I have found that in at least one case (the B&O MMC series) the compliance given by the manufacturer (in this case B&O) is the static compliance @ 30 c.u. This should give an arm f-res @ 8 Hz in my Mørch DP8 with the Green arm-tube (effective mass 7.5 gram). However, with the Feickert Adjust+ I measure the f-res @ 11 Hz which indicates that the dynamic compliance is only 11 c.u., in other words more that half the compliance given by the manufacturer.
So, I have concluded that there is no other way of gauging this problem that to measure/or listen to the cartridge
So, I have concluded that there is no other way of gauging this problem that to measure/or listen to the cartridge
Yes, I read that the static compliance value is approximately double the dynamic compliance value at 10 Hz and quadruple the value at 100 Hz.
Mørch states that the effective mass of the DP8 with the green tube (of which lenght...9" or 12"?) is 4g, not 7,5. Fine, just at which position/distance of the counterweight and the side weights does it apply to?
Due to lack of data, I don't think that one can derive compliance out of the resonant frequency measurement. But at least, your arm's side weights allow altering the effective mass without messing with the vertical tracking force once set.
Hi, Yes this problem exists with several manufactures. I bemuses my why, if they cannot measure this spec, then it does not give confidence in their over QC control of a cart.
Cheers
Cheers
Hi, No what he is showing is that there is more to it than achieving a resonant frequency in the 7 to 12 hz range, However this range is the most important to get right & minimize. Also unfortunately you cannot do these tests until you have manufactured the arm & tested in live conditions with a cart. What would be interesting is to see how several cart tests with the same arm change the frequency spikes.
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I think Korf showed that carts with very different compliances, when mounted in the same tonearm end up with almost same resonant frequency (despite dissimilar compliances).
When it comes to the world of analog audio, turntables remain an iconic symbol of timeless sound quality and musical authenticity. The pursuit of the perfect vinyl playback experience has led audiophiles and music enthusiasts to explore various factors that influence the overall audio output, and one of the crucial elements in this quest is the tonearm mass. Speed test copel Tonearm mass plays a pivotal role in achieving optimal tracking, minimizing distortion, and preserving the delicate grooves of vinyl records.
The 7.5 g that I gave as effective mass is including the MMC 1. Mørch also told me that when he designed the ICA200 (an integrated armtube for the Ortofon MC200) he fond that the dynamic compliance (i.e. the compliance of the cartridge was at leas half of the static compliance and that he therefore had to add more mass to the ICA200 to get he desired 12 Hz (yes that is what he aimed for).
Hi, Plugging that data into Korf the cart (MC200) compliance needs to be around 30. V/E advises that compliance is 13?
However the MMC 1 is 30 and has a Res Freq of around 8hz.
Cheers
However the MMC 1 is 30 and has a Res Freq of around 8hz.
Cheers
Hi DNic,
The ICA200 was specially made for the MC200 and Mørch never published the effective mass for that armtube. The production run was very small and the ICA series (he did an ICA for the LM series as well) was only available for one or two years in the early 1980s. When I bought mine in 1982, Mørch told me that he had to add quite a substantial amount of mass to the prototype arm (whose mass had been calculated based on the published compliance of the Ortofon cartridges) in order to lower the f-res to 12 Hz.
My point was/is that we are too hung up on the static compliance number: In my estimation, the best thing to do will be to measure the cartridge / arm combination when playing a record. The huge difference between the calculated f-res and the measured f-res in the case of the MMC1/green arm-tube bears this out.
@borchee: the side weights do affect tracking force (but, being so close to the fulcrum of the arm, have next to no influence on effective mass).
Korf’s blog #1 summarises possible influences on his results:
The ICA200 was specially made for the MC200 and Mørch never published the effective mass for that armtube. The production run was very small and the ICA series (he did an ICA for the LM series as well) was only available for one or two years in the early 1980s. When I bought mine in 1982, Mørch told me that he had to add quite a substantial amount of mass to the prototype arm (whose mass had been calculated based on the published compliance of the Ortofon cartridges) in order to lower the f-res to 12 Hz.
My point was/is that we are too hung up on the static compliance number: In my estimation, the best thing to do will be to measure the cartridge / arm combination when playing a record. The huge difference between the calculated f-res and the measured f-res in the case of the MMC1/green arm-tube bears this out.
@borchee: the side weights do affect tracking force (but, being so close to the fulcrum of the arm, have next to no influence on effective mass).
Korf’s blog #1 summarises possible influences on his results:
He forgets/ignores/has not considered that the static compliance may not be of any use.
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Hi, OK now I understand, yes the only way to correctly arrive at your RF is to measure it. But understandably designers have to have some guideline figure to go for. That would explain why Moech went for 12hz, to get lower that that would need a heavier wand.
Cheers
Cheers
In fact, what he did was to fill the armtube with lead (evenly distributed along the length of the arm). The choice of 12 Hz is a recommendation by Poul Ladegaard who at that time was working on identifying the optimal placement of the f-res for Brüel & Kjær as part of a larger project to document why turntables sound different (see here for Ladegaard’s AES paper on the subject)
Something's up there, the fundamental resonant frequency depends straight-forwardly on the effective mass and the (dynamic) compliance. Basic physics is that (mass on a spring), the issue is likely failing to measure the compliance under the right conditions, and with any kind of visco-elastic suspension compliance will vary with the various forces present (tracking and drag for instance), as will the damping (which also has an effect on resonant frequency too, as well as reducing the strength of the resonance).
Basically static compliance measurements aren't telling the whole story, expecially with an advanced catilever suspension designed to have good damping and be non-linear (same thing is done in vehicles to reduce the harsh bottoming-out of the suspension on overload - perhaps can be though of as a kinematic version of soft-clipping)
And there are two different modes, horizontal and vertical, which couple into each other in complex ways too, you probably get some odd effects from that if the resonant frequencies are different for the two planes. In fact that's probably a whole other can of worms to be opened here.
@Mark Tillotson: Indeed, the horisontal and vertical compliances are important and interact. However, all low frequencies are cut in mono (horisontally/laterally). Cutoff frequencies vary, but generally speaking, there is no stereo information below 150Hz. High lateral mass is the technical reason why air-bearing tangential arms, the Mørch DP-8 and the original Syrinx arm tend to sound very good in the low frequencies: these arms provide a steady platform for the reproduction of bass.
Ladegaard’s 1977 AES paper discusses the interaction of various resonances in the turntable system, but does not touch on the need for high lateral mass and low vertical mass. Mørch made a prototype DP-8 based on the UP-4 around that time. But 1980s bass-resolution was not sufficient to demonstrate the advantages of the design. It took another 30 years before it became evident that there was any aural advantage to the approach dictated by logic.
The measurements below with their almost linear (bass-)frequency response show the benefits of the high lateral/low vertical mass approach.
Ladegaard’s 1977 AES paper discusses the interaction of various resonances in the turntable system, but does not touch on the need for high lateral mass and low vertical mass. Mørch made a prototype DP-8 based on the UP-4 around that time. But 1980s bass-resolution was not sufficient to demonstrate the advantages of the design. It took another 30 years before it became evident that there was any aural advantage to the approach dictated by logic.
The measurements below with their almost linear (bass-)frequency response show the benefits of the high lateral/low vertical mass approach.
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BTW: these are Mørch’s measurements of the MMC1 in the Red armtube. Note how the vertical f-res is almost 19 Hz and that the amplitude is only around 5dB.
How did this number come up? The arm's effective mass is 4 g and the cartridge's mass is 1,6 g. Because we treat the cartridge like a point-mass located at the typ of the stylus (at effective lenght), the effective mass equals the actual mass. It should be 5,6 g and not 7,5 g.
I don't know how they concluded that the vertical resonance frequency was 19 Hz. I can't see any resonance frequency from the diagram at all. By the way, 19 Hz is too high if they are correct.
When I did resonance frequency tests, all the resonance frequencies were clearly defined.
https://www.diyaudio.com/community/threads/diy-air-bearing-linear-arm.268614/page-10
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