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Shure V15VxMR Intermodulation Distortion Measurements

Posted by John Elison (A) on May 24, 2004 at 10:20:46

The following graphs show how the Shure V15VxMR performs on intermodulation tests with a +12-dB test tone modulating a low-level 3,945-Hz test tone. Actually, the low-level test tone was supposed to be 4,000-Hz, but the manufacturer’s test tone generator must have been running a little slow. My turntable speed was right on target.

Those of you who own the Hi-Fi News test record will understand the significance of a +12-dB test tone. It is the same level as the first bias setting test tone, Band 6, Side 1. The only difference is the frequency—300-Hz on the Hi-Fi News test record compared to 200-Hz for this intermodulation test.

When intermodulation distortion occurs from modulating a low-level high frequency signal with a loud-level bass frequency, intermodulation side-bands form around the high frequency signal showing the distortion. The frequency of the side bands will be multiples of the low frequency signal added and subtracted to the high frequency signal. In contrast to harmonic distortion, intermodulation distortion is non-euphonic because the side bands are almost never harmonically related to the modulated signal.

Okay, harmonic distortion, especially 2nd harmonic distortion, is considered to be euphonic because it is harmonically related to the music. In fact, there have been listening tests conducted in which participants actually preferred the addition of anywhere from 2% to 5% 2nd harmonic distortion, depending on the type of music. On the other hand, intermodulation distortion is very undesirable and even small amounts of it tend to detract from one’s musical enjoyment.

This brings me to my latest theory regarding the sonic differences between MM cartridges and low-output MC cartridges. I have a theory that MC cartridges sound better because they produce more of the euphonic types of distortion and less of the non-euphonic types. From the measurements I’ve completed thus far, the Dynavector DRT XV-1 produces more than twice the harmonic distortion as the Shure V15VxMR, which is consistent with my theory. Now, if only the intermodulation tests would show the reverse, my theory might be valid. Unfortunately, I have not yet measured the Dynavector for intermodulation distortion. That will be my next project, which is to reinstall the Dynavector and conduct intermodulation measurements.

The excessively high levels of intermodulation distortion with a vertically modulated groove are rather disturbing and perplexing. We’re talking about almost 100% intermodulation distortion. I am very curious to find out what the Dynavector does on these tests.

Best regards,
John Elison

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