The Korf Blog

The inside story: our research, development and opinions

28 January 2020
Tonearm and Cartridge Matching, Part II
This is the second post in the series on low frequency interaction between the tonearm and the cartridge.

In our previous post, we've formulated The Plan, and done the first bullet point: measured the Ortofon/Jelco combo from 5 Hz to 20 kHz, and put it all on two charts. What the measurements showed was a bit removed from what the calculations suggested.

Today, it's time for the second 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

In addition to the Ortofon SL-15E that we've employed in the previous post, we will use our old acquaintance the Denon DL-103. Its compliance is specified at \( 5 \cdot 10^{-6}\) cm/dyne (5 µm/mN). This fits well with the required downforce of 2.5 gram. Unlike many other cartridges, there's no doubt that Denon's suspension is actually quite stiff.
And to give an opposite perspective, a Shure M97xE. While it is shown with its brush down, all our measurements were done with the brush up and the downforce correspondingly decreased.

Shure specifies the compliance at \( 25 \cdot 10^{-6}\) cm/dyne, but it's probably much higher. Various moving magnet Audio Technicas are specified as having 40 (!), and Shure definitely has a much softer suspension. The lower required downforce (less than a gram for Shure versus 1.8-2.2 g for ATs) supports this.


The Measurements
The accepted formula gives us 12 Hz resonant frequency for the Denon.
So if we take it at face value and plot Denon and Ortofon low frequency resonances together, we should get something like this.

Of course, the amplitudes might be different, and the curves would not be so neat and unbroken. But we definitely would see the frequency peaks, and we would see the frequency shift. The resonant peak must shift in frequency.

I've zoomed the charts on the 5-25 Hz area and made the X axis linear.
And what do we have in reality?
That doesn't look like shift at all. Maybe the vertical resonance would?
We see the change in amplitude all right, but the frequency shift is missing. This does not look much like resonant behaviour.


Extraordinary findings require extraordinary evidence, right? So let's see if using the Shure would result in the shift in the frequency of the resonant peak. Remember, specified lateral compliance of Shure is the same as Ortofon's, but we expect it to be higher. So our peak should be similar with the blue trace's, or slightly to the left. Right?
You can argue that the 6 Hz hump is the peak we're looking for, but this is splitting hairs. The main difference is in the lower overall motion, not in some particular frequency.


For completeness, here's the vertical comparison chart with Shure included.

What did we discover today?
Looks like the low frequency behaviour of the cartridge/tonearm combination is shaped more by Newton's third law than by the compliance resonance. Modern cartridges (meaning all those built in the last 60 years or so) have too much suspension damping and non-linearity for the resonances to dominate.

I would stop at this today, leaving conclusions proper until the last post in the series. This is heady stuff, and I fully expect some people to become very upset.

Besides, we are not done yet. So far, we're only studying the motion that is excited by the artificial test signals. What would happen when we expose our combinations to actual real life records? That's the topic for the next post.
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