Mission Freedom Loudspeaker

The Mission 770 Freedom was an award winning British loudspeaker produced by Mission Electronics, an audio company based in Huntingdon, United Kingdom. The Freedom model variants date from the late 70s through to the late 80s. In all of its incarnations it was a large stand (or rather 'pedestal') mounted loudspeaker of a two-way design, combining a convert|200|mm|adj=on woofer and convert|25|mm|adj=on tweeter in a reflex tuned cabinet.

The speaker's unique selling points were its innovative design, natural sound quality and extremely high power handling for a consumer (as opposed to a professional) system [Colloms, M. (1980). Hi-Fi Choice No 21 Loudspeakers(4). London: Sportscene.] . Mission was the first company to negotiate the patent rights for the commercial exploitation of polypropylene as a loudspeaker cone material [Mission Electronics (1987). The Human Touch [Product Brochure] . Cambridge: Mission Electronics Group.] and the speaker system as a whole was able to handle what HiFi Choice magazine regarded as an "extraordinary" amount of power [Colloms, M. (1980). Hi-Fi Choice No 21 Loudspeakers(4). London: Sportscene.] .

Mission 770 (circa 1978)

Mission 770II (circa 1980)

The original Mission 770 was very well received by press and public alike (e.g. What HiFi [What HiFi (1986) Buying Guide. London: Haymarket] ). The updated 'Mark II' version aimed to build on this success in the face of increasing competition and the growing popularity of home hi-fi in general [Kessler, K. & Harris, S. (2005). Sound bites: 50 years of hi-fi news. London: IPC.] .

The most significant change heralded by the Mark II model was the incorporation of a new mid/bass driver, which still used the innovative (and transparent) polypropylene diaphragm material, but employed an enlarged voice coil of convert|33|mm. Thermal performance, and by implication power handling, increased, along with a reduction in some previously noted distortion.

As before, reviews [Colloms, M. (1980). Hi-Fi Choice No 21 Loudspeakers(4). London: Sportscene] noted the excellent low-distortion performance, easy amplifier load and high sensitivity. The natural character of the sound was due in no small part to the even frequency response, which remained within narrow tolerances (±2 decibels from 65 hertz to 16 hertz).

HiFi Choice described the sound quality of this model as follows:

The sound was considered open and explicit but with a degree of 'hardness' and 'sharpness' in the lower treble. On the stereo sessions the imaging was only a little short of the top category, exhibiting good depth and excellent lateral image precision. On rock programme the 770 gave sharp definition to percussion and transients [...] Overall the ratings were impressive and generally justified the price

[Colloms, M. (1980). Hi-Fi Choice No 21 Loudspeakers(4). London: Sportscene.] (which was £370 in 1980 including stands).

Mission Freedom (circa 1986)

The coming of Compact Disc and digital audio heralded a significant change in loudspeaker design during the eighties [Attwood, D. (2002). Sound design. London: Octopus] . The MkII 770 was typical of the previous generation in having an easy amplifier load (in the days when 25 watts was considered ample for most living rooms) and its performance in the lowest bass registers was traded in favour of efficiency and low distortion. These design parameters matched the dominant source material, which was vinyl.

The advent of digital sources like CD created new and conflicting design imperatives (such was the expectation bound up in digital audio). These imperatives were: high sensitivity, very wide dynamic range, high power handling and wide frequency response. The last incarnation of the 770 Freedom was, as a result, a design that attempted to interpret these requirements through the use of a number of innovative features.

Introducing the new model Mission stated, "Following the extraordinary success of the original Mission 770, inferior copies flooded the market to such a degree that at Mission we decided to move on" [Sinclair. I. R. (2000). Audio & Hi-Fi Handbook. Oxford: Newnes.] . The Mark II 770 was updated again to become the Mission 737 renaissance. The 770 Freedom, however, became an entirely new loudspeaker designed to meet four goals:

Firstly, we [i.e. Mission] wanted to ensure that the frequency range offered greater extension. Secondly, our design team felt that the bass response could be tighter, more articulate, with more transient attack. Thirdly, we wanted to increase the dynamic headroom so that all non-linearities, compression, and saturation problems were eliminated. Finally, we wanted to enhance sensitivity and efficiency for the era of digital masters [Sinclair. I. R. (2000). Audio & Hi-Fi Handbook. Oxford: Newnes.]

Cabinet

The brand new cabinet was based around a transverse folded technique (the top, bottom and sides had 45 degree mitred faces, meaning that the back and the baffle were separate). The cabinet was increased somewhat in size but it was still a stand mount speaker (albeit a very large one). Purpose designed stands made of vinyl covered particle board fitted into slots in the speaker's base.

Mission adopted a very unusual baffle design for the 770 Freedom (mirroring some innovative approaches elsewhere in their range, e.g. the Mission 700 Leading Edge and the Mission 707). First of all it was very thick and constructed of MDF (still an innovative material in the 1980s). It was made of two MDF panels sandwiched together with the outward facing one wasted away considerably to create a time aligned/corrected baffle which had a convert|1|in|adj=on proud mounting for the woofer. A further strengthening brace was also included internally between that and the reflex port. The cabinet was part filled with acoustic wadding and the interior faces had a vico-elastic damping material applied (a black rubbery roof felt-like material).

Drivers

An unusual feature of the new 770 Freedom was the tweeter which, like the time aligned baffle, eschewed current practice in domestic loudspeaker design in favour of a feature more common in the professional audio sector. Horn loading; this affects dispersion (and thus stereo imaging) and sensitivity (with the potential to reduce distortion).

Unlike professional audio speakers that use horns, and tend to be employed in far larger spaces, the Freedom's elliptical horn was designed with the home user in mind.

This brand new double-chamber, impedance transformed super-elliptical tweeter is designed to offer extraordinary smoothness and realism - eliminating the remnants of typical dome tweeter sibilance and offering uncanny dispersion characteristics. The mathematics of impedance transformation uniquely ensures structural form integrity to the polymer dome under severe transient conditions. The unit is then oil cooled to avoid temperature related performance aberrations and increase saturation thresholds. [Sinclair. I. R. (2000). Audio & Hi-Fi Handbook. Oxford: Newnes.]

Polymer domes and oil cooling were at the cutting edge of tweeter design at the time, and that was before mounting it to a horn.

The horn was unusual in a number of respects. Firstly, horns are typically used with specially designed compression drivers; this horn was paired with a more normal 'direct radiator' dome tweeter. Secondly, the horn material was unusual and a hallmark of Mission's experimentation with advanced materials; it was made of injection moulded polypropylene reinforced with natural mineral fibres (this was the same material used to make the injection moulded frame for the grill covers as well as the baffles of the 707 and 700 Leading Edge models further down the range). The horn was also of an unusual profile; a super ellipse rather than the various paraboloids that were more common. The face of the horn also featured moulded 'whiskers' to reduce diffraction effects. Finally, the mid/bass driver crossed over to this innovative drive unit at an unusually low 1.9 kilohertz. This is of great benefit as it avoids the more typical range of 3 to 3.5 kilohertz at which the ear is most sensitive to the phase anomalies that result. Amongst other things, it appears that the horn increased sensitivity enough for the drive unit to operate meaningfully within this lower range.

The mid/bass driver was also highly unusual. It used a homopolymer mineral-loaded plastics material (belonging to the same family as polypropylene). It featured a large voice coil to aid power handling, distortion, thermal efficiency etc., and a natural rubber surround which was especially narrow compared to the wide inverted surround of the original 770 driver. In design terms, the surround itself represents a radiating surface and the source of considerable distortion at low frequencies. Minimising its width minimises the area of this unwanted radiation, thus helping to reduce distortion further [Mission Electronics (1992). The Human Touch [Product Brochure] . Cambridge: Mission Electronics Group.] . The front face of the unit was finished with an inverted dust cap (of the same homopolymer material) with the mission logo printed in white text. Around the back, and despite the superb bass performance available from the system, the magnet assembly is not especially large, but it is affixed to a cast magnesium basket structure. The unit, therefore, is built to very high quality standards using unusual materials. Incidentally, the drive units are marked on the back with 'Argonaut', and indeed, two of these units appear in the flagship 'Argonaut' speaker which is inspired by the Freedom design.

Mission themselves described the unit thus: "The cone material is carefully optimised for mass, rigidity, compliance, and 'Q' to offer hitherto unattained low frequency extension for a system of this size. The brass-plated pole piece with special geometry, together with high temperature voice coil materials and ventilation, increase motor output and power handling" [Mission Electronics (1987). The Human Touch [Product Brochure] . Cambridge: Mission Electronics Group.] .

Reflex Port

A stylistic as well as performance related update to the design was the use of a cellular port instead of the rather crude 'tunnel port' of old (through which one could clearly see the acoustic wadding inside). The principle of the cellular port design is to reduce turbulence and the characteristic 'chuffing' sound of ports as the air mass inside them is excited.

ound Quality

This was a quite different loudspeaker to previous designs; its performance was well in excess of what had come before, particularly in terms of bass extension which to this day is impressive with meaningful output measurable down to as low as 28 hertz. The effortlessness and speed of its delivery has also drawn favourable reviews [www.audioreview.com]

Mission described the performance of their latest model as follows: "When measured, the Freedoms are capable of extraordinary behaviour. The on-axis response is smooth, off-axis measurements exhibit minimal aberrations, and driven at 90 dB the midband distortion is close to 0.1% - approaching amplifier specifications!" [Mission Electronics (1987). The Human Touch [Product Brochure] . Cambridge: Mission Electronics Group.]

These speakers were described as 'state of the art reference monitors' [Mission Electronics (1987). The Human Touch [Product Brochure] . Cambridge: Mission Electronics Group.] and they are very revealing and transparent. The quality of recorded material shows through. Overall these speakers have a very clean and smooth sound and accurate stereo imaging [www.audioreview.com] due in no small part to the horn loaded tweeter. Vocals have real presence. They also have what could be described as a characteristically eighties sound, there is an emphasis on speed and attack and dynamics. Ironically, for most owners of first generation CD players the substantial bass output of this design could only be accessed decades later (when better, less bass-shy CD players arrived on the market) but Mission's tagline for the design was still warranted, "Of the 770 we have always said, '...and when you switch over to the 770's you will smile and say - that's Magic!'" [Mission Electronics (1987). The Human Touch [Product Brochure] . Cambridge: Mission Electronics Group.] .

Later Models

The last generation of Mission Freedoms occupied a place high up in a product range that included such classics as the Mission 70, the Cyrus 1 amplifier, the DAD7000 CD player, the 774LC tonearm, a line up that is today widely regarded as 'classic' [www.audioreview.com] . Of course, things move on and with the dawn of the 1990s the Freedom's became the floor standing 764's. The Freedom name was resurrected in more recent times but the design is unrecognisable from the original (being a floorstander).

Buying

Given their popularity good examples of all models of the 770 Freedom can occasionally be found. The original 770 and the Mark II are probably least well suited to general use with modern digital and home entertainment sources. This is not to say that their performance is poor, far from it, but they are a large speaker system for the amount of bass output available. They are also wider than they are deep, and thus rather unfashionably seventies looking. For the enthusiast, though, they will always offer a characteristically natural, airy sound.

A better choice for modern sources are the last generation Freedoms, although they are a very large speaker system by modern standards, and being stand mounted as well, their size is quite formidable in anything but large listening rooms. Unfortunately, stand mounting is highly recommended because the horn loaded tweeter is very directional in the vertical plane and they sound rather dull if not at ear-level [www.mission.co.uk] .

Stylistically, the choice of grey woodgrain finish and a pair of narrow black stripes, combined with bold red 'Freedom' graphics on the front, ensures that these speakers make quite a statement, but that aside, the performance is very good even by today's standards [www.audioreview.com] . As mentioned previously, the last generation Freedom's were, if anything, over-engineered for the sources and amplification then extant in the 1980s. This means that high power amplifiers and high bit-rate digital sources can now fully exploit their capabilities with excellent results.

It has to be remembered that trends in audio change, so modern loudspeakers need not be 'better' in all aspects of performance, indeed, modern loudspeakers have tended to emphasise the ability to generate good performance from smaller and more power hungry boxes. The trend now is towards very narrow tower style speakers which have constraints and characteristics unique to that design as do speakers like the Freedoms of a fundamentally different ethos. A speaker system of the size of the Freedoms (both in terms of cabinet and drive units) has become quite unusual; they have a different set of constraints and characteristics that listeners may prefer or not, either way they have a characteristically 'big-box' sound which many enthusiasts of today will appreciate.

There are some issues that the potential second hand buyer needs to be aware of. Some of the crossover components are prone to over-heating, to the extent that they begin to melt the plastic of the terminal plate to which they are affixed (this is visible by looking for melting next to the negative terminal). Likewise, the polymer dome tweeter degrades markedly with age, with the diaphragm shrinking over the pole piece and becoming dented and distorted as a result. These are difficult to replace as the mineral loaded plastic horn is glued to the face plate of the tweeter. In addition, the tweeter's motor assembly is encased in a sealed 'impedance transformed' case (as is correct with horn loading) that is also glued in place. Replacement of the drive unit for a modern equivalent would, therefore, be difficult. The mid/bass driver, however, is extremely durable and none of the materials used in its manufacture are prone to marked deterioration.

ee also

*Mission 737 Renaissance

Notes