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The Korf Blog

The inside story: our research,
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18 February 2020
Tonearm and Cartridge Matching, Part III
This is the third post in the series on low frequency interaction between the tonearm and the cartridge.

In our previous posts, we've formulated The Plan, and done the first two bullet points: measured the Ortofon/Jelco and Denon/Jelco combos. The low frequency results that we got were very far from the calculated predictions.

Today, it's time for the third part of The Plan:
Make sure our test rig is working fine and is picking up both high and low frequency resonances. We'll measure the low frequency set with it, and superimpose it over the usual 20Hz-20kHz sweep.
2
Change the cartridge to the one with different compliance, and see what the effect on the low frequency resonance would be.
3
See what the low frequency content of the usual LPs looks like. We'll use some nearly unplayable LPs from our collection to try and get the effects of warps and excentricity.
4
Do the analysis of the data and see if there are some recommendations to be made on matching tonearms and cartridges.

The Setup
We're using the same cartridges we've introduced in the previous posts. And today, we will largely focus on the Denon DL-103 and the Ortofon SL-15E. The very compliant and very well dampened Shure M97xE just doesn't generate enough low frequency vibration to entertain us. So in some charts the "Shure" line is missing—this means there was nothing but noise there at low frequencies.

First, the torture test. We'll play back the two nearly unplayable LPs, and see what the effect of vertical warps is. I sometimes use the first one ("Warp 1") as a cartridge suspension test—the older cartridges with dried out elastomers cannot navigate it at all.

For comparison's sake, we'll also measure what happens when we play back the normal LPs. Not warped, not perfectly flat, just average.
"Warp 1"
"Warp 2"

The Measurements
As a quick reminder, we are looking for the frequency peaks, and, if the low frequency resonance formula is true, we expect them to shift depending on the cartridge's compliance.

I've zoomed the charts on the 5-25 Hz area and made the X axis linear. Please also note that the vertical scale is different (compared to the previous posts) to accommodate larger peaks. First one is the huge warp from the first video ("Warp 1")
There's a defined 8 Hz peak, and then the 14 Hz peak with DL-103 only. And the Shure has completely ignored the whole roller coaster.

Here is the tiny almost imperceptible warp from the second video ("Warp 2")
Wow. The smaller warp generated basically the same "gs" as the huge one. If anything, the "Warp 2" should be the torture test, as the acceleration doesn't fall with rising compliance nearly as much as in "Warp 1".

Two peaks here, prominent with both Ortofon and Denon. 9 Hz and 6.5 Hz, exactly same frequencies with both of them.
We don't see the frequency shift with a change of compliance
Like with the test LP in the previous post, we see lots of things: huge amplitude changes, significant differences between different LPs. What we definitely don't see is the frequency shift with a change of compliance. The frequencies we observe are defined by their source—by the warps and irregularities in the record itself.
The contrast with the test LP measurement is also quite interesting. Here's the "Warp 1" together with the vertical HFNRR low frequency measurements converted to the same scale:
The difference in amplitude is immense. These warps really throw the tonearm about. And, just to compare, here's your common or garden LP with no significant warp:
But what about the horizontal movement? Excentricity or similar defects generate frequencies that are too low to be picked up by the accelerometers. But the cartridge+tonearm system translates some of the vertical movement over warps into horizontal one. And, of course, the bigger is the reaction to the warp, the more it is translated.

What did we discover today?
Our measurements have basically confirmed that the frequency of the motion is determined by the frequency of the excitation and not by the resonance of the cartridge/tonearm system. We did not see any frequency shift with different compliance cartridges.

I was impressed by the gs that even the small warps generate. No wonder there's significant translation into the plane tangential to the warps.
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