MANUFACTURER'S SPECIFICATIONS
Frequency Response: 20 Hz to 45 kHz.
Channel Separation: 32 dB at 1 kHz, 29 dB at 10 kHz.
Output Voltage: 3.8 mV at 1 kHz (5 cm/sec.).
Channel Balance: Within 1 dB @ 1 kHz.
Impedance: 2.7 kilohms at 1 kHz.
D.C. Resistance: 610 ohms.
Recommended Load Resistance: 30 to 100 kilohms.
Compliance: 42 x 10^-6 cm/dyne @ 100 Hz.
Tracking Force Range: 0.8 to 1.8 grams.
Weight: 6.2 grams.
Dimensions: 29 mm (1.14 in.) x 17.5 mm (0.69 in.) x 17 mm (0.67 in.).
Mounting Centers: 12.7 mm (0.5 in.).
Price: $175.00.
It isn't often that a brand-new line of phono cartridges is introduced in this country, especially one which includes four models all based upon a newly patented, improved induced magnet configuration. The rest of the Acutex International line of pickups includes a Model 315111E (which is similar to the 320111 but with a bi-radial, nude diamond stylus instead of the "STR" nude diamond found on the 320 which responds to CD-4 frequencies) with a suggested retail price of $135.00 and lower priced Models 312 and 310 which carry suggested retail prices of $85.00 and $65.00 respectively.
All of the aforementioned models feature a new tri-pole induced-magnet design. According to material contained in the patent concerning this new family of cartridges, previous forms of induced-magnet or moving-magnet cartridges have been limited in magnetic efficiency, crosstalk, and distortion characteristics because it has been extremely difficult to locate pole pieces sufficiently close to the armature of the system and thereby reduce the length of the magnetic circuit.
Furthermore, the patent description claims that because the conventional armature is supported by a damper member, the fulcrum upon which the armature moves is indefinite in location, making it impossible to concentrate the mass of the vibration system at a single point.
In the M320III STR and other cartridges in this series, a tri pole armature is attached to the base of the cantilever and is composed of three basic armatures facing in three different directions. One of them fixes the cantilever and increases rigidity, avoiding the possibility of "split vibration" in the vibrating assembly, while the other two armatures pick up the stereo signals and transmit them to the four induction coils.
Physically, the new cartridges are relatively easy to mount in most headshells, with gold-plated terminals provided on the model we tested. We did note that the diameter of these terminals is a bit on the small side, so that in order to obtain good contact between them and the slip-on terminals of the headshell we used (our tests were conducted using the new Empire Model 698 turntable and arm system), we had to pinch the slip-on connectors a bit before applying them to the cartridge terminals. (Editor's Note: While we do not consider this to be a problem of major importance, it would make things a good deal more convenient for folks who change cartridges often, like cartridge testers, if all the manufacturers would standardize on terminal size, location, grounding, color coding, etc. This would ultimately make possible a standard one-piece connector between cartridge and tonearm. E.P.) The entire stylus assembly is removed easily from the cartridge body by gently pulling it downward. A pivoting stylus guard protects the diamond tip during this procedure and also when the cartridge is not in use.
Laboratory Measurements
Our particular sample was a bit "hotter" than specified, delivering 4.3 millivolts at 1 kHz for a recorded velocity five centimeters per second. Frequency response was about ruler-flat from 20 Hz to 20 kHz, as illustrated in the graph of Fig. 1. It should be noted that this particular cartridge model has response out to 45,000 Hz and therefore exhibits the usual slight peak in response caused by stylus assembly resonance at a frequency well beyond the usual 20,000-Hz upper limit of our tests. Even more impressive was the separation characteristic which is also shown in Fig. 1.
Acutex's claims with respect to improved separation are no idle boast, since we measured a very impressive 33 dB at 1 kHz and an even more remarkable 29 dB (as claimed) at 10 kHz. We used a CBS STR-130 test record for these as well as the frequency response measurements, preferring it over the older STR-100 even though it is necessary to feed the output of the cartridge into a calibrated equalizer-preamp. In our lab we use an All-Test Devices Laboratory Reference preamplifier for that purpose, having found that its RIAA playback characteristic is about the most accurate we have tested.
Tracking force range is perhaps a bit high by today's standards for a cartridge in this price and performance category, even taking into account the fact that the "STR" shape (designed for tracing CD-4 records) engages more groove wall length and therefore imposes less actual pressure per square area than might at first be supposed. We found that this particular cartridge performed best when tracking force was set to 1.5 grams. Under those operating conditions with anti skating properly adjusted, we were able to obtain trackability figures of 37 cm/sec. at high frequencies, 40 cm/sec. at mid frequencies, and 30 cm/second at low frequencies. Reducing the tracking force to 1 gram also reduced high frequency trackability to 30 cm/second, as might be expected. We used Shure's TIR-103 test record for these tests.
Not content to accept the stylus description by its unrevealing initials (STR), we delved into the derivation of those letters and discovered (from the people at Acutex) that they stand for "symmetrical tri-radial"-the tip shape of the extended nude diamond tip used in this cartridge. Another description of the stylus tip states that it is an allyptical (not elliptical) shape.
Figure 2 is a 'scope photo of the square-wave reproduction capability of the cartridge and was photographed by applying the output signal directly from the cartridge while it was playing the square-wave test bands of the CBS STR-112 test record.
Use and Listening Tests
Before listening to a variety of musical discs as played with the M320111 STR cartridge, we decided to put it through its paces using Shure's newly released Era IV Obstacle Course Record (TIR-115). The first side of this disc consists of musical passages played by individual instruments (orchestral bells, flute, and harp) at incrementally increasing levels. Five levels are provided for each instrument and for the solo selections the M320III STR was able to successfully track all five (quite an accomplishment, incidentally). Side two of the record combines two instruments at increasing levels and is the more difficult to track. In this instance, the cartridge tracked all but the fifth band of the harp and flute combination, and all five of the flute and bell combination tracks. This test record also contains a test for arm-cartridge low-frequency resonance, and for the case of this cartridge mounted in the Empire arm, resonance was measured at 8 Hz, but was not severe enough to cause mistracking or groove hopping. All of these tests were conducted at the previously determined tracking force of 1.5 grams.
Subjectively, the cartridge sounded extremely smooth in response with not the slightest evidence of shrillness or peaked response at the high end, confirming our bench measurements. Interestingly, this cartridge is less susceptible to changes in performance as load resistance is varied than are most. This probably accounts for the broad values of loading resistance given in the published specifications. Between 100 and 150 pF of capacitance (including tonearm wiring) gave the best overall sonic balance to our ears, but variations in this regard also seemed to be less critical than with many other cartridges we have tested. Transient response had already been considered excellent using the orchestral bells test of the TTR-115, but was further confirmed when we played a variety of direct-to-disc records, notably the Sonic Arts Piano Fireworks album (SA-LSI) and Umbrella UMB-DD4 (Big Band Jazz), both distributed by Audio-Technica. A disc entitled Warren Smith and Masami Nakagawa, consisting of flute and percussion selections (RCA/RVC RVL-8502), gave further proof of the cartridge's ability to track complex low and high-frequency waveforms having sharp transients with little or no evidence of intermodulation distortion. In short, the M320III deserves to join the ranks of those high-end cartridges that set the standard for the rest of the industry.
-Leonard Feldman
Fig. 1--The frequency response (upper curve) and crosstalk characteristics
of the Acutex M32011I cartridge. Points above 20 kHz were plotted using the
JVC TRS-1003 CD-4 test record.
Fig. 2--Square-wave reproduction (1000 Hz) using the CBS STR-112 test record.
(Audio magazine, Jun. 1978)
Also see:
ADC Stereo Cartridge 10E MK IV (Dec. 1972)
ADCOM Crosscoil XC/VAN DEN HUL Moving-Coil Phono Cartridge (Jan. 1982)
Decca London International Tonearm & Mk VI Gold Elliptical Phono Cartridge (Aug. 1979)
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