I can't make a judgment about the tonearm's resonant frequency based on what you are saying. I can only know its resonant frequency based on the measurements. The following charts are provided by the maker himself. Can you see the 16 Hz vertical resonant frequency and lateral frequency?
The maker claimed there were no resonant frequencies for his tonearm. I am questioning such a conclusion. From the charts, I don't see any resonant frequencies. If the tonearm has no resonant frequencies, it contradicts the basic principle of tonearm design.
I know his tonearms are heavily damped by adding weights on the lateral plane. However, can damping eliminate resonant frequency completely? I don't know. Further study is needed. In theory, it can't. If there is no resonant frequency, it means the spring (the cartridge) is completely compressed. There is no springness on the cartridge. Playing back a record is not possible once the cartridge is completely compressed.
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The resonant frequency in the lateral direction is not just low due to the mass but also damped. There is silicon oil to damp lateral movement. Damping can diminish the peak as seen with the infamous Shure V15 damping brush. This is the behaviour of mine in the vertical direction with and with brush engaged.
Well...if the 190g of extra lateral mass is due to the side weights, then...
Guesstimating...mass center of the weights at the outer position is 45mm from the pivot. The effective length of the 12" arm is 307,4mm.
So, the effective mass of the side weights is: 190g x (45mm)^2 / (307,4mm)^2 = 4,07g.
It gets better...for the 9" arm with an effective length of 230mm, the side weights contribute 7,27g.
Thomas...yes, horizontal.
What I'm trying to bring across is that one can calculate s**t because of the imprecise, or lack thereof, data given/stated by manufacturers.
For example...Mørch specifies the effective mass of a complete (sans headshell, cartridge, screws...) DP-8 arm with the light (green) tube at 4g.With which length, 9 or 12"?! And at what position of the side weights?!
My calculation is correct, yet the results (can) exceed the stated effective mass.
What I'm trying to bring across is that one can calculate s**t because of the imprecise, or lack thereof, data given/stated by manufacturers.
For example...Mørch specifies the effective mass of a complete (sans headshell, cartridge, screws...) DP-8 arm with the light (green) tube at 4g.With which length, 9 or 12"?! And at what position of the side weights?!
My calculation is correct, yet the results (can) exceed the stated effective mass.
There is no green dot 12” arm tube. And, surprisingly, the red and blue 12” arm tubes are (by design) available in the same effective mass as the red and blue 9” versions.
BTW, we are now back to my original point about not relying of calculations, since manufacturers rarely specify whether their compliance figures are static or dynamic. I gave the exaple of the B&O MMC1 which B&O claims is 30 c.u. but which measures at 12 Hz f-res in the red armtube.
Also, Mørch has a long list of recommendations.
BTW, we are now back to my original point about not relying of calculations, since manufacturers rarely specify whether their compliance figures are static or dynamic. I gave the exaple of the B&O MMC1 which B&O claims is 30 c.u. but which measures at 12 Hz f-res in the red armtube.
Also, Mørch has a long list of recommendations.
Sorry, I don't understand the question. But, yes, they do. The question is just by how much.
If you mean the rotation around the rod, it's neglible.
To understand what effective mass is...
First of all, it doesn't exist in nature - it's merely a construct, a tool to help with calculations.
Bloody reflektions - I hit the answer button mistakenly. Will continue...
If you mean the rotation around the rod, it's neglible.
To understand what effective mass is...
First of all, it doesn't exist in nature - it's merely a construct, a tool to help with calculations.
Bloody reflektions - I hit the answer button mistakenly. Will continue...
There are currently three different standard wands and two with extended headshell and then also the 12 inch arms. Note that the effective masses were originally stated for the UP-4 and DP-6 arms which have been around for a long time. The DP-8 with its side weights is a recent arm, and the effective mass is quite different when the mass distribution of the counterweight has been so much altered.
As you know the horizontal excitation forces consists of the 0.55 Hz wow which can also manifest in 1.1 Hz overtones, but not much higher. As for the music, most bass content is mixed into mono. So any horizontal resonance frequency should be placed above the 0.55/1.1 Hz wow frequencies but below potential music content at 20 Hz. Two octaves above 1.1 Hz equals 4-5 Hz, which also is two octaves below 16-20 Hz.
The vertical excitation forces are mostly warps in the 3-6 Hz region, but warp disturbances can be seen even higher up in frequency. Placing the resonance at least 2 octaves above the 6 Hz warp frequency equals 24 Hz. Such a high vertical resonant frequency is not usually recommended, but as many know, there is no or little music information cut in the vertical mode (see above, they are most likely mono and horizontally cut). So a vertical resonant frequency of 20 Hz would effectively filter out LP "noise" while not affecting music.
This is also the idea of the DP-8 arm: iplace the vertical resonant frequency high, while still having the horisontal frequency low. In this way, you avoid warp noise while still having full level bass notes.
So...
Every body, with dimensions and mass bigger than zero, has a mass moment of inertia bigger than zero. This is the "unwillingness" of the body to any change of the current state of rotation.
The unwillingness to rotational change around an axis through the center of mass is a property of a body - it doesn't change with, say, gravity. Regarding the shape/distribution of mass and/or rotating the coordinate system, the inertia can be different between x, y and z axis. With a sphere all three are identical, regardless.
It is a product of mass and the square of distance to the axis of rotation.
The cantilever and suspension have to deal with it.
Now...with a tonearm....let's say around the vertical axis/pivot...
We neglect the proprietary vertical mass moment of inertia of every part (weights, tube, cartridge, shell, screws, wires, balls in bearing...you name it), simply because their mass and/or dimensions are usually very small...we consider them to be point-masses.
But...all of the parts rotating also rotate about the pivot. So, the mass moment of inertia (of each part) equals the product of the actual mass and the square of the distance between a part's center of mass and tonearm's pivot.
Now we add up all of the mass moments and divide the sum by the square of effective length (tip of the stylus to tonearm's pivot).
The result is the effective mass - an imaginary mass that exhibits the same amount of unwillingness to overcome by cantilever and suspension.
I'm not in any way bashing the quality of Mørch arms...the data yes, but this is a wide problem...exactly as compliance stated for different frequencies. AFAIK, nobody can give an exact answer what is the ratio between them.
We have a formula, bot no data to feed it with.
Every body, with dimensions and mass bigger than zero, has a mass moment of inertia bigger than zero. This is the "unwillingness" of the body to any change of the current state of rotation.
The unwillingness to rotational change around an axis through the center of mass is a property of a body - it doesn't change with, say, gravity. Regarding the shape/distribution of mass and/or rotating the coordinate system, the inertia can be different between x, y and z axis. With a sphere all three are identical, regardless.
It is a product of mass and the square of distance to the axis of rotation.
The cantilever and suspension have to deal with it.
Now...with a tonearm....let's say around the vertical axis/pivot...
We neglect the proprietary vertical mass moment of inertia of every part (weights, tube, cartridge, shell, screws, wires, balls in bearing...you name it), simply because their mass and/or dimensions are usually very small...we consider them to be point-masses.
But...all of the parts rotating also rotate about the pivot. So, the mass moment of inertia (of each part) equals the product of the actual mass and the square of the distance between a part's center of mass and tonearm's pivot.
Now we add up all of the mass moments and divide the sum by the square of effective length (tip of the stylus to tonearm's pivot).
The result is the effective mass - an imaginary mass that exhibits the same amount of unwillingness to overcome by cantilever and suspension.
I'm not in any way bashing the quality of Mørch arms...the data yes, but this is a wide problem...exactly as compliance stated for different frequencies. AFAIK, nobody can give an exact answer what is the ratio between them.
We have a formula, bot no data to feed it with.
Whom should I believe - you or the manufacturer? No pun intended, really!
Specs taken from: http://www.moerch.dk/spec1.htm
If you can provide the following regarding both (thin and thick) side weights:
- outer diameter (let's prosume the rod is of same material, so we can forget the inner diameter/the hole)
- thickness
- mass
- overall lenght (from arm's pivot to the end) of the rod they sit on
- lenght of the "free" rod (the portion from the tower to the end) on which the weights can be moved outwards/inwards
The DP-8 does not share the counterweight mass principle of the UP-4 and DP-6 arms; hence it is physically impossible to get the same resonant values as those for the older arms, everything else the same. This is just physics. This is also explained on their home-page:
"For this new model the effective mass for the horizontal mode of motion is many times larger than the effective mass for the vertical mode of motion - no matter the effective mass of the armtube used."
"For this new model the effective mass for the horizontal mode of motion is many times larger than the effective mass for the vertical mode of motion - no matter the effective mass of the armtube used."
Phisycs, exactly. Many times larger means nothing! So, what to believe - specs with a precise value or the "explanation"?
Do you know what the horizontal effective mass of a DP-8, with green 9" tube and without cartridge, headshell and screws, is...with side weights at their most inward and at their most outward position?...or perhaps where the manufacturer is declaring it? The position of the counterweight(-s) we'll just neglect.
Do you know what the horizontal effective mass of a DP-8, with green 9" tube and without cartridge, headshell and screws, is...with side weights at their most inward and at their most outward position?...or perhaps where the manufacturer is declaring it? The position of the counterweight(-s) we'll just neglect.
If you want to know send an email to Moerch about the masses and the asymmetric counterweights; there is a instruction of how to set up the counterweights at the homepage. From the weights and the mass of the pivot housing you might be able to make a calculation. Or you can estimate the center of gravity to 5 mm to pivot point for the vertical direction and 45 mm for the lateral and calculate the "many times larger" factor.
My Moerch UP-4/Shure V15Vx/JICO SAS/B with green arm tube gets a resonance of around 11 Hz which fits good with calculation. No need for me to go further with the DP-8. Would be interesting as experiment and lower the warp "noise", but expensive and too large for my arm board.
My Moerch UP-4/Shure V15Vx/JICO SAS/B with green arm tube gets a resonance of around 11 Hz which fits good with calculation. No need for me to go further with the DP-8. Would be interesting as experiment and lower the warp "noise", but expensive and too large for my arm board.
Nobody denies that damping can diminish the resonant peak. But the question is how much. In the diagram, the brush seems to eliminate the resonant peak. Can a silicone-damping device do the same? I don't think so. With the brush disengaged, the resonant frequency is there. But in Mørch’s test results without a stupid brush, the resonant frequency disappeared as well. It indicates something is wrong with his tests.
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