The Korf Blog

The inside story: our research, development and opinions

12 February 2018
Vibrational Energy of MC and MM Cartridges, Part II
We ended our last post with a clear answer: yes, the MC cartridges do dump a lot more vibrational energy into the tonearm. This time, we are adding 2 more cartridges to see the relationship between compliance, downforce and vibrational energy in a bit more detail.

The medium compliance MM
Here is the cartridge we are using for most of our vibrations tests. Audio Technica AT7V started its long life under a different name. Signet was Audio Technica's premium brand with a slightly mellower sonic signature, and AT7V used to be called Signet TK5E.

It is surprisingly good-sounding for such a modest price. Also, it is one of very few MM cartridges that actually are "flat" to 20kHz into the standard 47kOhm/200pF load.

If you believe AT's literature, AT7V's compliance is anywhere between 7 and 35 * 10-6 cm/dyne (for comparison, Denon DL-103 is 5). Its real compliance is around 10-12, straddling the middle between typical MM and MC cartridges.
The medium compliance MC
For a short time, AT-ART7 was a flagship in Audio Technica's lineup. It is a real super cartridge, easily holding its own against competitiors priced many times higher. Of course, attaching it to a bent aluminium headshell on a classic SAEC arm is not going to do it sonic justice — but we're going to measure it, not listen to it.

AT specifies its compliance a bit higher than AT7V's. Measurements show that it's exactly the same, give or take the inevitable error.
We had to truncate AT-ART7's line, because the incorrectly laid accelerometer cable fouled the bearings and invalidated the high frequency data. Still, the main arm tube resonances are there. First chart is AT7V and AT-ART7 versus a Shure M97xE:
AT-ART7 excites the 3rd harmonic at 775 Hz, but scarcely influences the counterweight. AT7V is closer to Shure in only exciting the first mode, but the counterweight resonance at 1100 Hz is a lot more pronounced.

Now strictly speaking, this isn't a correct statement. AT-ART7 is a heavy cartridge, and the counterweight had to be positioned all the way to the end of the stub, possibly damping it. But nevertheless, the fact that cartridges of same compliance and downforce (2g) differ so much in excitation harmonics is curious.
Second chart is AT7V and AT-ART7 versus a Denon DL-103, and it's easy to see the odd one out:
Both MCs, despite very different compliance and different downforce, present a similar picture and have a marked 3rd harmonic peak.
What can we bring out of it? First, the compliance specifications are very approximate. Cartridges of similar compliance but different construction differ a lot in their vibrational profiles.

Second, even the medium and high compliance MCs are a lot more demanding of tonearms than fixed-coil cartridges. Generator design, not compliance or downforce, determines the excitation spectrum.

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