one would fit the headshell, therefore its individual mass would always be included in the overall equation, and thus affect how the cartridge behaves accordingly :)

I've never tried using the stock Technics arm without its headshell, but I guess that for DJs and other users alike, it would give a whole new meaning to the term 'scratching'! :eyebrows: ;)

Marco.

[sc_ita]

:lolsign:
I have jusy found a service manual where it is clearly stated that the Tech has a "low 12-gram effective tonearm mass (including headshell, without cartridge...)".
You are right!
Now, I go immediately to add the 7.5g of lacking mass to my stock arm (slightly modded).

Thanks again, and good night,
Siro

[Marco]

Non c'e' problema - era una grande piacere! :cool:

Marco.

[DSJR]

I thought the arm seemed overly-lightweight as standard. IIRC, it's ancestors were rather more "solid."

[Marco]

I presume by that you mean the armtube itself, Dave? Perhaps; I'm not sure.

We're getting bogged down a bit with the headshell thing, though... The fact is, the headshell is an integral part of the arm and also the arm's effective mass.

Normally headshells are fixed, so the component parts of a tonearm, in terms of their individual mass, don't come under such scrutiny! ;)

An overall mass of 12g is perfectly adequate, and is actually greater than that of some tonearms currently produced by so-called 'hi-end' manufacturers... Of course, in many circumstances, reducing mass is an essential part of a tonearm's design principles. Heavier is not necessarily better.

Much depends on the partnering cartridge as to how ideal or not an arm's effective mass is. It's certainly a significant bonus with detachable headshell arms that this can be 'tuned' to suit the needs of individual cartridges, depending on which headshell is fitted. You can't do that with an RB300, for example :)

In my experience also, low-compliance cartridges (such as the Denon DL-103) prefer mass applied at the headshell end, than on the armtube and associated assembly, as this is the 'business end' which affects the performance of the cartridge most in terms of its need for extra mass.

In actual fact, the DL-103 works best on a fairly 'lossy' arm of medium-mass as standard, fitted with a heavy headshell. This is precisely why the Jelco SA-750D works so well with the 103, when partnered with an Audio-Technica LH-18 or one of the heavy-duty NOS magnesium headshells I use. Excellent results can also be obtained with some unipivots, such as Hadcocks, providing that their headshells have been suitably 'bolstered'.

Marco.

[anubisgrau]

well, it has always been regarded as a ultra low mass arm.

[Chivas]

Is the Jelco 750D's effective mass 20g with the headshell then? What is the mass of the Jelco headshell?

Cheers