The making of Bellatrix

The making of Bellatrix

After over 3 years of designing, Bellatrix is the most complex and best-sounding speaker I’ve built.

The making of Bellatrix 

The adventure with Bellatrix began in 2017. After the third generation of Proxima and Electra, which have been well received by the market, there was the time for something completely new and better in every respect.

For several months, there was a search for a new shape that would be immediately recognizable, different from the competition, and at the same time referred to the “flat boxes” of Proxima and Electra.

However, a larger volume was needed to  “handle” 2 bass speakers, so after building several mockups, initially made of cardboard, Bellatrix received a cross-section of an irregular octagon. The solid is additionally inclined backwards, beveled at the bottom and top at different angles, and its depth is still smaller than the width.

With all the complexity of the enclosure shape and so many different cutting angles, a template was created  for each wooden and metal element. The internal frame of the housing is assembled in a specially built assembly table. It took almost 9 months to create templates and cutting technology to obtain repeatability and assumed accuracy of the production of elements below 0.3 mm. All wooden elements of Bellatrix are formatted in a traditional way, without using CNC machines.

However, the visual effect is only a part of the enclosure design. What’s more important is hidden inside. The housing is ventilated downwards, but it is not the common bass-reflex. Bellatrix is divided by partitions into several interacting chambers that together form a distracting – dampening resonance system, which is an interpretation of the TQWT (tapered quarter-wave tube) enclosure.

The creation of such enclosure required the construction of a special prototype that could be opened, retuned and examined. The prototype allowed that each chamber could be tested during listening sessions, and also allowed to investigate how various dampening materials affect the sound of midrange and bass. The CRCdesign technology used in Divine Acoustics for years has received during designing of Bellatrix a new, more complex and more perfect form.

The result of more than a year of work is the enclosure, which does not have loose soft damping material inside. It has a number of reinforcements, crossbars and ribs, it is additionally reinforced with a steel truss that fastens the side walls with each other and distributes vibrations along the entire height. However, despite this, it is not a housing that completely dampens vibrations. Solutions used in its design allow some of its walls to remain “alive” for vibrations. The right amount of specially selected scattering material is mounted in precisely defined places.

Speakers  

The beginning of work on Bellatrix coincided with the introduction of a new series of speakers by Eton. After talking with Eton representative, I decided to order several types of new speakers for testing. What captivated me was the construction of the membrane: the use of cellulose in a modern and at the same time a bit vintage ways. The membranes are uncoated, as it was done many years ago, but at the same time due to the numerous ribs their very high stiffness was achieved,  unattainable then.

After applying the necessary modifications – the precise dampening of the speaker baskets (Bascet Accurate Dampening) and mounting the speakers on the pads separating them from the housing – 7-inch Etons of the Orchestra series began to reproduce the bass and mids of Bellatrix.

The complement to Eton must have been a high-quality tweeter. Its choice was not simple and lasted a long time.

The natural “partner” for cellulose midrange speakers is the tweeter made of silk. Both materials are natural, complement each other perfectly. There are plenty of tweeters with a silk membrane on the market, but there were really only few speakers that I could use for this project.

The first parameter taken into account is impedance. Bellatrix is a 2.5-way system, so in a wide range its impedance is 4 ohm nominal. The tweeter must have been 4 ohms to provide more “predictable” impedance for amplifiers driving Bellatrix. So all 8 and 6 ohm tweeters dropped out of the race.

The second selection criterion was the tweeter’s efficiency. It could not be too high, because the midrange will achieve no more than 87dB/1W/1m of efficiency. I get the impression that tweeter manufacturers, not knowing why, are taking part in the race to build a tweeter with the highest possible efficiency, even at the expense of sound quality. The market is flooded with tweeters that boast of 93, 95dB and more. And how to use it with a bass speaker that does not reach 90 decibels of efficiency? Suppress the tweeter to the limits of decency? By necessity add the voltage divider into crossover? To loose microdynamics? So all speakers  with efficiency above 90dB dropped out the race.

Finally, the choice is the Scan-Speak Illuminator ring radiator with all advanced technologies standing behind it. I chose the version with a large dampening chamber behind the diaphragm, very low resonance and the desired efficiency below 90dB. Why not the more popular version with a “clover” front? Precisely because of its higher efficiency.

For years, Divine Acoustics is using the TMI system, which consists in separating the tweeter from the main body of the housing. Due to the very small Scan-Speak front, a classic set of washers made of various materials had to undergo a metamorphosis. In this way, after many months of testing with different materials and their configurations, a new technology for using hard materials – CeraGem – was developed. Tweeter received its own subchassis, in which a system of multiple layers of dampening is integrated. The same technology was used in our Kepler vibrations absorbing feet.

The Bellatrix enclosures have a separate, very precisely suppressed chamber, in which the tweeter is mounted together with the entire system of suppressing its vibrations.

Crossover  

What should be the crossover that will control such carefully prepared speakers and will not undermine the effects of the work inserted in the cabinet design? Definitely extremely precise … How much time does it take to design it? As much as needed!

Over the years Divine Acoustics speakers had crossovers of different orders, as they developed they became more and more accurate. Over time, SGP (Single Ground Point) and RFpath – elimination of voltage divider in the tweeter path were developed. Designing Bellatrix, however, required to reorganize the entire crossover schematics, determine what slopes work best in a 2.5-way system, which elements affect individual sound features, and what the dependances are between them. In the course of work on the Bellatrix crossover, new design and assembly technologies have been developed. They are necessary to control sound quality and obtain repeatability in the construction of subsequent copies: ESM (Energy Storage Management) and FDC (Fully Directional Circuit).  

Finally, despite the use of 1st and 2nd order filters, the Bellatrix crossover network contains more than 50 elements mounted on a point-to-point method, on both sides of a board without paths. Laying out of a single ground point  took several months, and the “blending” of Scan-Speak with the Etons was the result of over a year of listening sessions and hundreds of micro-corrections. To design such high quality speakers,  spending so much time is really needed.

The crossover is mounted in its own enclosure. During assembly, the checklist includes over 200 measuring points.

The capacitors used are Miflex: copper KFPM and polypropylene MKP-14 and Jantzen Audio: Alumen, Z-Superior and Z-Standard. Capacitors are combined into packages to obtain the highest precision of the required capacity – each package combines at least 2 types of capacitors that complement each other in terms of timbre of sound.

The coils were prepared with “laboratory” precision, they are weighed, measured with the highest available accuracy and isolated with cotton to eliminate RFI/EMI interference.  

The resistors used are noninductive Superes with an accuracy of 1% additionally shunted by precise metallic resistors for obtaining highly accurate and repeatable resistance.

Designing of Bellatrix turned out to be an amazing adventure, full of moments of euphoria and doubt. Currently, final works are underway: packaging design, final tests, preparation of the production process.

The new  Divine Acoustics flagship speaker beautifully named Bellatrix will be available in the coming months.

 

In a modern audio system with excellent parameters and extremely low distortion, the speaker is still the weakest link. Due to its complex electromechanical construction, it introduces the most distortion into the sound. To lower them and to ensure that the music is reproduced as faithfully as possible, the elements of the loudspeakers, in particular the crossovers, should be made with the greatest accuracy and complete repeatability.

In Divine Acoustics’ crossover circuits, instead of a single capacitor of a certain value from the basic capacitances list,  packages of capacitors are used to achieve the desired cumulative capacitance with high accuracy and the smallest difference between production units. The individual packages use capacitors of different manufacturers and different series to complement each other in terms of timbre of sound.

With capacities accuracy of 0.01uF obtained after assembling of 2 or 3 various capacitors, the order of charging and discharging individual components of the package gets major importance for gaining desired quality of sound. Badly juxtaposed – they interfere with each other, make it difficult for the amplifier to properly control the speaker and cause the sound to degrade.

It turns out that even quite substantial changes in sound quality caused only by differences in the connection of the same capacitors are immeasurable by the measuring apparatus.

To obtain the desired sound quality of the speakers, in particular high resolution, micro and macro dynamics and the ability to correctly determine the location of instruments on the soundstage, the operation of each of the capacitor packages is determined in the designing process during long listening tests. Very careful direct assembly of the crossover elements together with their proper preassembling preparation and measurements contributes to full production repeatability and low distortions, and thus very high quality sound of the loudspeaker.  

 

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The most important part of the designing process at Divine Acoustics are long months of extensive listening tests conducted under controlled conditions. During the tests of the parts used for the production of crossovers, parameters which cannot be measured with measuring equipment, but which also affect the final sound effect, are also examined and determined. One of them is directivity of the signal flow.

In our loudspeakers, all parts in the crossovers and internal wiring are mounted with the correct directivity determined during the listening tests.

In order to provide a fully directional signal path in our flagship Bellatrix speaker, Divine Acoustics created exclusive binding posts in which the signal runs through elements made of pure uncoated copper with the directivity specified in the listening tests. This ensures a fully directional signal path from the speaker connecting terminals, through internal wiring and crossover components, up to the coils of transducer.