Truly straight underhung tonearms for hifi use

" The product page from the Sakura Systems website, U.S. importer of RS Labs, says, “most of today’s tonearms come with the offset angle to minimize tracking error. The distortion caused by tracking error can easily be explained geometrically and easy to solve geometrically by giving an offset angle to the arm, but the actual effect of the tracking error on the sound is less serious than that of the strong inside force caused by the offset angle. The inside force changes dramatically by the frequency and amplitude of the signal, and a static canceling system is not effective enough. Overly concerned on tracking error, arms with offset angle and forget the forest by just focusing on the tree. Straight arm has tracking error, but it is far less damaging to the signal than the strong inside force caused by the offset angle "

IMO there's some truth to what's said above, I just don't know which is the more damaging compromise in the end. I'd still be inclined to prefer getting the geometry right, but I'm not so sure anymore :)

I don´t know but I don´t see this as really correct.

It might be better to look at what is driving the needle, which is normal forces. That means that there will be vectors that is pushing the needle in all different directions.

So for inner groove walls with large modulation angles the force that pushes the needle will be small, and at a certain angle the needle will loose contact with the outer wall, because the needle has to go somewhere if the force to push the needle is too small.
For outer groove wall the force to push will be much larger.

This is not the same as the skating force changes, this force is very slow and mostly depending on an average friction force. Even with compensated skating force, the driving force will be different. (We know how overcompensating AS can make tracking of difficult test tones easier)

So for a totally straight arm with no offset we will still to some extent have variations in driving force, depending on the length of the arm, but to a much lesser degree.

I think.
 
Last edited:
It had a straight underhung tonearm.

The manual was quite specific about cartridge mounting and achieving the correct underhand etc..

It always sounded better than my correctly aligned SL1200

I tried an elliptical stylus as an experiment, Ortofon OM10, despite the fact that the alignment was visibly WAY WAY off at the beginning and to a lesser extent at the end of a record it sounded good, no discernible distortion or any other obvious artefacts.

I'm not saying that it was a HiFi table or anything, just that the sound did not seem suffer due to the funky arm.

Where did the manual say to put the null point, if I may ask?
Do you have the distance from the spindle?
Thanks,
 
I don´t know but I don´t see this as really correct.

It might be better to look at what is driving the needle, which is normal forces. That means that there will be vectors that is pushing the needle in all different directions.

So for inner groove walls with large modulation angles the force that pushes the needle will be small, and at a certain angle the needle will loose contact with the outer wall, because the needle has to go somewhere if the force to push the needle is too small.
For outer groove wall the force to push will be much larger.

This is not the same as the skating force changes, this force is very slow and mostly depending on an average friction force. Even with compensated skating force, the driving force will be different. (We know how overcompensating AS can make tracking of difficult test tones easier)

So for a totally straight arm with no offset we will still to some extent have variations in driving force, depending on the length of the arm, but to a much lesser degree.

I think.

Hard to tell from a distance. If the cantilever line coincides with the pivot then torsional forces are reduced. Skating is said to be so low compensation is unnecessary. As always, VTF is the primary force that holds it in-groove.

I think you just have to try it and see what happens.
 
Where did the manual say to put the null point, if I may ask?
Do you have the distance from the spindle?
Thanks,

Sorry, I may have over stated things a little.

The manual simply states that the cartridge must be square in the headshell and that the stylus point must be 50mm from the tonearm locking collar to achieve optimum performance of the anti-skip tonearm, or something like that.

So null points are never mentioned.
 
Hard to tell from a distance. If the cantilever line coincides with the pivot then torsional forces are reduced. Skating is said to be so low compensation is unnecessary. As always, VTF is the primary force that holds it in-groove.

I think you just have to try it and see what happens.

Yes good point, the torsional forces are also reduced.

My point was that as the 'driving' forces varies this can effect how smoothly the needle moves in the groove. Friction and damping of the needle must be overcomed with very different forces, with an offset arm.
 
Sorry, I may have over stated things a little.

The manual simply states that the cartridge must be square in the headshell and that the stylus point must be 50mm from the tonearm locking collar to achieve optimum performance of the anti-skip tonearm, or something like that.

So null points are never mentioned.

Thanks for checking. That 50mm setting coincides with a null somewhere.

VE has a free protractor called Chpratz. It's just a straight line with a calibrated grid from 60 to 150mm - the groove area. This would be useful for these settings and experimentation. It's also useful for alternate alignments on conventional arms.
One of the reviews of the Viv arm put the null around 100mm from the spindle. That's 5mm less than the middle of the groove area, not 5mm less than 1/2 the distance from the spindle. That's an important distinction.
neo
 
I did a little sketch and it seems to me an arm between 14"-16" and a nullpoint at about 80mm would be rather good.
 
Of course, when you get out to 16", an offset arm becomes very good too, assuming you can deal with the mass and dynamic issues.
 
For what it's worth, with the Viv Lab Rigid Float, which is a straight arm (and a bit funky in other ways as well and costs $4000+), it seems many people actually prefer the sound of the shortest 7" version. The designer begun with a really long tonearm, but kept making it shorter and shorter, until settling down on offering it as 7, 9 and 12 inch versions (if I recall correctly). But that's subjective and it's possible it's a resonance / rigidity thing, or just that the increased harmonic distortion pleases the ear or what ever...
 
Hello muovimies,
Have you made any progress on your truly-straight tonearm experiment?
Interested in following this.
Thanks, DM
 
I had a Vestax PDX3000

It had a straight underhung tonearm.

The manual was quite specific about cartridge mounting and achieving the correct underhand etc..

It always sounded better than my correctly aligned SL1200

I tried an elliptical stylus as an experiment, Ortofon OM10, despite the fact that the alignment was visibly WAY WAY off at the beginning and to a lesser extent at the end of a record it sounded good, no discernible distortion or any other obvious artefacts.

I'm not saying that it was a HiFi table or anything, just that the sound did not seem suffer due to the funky arm.

Interesting topic. I have Stanton STR8-150 (straight, underhang) and Technics SL-1200 and to me the straight arm sounds better although people keep telling it's wrong and will ruin my records. I originally got Stanton to play only shellac/78 rpm but now prefer to use it for vinyl as well (of course with different cartridge/stylus).
 
"The biggest problem was channel balance and extraction of fine detail at the outer grooves, where the alignment was most off"
This pretty much sums up the main reason of aligning the stylus ( and cantilever) as accurately as you can to the null points of a specific geometry.
If you start with your actual tonearm mounting distance to within 0.5mm accuracy and generate your efffective length from this... to a *known* geometry..Baerwald, Stevension, Rega, Heybrook etc, then alignment to the two null points on that effective length arc will automatically set the offset angle to what it *must* be in relation to the first two dimensions.
Both dimensions and the offset angle are fixed in relation to a specific geometry..
Get one wrong and the rest are also wrong.
Get all of those right... and you have reduced to a minimum one of the variables that can obstruct your turntable rig from extracting the cleanest signal possible..
It is better to do this first stage correctly... before that signal has to overcome the other hurdles without losing too much fidelity in the process... bias, tracking force, vta, signal cable quality, speed accuracy, stylus quality, cartridge quality, vibration etc...

Deliberately ignoring accurate geometry alignment to begin with , seems to defeat the main purpose of a transcription quality turntable..By this , I mean that even something as humble as a Pioneer PL12D , when well aligned...is as good a transcription device as anything you'll find, up to and including a technics 1210 or Rega Planar 3. .And, it is probably a bit more immune to external vibration than both anyway...which is a good thing..( yes I've tinkered with all all three in the past).
Stick to the basics if good sound quality is most important... they've had a long time to work the variables out and refine them for stereo playback... might as well toe the line and enjoy the music..
 
Last edited:
btw,
A badly aligned cartridge will do more than just increase audible distortion..it will also permanently erode those precise fine details that you are trying to reproduce... maybe not so quickly if using a spherical stylus which sits a little higher in the groove walls than a true elliptical and misses out on high frequency detail anyway... but a badly aligned elliptical can ruin a good pressing in a single play...you just wont notice it until you hear that record being played the next time by a properly aligned cartridge.
 
Muovimies' impressions exactly matches that of this review of the RS A1 sonic qualities. "Dynamic, punchy, relaxed".....

What's not to like?
 
Last edited:
btw,
A badly aligned cartridge will do more than just increase audible distortion..it will also permanently erode those precise fine details that you are trying to reproduce... maybe not so quickly if using a spherical stylus which sits a little higher in the groove walls than a true elliptical and misses out on high frequency detail anyway... but a badly aligned elliptical can ruin a good pressing in a single play...you just wont notice it until you hear that record being played the next time by a properly aligned cartridge.

How do you define "badly aligned"?
 
The ‘improvements’ being observed with ‘truly straight underhung arms’ in this thread and elsewhere are related to the geometric effects of eliminating the offset angle. Conventional pivoted arms include an offset angle to minimize tracking error and "overhang" the spindle on their inward swing. There is a not-so-obvious and undesirable consequence of the offset angle, besides skating. When the arm and cartridge ‘bob’ sideways, such as can occur during jarring bumps or footfalls, the left and right sideways deflection of the stylus that occurs from horizontal motion of the cartridge is dynamically decreasing and increasing the effective length of the arm. This translates into a fore and aft motion of the stylus tip, or ‘scrubbing’, along the groove. The amount of horizontal stylus displacement that gets translated into ‘scrubbing’ is mainly proportional to the Sine of the offset angle (Sine of typical 24 degrees = 0.4), and is a constant ratio. There is also some dynamic length altering or scrubbing effect from the horizontal stylus displacement about the cantilever pivot, but this is small in comparison to that from the offset angle, and this contribution approaches zero for very small amounts of cantilever deflection (Sine of 0 degrees = 0). The lion’s share is from the offset angle.

Look at this sketch from Shure of an offset pivoted arm:

_a horz vibr 400x445.gif


http://shure.custhelp.com/app/answers/d ... b0ZiWWs%3D

This scrubbing motion of the stylus tip along the groove causes frequency modulation (FM) of the signal in the groove. This form of FM distortion has the same audible effect as flutter in a tape recorder or a movie film projector. The warble-like sound of flutter in a malfunctioning tape deck or old projector is a familiar and easily recognizable audio effect. Unlike tape decks or projectors where the effect is somewhat constant due to problems in the mechanism, the flutter effect with FM distortion in disc playback is typically transitory. The effect can be demonstrated with a sustained source of stimulation at the mass/compliance resonance frequency, such as low frequency resonance sweep signals found on certain test records. Jarring and footfalls aren’t the only dynamic sources of stylus scrubbing. Dynamic variations in stylus friction drag force caused by rapidly changing groove modulation levels can also cause a dynamic variation in skating forces. This dynamic change in stylus friction drag can translate into dynamic horizontal vibration of the arm which, in turn, can cause stylus scrubbing and sometimes audible flutter effects. All things being equal (which is rare), longer arms with less offset angle have an advantage.

In the case of a straight arm with no offset angle, the friction drag force vector on the stylus is in line with the pivot. As such, dynamic variations of friction drag force on the stylus don’t translate into dynamic horizontal/sideways vibration. No sideways movement, hence, no induced FM or flutter on a crescendo. I think this is the operative factor being observed in reviews of the RS-Labs and other ‘straight’ arms. As was the case for offset arms, straight arms too will see some scrubbing from the horizontal stylus displacement about the cantilever pivot, but this is small in comparison to that caused by an offset angle, and this contribution approaches zero for very small amounts of cantilever deflection (Sine of 0 degrees = 0).

Here is my own sketch of what happens with a ‘truly straight’ arm:

_b straight vibr 512x280.jpg

For the same ‘lateral vibration’ or horizontal deflection of the stylus, the only scrubbing that occurs with the straight arm is that from the horizontal stylus displacement about the cantilever pivot. The absence of an offset angle greatly reduces the total magnitude of fore and aft scrubbing along the groove. I think the positive comments from reviewers of RS Labs and similar straight arms stem from this reduction of FM distortion caused by stylus scrubbing. The tradeoff with ‘truly straight underhung’ arms is high tracking error distortion. A straight underhung arm will also exhibit skating effects dependent on the amount of tracking error at a given point. Interestingly though, while the friction drag force on the stylus will cause skating everywhere except at the null point, the resultant stylus friction drag force vector on the cantilever is in line with the cantilever and the arm pivot, so stylus friction drag doesn’t cause any side-force vector on the cantilever or sideways deflection of the stylus cantilever and, hence, no scrubbing. Oddly enough, whatever skating forces do exist on a straight arm will show up as increased stylus contact pressure on one side of the groove or other, depending on the null point, but will not show up as a side-force on the cantilever!

And, what about vertical scrubbing effects? The RS-A1 arm design does something similar in the vertical direction that ‘truly straight’ arms do in the horizontal direction:

_c rs2a 465x300.jpg

Here is another sketch:

Vertical Vibration 2000x1114.jpg

The RS-A1 arm pivot is very high above the record surface. As the arm pivot gets raised higher, it decreases the angle ‘beta’ in the figure, which has an effect in the vertical direction that is similar to decreasing the offset angle in the horizontal direction. This would decrease stylus tip scrubbing effects caused by dynamic deflections of the stylus in the vertical direction. The relative effect of the high pivot would depend on the geometry fixed by the arm pivot height and the cartridge VTA. The results would vary greatly from user to user, depending on individual arm setup and actual cartridge VTA. The high pivot may help reduce stylus tip scrubbing from vertical vibration but the tradeoff is that it makes warp wow effects worse. More ways to pick your poison…

So, a given point on a disc might sound better/worse with a conventional pivoted arm having lower tracking error distortion, or a straight arm having lower scrubbing/FM distortion. It depends on the program material, null points chosen, and perhaps other factors. Of course, the tracking error issues of ‘truly straight’ arms could be addressed by moving the arm pivot with a servo to maintain tangency, aka make it into a linear tracker, but that would be getting off topic and risk starting a food fight ;).

Disclosure statement: I don’t own, use, or endorse RS Labs or DJ straight arms.

Ray K
 
The straight tonearm was debunked by outfits like Shure and RCA generations ago, by credentialed engineers in corporate laboratories. Their findings were subject to peer review. That's a different thing from getting ideas validated on a hobbyist audio forum. But that straight-tonearm horse might still have some life in it...beat-beat-beat.

The standards of proof are much lower now than they were decades ago, thanks to a much-less-demanding audience, for which boutique audio gear manufacturers are very thankful.
 
Last edited:
The high pivot may help reduce stylus tip scrubbing from vertical vibration but the tradeoff is that it makes warp wow effects worse.
Ray K

the higher the vertical pivot sits above a horizontal line from the stylus the greater the warp wow. a 9" pivoted arm with the vertical pivots 3/8" above that line (fairly typical number) will produce approx. 0.1% warp wow over a 1/16th" warp. arms with vertical pivot in line with stylus will produce 0.05%. The arm example with the extremely high vertical pivot would have a tremendous amount of warp wow
 
"How do you define "badly aligned"?
by badly aligned , I mean that the cartridge doesn't trace the groove as close to the angle of the original cutting head as possible for the duration of an entire side of an lp.
If you can get this as close as possible to 90 degrees at two null points for a radial arm...and specify those null points to a *known geometry* based on your tonearm's *actual* mounting distance, then you can reduce the distortion to a minimum elsewhere across the record's surface depending on what types of records you listen to most, what type of stylus profile you use , the length of your arm (effective length) etc..
You can also optimize your cartridge's alignment depending on whether you prefer to play 7" singles, 12" 45s , 12" lps 10" lps, mono recordings , stereo or a compromise between all of them in favour of stevenson , baerwald , heybrook, rega etc.
 
Back
Top Bottom