3 WAY HIGH EFFICIENCY SEMI ACTIVE HORN SPEAKERS
Thinking "outside of the box" The Aurora is our newest speaker design, carrying some trickle down technology from our top model the Contendo, as well as some newly developed technologies
The Aurora project
Starting as a personal side project, the design and breakthroughs we achieved merged into what is now our frontrunner in our speaker portfolio.
The initial idea of the project was to design the best possible bass loading module (basshorn aside), to be used with a new horn design we had in the works. The hybrid open baffle / aperiodic bass loading outperformed my expectations, and lead us to push the company design and manufacturing resources to this project, to be our new main speaker offering.
This effort resulted to a new diffraction-less midrange horn, as well as our new horn/dipole ribbon tweeter design. Add some crossover technology borrowed from our top speaker the Contendo, and we present to you the Aurora!
DESIGNER
The "Swirl" Midrange Horn
As in all our horn designs, one of the things we want to overcome is the problem of diffraction that almost every horn suffers from. Diffraction is one of the major sources of so-called “horn sound”. A true horn that is properly designed and implemented should not, and will not, have an identifiable sound of its own.
On our Symphonia and Contendo speakers, we developed a round tractrix horn, modified with a specially-designed 360 degree diffraction-less flare. By using a bullet shaped enclosure, we were able to completely eliminate coloration caused by diffraction, and also avoid smearing of transient information.
In the case of the Aurora, the midrange horn had to be mounted on a cube, thus cancelling our choice of the 360 degree flare. The real challenge was how to transition from a tractrix horn shape to morph to a cube edge while eliminating diffraction. An axi-linear transition would not eliminate all diffraction points. The unique solution we came up with was to a make swirl transition. Subsequent tests (many) in the lab showed that this geometry was the only one that truly minimized diffraction points. That decided, another challenge presented itself – how to actually manufacture the swirl horn! However, our lab is no stranger to manufacturing things never been done before (ref our Contendo Horn Speaker).
The complete 45cm + 15cm solid aluminum end flare horn is assembled as a stacked ply construction, and milled on our 5-axis station, making the whole geometry possible as a production item to the required standards. The horn walls are not less than 10cm thick at any point, and the end aluminum section has 5cm thick walls, resulting in a true resonant free construction.
The Midrange Compression Driver
Most horn speakers are designed with midrange horns covering >500Hz. We designed the Aurora midrange horn to cover 280-3000Hz, thus covering as much of the crucial lower midrange as possible. The Aurora midrange horn covers the significant <500Hz range crucial for male and female vocals as well and most instruments.. However, we found no contemporary driver able to successfully cover sub 500Hz range, especially top performance drivers.
The answer came by using a very special bespoke driver, which we also use in our top Contendo speaker system. The driver can be used down to 80Hz in basshorns and is more that up to the task being loaded in our 280Hz horn. We believe it’s sonic performance is second to none in the frequency range that it is used.
The Ribbon Tweeter
The development of the Aurora’s tweeter came at a time when we already had developed a number of horn loaded true ribbon tweeters, both prototype and production models.We went a step ahead and produced the (probably) first dipole horn loaded tweeter.
Quote from previous designs:’I was always mesmerised by the sound of a true ribbon, especially Raal’s designs, but usually direct radiating ribbons lack the punch and dynamics of a high-frequency compression driver. On the other hand, no compression driver could ever deliver the detail, accuracy and bandwidth of a true ribbon transducer. So we began research on whether it was possible to combine the two approaches to get the best of both worlds.
A normal ribbon is not designed to operate at high acoustic pressures typically present at the throat of a horn. It soon became clear a special ribbon would need to be designed. After modification and experimentation on the Raal tweeter, we found the end result to more than meet our expectations. However, horn loading the ribbon still presented challenges. We were reluctant to use conventional solutions such as wave guides or directivity control apparatuses that would be inadequate for the task, so we endeavored to find a new approach.
This lead us to design a horn flare that specifically loaded the ribbon as a true horn. Nevertheless, the line source emission characteristic of the ribbon made this extremely difficult. Diffraction is secondary sound emission, and takes place in geometric anomalies, transitions of geometry and changes in curvature. It’s very much audible and almost impossible to eliminate. In horns, diffraction is present at the horn termination for round horns. In rectangular horns the problem is more pronounced.
The solution was the implementation of our diffraction-less 360 degree horn technology. We designed the horn flare to expand to 360 degrees, while maintaining the flare curve’s second derivative constant, keeping the curvature slope constant. Precise measurements were made of each iteration in an attempt to match the simulation and theory to its real-world acoustic performance.
We found variations of just 0.2mm to have detrimental effects on the horn’s performance. Manufacturing them to specs from wood was also challenging. In the end, a total of fifteen different flares were designed, built, measured and eventually discarded before we settled on the final design that performed as we wanted.
The ribbon horn combination response is shaped to measure flat from 3KHz upwards. It delivers detail and resolution associated with only the very best ribbons, with the solid punch and dynamics of the very best high frequency compression drivers. Distortion characteristics at 114db are lower that those of the best dome tweeters at 95db. What’s more, the diffraction-less nature of the horn enclosure gives the tweeter unmatched time domain performance.”
But for the Aurora, this was not enough. We worked with Raal to come with a true ribbon that could be horn loaded but be dipole at the same time, to be in alignment with the Aurora concept.The ribbon is a true flatfoil pure aluminum(no former/carrier) ribbon with a very strong and linear magnetic circuit.
Bass Loading Innovation
The initial prototype concept was as an exercise to develop the best (non horn) bass module for a new speaker. Closed box and bass reflex technologies were quickly discarded, and conventional open baffle topology was not quite there for what we wanting to achieve.
The basic principle was we took a large open baffle with four drivers, and folded it back on itself to form a cube / sphere. By doing this, you gain some quite new characteristics.
First, the loading of the room becomes much more even, as the four drivers occupy four different points in space across two axis, and are not positioned on a plane as conventional wisdom dictates. Since no driver is equidistant to another from proximate boundaries, the proximity modes are evened out. This results to much more even and efficient room loading. This was clearly a breakthrough.
Second, the four drivers in effect now form a virtual driver, with the center of the drivers at the center of the cube. This opens up interesting time-alignment possibilities (more below).
The semi-open back of the cube presents a surface which is bit smaller than the total moving cone surface. This creates some back pressure to the cube’s drivers, which is impossible to achieve in an open baffle configuration. By doing so, the usable output is maximized, resulting in a much more dynamic and efficient output in the lower frequencies, and delivering a more even bass response than any open baffle system, while at the same time being faster and resonant free that plague boxed speaker technologies.
The woofers chosen for the concept are designed and manufactured from an elite manufacturer in bass drivers. Their light cone / linear surround suspension is crucial to the performance in the upper midbass / lower midrange, while their powerful motor provides ample headroom and system sensitivity.
The bass module is driven by its own filters and amplifier system, resulting in a sensitivity is 100db/W. Driven by its own 250W amplifier, there is enough headroom for any application. The internal amplifiers can by bypassed on the fly without modification, allowing the use of alternative amplification for added flexibility.
Time Alignment
The Aurora speaker is a true time-aligned speaker across all 3 axis. This is achieved in two ways.
The four bass drivers mounted across the sides of the cube form a “virtual” driver, with the center of said driver to be the center of the cube. This gave us some interesting possibilities and a route to achieving true time alignment, this making the midrange and bass module work as a single point source.
Single point sources are emulated by co-axial drivers (example: a tweeter mounted at the center of a woofer), however you cannot time align them, as no two drivers can coexist in same space. The tweeter has to be positioned at the front or in same cases at the back of the woofer voice coil. In a way , with at co-axial driver you sacrifice the time aligment for the advantage of emulating a single point source.
The virtual bass driver of the Aurora give us the opportunity to achieve both, by having the midrange compression driver at the center of the cube (offset to the back to compensate), means that the midrange and bass can be both time aligned and co-axial at same time!
Time alignment in a speaker is not just a physical alignment of the voice coils of the drivers. Significant offset occurs when we take take other factors into account To truly time align two drivers, we had to develop a custom measurement rig with proprietary measurement routines. This allowed us to move the drivers and measure time alignment in real time.
This is the reason why the ribbon tweeter is mounted to the rear of the cube. That position is the true time aligned position to the midrange driver. The tweeter location was measured in real time at the listening position and the distance was embedded in the design process at the early stages.
Crossover / BlueTooth System
We strongly believe that a speaker has to be adjustable in a number of ways, to help the user optimize the speaker performance to each individual space. A none adjustable speaker cannot be optimized in all spaces as no room is the same, in size, reverberation times, absorption and frequency rates etc. Our Crossover Bluetooth module was developed for our top speaker design, the Contendo, and we felt that the Aurora can and must borrow this technology. The system consists of an array of filters & passive components, multi tap attenuation transformers, and passive line filters, and a complex relay switching system that selects multiple filter attenuation combinations. A Bluetooth receiver / processor is used to control the relay system, and a phone / pad application was develop to control the complete system.
The result is a system that allows the user, to change multiple independent variables of the speaker, at the comfort of his listening seat, in real time. All this is accomplished in passive/analog domain, no DSP or active filters are used , and everything is achieved in the analog domain. Some basic settings such as bass and midrange level can be used to alter the performance of the speaker depending on listening space environment / area / volume. Some more advanced settings are also possible to allow the speaker to vary its performance to better suit the user’s system and taste.
The value of this system was evident when we tested the Aurora in spaces from 20sqm to 400sqm. We believe no speaker can perform optimally in spaces that vary 20x without the abilities that our Crossover module can provide.
Aries Cerat system including: Kassandra Signature DAC, Ageto Preamplifier, Talos Signature Phono Stage, Ianus Quintessence Monoblocks & Aurora Horn Speakers
Technical Specifications
