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Interview with Legacy Audio on the Aeris Loudspeaker System

by July 13, 2014
The Legacy Audio Aeris.

The Legacy Audio Aeris.

As regular readers will know, we here at Audioholics have been fans of Legacy Audio for a while now. While their products aren’t inexpensive, higher end models like the Aeris, Whisper XDS, and Helix are technical tour-de-forces thanks to the utilization of an advanced DSP correction system, as well as top notch engineering and parts. We were able to sit down and have a chat with Bill Dudleston, Legacy Audio’s founder, President, and brain behind the operation to gain some insights into the Aeris Loudspeaker.

AH: What can you tell us about the DSP correction system utilized in the Aeris?

Bill: Signal routing and processing for the Aeris is accomplished via the 4 input x 8 output matrix Wavelaunch processor built by Xilica of Canada, and controlled via XConsole software. Each balanced input and output of the routing matrix has independent level adjustment and each output can be configured as a submix of any of the inputs. The included Aeris algorithm divides the left and right inputs with a customized high pass and low pass network to form a stereo 2-way crossover.   The transfer function for each loudspeaker is pre-programmed at Legacy for linear, time aligned output from each driver, correcting minor anomalies inherent in the combined array.  The output side of the matrix is factory configured for Aeris, the input side (left side of the matrix display in the software) is for you or your installer to make adjustments in your room. 

Legacy Audio Wavelaunch Processor

Legacy Audio's Wavelaunch processor performs crossover functions, time alignment, PEQ, and more.

Eight additional parametric filters and 31 bands of graphic equalization are available on each input for the installer or end user to optimize the final combined response in their room.   While the output side of the matrix is factory configured for Aeris, the input side (left side of the matrix display in the software) is to make adjustments in your room.

The Aeris’s DSP system also hosts a proprietary algorithm which improves stereo separation and depth by subtracting an appropriate portion of the Left bass signal from the Right speaker and likewise the Right bass signal from the Left speaker.  An important adjustment in the time domain for the arrival path is also factored in. The resulting improvement in depth and localization can be demonstrated by defeating this feature (mute inputs 3,4) on the front panel of the processor.  Note that the algorithm benefits any stereo listening position and does not attempt to diminish acoustic shadowing across the head, as this is an essential part of the stereo process (unless your recording is specifically binaural).  The algorithm is not a mere ambience injection (L-R) circuit which can be phasey, echoey, or cause instruments to wander unpredictably. The Aeris algorithm has been empirically derived from bounded space studies.

AH: Can you discuss how being in a real room impacts the sound of the Aeris, and how you deal with the resulting anomalies in response?

Bill: Loudspeakers and room boundaries are subject to reinforcement, resonance and reverberation.  Constructive reinforcement of lowest frequencies can be quite beneficial if one has the Aeris system’s capability to adjust the loudspeaker to utilize this boundary gain. This increase in radiation impedance, or room gain, significantly reduces cone excursion requirements, thus decreasing distortion. Resonance reduction is a bit more complicated, requiring both amplitude and time domain adjustment which the Aeris Wavelaunch processor is well equipped to handle. Finally, reverberation is minimized by reducing sidewall reflections via the radiation nulls to the side of the speaker.  The open-air arrangement seen on the Aeris behaves as a dipole from 80 Hz to 3kHz, summing into a cardioid pattern with the bass drivers in the band from 80 Hz to 200 Hz. Listening panels in controlled trials have determined that imaging precision and soundstage width is consistently improved over the Legacy Focus system for example, which utilizes a similar, but monopolar driver layout.  

Aeris Side - Rear View

A side/rear view of the Aeris shows the open air arrangement, creating a dipole configuration from 80Hz-3kHz.

AH: What can you tell us about the development of the AMT (air motion tweeter) drivers used on the Aeris?

Bill:  The development of the Aeris loudspeaker system gave me the opportunity to tool a new AMT folded ribbon tweeter to integrate with the smoothest high efficiency 8” midrange built to date. This silky 8” mid has a range of 7 octaves with nary a wrinkle in the response, yet a sensitivity of 98dB. My initiative of providing a 4” AMT that could compliment these capabilities was met with by accordion-folding sixteen square inches of Kapton into a 4” long, 1” wide chamber. Neodymium was employed to provide the flux density required. The solution was made even more elegant by mounting the new 4” ribbon on the same faceplate as its complementary 1” AMT ribbon super-tweeter. The results were more uniform dispersion and tremendous attack. The effortless way it forcefully squeezes out acoustic energy is readily verified by placing ones hand over the driver faceplate and feeling the suction against your palm (nope, you won’t hurt it). These new drivers may be refined, but are equally rugged.

Legacy Advanced AMT Array

Legacy's AMT (air motion tweeter) array allows the system's top end to keep up with the 98dB sensitive 8" midrange driver.

AH: Why did you choose to implement a powered subwoofer section on the Aeris, versus a conventional passive array?

Bill: Each Aeris loudspeaker hosts a separate 500 watt ICEpower amplifier module to power each of the two 12” woofers. The amplifiers are full bandwidth capable designs and operate at high efficiency.  A single XLR input is provided on the rear panel of the speaker which is fed by the corresponding bass output channel of the processor. This reduces intermodulation distortion and allows your main amplifier to drive the upper portion of the speaker without bucking the back-EMF from the bass drivers. 

Aeris Plate Amp

The Aeris' plate amplifier feeds 500W to each of the built in 12" subwoofer drivers.

The active subwoofer also means the remainder of the package can aim to achieve an exceptionally high sensitivity (rated at 95.4dB for the Aeris), which translates to greater acceleration for better tracking capability and tremendous dynamic range. The distortion level is also exceedingly low due to careful attention to design of the magnetic structure of each driver.

AH: Where can fellow Audioholics demo the Aeris and other Legacy Audio systems?

Bill: You can hear the full line of Legacy speakers at our factory in Springfield, IL or our Los Angeles showroom. We also have about a dozen additional domestic showrooms and a growing number of international distributors. One extraordinary venue for our commercial line is the state-of-the-art Giant Screen Theater at Peoria Riverfront Museum. This theater utilizes 5 of our doubleHelix loudspeakers across the front and includes 40 DSP channels. More information on this particular install is available here.


About the author:
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Steve Munz is a “different” addition to Audioholics’ stable of contributors in that he is neither an engineer like Gene, nor has he worked in the industry like Cliff. In fact, Steve’s day job is network administration and accounting.

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