Allow me to enlarge.
Because we have a stiffer spring and a larger mass moving, we ideally apply additional damping to the arm, because the stiffer spring and greater mass will result in MORE movement at the resonance frequency.
Just compare to a car suspension, imagine you put very heavy wheels and tyres onto more stiff suspension. Without an shock absorber the wheel will oscillate more violently. Add a shock damper, voila, the oscillation is damped.
The LF resonance of arm & cartridge are not really that different.
But we are talking about a second set of resonances.
A tonearm is ultimately related to a bridge. It is a bridge between two points, one more or less fixed point (ideally the pivot is fixed 100% dynamically from the view of the cartridge in the audio range) and one that is suspended (by the cartridge cantilever and it's suspension and damper).
We know bridges have bending modes that have their own resonances. The famous "Army unit collapsing a bridge marching over it in lock step" story illustrates this. We are talking about the same resonances.
Typical old style tonearm's use constant wall thickness and constant diameter tubing. This obviously makes for a structure with a strong single resonance. Now resonance can be damped using a rubber type damper at the end (or both ends) of the tube. Damping resonances at the end of a structure is known as edge termination and is for example used in speaker drivers where the same problem exists. The rubber surround and the "lip" attached to the code edge perform that damping.
One can also use a rubbery insert in the tube that produces some damping or coat the inside of tube. This is rarely done due to the added complexity. Using a "S-Shaped" tube breaks up resonances into multiple sections that have higher resonance frequencies, with the fundamental resonance reduced.
Given that the pivot needs to be rigid, the point where the tube resonance can be terminated and damped is the headshell end. Moreover, the headshell end is also the point where we vibrate the tube with energy passed from stylus and cantilever.
Having a rigid coupling between Cartridge/Headshell will be most efficient in sending vibration energy into the arm tube and will in turn excite sympathetic resonance, which will in turn vibrate the cartridge, leading to an unwanted input into the cartridge. So it is desirable to defeat or minimise these resonances and isolate the cartridge from them, as well as isolating the arm from the cartridge's vibration energy.
Having a lossy connection between Arm and headshell makes the conduction of vibration energy less effective and can provide edge/end termination of resonances in the Arm structure. It will also reduce the conduction back into the cartridge of any resonant energy of the arm tube resonance.
Even without resonance, vibration energy send into the arm structure will propagate as wave in the metal to the pivot point where it will reflect back to the source. A good illustration is the wave reflection in a water tank. A similar process applies to high frequency cables in electronics:
Having an Arm structure that is not "regular" (varying tube diameter and varying in wall thickness) can reduce resonance, but not reflections. To cancel reflections needs additional damping in such a structure. Rigid coupling between Headshell and Arm Tube will maximally transmit vibration energy back & force. And no, the Arm Pivot and weight of structure attached to it does not "ground" or "drain" vibration energy, the more rigid the pivot etc. the more energy is reflected back towards the cartridge.
The next part in the system is the cartridge. Older cartridges have cases with a very loose coupling between the actual pickup and usually plastic case. Some cartridges (e.g. reportedly the Denon DL-103) are even designed to have deliberate anti-resonance in the cartridge case for resonances in the pickup (Generator, Cantilever & Stylus).
Others, especially modern "High End" cartridges have rigid cases and rigid links between case and pickup. This creates differing conditions for the propagation of vibrational energy from stylus & cantilever into the Arm structure and back.
For the DL-103 the top plate of the case should be allowed to resonate freely. The included soft plastic O-Rings should be placed between headshell and cartridge. They from a first line of damping and lossy coupling. Note this is strictly applicable to DL-103.
For the DL-103, the Arm should not be of a rigid type, to further avoid transmitting vibration energy into the Arm structure and resonant and reflected energy from returning to the cartridge.
Other Cartridge/Arm combinations need to be considered individually.
The HiFi News Test LP should be used to adjust effective arm weight to get the VLF resonance frequency right. Some form of fluid or eddy current damper is desirable to damp the VLF resonance.
Placing led tape at the golden ratio point on the arm tube can be used to adjust effective arm weight AND to provide damping of both resonances and vibration transmission. One can also shift the tape along the length of the arm to find the "best spot".
If a spring based anti-skating mechanism is used, ideally this is removed and replaced with a string/weight Anti-skate.
See here, two arms have lead tape. Only the Ortofon Arm which is designed together with the SPU Cartridge and Headshell as system is left without " tweaking"
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