The Mission System Mission 780 Argonaut loudspeaker
As I said earlier, the classic Mission 770 was very much a BBC-influenced design, conforming to the British idea of a low-sensitivity, reflex-loaded, "monitor" speaker, though it had excellent upper-bass clarity compared with its similar-sized contemporaries, the Rogers Studio Monitor and Spendor BC1. The top of Mission's 1987 line, the 780 Argonaut has very little in common with the original 770. A tall, attractively styled, floor-standing sealed-box design, it uses two 8.5" polypropylene-coned woofers, with inverted dust caps bearing the Mission logo. Between the woofers is mounted what Mission calls a "Super Elliptic Impedance Transformed Tweeter." In English, this is a plastic-dome tweeter, loaded with a short flared horn with an elliptical mouth. (A horn acts as a transformer between the high acoustic source impedance of the small-area dome and the low air-mass load impedance.) The horn both maximizes the treble unit's sensitivity and optimizes its dispersion.
The unit is made by the Danish Vifa company, but is exclusive to Mission. The drive-units are time-aligned, the woofers being mounted forward of the tweeter on sub-baffles that look to be made from structural foam (though this doesn't mean that the speaker is phase-linear, this being dependent on the crossover configuration). The edges of the sub-baffles are sloped to echo the horn flare, with "Argonaut" printed in red on the top slope of the bottom baffle .
The cabinet is made from MDF, and is extensively braced. The rear panel is inset, to increase rigidity, and the base is fitted with bushes to take standard screw-in spikes. The crossover uses high-quality components, and electrical connection is via two pairs of five-way binding posts on the rear panel. The tweeter and woofers can be driven separately, either biwired or biamped, though, as supplied, jumpers connect the two pairs of posts for conventional wiring. The knobs of these are my preferred hexagonal profile, so that a nut driver can be used to tighten them up. All in all, the 780 Argonaut is an extremely well-engineered and finished product.
The sound: Following Mission's recommendations, the 780s were positioned about 9" in front of the rear wall, spaced by about six feet and firing straight ahead without any toe-in. Spikes were screwed to the speakers' bases to couple them to the floor beneath the rug. In addition, the near-wall placement made it easy for additional braces, cut from broom handle, to be wedged between the speakers' rear panels and the wall, something I had found to be beneficial with the Linn Sara. The initial auditioning was done with the speakers conventionally wired, driven by the Krell KSA-50.
No doubt about it, the 780s are loud speakers, being some 10dB more sensitive than my Celestions. In addition, the dynamics were excellent, not only regarding "jump factor"the ability to go very loud very quicklybut also the differentiation between subtly different sounds. Though he felt it to be well-controlled in his review of the 780 (Hi-Fi Answers, March 1987), Alvin Gold found the 780's bass somewhat lightweight. The Argonaut's low-frequency performance was about the best I have heard in my room, however: there was well-controlled low bass apparent, with one of the tightest, most detailed upper-bass regions I have experienced; only the Linn Isobarik and Celestion SL600 are in the same class. The bass guitar chording in Peter Gabriel's "Don't Give Up" had excellent "edges," for example, with accurate weight.
The midrange seemed well-detailed, with only a slightly hollow coloration apparent, and that only to a slight degree, woodwind sounding very neutral. Higher in frequency, however, I was less happy. The presence region seemed rather "shouty," and setting playback levels, particularly with vocal recordings, was difficult, the speaker unexpectedly sounding too "loud," depending both on the type of music and the way it had been recorded. The top octave was a little exaggerated, resulting in strings becoming slightly wiry. This sparkle lent itself to reproduction of percussion and brass instruments, however, the blatty fizz of trumpets and trombones played loud coming over very well indeed. For some reason, this forward quality in the treble seemed much less bothersome with CD replay than it did from LP. I can only suggest an incompatibility between the 780's treble voicing and the typical MC cartridge's response shaping.
Imaging was excellent for a wall-placed loudspeaker, that detailed midrange retrieving ambient clues to create a wide, spacious stage. If depth was not reproduced with as much panache as with the SL600s, the 780s are still no slouches in this area.
Changing to biwiring, again with the Krell driving the speakers, seemed to add slightly more LF extension. Notes started and stopped more positively, and the treble was cleaner, if still somewhat unsubtle.
Overall, my listening suggests the 780 to be a mixture of the outstanding and the ordinary. Below 2kHz, it is one of the best dynamic loudspeakers I have used, with a superbly tuned bass alignment, excellent dynamics, and a relatively neutral midrange. Above 2kHz, it is rather aggressive and will require careful system and room matching to produce a consistently musical sound. Considering, however, that it is aimed at a wider market than the US high end, its basic sound quality blows the socks off similarly priced mass-market speakers that I have heard. Its idiosyncratic treble will mean that you will either love or hate the 780; if the former, it could be considered good value, even at its highish price.
Measurements: Nearfield, the LF response was 6dB down at 38Hz, quite a high frequency considering the size of the box. Mission's designers, however, have sacrificed some extension in order to squeeze as much sensitivity as possible from the drive-units. (All things being equal, cabinet volume, sensitivity, and bass extension are locked together in an intimate mathematical embrace.) In-room, the spatially averaged response was flat down to 40Hz, thus reproducing the fundamental frequencies of all instruments down to the double bass and bass guitar in full measure. The in-room -6dB point was a low 32Hz, reinforcing the point made by Martin Colloms (in Vol.10 No.5) that a well-designed sealed-box loudspeaker in a typical room will get considerable help from the room acoustics at frequencies below 60Hz. And well-designed the 780's bass is: there is negligible rise at resonance, and the only unevennessin the mid- and upper-bass responseis due to the proximity of the rear wall in the recommended positioning.
The averaged response (fig.1) was superbly flat through the midrange, ±1.1dB limits sufficing from 160Hz to 2.5kHz. Above that frequency, however, there was a little too much energy in the 3.15kHz and 6.3kHz bands. In addition, the extreme HF response on the tweeter axis didn't roll off early enough. This was ameliorated in use by the fact that the listener sits about 15° above the tweeter axis; with the speakers firing straight ahead into the room, the listener will then also be about 15° off-axis laterally. The measured in-room response for this listening position lowers the presence peak and gives a slightly better integration between the upper bass and lower midrange, at the expense of the evenness of the upper midrange. Nevertheless, excellent ±1.9dB limits still hold for the spatially averaged response on this axis over two decades, from 40Hz to 4kHz!
However, though the direct sound appears to be pretty flat, a side effect of the excess on-axis HF energy is that the reverberant soundfield also has a lifted treble. Whether this will be bothersome or not will depend on a number of factors, including the size of the room, the proximity of the side walls, how close you sit to the speakers, and the degree of HF absorption offered by the room furnishings. Although my room is well-behaved regarding flutter echo, it is quite reflective; this non-flat nature of the treble reverberation, coupled with the 780's slightly peaky low treble and my fairly close seating position about seven feet from the speakers, would probably explain why I felt the speaker's HF to be rather aggressive.
The fact that the high- and low-pass legs of the crossover can be separated enabled me to measure the tweeter and woofer response independently. The crossover point of my pair appeared to be a little higher than spec at 2.2kHz. Acoustic crossover slopes appear to be 18dB/octave for the low- and 12dB/octave for the high-pass, though the fact that the tweeter peaks a little bit at 3.15kHz makes this an approximate measurement, at best. Listening to the drive-units on their ownsomething recommended by Jimmy Hughes in Hi-Fi Answers a couple of years backrevealed the woofers to be well-behaved, if a little hollow-sounding, through the midrange, with no severe discontinuities in their response. The sound was quite musical, though there was a complete lack of HF, of course.
Listening to the tweeter on its own with a pink noise signal revealed a slight hardness around 3kHz and excessive energy in the top octave, but not as much treble peakiness as I had suspected from my full-range listening. The tweeter response seemed a little critical in the vertical plane, but well-maintained laterally to about ±15°. Having become familiar with the signature of the tweeter on its own, I found with full-range pink noise that it didn't integrate as well with the woofers as I would have liked. (The original 770 was superb in this respect, there being no indication that some frequencies came from the woofer and some from the tweeter, even close up.)
The impedance magnitude plot (fig.2) showed the LF resonance to lie at 49Hz, the value averaging 4 ohms through the lower midrange and rising to around 8 ohms at 1kHz. Though Mission says in its literature that, as a 4 ohm design, the 780 needs a "modern" amplifier to drive it properly, it should not present a drive problem to amplifiers, particularly in view of its high sensitivity, measuring a genuine 93dB/W/m for the 1kHz 1/3-octave noise band.