Oracle Mentor Loudspeaker

      Date posted: February 24, 1999

Oracle Mentor Studio System Loudspeaker

Sugg. Retail: $5000 (CAN)
Manufacturer: Agence Commerciale ACI Inc.,
4124 Blvd. Industriel,
Sherbrooke, Que. J1L 2S6
(819) 573-5488 FAX 573-0154

(Reprinted from the Winter 1999 Audio Ideas Guide)

      The Oracle speaker project goes back quite a few years, and the Mentor Studio system is the culmination of that project, and its sleek finish reflects (quite literally) the tradition of craftsmanship associated with Oracle. Our review pair were finished in a shiny burgundy lacquer that looked as if it had been lovingly rubbed and polished by skilled hands.

      The Mentor Studio comes in two tapered sections, the lower low-frequency one containing a single woven Kevlar woofer facing to the rear, the front appearing to be a simple pedestal; it’s also ported to the rear, the port just above the driver. The top is indented and covered with velvet, onto which fits a hardwood (probably ebony) isolation plate. The Monitor section of the Mentor sits on top of this plate, and contains an easily recognizable DynAudio 6 1/2″ mid/bass driver with a fabric dome tweeter above. Black velvet also covers the baffle around the drivers to minimize diffraction, while an acoustic lens surrounds the tweeter to further control its radiation pattern. Each speaker section has its own input terminals, gold-plated 5-way posts of high quality, and parallel bi-wiring or bi-amping is required. The Back of the Oracle Mentor Studio System Loudspeaker

      In conversation Jacques Riendeau commented that the lower woofer section is less intended to provide deeper bass than to offer more bass; as the measurements show, the Mentor could use subwoofer augmentation, down 6 dB at 50 Hz, and is even specified to have extension only to 45 Hz (+/-3 dB). But if we look closely at the low end rolloff, we see that in the Pink Noise Sweep (PNS) curve the Mentor is down only 10 dB at 30 Hz, so with careful placement quite decent bass response can be achieved using boundary reinforcement. The lower PNS trace in the bass at top is for the Monitor section of the Mentor without the bass section playing. Oracle Mentor Frequency Response

      Looking at the rest of the spectrum, we see very smooth response from below 100 Hz through the midrange to about 3 kHz, with a rolloff above of 3-to-4 dB in the treble region. This should give the Mentor a very neutral, but slightly laid back character, and should result in very natural timbres in smaller rooms, that is, at fairly close listening distances.

      The quasi-anechoic curve, seen between the top and bottom families of curves is taken on axis at 1 metre (see the sidebar, How We Measure Loudspeakers), and shows the unsmoothed midrange and treble response of the speaker. Here it indicates a dip just above the 3 kHz crossover point that is also seen in the axial curves taken at 0, 15, 30, and 60o off axis. Naturally, when we add these together to get the Summed Axial Response (SAR) that overlays the PNS, this dip is also seen at top. However, as can be seen in the PNS, this tends to smooth when we measure the overall energy radiation with pink noise, and, in my view, the PNS better reflects what the listener will hear.

      What he or she will also hear is a very consistent timbral balance anywhere in the room, the axial curves showing excellent control of diffraction and very even dispersion into the room. Both the tweeter lens and the velvet flocking have a beneficial acoustic effect. Oracle Mentor Impedence Graph

      The impedance of the Mentor is very smooth except in the bass where the usual peaks associated with ported systems are seen. From 200 Hz up it hovers around 4 ohms, with a slight rise in the upper octaves. The woofer section’s impedance can be seen at top, and its peak of 65 ohms is considerably higher than that of the monitor section’s 10 ohm maximum. Electrical phase does some funny things in the bass at 30 Hz, but this is of no consequence; through the midrange it is quite smooth, with a gentle 30o shift above crossover. Despite its low impedance, the Mentor should be a fairly benign load for amplifiers, with a moderate phase angle and well controlled impedance, but solid state is definitely in order, and the more current the better.

      After listening to the Mentor Studio system for quite some time, I would characterize it as a very refined reproducer designed to work best in smaller rooms at fairly close quarters. In comparison to our Veritas reference, I could hear that little extra bit of energy around 2 kHz, as well as the top end attenuation, but continued listening revealed its inherent musicality and natural character with all sorts of music. Male and female voice were well conveyed, and instruments had the appropriate timbres, while percussion was never splashy or harsh. The tweeter was quick and agile, also delivering great detail and a soundstage with depth and dimension. Its dynamic capabilities were also excellent for its size, the extra woofers helping here.

      Speaking of woofers, though the Mentor system did not plumb the depths, it did deliver bass that was very specific in its pitch accuracy, most likely the result of tuning the system for speed rather than extension. Jazz lovers will be thrilled by how well this system reproduces standup acoustic bass, something I’ve developed a special interest in lately.

      Though some other speaker reviewers have been unable to associate unusually good phase accuracy with better sound reproduction, in my experience, speakers with the least electrical phase shift through crossover tend to have a rightness of sound, as well as better soundstaging and depth. Even if they are not fully acoustically time aligned, they do get the music through the crossover to the drivers relatively unscathed in terms of time.

      That is certainly the case with the Oracle Mentor Studio system. It exhibits a very effortless, natural quality with all types of music,especially with acoustic jazz and other small ensemble genres. That in-the-room presence will, I’m sure, endear many to the Mentor, as will its superb finish and elegant design. If we seem to be talking your language here, plan a visit to your nearest Oracle dealer.

Andrew Marshall

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