Opera Caruso

Cross-Linked-Dipole
Caruso Model is our top range loudspeakers system built in a limited number of pieces with user defined cabinet design and finishing.   The goal is to realize a top quality, full band loudspeaker system with a realistic stage reconstruction but still easy to drive by amplifies and non critical from the room positioning point of view.  
The Caruso model implement all the technical solution developed by Opera in the last 3 years: the “progressive” low pass filter developed for the Divina model,  the CLD (Crossed Linked Dipole) developed for the Tebaldi model, the new 8” inches woofer. All these added to our studies on psycho-acoustic and room acoustic.
Caruso model is a 200 litres, over 100 Kg., floor standing loudspeaker. You can look at the Caruso as a two-way system with a passive sub-woofer in the same cabinet. On the Caruso' s front panel there are four mid-woofer and the tweeter which are responsible for the direct sound (and a lot of the reflected sound as well). The front system is very similar to the Divina model: same midrange size, the same cross-over topology, the same tweeter. Four 8" woofers are placed on one side of the cabinet. On the rear side of the Caruso cabinet there is the CLS rear radiantig system with 4 tweeters high-pass filtered at 2 kHz. Thanks to double dipole arrangement of the CLD these tweeters feed ONLY the reflected sound field.

The Cabinet
The cabinet of Caruso is realised in finely-shaped MDF veneered in real wood finely polished and is highly defined by the user who can define (within the limits imposed by the project) the shape of the cabinet.
The the cabinet is divided into two main blocks each one divided into three sealed chambers (one for midranges and one for each woofer), Inside the chambers there are thick wooden bracer. This reinforces the structure and also raises the frequency of the first normal resonance mode of the chambers. The inside of the cabinet is filled with a good quantity of acrylic wadding which helps to eliminate internal reflections and resonance and aids bass frequency damping.

Drivers
The 8" woofer come from the one we use for the Tebaldi with some changes to match the TEB loading. Woofer and Midrange are made by Seas. The main characteristic of the Seas drivers is the “Excel motor” with copper rings above and below the T-shaped pole piece and the solid copper phase plug which gives superior heat dispersion.  That means, also thanks to the wide linear excursion of the moving coil, little distortion  and negligible compression. The woofer has a very stiff aluminium cone,  natural rubber surround and  aluminium voice coil former.  This woofer has an excellent response up to 1000 Hz with very low distortion as requested by the 6 dB/octave low pass filter.  The midrange is a real 5” mid-woofer with 10 millimetre linear excursion and a magnesium cone which, in our opinion, has some advantages in the midrange response. Thanks to the high radiating surface and to the top quality of the drivers the Caruso model exhibit a very  low harmonic and intermodulation distortion (less than 0.1% in the critical mid-low frequency range at 100 db SPL). The tweeter is the well known ScanSpeak 9700 that exhibit 1 millimetre linear displacement and a very low resonance frequency which allow a 2KHz/12dB high pass filter with very low distortion and no compression.

Effect of the cooper rings on coil inductance (red with copper rings)
 
Effect of copper ring on current distortion (below with copper rings)

The Low  Frequency Section
Each 8” sub-woofer has its own 50 litres chamber and they all work in TEB (Totally Enclosed Box). The maximum dimension of one chamber is about 80 cm and the first mode is about 215 Hz which is higher than the cross-over point. Efficiency of the TEB is not as high as the reflex alignment can be but TEB gives some advantages: there are no duct (no cavitation noise) and no passive radiators (no mechanical losses) and the cone movements is fully controlled by his rear air volume. More over the low frequency slope of the TEB is less sharp than Reflex one and so the bass are more deep.      
Caruso' s woofer are placed in an uncommon position: they are all on the same side of the cabinet. In this way the great part of the acoustic load, starting from less than 100 Hz, is due to the large cabinet itself, Only a little part of the acoustic load, at the very low frequency, still depends upon lateral walls. This make the Caruso insensible to the relative position of the lateral walls. Because the mid-bass response is less depending from loudspeakers positioning, you can select the cross-over frequency at 160 or 200 Hz (always with 6 dB/octave slope) to match your needs for the mid-low frequency band reproduction. The woofers of the right channel should face those of the left channel. 
The Acoustic barycentre of the woofers  is placed 25 cm behind the mid-woofers (not below the midrange as usual in three way system) and they radiate the upper part of their frequency range toward the rear wall. The upper and lower woofers have an additional 6 dB low pass filter. In practice the four woofers group consist of two sub-group of nearly parallel drivers. The sound radiation is omni directional at very low frequency and became directional, going toward the rear wall, in the mid bass.

The Cross-over
The Caruso cross-over is not as complicated as it may seem. The following figure show a simplified scheme. 
Now compare the simplified scheme  with the real circuit…note two switches: one select the woofer-midrange cross-over point (160-200 Hz) while the second smooth the front tweeter emission. The CLD emission level is fixed.
Cross-over frequencies are 160 or 200 (woofer-midrange) and 2000 Hz (midrange-tweeter)  with 6 or 12 dB per octave slope. The cross-over is divided into 6 different boards to keep coil far from each other avoiding cross-talk due to magnetic induction. The woofers are connected out of phase, mid and tweeter are in phase.
The following figure shows the vertical dispersion pattern for two (nearly-parallel) and four (progressive low pass) mid-woofer. In the progressive low pass, even if the vertical dimension of the whole source is doubled,  radiation pattern show only minor changes.
Two mid-woofer (nearly-parallel) and four mid-woofer (progressive low-pass): vertical radiation pattern from 500 to 2000 hz)
Simpler solutions (like two mid-woofer in parallel) show zeros on various angles.
Two mid-woofer: vertical radiation pattern from 500 to 2000 hz)
In the following figure you can see the emissions of many instrument and voices and how they are reproduced by the Caruso and Tebaldi models (Tebaldi and Caruso have the same cross-over frequencies): for example the contralto and soprano voices (but also the violin, oboe, flute, ottavin, viola) are fully reproduced by Caruso’ s midranges. In our opinion choosing a low cross-over frequency for the midrange give a better performance and a more natural vertical dimension to the sound stage.

The “isotipica” region, mono recordings
In the Italian literature you find the definition of the “isotipica” region (literal: same kind region). When you are inside the isotipica region you hear the mono signals as coming from the centre of the two stereo loudspeakers. The “isotipica region” is very little. This is a problem when there are many people listening. One way to enlarge the isotipica region is to multiply the number of sources ( two for the right and two for the left channels). As the isotipica region enlarge, the focusing of the mono recordings became poorer. The rear  system acts as a second couple of sources that are about 80 cm. behind the “main” source and thus “enlarge” the isotipica region. This is why you may exclude the rear system with mono recordings.        
 
Technical Specifications: Opera Caruso
System           Floor Standing - TEB Finishing: user defined
Loudspeakers Four 8” woofers, aluminium cone
                     Four 5” midrange, magnesium come
                     One 1” inch front  tweeter –  silk dome, decompression chamber  CLD  rear radiating system (four tweeter)
Number of Way  3 ways + rear CLD
Frequency response 20 -20000 Hz 
Cross-over Hard wireing
                    6 dB/octave for the woofer  
                   12 dB with progressive low pass for midrange
                   12 dB/octave High pass for the tweeter
Cross-over frequency 160-200 and 2000 Hz
Maximum power More than 500 watt RMS
Suggested amplifier From 10-15 Watt RMS (without clipping)
Sensibility    89 dB/2.83 Volt/1 metre
Nominal impedance 4 ohm (Zmin >3.5 ohm)
Position within surroundings At least  30 cm from side walls
                         At least  20 cm from rear wall
Dimensions:  370 x 750 x 1570  mm  W x D x H
Net Weight:  130 Kg