Supravox emerged from a
company that was founded in France in the 1930s, and proved successful in the
heyday of field-coil driver production. Since 1945 the company has
successfully developed in house technologies and continued producing
loudspeakers, almost uninterrupted, to the present day. This Supravox 215
EXC is one of very few survivors of a once dominant species. This raw
drive unit comes in several forms, depending on the magnet type used in its
motor. This EXC version uses a large ‘field-coil' electromagnet and
costs around £2,000/pair; normal permanent ferrite and alnico magnet versions
are also available.
The fact that field-coil (electromagnet) energized
loudspeaker drive units still exist is a triumph for the enthusiasts who've
managed to conserve what they consider to be a worthwhile engineering
approach, in spite of the fact that it has subsequently been almost swamped by
advances in technology and mass production.
Back in the earliest 1930s days of hi-fi, powerful permanent
magnets were exceptionally heavy. The only way to create the required magnetic
field strength in a manageable packaged loudspeaker was to use a field-coil
magnet. Back then the coils were designed to work at a high voltage (100s of
volts DC), and were often also used as a filter choke in a valve amp's high
tension power supply. Hum could frequently be a problem.
The ubiquitous modern direct radiating moving coil
loudspeaker that dominates audio today was made possible by subsequent
advances in magnetic materials. When relatively lightweight permanent magnets
with high field strength became available (in practical terms after the Second
World War), and proved capable of delivering an acceptable result in both
sensitivity and sound quality, field-coil drive units were rendered all but
obsolete and extinct. However, some devotees still believed field-coil drivers
were intrinsically better, so limited development continued for these extreme
Although design diversity was the rule rather than the
exception, loudspeaker companies all searched for wide bandwidth, good
efficiency and domestically acceptable products, especially after two
loudspeakers were needed once stereophony arrived in the late 1950s. Cheap
permanent magnet moving-coil cone loudspeakers that could fit into small
cabinets and were relatively easy to make proliferated. In search of better
performance and advanced technical specification, the industry developed
complex multi-driver systems in similar compact packages.
visiting PM a couple or years ago, I heard some vintage Voigt Domestic
Corner Horns using single field-coil drivers. They sounded so interesting
and musically natural that I began to wonder why even the high end had
virtually abandoned such technology. Looking back, had the industry taken the
best direction for musical satisfaction?
I believe it's easy to understand why the industry followed
the course it did. Once the systems of mass production are set in motion, it's
far easier to make advances in those technologies familiar to engineers. Most
of the industry and the market accepted that the development and refinement of
permanent magnet driver technologies was capable of producing ever better
loudspeakers. Field-coil technology had been usurped; long live the simpler
and cheaper permanent magnet solution.
However, like so many activities that captivate people
emotionally, hi-fi is divided into factions. Although such factions may remain
aware of mainstream trends, they independently adopt pertinent techniques to
develop extremes of performance in their own desired directions. Most of us
(including hi-fi reviewers) necessarily receive mainstream products with
widespread availability. While we may become aware of the rarer and more
exotic components around the periphery, those interesting technologies are
constrained by restricted access and tend to remain forever out of sight for
all but the inquisitive few.
We seem to expect the best to rise to the top, but these
days I consider that the companies with the better marketing muscle and
expertise tend to dominate the scene. Although the internet has made it far
easier, significant time and energy is needed to discover that enthusiasts
around the world are forging alternate paths to excellence.
One unfortunate down side is that the cost of small scale
production often means that many of these exotic products have price tags that
will forever ensure their exclusivity. With the contraction of interest in
performance driven hi-fi and the decrease of interest in quality audio by the
major electronics manufactures, we may yet see a greater acceptance of and
interest in the smaller firms creating their uniquely exotic solutions.
Supravox emerged from a company called Super Electro
Mecanique (SEM) that was founded in France in the 1930s. Since 1945 the
company successfully developed in-house technology and continued production,
almost uninterrupted, to the present day, establishing the Supravox name in
The 215 EXC reviewed here is a full-range raw drive
unit with a low mass hyperbolic paper cone. It has a stationary phase plug in
the centre, no extra whizzer cone to lift the treble, and a concertina form
coated paper surround that gives a maximum linear displacement of +/-10mm. A
massive field-coil electromagnet replaces the normal ferrite or alnico
permanent magnets. In many ways this old fashioned looking unit seems an
unlikely candidate to produce a high end sound. It may be said to be capable
of full-range operation, but looks more like a powerful midrange driver.
On opposite sides of the magnet assembly, mounted on the
thick aluminium frame, two pairs of gold plated 4mm socket/binding posts
accommodate the signal and power supply connections. An external power supply
is required to energise the field-coil (not supplied), and Supravox recommends
a 10-14V DC output with a 5A capability. Changing the voltage to the
field-coil alters the field strength which changes various driver parameters,
especially bass damping and sensitivity. For the technically minded, Supravox
provides a table of how these vary with voltage. Assuming no need for a
crossover and feeding the electromagnet with 8-13V, sensitivity ranges from
98-100dB/W/m. Even though it has a 4ohm voice coil, this level of efficiency
gives the partnering power amplifier a relatively easy life; even low power
valve amps should go realistically loud.
Alongside the Supravox drive units, we also borrowed a pair
of thick rectangular acrylic open baffles to mount them. Open baffle mounting
is an uncommon technique today, and has both positive and negative aspects.
The down side includes a reduction in bass output caused by cancellation
between the sound energy from the back and the front of the cone (as happens
with all open-back or di-polar speakers). The usual closed cabinet traps and
dissipates this backward firing energy, creating the low frequency equivalent
of a baffle of infinite size. However, internal enclosure resonances and
reflections produce their own sounds, so a well-designed open baffle may sound
more open and less coloured, especially in the midrange. When open baffle size
and the driver positioning on it is optimised, surprisingly promising results
can be obtained with fascinating consequences.
For those who don't want to get into DIY, the stylish
acrylic 650x1055x20mm (WxHxD) open baffle we used is available for £1,000/pair
from UK Supravox importer Real Hi-Fi. The driver cut-out is asymmetrically
placed to reduce baffle cancellation dips, with its centre 655mm from the
floor and 252mm from the nearest side. The driver sits in a recessed cut out,
with bolts to hold the driver in place, and also to mount the baffle on a
brushed aluminium stand. This stand is a single 10mm bent sheet with a
semicircular top and cut-out for the driver motor. The baffle tilts back 15
degrees, while the stand has a footprint 450mm deep. The effect is
contemporary, stylish, and actually far less obtrusive in my room than a
normal box loudspeaker.
The speaker requires a DC power supply and connecting cable
as well as the normal speaker cable connection. There's no crossover so the
amplifier is connected straight to the voice coil, ensuring minimal signal
losses and no crossover phase anomalies or delays.
Using a fairly standard lab power supply set to 10V, and
with the speakers connected to the Exposure MCS system (Vol5
No3) I was immediately rewarded with a fast, dynamic and very
detailed sound. I had to experiment with placement a bit to get an acceptable
frequency balance, but that holds true for any loudspeaker. Very quickly the
Supravox speakers were giving the sort of sound that makes you want to listen
to all the recordings you love, because fresh detail and fine nuances keep
I have experienced this effect before with other
breakthrough products, but never in quite such an effortless fashion. I know
from past experience that certain frequency or phase anomalies can result in
similar positive psychoacoustic effects, but in my opinion never in quite this
way. I ended up listening for a very long time, though towards the end I was
becoming fatigued and beginning to be bothered by some tonal balance
forwardness and also a degree of image imprecision.
After further reflection I accepted that the Supravoxes were
capable of exceptional performance in some respects, and was driven to try and
extract even more quality and therefore overcome my reservations. My next
session was therefore rather more scientific. I began by varying the
field-coil power supply voltage and while this can create subtle but
worthwhile differences, I still wasn't satisfied. I was still hearing lots
more information than that available from far more expensive, exotic and past
favourite loudspeakers, but that forward presentation still worried me.
It might have been that they needed to be run in for longer,
but I also had a suspicion that the power supply might be a critical component
– the one I was using wasn't particularly low noise and was more industrial
than audiophile. Then I remembered a couple of 12V 21Ah batteries in the shed.
Hoping they were still capable of maintaining 12V at around 2A for a
reasonably long listening session, I put them on charge and meanwhile left the
drivers running in for a bit longer.
With fully charged batteries supplying 12V now installed,
and no other changes, my reservations over the Supravox presentation had
completely evaporated. Not only had the tonal forwardness gone but the
Supravox speakers now revealed an additional and extraordinary range of
virtues. They just thrived on that clean supply. Their intrinsic abilities
meant that the system sounded more dynamically lifelike than I've ever
experienced from any hi-fi before. Even old recordings could really surprise,
and several times I thought someone had entered the room, as reproduced voices
and noises sounded so real and present.
and poor mixing techniques were revealed with a precision that may annoy some
people, but I'm learning to accept these as part of the performance of that
particular recording. Ultimately the overall result is delightfully
interesting and involving, and comes the closest I have yet heard at producing
dynamically coherent and convincing music. These speakers are capable of
exquisite timing and sonic coherence, somehow always extracting the best from
the rest of the system. They even managed to create a level of musical
performance that transcends what I previously could have expected from the
system driving them.
I tried other amplifiers, cables and sources, and liked the 215
EXCs even more for their abilities to convey the best attributes of all
the good electronics I had to hand. But they just as easily reveal any
abhorrent characteristics and deficiencies in flawed amplifiers and sources.
Note that this open baffle speaker design is not tonally
perfect. In my listening room it can never be called particularly neutral, and
I couldn't find a position that produced much deep bass, due to the finite
baffle size. However, whereas I'd complain about midrange frequency anomalies
with most loudspeakers I've heard, here the Supravoxes haven't yet troubled me
– it's as if what they do so well transcends all else. The mid is sweet and
open with quite astonishing levels of detail.
Interestingly, I'm more critical of its sound in the room
than with many other speakers when I'm not seated in the ideal listening
position: this may be something to do with my room and the open baffle
mounting, and I'll have to experiment further here. The treble is surprisingly
good, far better than I actually expected from a cone of this shape and size,
but the high treble does seem a little reticent, lacking some air and sparkle.
Focus is also good, with solid and stable images and a surprisingly wide and
deep soundstage. Soundstage height reveals some amplifier characteristics, and
the Proteus Diamond MkII provided a higher image than the Exposure MCX.
There's definitely a sweet spot here, where everything snaps into focus and it
sounds more tonally right, but even when sat slightly away from this, I really
didn't find that much to complain about; it still has good balance and I can
still clearly hear all the startling midrange detail and dynamics.
Irrespective of music genre, the Supravox 215 EXCs
remain so communicative I could simply enjoy them on all the recordings I
played. They have an ability to reveal the music structure and excite one so
effortlessly that the senses are rewarded in an amazingly consistent fashion.
Although they are totally exceptional in their ability
to reveal information, this loudspeaker isn't necessarily for everyone. Those
who insist on a flat and extended frequency response with deep bass should
look elsewhere. Some are happy driving a bland people carrier, which is
efficient and dull and will get from A to B safely without incident or
excitement. Others seek the thrill of dynamically superior, critically tuned
sports car which excites the senses with every bump and turn in the journey.
The difference between the two is stark, and obvious to those who are
interested. The difference between the Supravox 215 EXC and other
loudspeaker systems that I have tried which claim a similar
performance-oriented purpose is just as stark.
I'm sure this Supravox driver could be built into a more
complex system by using it with other units that can supplement its small
deficiencies at the frequency extremes. But then you would be adding some
crossover components, and I can't guess how much of the essence of its
lifelike performance would be lost. David Cathro has been working with this
driver in just such a system (HIFICRITIC Vol5 No2),
and tells me that the ability to alter the drivers by adjusting the voltage
can be very helpful in seamlessly blending drive units together. (He uses a
field coil bass driver as well.) I'm told that some simple equalisation will
produce a far flatter response and may actually improve the sense of timing
and realism, but then that wouldn't be the speaker system that was supplied to
Whatever one's ambitions for experimentation, if lifelike
dynamics and the ability to create the most impressive combination of realism
and structural information are what is important, this speaker is guaranteed
to satisfy and enthrall.
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