Hi Fleib: Cartridge suspensions should only allow vertical, horizontal and 45-degree flexing modes, but in reality nearly all cartridge suspensions also allow twisting, and if a given suspension doesn't contain a tension wire, fore-aft motion as well.
If you measure crosstalk on an oscilloscope using a test LP, you will see that it causes the test signal waveform to break apart and spreads the sections over both channels rather than one. Breaking a waveform apart is never a good idea for sonics, since doing so generates high-order distortion products which are unpleasant to the ear. For this reason I consider cartridge crosstalk to be a type of distortion, rather than merely a channel separation problem.
No matter how rigid the cantilever and secure the the stylus tip mount, the flexible nature of the cantilever suspension allows the cantilever and stylus to rotate as a unit, leading to worsened crosstalk. As opposed to normal crosstalk which is due to misalignment of generator and stylus, crosstalk such as this is dynamic in nature, and increases and decreases as the LP groove modulations rise and fall.
Therefore, although a cartridge with a lurking dynamic crosstalk issue will probably measure OK and sound OK on simple music, on big orchestra peaks, congestion and imaging problems may occur.
The farther the stylus protrudes from the centerline of the cantilever, the more effective it is as a crank, making it easier for the LP groove to twist the cantilever and generator around (with the suspension acting as the pivot). A very short stylus reduces the level-dependent twisting effects by being less effective as a crank. At the other end of the cantilever, a large surface-area boss (typical of many MCs and the Audio-Technica MMs), combined with a large diameter damping system will act in a similar manner as a disc brake, reducing cantilever and generator twisting.
Although not much can be done with rigid cantilevers (sapphire, boron, diamond etc.) to reduce the twisting effects other than shortening the distance that the stylus protrudes from the cantilever centerline, it is possible to design an alloy tube cantilever to circumvent this effect - if the cantilever is made with a kink in it (corresponding to the VTA angle) which starts to bend a little farther back than is normal for alloy tube cantilevers, the patch where the stylus contacts the LP groove can be placed directly on the cantilever longitudinal axis. This avoids the dynamic crosstalk issue by removing the crank effect of the stylus.
In more ways than one, it is easier to make a high-quality phono cartridge when the cantilever is made from a ductile material rather than the rigid, brittle materials that are commonly viewed as "better". Rigid cantilever materials have no "give", meaning that the slot, hole or surface for the stylus mounting must be made larger than the stylus, and this necessary oversizing forces the mounting tolerances to be poorer. A ductile cantilever material can be fitted with an undersized mounting hole so that the stylus is press-fit into place, and this will help keep the position (front-to-back, side-to-side) and angle (azimuth, SRA) of the stylus closer to the intent of the cartridge designer. And since the ductile cantilever can be bent without damage during forming, it is possible to cancel out some of the geometrical effects that would otherwise occur (per the above paragraph).
Returning to rigid cantilevers, please look at this.
www.accuphase.com/cat/ac-3en.pdf
If you compare the photo of Technics cantilever to the cantilever cross-section drawing in the Accuphase AC-3 pdf, the Accuphase drawing suggests that the contact point between stylus and LP groove was kept closer to the center axis of the cantilever, and it also shows that the stylus block passes through both upper and lower cantilever walls, which should help keep consistent stylus mounting accuracy.
This doesn't mean that a long stylus only has downsides to - it confers advantages as well. A longer stylus makes it feasible to reduce the cantilever length (for a given cantilever rake angle), so if the designer's top priority is to reduce cantilever length, a longer stylus (and/or higher cantilever rake angle) will be effective.
Most notably, a longer stylus will be far more resistant to jamming due to dirt accumulation than a shorter stylus would be, and this is important for a volume-sales product that may see a fair amount of casual use. Back when Lyra was making cartridges with 0.06x0.06mm stylii (smaller than what is on the Technics, and up there with the Denon DL-1000A), we'd get back cartridges where the user claimed that the stylus was broken off. In many cases, the stylus was intact and perfectly fine - it was simply that the tiny stylus size made it prone to vanish in accumulated dirt, and once that happened, the cartridge wouldn't play - the cantilever would just slide across the LP as though the stylus was missing.
Here is also a link for the AC-1 pdf. You can see how it used an alloy tubular cantilever which was bent into shape (although for crosstalk purposes it would have been better if the bend started a little further back).
www.accuphase.com/cat/ac-1en.pdf
FWIW, tubular cantilevers are not more rigid than rod cantilevers of the same material, unless the outer diameter of the tubular cantilever is larger than the OD of the rod cantilever. But a larger OD will cause the stylus to protrude by a greater distance from the cantilever centerline, which we have seen is a disadvantage when it comes to crosstalk.
Finally, allow me to point out that most design choices in a phono cartridge bring side-effects. Very few design choices only confer advantages with no negatives. As one example, it is no accident that the great majority of phono cartridges ever made have converged on a cantilever length of around 6mm. Any designer can specify a shorter cantilever, but doing so brings direct and indirect performance penalties which need to be carefully considered, and doing so also inevitably forces design work-arounds in various areas which may upset the balance of the design as a whole.
On a different topic, here is an online simulation tool for RLC circuits.
http://sim.okawa-denshi.jp/en/RLCtool.php
It allows for the user to enter their own values for resistance, capacitance and inductance (thereby making it feasible to do a simple electrical modeling of an MM, MI or MC phono cartridge), and it can show the phase response, step response, overshoot and other parameters in addition to the frequency response. This is a nice tool to complement Jim Hagerman's cartridge loading page, to get a better idea of phono cartridge behavior in the electrical domain.
Hope this was of interest.
kind regards, jonathan
If you measure crosstalk on an oscilloscope using a test LP, you will see that it causes the test signal waveform to break apart and spreads the sections over both channels rather than one. Breaking a waveform apart is never a good idea for sonics, since doing so generates high-order distortion products which are unpleasant to the ear. For this reason I consider cartridge crosstalk to be a type of distortion, rather than merely a channel separation problem.
No matter how rigid the cantilever and secure the the stylus tip mount, the flexible nature of the cantilever suspension allows the cantilever and stylus to rotate as a unit, leading to worsened crosstalk. As opposed to normal crosstalk which is due to misalignment of generator and stylus, crosstalk such as this is dynamic in nature, and increases and decreases as the LP groove modulations rise and fall.
Therefore, although a cartridge with a lurking dynamic crosstalk issue will probably measure OK and sound OK on simple music, on big orchestra peaks, congestion and imaging problems may occur.
The farther the stylus protrudes from the centerline of the cantilever, the more effective it is as a crank, making it easier for the LP groove to twist the cantilever and generator around (with the suspension acting as the pivot). A very short stylus reduces the level-dependent twisting effects by being less effective as a crank. At the other end of the cantilever, a large surface-area boss (typical of many MCs and the Audio-Technica MMs), combined with a large diameter damping system will act in a similar manner as a disc brake, reducing cantilever and generator twisting.
Although not much can be done with rigid cantilevers (sapphire, boron, diamond etc.) to reduce the twisting effects other than shortening the distance that the stylus protrudes from the cantilever centerline, it is possible to design an alloy tube cantilever to circumvent this effect - if the cantilever is made with a kink in it (corresponding to the VTA angle) which starts to bend a little farther back than is normal for alloy tube cantilevers, the patch where the stylus contacts the LP groove can be placed directly on the cantilever longitudinal axis. This avoids the dynamic crosstalk issue by removing the crank effect of the stylus.
In more ways than one, it is easier to make a high-quality phono cartridge when the cantilever is made from a ductile material rather than the rigid, brittle materials that are commonly viewed as "better". Rigid cantilever materials have no "give", meaning that the slot, hole or surface for the stylus mounting must be made larger than the stylus, and this necessary oversizing forces the mounting tolerances to be poorer. A ductile cantilever material can be fitted with an undersized mounting hole so that the stylus is press-fit into place, and this will help keep the position (front-to-back, side-to-side) and angle (azimuth, SRA) of the stylus closer to the intent of the cartridge designer. And since the ductile cantilever can be bent without damage during forming, it is possible to cancel out some of the geometrical effects that would otherwise occur (per the above paragraph).
Returning to rigid cantilevers, please look at this.
www.accuphase.com/cat/ac-3en.pdf
If you compare the photo of Technics cantilever to the cantilever cross-section drawing in the Accuphase AC-3 pdf, the Accuphase drawing suggests that the contact point between stylus and LP groove was kept closer to the center axis of the cantilever, and it also shows that the stylus block passes through both upper and lower cantilever walls, which should help keep consistent stylus mounting accuracy.
This doesn't mean that a long stylus only has downsides to - it confers advantages as well. A longer stylus makes it feasible to reduce the cantilever length (for a given cantilever rake angle), so if the designer's top priority is to reduce cantilever length, a longer stylus (and/or higher cantilever rake angle) will be effective.
Most notably, a longer stylus will be far more resistant to jamming due to dirt accumulation than a shorter stylus would be, and this is important for a volume-sales product that may see a fair amount of casual use. Back when Lyra was making cartridges with 0.06x0.06mm stylii (smaller than what is on the Technics, and up there with the Denon DL-1000A), we'd get back cartridges where the user claimed that the stylus was broken off. In many cases, the stylus was intact and perfectly fine - it was simply that the tiny stylus size made it prone to vanish in accumulated dirt, and once that happened, the cartridge wouldn't play - the cantilever would just slide across the LP as though the stylus was missing.
Here is also a link for the AC-1 pdf. You can see how it used an alloy tubular cantilever which was bent into shape (although for crosstalk purposes it would have been better if the bend started a little further back).
www.accuphase.com/cat/ac-1en.pdf
FWIW, tubular cantilevers are not more rigid than rod cantilevers of the same material, unless the outer diameter of the tubular cantilever is larger than the OD of the rod cantilever. But a larger OD will cause the stylus to protrude by a greater distance from the cantilever centerline, which we have seen is a disadvantage when it comes to crosstalk.
Finally, allow me to point out that most design choices in a phono cartridge bring side-effects. Very few design choices only confer advantages with no negatives. As one example, it is no accident that the great majority of phono cartridges ever made have converged on a cantilever length of around 6mm. Any designer can specify a shorter cantilever, but doing so brings direct and indirect performance penalties which need to be carefully considered, and doing so also inevitably forces design work-arounds in various areas which may upset the balance of the design as a whole.
On a different topic, here is an online simulation tool for RLC circuits.
http://sim.okawa-denshi.jp/en/RLCtool.php
It allows for the user to enter their own values for resistance, capacitance and inductance (thereby making it feasible to do a simple electrical modeling of an MM, MI or MC phono cartridge), and it can show the phase response, step response, overshoot and other parameters in addition to the frequency response. This is a nice tool to complement Jim Hagerman's cartridge loading page, to get a better idea of phono cartridge behavior in the electrical domain.
Hope this was of interest.
kind regards, jonathan