[Main Speaker] Avantgarde Acoustic / Duo Mezzo Duo Mezzo Fact Sheet  

Duo Mezzo Fact Sheet

 
THE SYSTEM

Taking advantage of the unrivalled performance of the horn principle by consequentially extending it to the lower octaves, the Duo Mezzo is the first spherical full range horn systems in the Duo product line. An utterly thrilling way to experience the magic of the ultimate spherical full–range horn principle. 

The Duo Mezzo is a 2–way spherical horn system complemented in the low frequencies with the active Short Basshorn subwoofer. By utilizing two powerful 12 inch drivers loaded to a short hornflare, the dynamic headroom of the bass has been significantly improved, compared to the even very powerful Duo Grosso. 

Its ultra high sensitivity (107 dB/W/m) at 18 ohms system impedance and its hybrid concept with self–powered horn loaded subwoofer makes it easy to drive with any amplifier. Even with low powered tube amps the Duo Mezzo is able to deliver a powerful, dynamic and three–dimensional sound, because the power–demanding work at low frequencies is managed by the self–amplified Short Basshorn.

OMEGA TECHNOLOGY

To significantly improve the sound quality Avantgarde Acoustic™´s Omega approach is based on two major concepts: simplification of the passive crossover design and high impedance voice coils.

Different to 2nd order conventional passive crossover with six components for a 2-way speaker, the Duo Mezzo omega crossover has only two components for the tweeter and no component for the midrange. Using no crossover in the midrange is usually not easy due to the large overlapping of the frequency response. Using their “Controlled Dispersion Characteristic” of the driver/horn configuration, Avantgarde Acoustic™ effectively controls the output. 

This is how CDC works: The lower cut-off frequency of a horn loudspeaker is determined by the size of the horn. The larger the horn, the lower the response. Below the cut-off frequency of the horn, the response falls off steeply at 18 dB/octave. Avantgarde Acoustic™ speakers thus operate only down to their cut-off frequency limit and require no high pass filters. The upper

frequency response is determined by the driver. However, it can as well be influenced acoustically by the horn. For this purpose, Avantgarde Acoustic™ places a small chamber between the driver’s membrane and the horn throat. The driver does not emit directly but via a small air chamber into the horn throat opening. This air volume operates as a kind of band-pass filter and automatically filters frequencies above the resonance volume of the chamber (at 6 dB/oct.). By choosing an adequate driver with a natural roll-off at 6 dB in this frequency range, Avantgarde Acoustic™ obtains an acoustic attenuation of the frequency response of 12 dB without any passive frequency crossover. No further low pass filters are necessary! The CDC system thus causes the midrange to only operate within their operational band and steeply fall off at the transition points.

The attached graphics show the difference of conventional and the new Omega voice coils. To achieve very high resistance the voice coils of the Omega drivers are made with very long but very thin wires. Up to four windings are placed on the voice coil former. Elaborate production technology is required as the wire is so thin and easily breaks and the voice coil gap is so narrow. Now, why is the horn manufacturer taking so much energy and effort to simplify the passive crossovers and enhancing the impedance of their voice coils?. 

The key point is the damping factor. Damping factor is the technical term for the ability of an amplifier to control the movement of the 

membrane. E.g. simply speaking the force the amplifier applies to the voice coil to follow exactly the musical signal. According to common knowledge the damping factor is determined by the quotient of load impedance (driver) and output impedance of the amplifier. An amplifier with an output impedance of 0,04 ohm will thus theoretically have a damping factor of 100 when connected to an 4 ohm speaker. But this is a purely theoretical figure! In real life the signal has to pass a speaker cable and the passive crossover components till it reaches the voice coil. Using a typical 5m long speaker cable with an W-resistance of 0,36 ohm and a resistance of the crossover coil of 0,6 ohm, the effective real damping factor will decrease to a value of only 4! Connecting the same amplifier/cable configuration to the Duo omega will result in a real damping factor of 18, which gives 4,5 times more control and presicion! E.g. the control of the amp will increase by 450% and at the same time will reduce the negative effects of long speaker cables by 80%. 

As a result the Omega drivers have more authority, less distortions and an excellent detailled response characteristics.

THE CPC CROSSOVER

Although the Omega midrange driver is running full range without any crossover, the Omega tweeter requires a passive filter for thermal protection. As with all their products Avantgarde Acoustic™ was taking a very puristic approach. Less is more is the design philosophy. 

A potential limitation of any passive crossover is the capacitor required to filter low frequencies. A capacitor consists of two plates or conductors. As both plates are separated by a dielectric or insulator, the conductors have no direct contact but the signal is passed through a dielectric field. Every time the music signal is changing from the positive to the negative half-wave and vice versa the dielectric field gets inverted. The permanent change of direction of the field in a capacitor - a phenomen called “dielectric memory effect”- causes distortions which get worse the closer the signal passes through the zero point and are at a max just when the electric field changes its direction. 

To avoid these distortions Avantgarde Acoustic™ uses with the “Capacitor Polarisation Circuit” an elaborate approach. Different to conventional capacitors the CPC–capacitor has multiple conductor–foils connected with a special electric layout shown in the attached graphics. The CPC module up-converts the income music signal to the required voltage to bias the conductors. Only the inner conductor is biased with DC. In the CPC module a voltage cascade through a network of diodes increases the voltage of the music signal to a multiple. This high direct current is than fed into the inner conductor. Furthermore is the diode circuit electrically decoupled through a very high impedance transformer to avoid any backlash to the music signal. Already a view moments after turning on the music the CPC module has generated the required direct current to bias the capacitor. As the CPC diode cascade can buildup voltages by far beyond allowable levels, Avantgarde Acoustic™ has included a protective circuit to avoid overloading the capacitor.

The CPC biased capacitor has less distortions and can more precisely handle incremental signal variations.

THE ADRIC HORNSUBWOOFER

Basshorn systems are a myth and enjoy a legendary but at the same time – when they are constructed too small – an ambivalent reputation. Too small dimension will inevitably cause bouncy impedance curves and a boomy frequency response.

To cope with this problem, the technical literature recommends using drivers with very stiff suspension, light moving mass and small rear chamber volumes. This way the resonance frequency of the driver FO is set at or above the cut-off frequency of the horn FO.

As the driver does radiate significantly less energy below his resonance frequency reflections back into the horn are minimized. In other words the driver parameters are matched to the horn in a way, that the response for the given horn is optimized. This shows the major drawback of reactance annulling. The lowest frequency is only determined by the size of the horn. So reactance annulling improves the response but cannot make horns go lower in frequency!

Contrary to all common knowledge, Avantgarde Acoustic™´s approach purposely works without reactance annulling. Unlike the drivers used in their ADRIC basshorn systems have a low resonance frequency with relatively soft suspension. These are applied in a front loaded horn with a big rear volume behind the driver to allow for high acoustical output at low frequencies. To compensate for the inescapable impedance irregularities - caused by the resonance frequency of the driver being lower than the cutoff frequency of the horn - the Avantgarde Acoustic™ uses its patented “Active Dynamic Radiation Impedance Compensation”. The way ADRIC works is shown in the graphic. The upper chart shows the typical bumpy impedance curve caused by a driver with low resonance frequency connected to a relatively small horn. The output voltage of the ADRIC amp is shown in the chart below. At rising impedance of its load the ADRIC amplifier with negative output impedance generates an inversely proportional output voltage. It is practically the inverse of the frequency curve.

The thick black line in the next chart shows the resulting frequency curve driven with an ADRIC amplifier. The circuit linearizes the peak at the resonance frequency of the driver 1, the peak caused by back reflections at the cut-off frequency of the horn 2, the spikes caused by cabinet resonances and further room induced reflections 3. Furthermore ADRIC flattens the upper frequency response of the horn, caused by the higher inductivity of the driver at higher frequencies 5. As the motional feedback circuit of ADRIC compensates as well for all cabinet induced influences, even the frequency response below the resonance frequency of the driver is beeing linearized 4. ADRIC thus automatically compensates all waviness and ripples induced by cabinet, horn, driver and room.

The drop below the cut-off frequency of the horn is caused by the difference in sensitivity between horn and sealed enclosure. Using an active equalization with the respective filter characteristics (see lower chart) will flatten this drop. As a result all Avantgarde Acoustic™ ADRIC horn bass system will have a perfectly flat frequency response.

he proprietary ADRIC technology of Avantgarde Acoustic™ thus ensures that relative small hornsize and overwhelming low frequency extension does not necessarily exclude. It is based on our fundamental research of the electro-acoustical interdependencies of wavefronts being induced in horn funnels. The complex ADRIC circuits detect the characteristic impedance peaks and precisely compensate through ultrafast analogue feedback loops. 

THE MIDRANGE HORN DRIVER

The outmost care at choosing the drivers is the key to successfully transforming the theoretical advantages of the horn technology into an outstanding High End speaker. As mostly people focus on treble and bass response, Avantgarde Acoustic™ considers the midrange as the “heart” of each speaker system.

The Duo Mezzo offers the same technology as Avantgarde´s flagship model Trio. It features a sophisticated M2 omega driver with high impedance technology loading a 670 mm spherical midrange. 

The M2 omega is a 170 mm (7 inch) midrange driver with a 100 mm (4 inch) dome especially developed for the Duo and optimized for a large, linear excursion. 

Avantgarde Acoustic™ managed to increase the effective magnetic flow in the air-gap of the driver by eliminating the usual copper inlay of the pole-piece. The roll-off at higher frequencies caused by the higher inductivity of the voice coil and a specially designed dome was set to the exact crossover point of the tweeter.

Furthermore Avantgarde Acoustic™ added a powerful Alnico magnet to this new M2 omega development. This precious magnet material generates a powerful magnetic field which homogeneously controls the movement of the voice coil.

The M2 omega has a very low cut–off frequency with seamingless and crossover–less integration to the subwoofer. The design of the dome ensures a phase–neutral radiation of the sound waves into the midrange horn SH6704 and wide bandwidth of the extended midrange down to 170 Hz. 

The kevlar midrange cone of the M2 omega is coated with trillions of tiny microfibres generating a “Velours Damping Effect”. This incrementally small fur of the VDE technology cone effectively reduces partial resonances of the cone itself. Furthermore the microscopc fibres of the VDE technology help to effectively absorb high frequency distortions.

The Avantgarde Acoustic™ proprietary CDC system features a controlled roll–off at 2,000 Hz, and allows us to completely eliminate all passive crossover components in the signal path. This way the M2 omega gets the pure and non–distorted full–range signal directly from the amplifier! The nominal impedance of the M2 omega is a staggering 18 ohm and the sensitivity is 107 dB (1Watt/1m).

THE TWEETER HORN DRIVER

As the performance of the M2 omega midrange driver achieved Trio levels, Avantgarde Acoustic™ was able to use their flagship tweeter H3 omega for the new Duo Mezzo system.

This exceptional driver combines the smoothness of an electrostatic driver and the power of a strong 1 inch horn driver. The H3 omega features a voice coil former made of Kapton with a minimised air gap, a special geometrical shape of the 17 ohm voice coil and an ultra light diaphragm. 

The mere force of the 3 kg (6.5 lb) magnet on the voice coil guarantees 100% detail and precision even at low volume levels, and provides the Duo Mezzo with compression-free sound reproduction at extreme sound pressure levels. 

With the spherical horn SH1801 the H3 omega offers an ultra wide bandwidth down to 900 Hz. Due to the passive crossover point being at 2,000 Hz Avantgarde Acoustic™ achieves a seamingless smooth sound with incredible dynamic headroom.

THE SUBWOOFER DRIVER

The Duo Mezzo is supplied with the active Short Basshorn subwoofer, which is driven by two powerful 30 cm (12 inch) 600 watts (RMS) long-excursion drivers.

The 12–ND600 is the result of an extensive and intense research of every single constituent part of an electro-dynamic loudspeaker,rethinking the basics and taking care of every detail, to withstand the extreme power conditions it has been designed to work in.All this investigation is reflected in the new and innovative technologies developed by Avantgarde Acoustic™ and applied in this new transducer.

The 12–ND600 features a 4 inch voice coil with laminated former combining two different advanced technology materials to enhance the voice coil life and to ensure an optimum force transmission. A forced convection mechanism results in low power compression. This design has been optimized with the extensive use of miniature high temperature probes and real-time temperature acquisition systems, together with a thermographic camera to obtain real images of the heat distribution in the voice coil and forced convection effects.

The Double Conex Spider with its diaphragm surround and the double spider have been carefully designed with the assistance ofFinite Element calculations in order to match coherently, enabling long and controlled cone displacements.

The 12–ND600 long excursion drive unit is characterized by its extremely high efficiency and utmost power handling capabilities. The extended controlled excursion is +/– 8 mm. Exclusive neodym magnets with a special under–pole magnet topology are used to maximize the flux density in the air gap and to eliminate energy leakage of the magnetic field. The powerful neodym magnet with a very strong BL power factor and the very stiff but light membrane will ensure highest resolution and authority even with complex signals at extreme sound pressure levels.

THE SUBWOOFER AMPLIFIER

The integrated active HPA 106 electronics consists of two powerful 250 watt amplifiers and an active frequency crossover. A forceful 540VA toroidal transformer and an energy reservoir of 120.000 μF providing ample energy reserves and dynamic headroom. Up to 1.000 Watts of class A/B amplifier power provide for sufficient reserves under any condition. The toroidal mains transformer is mechanically decoupled to prevent resonances.

In order to achieve full control to overcome the inertia of the driver mass, the HPA 106 is equipped with Avantgarde´s genuine ADRIC circuitry. These ultrafast analogue electronics compensate detect and compensate for characteristic impedance fluctuations of the bass driver voice coil - effected by small horn mouth dimensions - by a fast analogue feedback loop. As a result the Short Basshorn of the Duo Mezzo achieves an astonishingly flat frequency response down to 18 Hz! Furthermore, even at very low listening levels – when the music signal is too weak to overcome the inertia of the bass driver mass – the adaptive motional feedback circuitry will seamlessly increase its power output for a full and rich bass response.

The active crossover allows the adjustment of a number of parameters thus ensuring a very easy and fast installation of the system even in acoustically critical situations. A 3–position subsonic switch, variable settings for the input sensitivity and crossover frequencies make the HPA 106 extremely versatile. The HPA 106 can be remotely switched on/off using the 12V trigger signal.

The HPA 106 is driven via high power speaker terminals for direct connection to integrated amps, power amplifiers or receivers or alternatively via XLR terminals. The signal take–off is not only at high impedance, but is also balanced and transformer coupled. This floats the subwoofer ground, avoiding hum loops and eases connection to balanced and bridged amplifier designs.

MECHANICAL CONSTRUCTION

The midrange horn is mounted into a circular housing cylinder with a solid cast aluminium back cover on its back end. The tweeter is located in a circular housing cylinder in the upper part of the horn subwoofer enclosure.

The recessed profile of the cabinet in exclusive wood finish with its slender rear section gives reminiscence to classical instruments but at the same time continues the heritage of the characteristic tripod concept of the Duo line. The hornflare in brushed stainless steel finish is visually detached from the wooden cabinet by a subtle 6 mm shadow gap. With this small gap the hornflare seems to float in a frame build by the cabinet. It underlines the importance of the basshorn flare and puts it elegantly in scene. 

The Duo Mezzo has been designed by the Swiss designers Tobias Adami and Hannes Wettstein from zed. of Zurich. The almost minimalistic style of the Swiss designers gives the Duo Mezzo a straight and timeless appearance.

A selection of ten standard colors is available for the horns. This includes eight metallic lacquer finishes, the uni–color „Saona Beach Cream“ finish and the moderne „Stealth Nocturne Grey“ finish. The special „Shiny Citrine Orange“ multi–layer coating is available as an option.

On this page you will only find a small selection of thumbnails of the color combinations possible. For a better overview you should visit our website www.avantgarde-acoustic.com.

Here you can download a special Color & Finishes.pdf for each product. In this document you can find a nice overview of all combinations available. This will quickly guide you to your favorite horn–wooden veneer combinations.

COLOR CONFIGURATOR

On our website www.avantgarde-acoustic.com you will find as well a comprehensive color selection tool. Just go to the respective product within the HORN–section. Under DESIGN you can select the color of the horn and veneer of the enclosure. If you have found your favorite color combination, simply click on the download–button for a high resolution picture (6 mb).
duo_mezzo-g2_fact_sheet_engl.pdf
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