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The MTA F-60 showed two very distinct characters with the Audio Space/Bel Canto versus the matching Feastrex CV4055 - very different, with different strengths and both quite enticing. With the company’s matching amplifier the sound was classic tube: illuminated in the midrange, rich in the lower midrange through upper bass, sweet in the high frequencies yet extremely well extended in the bottom end. How extended? The specification of 35 cycles was met with useable output even below that figure. This was remarkable and a real challenge to overachieving bass champions like the Ologe One and especially the Mark & Daniel models. The cabinet made some contribution of course, adding a little greater dimensionality and sense of weight but was otherwise surprisingly unobtrusive. Did the Feastrex play with the same gusto and swagger as the Ologe or M+D? No. The Feastrex was a gentler creature in that department. Frequency response is not the same as dynamic ability. The watchwords are deep and comparatively understated. But let’s be realistic. This was a 5-inch widebander accomplishing essentially full-range response by virtually any standard. If the maximum attainable volume level merely achieved ‘impolite’, in that context is was extraordinary performance.

Detail level with the tube amp favored the organic over exposition. Resolution was integrated with the character of the instrument. The combination lost some transient vigor in comparison to the Audio Space/ Bel Canto duo but did not sound slow. Dynamic range was somewhat compressed, with the pair requiring slightly elevated levels to speak with authenticity. This raised the dynamic floor to achieve better low-level detail retrieval and thus limited the palette due to lower absolute levels.

The greatest dynamic range was reserved for the midrange and upper midrange, reminiscent of the Ologe One but with lower absolute limits. The Feastrex duo was well matched to maximize individual abilities and minimize weaknesses, allowing for a very relaxed presentation with sufficient range to be engaging but never pushed to distress. For me the pairing always operated in its comfort zone.

The soundstage was consistently wide and fairly deep, with the CV4055 contributing a bit more forward projection than the Audiospace/Bel Canto. Overall focus was quite good and exhibited traditional tube dimensionality. Hall acoustics were somewhat darker and denser, trading some illumination for more instrumental solidity. Emphasis  was on cohesiveness of space and performers and natural rather than spot-lit.

The Audio Space/Bel Canto combination revealed a very different loudspeaker. If the Feastrex duo was the lady—dark, sultry and seductive—this was the muscular and agile tiger. The Audio Space/Bel Canto pair matched the CV4055 in its ability to illuminate the midrange but the overall frequency balance was very much in the transparency camp. Make that electrostatic transparency. The upper midrange through highs were extended and sweet wherever the recording allowed but otherwise gravitated a small amount towards the more neutral side of the spectrum. The lower midrange through upper bass transition was solid and mildly warm but less prominent than the tube rendition. It was in the lower bass region that things became quite different. With the Bel Canto the speakers only reached a useable depth of about 60 cycles and then gently rolled off. Still respectable and hardly bass shy considering driver size, this clearly diverged from the 30 cycles attainable from the matching Feastrex CV4055 amp. Curious to find a definitive cause, I contacted both Feastrex and Bel Canto.

Feastrex confirmed that although the amplifier was well matched to the speakers, it had not been custom tailored to achieve any extended response by trickery. John Stronczer of Bel Canto offered this explanation: “This is a classic impedance and damping factor issue. The output impedance of the tube amp is likely quite high—perhaps 2-3 or more ohms (low damping factor)—while the eVo amp is more like 0.1 ohms or less at low frequencies (high damping factor). The driver impedance will peak in the low frequencies at the driver/cabinet resonance point and could spike up to 20-50 or more ohms at the resonance frequency. This will interact with the high output impedance of the tube amp to cause an increase in LF level while the low output impedance of the eVo amp will not show this rise in LF performance but will damp the resonant peak. There is no problem here, just a normal result of differing output impedance reactions with different amp technologies. It’s a normal interaction and the result of a high damping factor compared to a low damping factor on the amps in question.”

Maximum bass extension is of course only a single parameter in the story of any speaker‘s capability and the Audio Space/Bel Canto pairing unleashed unexpected and dramatic potentials in the heart of the Feastrex. [Such potential overdamping of highly efficient lightweight drivers had Nelson Pass release two current-mode transistor amps with high output impedance under the FirstWatt brand particularly for such speakers. A loss of an octave or more of bass extension can be quite typical when mating a high-efficiency widebander with good self-damping to very low output impedance. – Ed]

Detail level and dynamics shone like the sun. The electrostatic analogy continued with these traits. While the speaker showed absolute volume limits and could be driven to distress with extremely wide dynamic swings, the vast majority of the time the combination showed a broader than anticipated dynamic palette with an immense amount of detail presented in extremely coherent fashion. The Audio Space/Bel Canto pairing was able to retain dynamic gradation into much lower levels and exercised ferocious transient control over the Feastrex. This generated a wider overall dynamic range at natural acoustic playback levels that tracked detail and dynamic shifts with a vengeance. Here was a widebander doing a very good impersonation of a small full-range electrostat. How did it sound? Breathtaking! Literally. I could hear the carefully measured drawing of breath by a performer to reach the right dynamic inflection of a note, soft or forte. The Feastrex was granting insight into the art and craft of music on an intimate level. This was top-tier performance in this regard.

Soundstage presentation was recording dependant rather than a product of the loudspeaker. If information dictated wide, deep and tall, this was faithfully reproduced. If it was restricted, that too was evident. Hall information was very rich with good separation of instruments on the stage. There was intense clarity derived from the virtues of high resolution, transparency and broadband coherence. This was a presentation that afforded a vivid view into performer intent and the engineer’s skill placing them within the environment.

With these observations made, it was time to have a little fun. The Feastrex was turned into what can be termed a 2.1 speaker system, almost full-range with the addition of an electronic crossover and subwoofer. The amplifier was taken out of its comfort zone and asked to see how it would perform within an unfamiliar and potential mismatch. The MTA F-60 augmented by a Paradigm Servo sub proved an interesting combination with the Audio Space/Bel Canto. The signature of the Feastrex remained predominant but with additional extension into true subsonic territory. Best results were obtained with the subwoofer output set understated, creating a natural augmentation only of the main speaker. There was a small increase in the MTA F-60’s dynamic ability afforded by more restricted bandwidth but nothing dramatic. Gains were purely in extended response and a continuation of dynamic agility at those lower frequencies which matched the Feastrex. The key was driver control, with the massive magnet structure on the Feastrex running alongside the tight-fisted servo system of the sub.