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Here a few more fundamental design principles come into play. The first is no damping material. Its use would have damped microdynamics and killed musical liveliness to get banned altogether. The second is a direct consequence of the first. If no damping material is used yet the enclosure cannot and should not contribute any coloration, peak or resonance, how does one deal with the back wave of the driver? Auditorium 23 chose to tune their resonances to add body even if a recording doesn’t exhibit this body in the first place. Ocellia chose to spread their resonances across a very broad range of frequencies at very low amplitude to ensure that any stored energy will be shed very quickly. The only thing the two approaches have in common is the use of very thin enclosure walls (just 4mm thick for Ocellia). Where the Germans use their thin walls in an attempt to mimic the tone boards of instruments and enrich the sound, the French use them to not store but dissipate vibrations extremely quickly and not slur the musical signal.
Like Tannoy, Ocellia speakers have a 5th terminal to ground the driver
The real secret to a Calliope enclosure is internal panel bracing made from a very thin wood lattice which forms a grid on each inner sidewall. Each cell of this grid is of different dimensions to not share the same resonant frequency. Furthermore, opposing cells across from each other exhibit different dimensions to negate possible standing waves. This design coupled with extremely light and thin yet rigid walls ensures that resonances remain very short in duration and very low in amplitude - much lower indeed than any music played to be lost in the noise floor of the overall system.

It is possible to buy PHY-based speakers for less than half the price of an Ocellia Calliope. They apparently all tune their enclosures to add tone and richness. Listening to an Ocellia will quickly tell you of a quite different philosophy. You won't hear artificial warmth but instead truth and honesty good or bad. The craftsmanship and manual labor that go into delivering this critical difference are huge. If you care about said difference or simply admire excellence in craftsmanship, the asking price is actually very reasonable in light of the time and effort involved in creating each unique speaker. If you adhere to the philosophy of the enclosure tuned like a musical instrument, Auditorium 23 would fit your tastes better. Listening to Ocellia speaker over four months I must admit that Samuel Furon's approach delivers a very enticing truthfulness of tone and microdynamics that I will attempt to describe in this article.

 
The model under review goes by the lovely name Calliope .21 Twin Signature; the .21 reference indicating a speaker built around the 21cm version of the PHY driver. A more expensive .30 speaker sports the 30cm PHY transducer instead. Looking at the pictures, the Twin nomenclature should be quite obvious. It refers to the $3.770 option which adds two PHY piezo tweeters per channel.


These tweeters may not have a reputation for being the ultimate in extension or extreme finesse (Genesis' circular ribbons are better at this ultra-fine resolution game for example) but PHY tweeters make up for those relative weaknesses by being perfect acoustic matches to their widebanders to require no electrical high-pass filters to complement the top octaves. This keeps what on paper would be a two-way design strictly crossover less.


The pair I reviewed offered the option to adjust the tweeter level to better match room acoustics of either highly damped or overly lively rooms.

The benefit of two tweeters per side according to Samuel Furon is more flexibility in how the tweeters are positioned in the enclosure and thus more accurate phase integration which delivers greater benefits than extreme resolution when it comes to natural treble tones.


Finally the Signature tag refers to another $3.770 option of further refinements especially to driver inertia. As much as the sidewalls of the Calliope are thin and low in mass to evacuate vibrations quickly, the front baffle should be as heavy and inert as possible to provide the PHY driver with the most stable wave-launch plate to operate from. The Signature version adds substantial mass and density to the front and at the bottom over the internal bracing and locking of the PHY bronze basket that are part of the standard version.


Music is created when the driver membranes move back and forth under electrical stimulation. Microdynamics come from the ability of this membrane to start, stop, accelerate and change direction on a dime. The more rigid and inert the reference plane, the more dynamic the driver will sound. The obvious corollary is that if the front panel to which the driver is mounted isn’t completely static and immobile, it will start vibrating in the opposite direction to the membrane to prevent the membrane from instantly changing directions. Thus the Signature version of the Calliope goes even further to prevent the front baffle from contributing anything to the sound and blur musical micro detail.


The final available $1.287 option is the possibility to add Franck Tchang silver or copper resonators behind the PHY drivers. Samuel Furon is another of us lunatics who actually believes that these little metal cups can have very beneficial effects when used properly. More on this in the listening impressions. The resonators are easily removed. I was able to listen to the Ocellias with and without silver cups installed.


This pretty much rounds up introductions except for a few secondary details. As indicated in my Ocellia cable reviews, the Calliope speakers are equipped with a grounding post next to the traditional binding posts. This provides a static electricity drain away from the membranes as a nice cheap upgrade that yields consistent audible benefits in midrange fluidity - not a revolution but enough of a change to fully justify the effort of enabling the connection. Finally the Calliopes do have an open bottom but are mounted on adjustable spikes. Careful attention should be given to rake angle to ensure proper treble integration. Similarly it is highly recommended to assess the effect of opening the back door on bass reproduction. In my environment completely closing the door yielded a little more bass control but also a certain level of midrange stress I didn’t care for.


So I kept the door opened about an inch which seemed to cause no issue with room interactions yet removed any sense of midrange tension. This flexibility allows the speaker to behave almost like a back-folded open baffle if the door is fully opened; or to control how much of the back wave gets directed at the back wall versus floor depending on how wide the door is opened. Although I had no problem with bass integration, I assume this little added control might help in challenging setups. This rather lengthy introduction was necessary to cover the unique design elements of the Ocellia Calliope speakers in detail as a lot of what one hears stems directly from all these design choices.