Hello Peterayaer,
An arc protractor works perfectly for one specific effective length only. This requires the cartridge to be moved (i.e. in the headshell slots) to match that length as precisely as possible. Any arc protractor designed for a particular arm cartridge combination(-your question above) should have taken actual measurements as a base for fabrication. Unfortunately, as described by Jonathan Carr, the sample to sample variation in cartridges(screw hole to stylus distance) often exceeds what could be seen as an acceptable tolerance (= below human eyesight limitations), resulting in grounds for error even if the same arm and cart model are used.
But the Null points on an arc protractor are valid regardless of the arc itself. It is only the circle segment line which needs to be re-drawn.
Cheers,
Frank |
Hello to everyone,
A few facts that proove some of the above wrong or, at least, serve as food for thought.
Actual Lyra cartridge measurements, mounting hole to stylus:
Dorian: 10mm
Helikon: 8mm
Titan: 9,5mm
Olympos SL: 9,3mm
Other examples showing that there was never a "norm":
Clearaudio Insider Ref. Wood: 8mm
EMT JSD6: 10mm
Koetsu Black Gold Line. 10,8mm
Decca Maroon: 11mm
Denon DL102: 12mm
I have encountered anything from 6 to 13mm(9,3mm the average so far)...
It is not true that the sonic difference between an arm of 9" vs 12" eff. length is solely attributable to the reduced tracing error related distorsions if the arm cartridge resonance with a specific cartridge is identical.
Simple proof: They will sound different even at the null points.
Some reasons for perceived(and measurable) differences in well known arms:
Higher load(reduced bearing "chatter") on the (knife edge)arm bearings(SME 3009 vs. 3012) due to larger counterweight mass.
Energy storage and release differences due to heavier counterweight on longer arm.
Torsional and bending stiffness reduced on longer arm since most manufacturers maintain the armtube diameter and wall thickness on their 12" arms, i.e. Moerch(likely for aesthetics and/or cost saving).
Consequently, the resonance spectrum(as in "ringing", not fundamental arm cart res.) of the longer arm differs from that of the shorter arm.
It makes no qualitative difference whether one approaches the choice of tonarm geometry from the eff. length or the pivot to spindle distance. The clear advantage of changing the pivot to spindle distance to adjust overhang is simply that one doesn't need to readjust VTF. There is also no risk to accidentally "turn" the cartridge while moving it forward or backward in the slots or while tightening the cartridge screws.
A mechanism allowing for the change of arm position(p-s distance) à la SME, LaLuce or my own is simply harder to produce than a slotted headshell. BUT(!!!), if one chooses this geometry alteration scheme, one also HAS to allow for changing offset angle, albeit within a very small range. Typically there is enough "slack" between cartridge screws and headshell holes for that and a separate, "turning" cartridge mounting plate offers even more room for adjustment.
The best protractor is the one that, for an individual, repeatedly results in an alignment close to perfect. So it is not a question of which protractor, but which person uses it(as long as the protractors are otherwise geometrically correct).
There is no "universally perfect" tonearm alignment. For each record, one perfect alignment exists, defined by the actual used/grooved area. To find the best compromise for YOU, you just need to examine/measure all of your records to come up with an average figure which will differ from IEC or DIN standard.
Many "old school" arms were used to play back singles and transcription discs at broadcast stations. The often questioned choice of an inner Null point near or at the LP "end" groove(r=53mm) makes sense when you want to playback singles(end groove r=48mm) without excessive tracing error related distorsions. Not recommendable if you sold all your singles at a yard sale years ago...
Bob Grahams pivot to spindle jig and hinged overhang gauge work well if you achieved what he wants you to achieve. But if your pivot to spindle distance is off due to poor machining skills(I've seen this more than once)you are repeating the resulting mistake with any new cartridge that you are mounting. Any maybe you have a different idea about the best alignment...
Any cartridge can only perform optimally if the alignment is as close to perfect as possible. In reality cartridge cantilevers/stylii are rarely at 90° angle to a line connecting the mounting holes. Any arm that doesn't allow for at least 2° of offset angle variation/alteration may limit the cart's performance. Don't get me wrong, I don't advocate sloppy cartridge manufacturing, but reality equals imperfection. And as cart suspensions age or with too much skating compensation, the problem gets worse.
Same for Azimuth...
The original question was never addressed. Do linear arm sound better across...
Short answer: yes, but only if you compared two otherwise identical arms. No commercial examples exists, so that debate is pointless.
Let me repeat that it is not correct to say that a tonearm has to have a fixed pivot to spindle distance to be regarded as having a "correct" geometry. If the arm features the required provision to alter the offset angle, it's just as "correct". It will have a "nominal" eff. length, the actual eff. length being a function of the cartridge in use. Arc protractors and Graham style alignment gauges(as good as they are)are therefore out...
One could derive a question from this thread's headline which is directly related to the original post:
What is the threshold for the audibility of tracing error related distorsions? - and: How "tolerant" are the various stylus profiles as tracing error increases?
Time for dinner...
Cheerio,
Frank |
Hi Axel and the rest of the "gang",
Here are the figures relevant for an SME V:
Let's say cart A has a mounting hole to stylus distance of 9,5mm, cart B is unusually "short" and features 6,5mm mh-s distance and finally, we have cart C, the Jaguar E-type of cartridges with 12,5mm mh-s distance
Required for Baerwald alignment(other alignments possible too):
A: 233,15mm eff., offset angle: 23,63°, pivot to spindle distance: 215,35mm, overhang: 17,79mm
B: 230,15mm eff., offset angle: 23,96°, pivot to spindle distance: 212,11mm, overhang: 18,04mm
C: 236,15mm eff., offset angle: 23,31°, pivot to spindle distance: 218,61mm, overhang: 17,55mm
So all that is required is enough slack to rotate the cartridge by little more than 0,3° either way and slide the base forward or backward about 3,5mm, both of which are easily achieved.
Even the "tightest" headshell holes leave enough room and before anyone takes out a reamer to mess with his SME, just reduce(every household needs a small lathe ;-) the diameter of ONE cartridge mounting screw towards the head, leave the bottom part where the thread engages with the cart alone and you have enough leeway for even badly skewed cantilevers(better just send such carts back to the manufacturer).
And many cartridges have cantilevers that are off by more than the above mentioned 0,3°.
Have fun guys...
Frank |
Hello Axel,
Believe me, I'm anal about cartridge alignment...
If the generator isn't mounted dead center inside the cartridge housing and you can't shift it by 0,3mm, then you'll have to rotate it and slide it forward or backward, depending on the generator being closer to the right side or the left side of the cartridge body.
BUT, the magnitude you described will cause an error so small as to make it near impossible to correct for it reliably and repeatably.
As an example, let's assume your cartridge generator is so far offset(sideways) that it causes the actual offset to be reduced by 0,5°(a larger figure than what can possibly result form generator displacement). Your eff. length is shorter than "normal"(let's say, by 0,3mm), if you have that cart mounted in an arm with fixed holes.
Here's what you get(SME V specs as a base):
Unaltered:
eff.L.: 233,15mm, Null points 66 and 121, average distorsion 0,42%
Now it gets interesting: distorsion at 61mm(inner groove area): 0,54%
Reduce the offset due to shift by 0,5°:
eff. L.: 233,15mm, Null points 71,4 and 111,8mm, average distorsion 0,389%
Distorsion at 61mm: 0,95%%
Additional compensation of eff. length due to shift, -0,3mm:
eff. L.: 232,85mm, Null points 71,8 and 111,1mm, average distorsion 0,393%
Distorsion at 61mm: 1%
Draw you own conclusions...
My take on this: Most people can make out a 0,3mm difference when aligning a cartridge. VERY few can tell the offset angle(sometimes referred to as "zenith") being off by any less than 1-2° !
It's the inner groove area where this really comes into play.
Cheers,
Frank |
Hello Dertonarm,
Since my record collection numbers about 10000 with more than 60% being classical(and about 1/2 of those dating to 1965 and earlier), I know exactly what you are talking about.
I chose singles as an obvious example to make a point about tonearms used on broadcast turntables.
Yes, the IEC norm exists(the AES merely recommended it), but, as you said, was never universally adapted. We just have to deal with what's in existence. TP4 as a norm wasn't that big a success and a norm for 1/2" mount carts would limit cartridge designers in the future. If everyone would agree on a reasonable range for several cartridge dimensions, not just the mounting hole to stylus distance, but i.e. the height of the cart too, the consumers might be benefitting from it.
You are comparing yourself with Galileo? I hope you're not implying we're all out to crucify you , yet still live in the dark ages.
I for one like a civilized discourse, but not ego battles. So please come back anytime..
The remark about "increasing sales" is inappropriate and unfounded. If you have something to say, say it straight.
Ein schönes 1.Mai-Wochenende wünscht
Frank |
Hi again,
Dertonarm:
"Dear all, after we have now learned that finally all parameters of the tonearm geometry are variable, nothing can stop us now entering analog heaven."
Yup, if your tonearm offers the key parameters to be varied, you can indeed implement standard alignments(B,L,S) or even move the Nullpoints according to your own preferences(better do the math first...)
"If any of you will still suffer inner groove distortion....... well, don't worry that happens. Move your tonearm, rotate the cartridge. If it distorts now at the run-in grooves? Hey - be flexible. Times may be hard, but modern."
Cynicism doesn't help. Applying math does.
Best,
Frank |
