Opera Callas Divina 2004/2005

 

With the new loudspeakers of the Callas Series, Opera`s intention is to recreate within the

home environment,  the emotion and pleasure of listening to music:  to provide a stable and focused musical soundstage in three dimensions with correct timbre, dynamics and detail, and to do this with no sense of listening fatigue.

 

To achieve this goal, every single technical aspect of the design was subjected to intense  musical listening tests at Opera.

 

 

The new loudspeakers of the Callas Series use techniques and components which reflect the state-of-the-art in electroacoustic design, including controlled-diffraction cabinets, drive units and crossovers. Every type of distorsion has been analysed, quantified and reduced. The sonic result is tonally correct, convincing, involving and most of all, enjoyable to listen to. The Callas Series loudspeakers are elegant and beautifully finished, and will discreetly enhance any room.

 

System

 

The Divina model is a floor-standing loudspeakers system with a linear array of small diameter woofer for the mid-low frequencies and a state-of-the-art one inch fabric tweeter for the high range. An extra tweeter, placed on the rear side of the cabinet, fills up the overall power response.

Diva and Divina share the same project philosophy: to recreate well defined, focused and stable acoustic stage image as the best small two way system can do.

 

Far from theory results are clearly audible: the new Diva and Divina loudspeakers system perform as a small two way-system but with the power, dynamic and low freq. extension that only bigger diameter woofer can perform.

 

 

The cabinet

 

The cabinet is made in a mix of MDF and plywood, with teardrop-section curved sides, veneered and finely lacquered in the best Italian tradition. The front baffle is finished in leather. This, along with the benefit to appearance also serves to reduce edge diffraction.

Internally there are a number of interlocked braces which serve to increase the rigidity across the cabinet.

Thanks to the chosen geometry, together with other detail design features the Divina model obtains a substantial increase in low frequency radiation from the reflex port which extends the bass response to the very lowest frequencies.

 

 

The duct is placed in the rear side of the cabinet near the floor where low frequency radiation impedance is larger and duct noise, if any, less audible. 

 

A good quantity of lining material is carefully placed inside the cabinet.

 

The Components

 

 

The 4 Woofers and the front tweeter, are made in Norway by ScanSpeak and modified for Opera Loudspeakers application.

The tweeter has a one inch soft precoated fabric dome loaded by a wide decompression rear chamber , there is no magnetic fluid in the gap. The excursion of the dome is 3 mm. pick-to-pick (!). It sounds clear, linear and free from any coloration. Woofer and tweeter have both a very small value for the voice coil inductance which reduce to a minimum distortion due to impedance coil and flux variations. The rear tweeter has a one inch fabric diaphragm an a neodymium magnet.

 

The woofer has extreme characteristics and it is 80% hand-made.  This same woofer performs excellent in high-end two-ways system (and the Callas model is the prove of that). When  4 woofers like that are used in the same system, the acoustic quality of the reproduction is dramatically increased.

 

Why we use many small woofers

 

Many loudspeakers systems use more drivers in the same frequency range. Here very high quality drivers are used and they are wired  with an original filter network especially designed for them.

 

Using an array of small diameter drivers gives a lot of mechanical, electrical and thermic advantages over a single driver.

 

When more equal drivers are used in the same frequency range, the total radiating surface is the sum of all the drivers' surfaces and thus is equivalent to the surface of a single larger diameter unit: the four Divinas’ woofers act as a 10 inches unit.  Anyway the diaphragm properties, i.e. normal modes, are those of the single small diameter driver unit. Substantially we get the volume displacement of a 10" driver with a 5" midrange frequency reproduction. Obviously, to make things work, the small woofers must allow  wide cone excursion: two centimetres pick-to-pick in our case (!).

 

An other important advantage of woofers array is that you need no cross-over section between woofer and bass-midrange unit as in a conventional three-ways system. This is simply because midrange and woofer units are the same. So no phase or polarity problem as well as frequency response faults may exist in the mid-bass frequency range.

 

Less filter components also means less attenuation loss, less distortion, less differences between the left and right stereo channels with more advantage for stability of the stereophonic image.

 

Thermic properties:

 

Suppose you are playing music with a, say, 100 Watt amplifier. The current flowing across the woofer's moving coil produce heat that raise the temperature of the coil  thus dilatation occurs and the ohmic resistance of the coil increases. All this effects make the driver's parameters current dependent (that is non linear).

 

Four moving coils are less heated than a single one because each of them has to manage a fraction of the total power coming from the amplifier (one quarter for Divina). Thus we get less heating, less dilatation, better mechanical stability, less non-linearity, longer driver's safe life and much better stability in electrical loudspeakers parameters in dynamical condition.

 

All these give higher power handling capability and reduce to a minimum some kind of dynamic distortion you have probably heard with strong transient reproduction.

In direct radiator loudspeakers, all known kind of distortions are related to displacement and velocity of the driver cone diaphragm: the more displacement, the more velocity, the more distortion. Once fixed an SPL level for a driver, with 4 drivers the displacement is one quarter... in this condition not only distortion due to displacement is reduced but there will be not enough energy available to excite the normal modes of the diaphragm so that they are cancelled (remember that energy goes with the square of velocity so 1/4 velocity means 1/16 energy).

 

Using more identical drivers enhance the good characteristics and decrease the bad ones. This is why Divina sound so dynamical, analytical and natural and sweet at the same time even at high SPL level.  Opera Callas Divina has one of the lowest level of intermodulation distortion ever measured.

 

 

 

The Cross-Over Filter

 

 

With many vertically aligned woofers the polar dispersion on the horizontal plane, say two meter away from the cabinet, remains the same as a single unit: wide and regular. But the linear dimension of the whole source increases and, while increasing frequency, the vertical dispersion angle is decreased because of interference.

 

To avoid this undesired effect and to keep the polar dispersion characteristic of the whole system similar to a small two-way system, Opera developed the low-pass progressive cross-over network:  each woofer frequency response is up-limited at different cut-off frequency so that in the low frequency region all woofers act as a single large diameter driver while, in the cross-over frequency range with the tweeter, only one woofer is fully powered.

 

The system is a non conventional multi-way loudspeaker system with a low-pass sections for each woofer and a single high-pass section for the front tweeter. Low-pass filter roll-off are smooth, less than 6 dB/octave, and the emission coherence in mathematically proved.

 

Because of the coupling between drivers, cross-over an cabinet only one woofer at time is allowed to resonate.

We believe that the cost of a diffuser has to be assessed together with the cost of the amplifier more suited to drive  it. Opera Callas Divina is a nominal 6 ohm diffuser that can be easily driven by a wide range of amplifiers, either with valves or solid.

 

 

 

The frequency and power response

 

The frequency response curve is partially shaped according to loudness curves obtained by Churcher-King and Pollak which are better, for hi-fi listening, than the well known Fletcher e Munson loudness curves. Doing this Opera Loudspeakers can recreate, in home listening, the real instruments size and feeling.

 

Frequency response, in normal rooms, range from 20 to 20000 Hz. For a better balance of the power response a small neodymium tweeter has been added on the rear side of the Divina. The rear tweeter works in a frequency region where the main front tweeter starts focusing energy on his axis. The effect of the rear tweeter depends on the room walls absorbing properties. In some “live” room it may be useless  so you are allowed to switch it off.

 

 

Note:

Woofer and tweeter need at least 20 hour playing to reach the best performance.

 

 

 

Position in the listening room

 

Opera Callas Divina is a floor standing system. We advise against placing the diffuser in a corner and one needs to keep a minimum distance of at least 50 cm from the side walls. The best position within the surroundings has to be found experimentally.

In case two pairs of Opera Callas Divina diffusers are used, these have to be connected in series or if the rear tweeter are not connected, in parallel as illustrated in the figure below.

 

Positioning of two pairs of Opera Callas Divina, suggested by Righini

(rear tweeters not connected)

 

 

 

Technical Specifications: Opera Callas Divina

 

 

System

Floor Standig – Bass Reflex , rear duct

Finishing: wood and hide

 

Loudspeakers

4 woofer 5” with paper cone

 

 

1 tweeter with a 1”  silk dome with decompression chamber

1 rear tweeter with 1” silk dome with Neodinim magnet

 

Number of Way

Frequency response

32 -20000 Hz 

Cross-over

On Printed Circuit Board

 

 

12 dB/octave for the woofer with progressive Low pass  

 

 

12 dB/octave for the il tweeter

 

 

Cross-over frequency around 2000 Hz

 

Maximum power

 240 watt RMS

 

Suggested amplifier

From 10-15 Watt RMS to 500 Watt RMS (no clipping)

 

Sensibility

89 dB/2.83 Volt/1 metre

 

Nominal impedance

6 ohm (Zmin >4.4 ohm)

 

Position within surroundings

At least  50 cm from side walls

 

 

 

 

Dimensions

Xxxxxx

 

Net Weight

Xxxxx

 

Packed weight

Xxxxx