Headshell weight

[paulfromcamden]

I have a bunch of randomly acquired headshells and they vary significantly in weight - from a reassuringly chunky Fidelity Research model to a featherweight ADC job.

What difference does the weight of the headshelll make?

Is this about matching to cartridge and/or arm? Or is something else going on?

 

[Tony L]

Arm mass and cartridge compliance are key parameters in getting good tracking over warps, avoiding ‘cone-flap’ in speakers etc. Different weight headshells can help optimise things a lot.

PS Nice little chart here:

Total effective mass on one axis (arm, cart, mounting hardware etc) and on the other the cartridge compliance. Aim for the middle of the blue zone!

 

[Craig B]

I have a bunch of randomly acquired headshells and they vary significantly in weight - from a reassuringly chunky Fidelity Research model to a featherweight ADC job.

What difference does the weight of the headshelll make?

Is this about matching to cartridge and/or arm? Or is something else going on?

WRT the chart that Tony posted above, keep in mind that fitting your lightest or heaviest headshell combined with moving the counterweight either closer or further away from the arm pivot for the same downforce (for a given cartridge mass) will alter tonearm effective mass. SME knew what they were on about with their tonearms here, listing this as 'average effective mass' as all depends upon weight distribution either side of a point of rotation (i.e. I = M * R^2). For example, contrast an SPU-G or -G/T @ 30g up front with the largest companion weight out back vs. a lightweight Shure MM in the perforated S.2 shell with standard or reduced mass (depending upon arm variant) weight out back. One workaround for this, particularly in those cases where the counterweight remains the same, is to take the tonearm's published effective mass with supplied headshell fitted then add or subtract the difference in headshell mass to or from the cartridge plus hardware figure.

 

[Vinny]

The effective mass of a tonearm is not actually mass at all, but inertia, and inertia is obtained by multiplying the mass of a component by the square of the distance between the centre of mass of the component and the pivot - headshell, armtube, and CBW are the major/significant components of all toenarms (the yolk/bearing assembly is generally reasonably symetrical about the pivot, so has essentially no distance between centre of its mass and pivot and the CBW stub-shaft is generally (very) small with a CoG close to the pivot).

Beacuse the centre of mass (also called centre of gravity) of the headshell is so far from the pivot, the contibution of its inertia to the total inertia (effective mass) of the tonearm, is disproportionately large due to that distance being squared in the calculation.

Headshell mass is very important/has a major influence on your tonearm.

NOTE - due to similar logic, using a heavier CBW reduces effective mass/inertia of the tonearm. Taking an extreme and unrealistic example - double the mass and you will halve the distance pivot to CoG, so one quater of the contribution due to distance, mutiplied by doube the mass.

Inertia is a measure of how resistant a body is to being disturbed either from rest or continuing in its steady motion - a measure of "stability", if you like.

 

[eisenach]

You can see why CD caught on !

 

[Vinny]

You can see why CD caught on !

Although precious few current tonearms have changeable headshells, so life is simpler, and no-one actually needs more than a simple chart in cases where the headshell is fixed, and no knowledge of the maths/reasons.

There is a quick and dirty way to measure effective mass of tonearms, posted on VE - I have used it to measure a Hadcock, which gets quoted as being numerous and wildly varying numbers and hasn't so far as I am aware, ever been posted by the manufacturer.
I got in the order of 6-7g - very low indeed.

 

[Vinny]

Note that even the "abbreviated" units for effective mass chosen by the hifi community/manufacturers, are confusing.

The units are (if memory is correct), actually gm^2. They are certainly a mass multiplied by the square of a distance/length. In real life engineering it would be kgm^2

 

[Big Tabs]

What difference does the weight of the headshelll make?

This interests me as well - but the graph thingy that Tony L has put up means nothing to me without some explanation of how to understand it..

No Crystal Clear English in the hi-fi world.

I do find it irritating that no one explains anything in a way that can be understood.
That would take away their power base though.

 

[Vinny]

the graph thingy that Tony L has put up means nothing to me without some explanation of how to understand it..

You don't actually need to understand it beyond the fact that cart' compliance interplays with tonearm effective mass and that there is a "sweet spot" (actually a "sweet band").

If you use an arm with changeable headshells, you could calculate what differences they make to effective mass of the tonearm, but otherwise just need to appreciate that adding weight to the headshell adds effective mass.

 

[Big Tabs]

You don't actually need to understand it beyond the fact that cart' compiance interplays with tonearm effective mass and that there is a "sweet spot" (actually a "sweet band").

If you use an arm with changeable headshells, you could calculate what differences they make to effective mass of the tonearm, but otherwise just need to appreciate that adding weight to the headshell adds effective mass.

what is ‘cartridge compliance?’

 

[Vinny]

Note also that any change in CBW position after changing headshell weight is essentially irrelevant.

The position of the CBW is determined by the maths of a simple lever/"balance beam", which uses distance, not distance squared. The CBW is so heavy and close to the pivot that it's change in position, and hence inertia, is slight.

 

[Vinny]

what is ‘cartridge compliance?’

It is a measure of the "springiness" of the cantilever suspension. It is quoted for all cart's, somewhere - look for dynes in spec's.

 

[matt j]

what is ‘cartridge compliance?’

How hard or soft the suspension is, is how I take it. Carts vary quite a lot with compliance, so matching that to the mass of the arm is generally considered a good idea, although in practice there are quite a few examples where it doesn't seem to make much difference!

 

[andrewd]

what is ‘cartridge compliance?’

Compliance is the opposite of stiffness. A cartridge with a stiff, rigid ‘suspension’ has low compliance, and benefits from more weight on the headshell. A cartridge with soft suspension has high compliance and benefits from lighter headshells.

Unfortunately the standards for reporting compliance are confusing as f*ck. Compliance can be reported as ‘static’ or ‘dynamic’ and you need to know the conversion factor to convert from one to another.

 

[matt j]

As with many things, where multiple countries are involved multiple ways of measuring things comes into play as mentioned above. It can be a bit of a minefield. I think us, the Japanese and Americans all do it differently, the Yanks obviously measure it in micro pounds per furlong or some other 17th century nonsense.

 

[Vinny]

In real life?

An awareness is all that is needed, plus a pair (or even one) ear(s) and eye(s).

Does it track OK? Does it sound good/better/worse?

 

[vacuum_tubes]

How hard or soft the suspension is, is how I take it.

Same here, I think of it as a car, if the car has hard suspension (low compliance) and low mass it will not absorb bumps and bounce down the road, if it has soft suspension (high compliance) and high mass it will bottom out and be syrupy. The suspension and weight of the car needs to be balanced.

 

[Avon]

Could someone please explain the difference between static and dynamic cartridge compliance?

Also, Japanese manufacturers quote compliance at a different frequency to the rest of the world (?). The graph above has no mention of that frequency. Could someone please explain that?

 

[Vinny]

Just to cover everything...
The effective mass of a fully working tonearm is significantly more than that quoted by the tonearm manufacturer due to the inertia of the cartridge - a few grammes, but a long way from the pivot - it will add in the same order of inertia as the headshell.

Obviously this can't be legislated for by the tonearm manufacturer, so it is completely ignored.

Worth bearing in mind if using a very light or very heavy cart'.

 

[Vinny]

Could someone please explain the difference between static and dynamic cartridge compliance?

Also, Japanese manufacturers quote compliance at a different frequency to the rest of the world (?). The graph above has no mention of that frequency. Could someone please explain that?

There is no way to convert static to dynamic or allow for frequency for a cart' for which you have no comprehensive design/engineering data. It is a complication and PITA, but you just have to ignore.
If still curious and interested enough, Wiki is your friend, or if REALLY keen to understand, you need to join a maths or physics forum.

You will need to search in relation to springs.