• Interview with François Deffarges (Nexo)

    François Deffarges was born in 1964 in Copenhaguen, Denmark; he received a bachelor's degree in audio recording and reproduction from the Ecole Louis Lumière in Paris, France, in 1985, and a master's degree in acoustics from the CNAM in Paris, France in 1991. After ten years on the road as a sound reinforcement engineer for various artists, he joined Nexo R&D Department. In 2000, Eric Vincenot and Mr Deffarges filed a patent on a hyperboloid waveguide, which originated the development of GEO series. He was appointed Research & Development Director in 2005.
    We thank Mr. Deffarges for kindly accepting to be interviewed by Doctor ProAudio. Questions combine forum users' suggestions as well as editorial ones.


    ¤ [Doctor ProAudio] - Let’s start from the beginning. How and when did you become interested in sound? What made you decide to pursue a career in sound reinforcement?
    ¤ [François Deffarges] - I grew up in Brazil, a country where music is a celebration of life. Therefore, music is in my life since very young, and it has been an easy decision to make when I was 15 that this was the domain I would be working in. That passion is intact today, although my musical tastes have broadened!

    ¤ [DoPA] - What does music mean for you?
    ¤ [PQ] - Emotion, poetry, esthetics. All things impossible to rationalize!

    ¤ [DoPA] - What made you decide to pursue a career in audio?
    ¤ [PQ] - Sound is a very unique domain, which covers art, psychology, sociology, communication, science and … business. And sound reinforcement is all about it happening live!

    ¤ [DoPA] - 10 years ago line arrays were a French oddity and now they are all over the place, even though they cannot offer all of the possibilities of conventional arrays, such as a variable horizontal coverage angle (with a few notable exceptions, including yourselves). Are line arrays here to stay? What comes next?
    ¤ [FD] - Line arrays is a generic expression that defines the vertical hang we see in most of the events today, where vertical curvature governs coverage. But in a broader approach, line array exist because recent technologies allowed designing non-interfering systems. And these technologies also apply to single cabinets as well as to horizontal arrays. So, these non-interfering solutions are definitely here to stay. Future is about improved radiation control and sound image over the audience. DSP is a key element in these challenges.

    ¤ [DoPA] - Some people object to locked system controllers for advanced users. What would you say to those?
    ¤ [FD] - I don’t think there is a debate around locking or unlocking controllers parameters, but rather on which parameters are to be defined by who. Nexo controllers feature heavily sophisticated algorithms for coil temperature, membrane excursion and distortion measurements, rear to front signal optimized relationships for cardioid systems, linear frequency and phase implementation, etc… Months of measurements and listening tests are required at R&D before final parameters are integrated to the product. And this specific set of parameters belongs to the product. Another set of parameters – such as delay, fine EQ, program dynamic control - are specific to on-site system tuning. They depend on system design, acoustic environment and program content, and belong to the solution.

    ¤ [DoPA] - How does Yamaha’s purchasing of Nexo affect your product development?
    ¤ [FD] - Yamaha is world leader in Digital audio and in Digital Signal Processing and Nexo is among the world leaders in professional loudspeakers industry. So, the move of Nexo into the Yamaha group is in fact a very natural move on a technical standpoint, where Yamaha’s resources and know-how nicely complement Nexo’s skills. NXAMP4x1 and NXAMP4x4 turned such statement into practical user benefits. Over the last 18 months – with significant help from Yamaha -, Nexo R&D has also greatly improved its product development methodology, leading to improved product performance and quality.

    ¤ [DoPA] - Now that there’s amplification bearing a Nexo logo, would self-powered speakers be something that Nexo could be interested in?
    ¤ [FD] - We permanently investigate available solutions, current situation being that power modules are not capable of delivering required power for our drivers. A powered Nexo product would be a downgrade of current NXAMP solution, and this is not what the market expects. However, there is no question on a long term basis that powered solution will become globally competitive.

    ¤ [DoPA] - The PS-15 is undoubtedly one of the most successful 15” 2-way boxes (probably the industry’s most common format) in the history of sound reinforcement. Where’s the secret?
    ¤ [FD] - As often in a success story, there is the right combination of key factors. Among these, I would quote versatility, ease of use, SPL to volume ratio. And PS-R2 recent release brings that combination again to a higher level.

    ¤ [DoPA] - What is you approach to designing a speaker system?
    ¤ [FD] - One approach is based on customers need, and requires comprehensive knowledge of his environment. The other approach is based on innovation and creativity, permanent Nexo R&D challenge being to bring new concepts to the market.

    ¤ [DoPA] - While most manufacturers started their line-array product lines from the largest model, Nexo started from the smallest (GEO S8). Why was that?
    ¤ [FD] - GEO S8 is a good illustration of above statement. GEO S8 brought a solution that no one anticipated. And the product was quickly and widely adopted because of its ability to cover an enormous range of applications that competition had not addressed. A nice “Blue ocean” story.

    ¤ [DoPA] - Some people found strange that a high-end system would use a passive crossover …
    ¤ [FD] - As a reminder, our high end flagship – GEO T – is a full active system, GeoD down to PS15 are switchable passive / active, GEO S8, PS10 and PS8 are passive only. One might think that passive / active cross-over determines product positioning, but customer requirement is always on end result. We tend to offer choice between passive / active so that customers can optimize their solution according to their own needs prioritization.

    ¤ [DoPA] - GEO-T is a symmetric system while GEO-D is not. Is symmetry important?
    ¤ [FD] - I see one essential benefit to symmetry, which is undifferentiated left and right systems. Acoustically, symmetry is more of a constraint (minimum distances not to be exceeded between drivers, increased diffraction effects over coverage etc…).

    ¤ [DoPA] - The Hyperbolic Reflective Wavesource (HRW™) has been instrumental for Nexo’s product this century. The virtual source for the high frequency band is placed outside the box so that a circular array of boxes, with splayed at the nominal inter-box angle, will have a common source origin, hence providing ideal summation in theory, and significantly fewer artifacts in practice, as compared to using conventional horns. A few questions on that:

      • What happens at angles other than the nominal angle? Say, S830 boxes arrayed at 15 degree angles? (The virtual sources would each be at a different virtual point, unlike for 30 degree splay).

        [FD] - One always has to look at wave shape deviation in relation to ideal curvature, which should never exceed ¼ of a wavelength of maximum frequency. This deviation is governed by wave front angle and waveguide height. Two GEO cabinets can be splayed: - below nominal angle provided no interferences occur below 20 kHz; - above nominal angle provided no coverage hole appears below 20 kHz.
      • [DoPA] - The concept is easy to understand for a circular array. However, Nexo uses it for the so-called line arrays (Nexo uses the term Tangent array), for which everyone else uses some form or ribbon emulation in one way or other. Can you enlighten us on that?

        [FD] - A major technical benefit of the GEO patent is that – unlike ribbon solutions – it allows to curve wave front up to high angle values. “Tangent Arrays” concept was introduced in 2001 when we launched GEO S830 in conjunction with GEO S805: two wave fronts with different curvature could be coupled without discontinuity (which is tangency definition). This has proven to be a much more efficient solution than the gain attenuation that was applied to downfills in vertical assemblies.

    ¤ [DoPA] - Nexo is an advocate for cardioid systems for both subwoofers (as well as low frequencies in full-range systems). With respect to subwoofers, can you tell us about the role ports take in your cardioid subwoofers?
    ¤ [FD] - The real challenge in cardioid systems is to combine directional effect with efficiency. In our industry, no user will accept a system with 2 drivers producing less than one for the sake of directivity! Efficiency is achieved by properly positioning all radiating surfaces so that not only rear radiation is massively attenuated, but drivers sum up properly in the audience direction. Nexo R&D spent years in defining proper DSP algorithms together with optimized architecture for maximized efficiency. And this is an on-going process.

    ¤ [DoPA] - It is becoming common-place to design complex subwoofers arrays to provide uniform coverage and/or minimize left-right power alley type effects. Do you have plans for GeoSoft to include subwoofer modeling capabilities?
    ¤ [FD] - We will be presenting Nexo NS-1 software at Frankfurt PLS, which includes this capability, among many new ones.


    ¤ [DoPA] - Which side of the Atlantic would you say the best competitor products come from?
    ¤ [FD] - We have strong respect for what is being achieved by competition through very different strategies, both sides of the Atlantic!.

    ¤ [DoPA] - If you could not manufacture speakers, what we would you like to manufacture?
    ¤ [FD] - Something connected in a way or another to people’s emotions. Designing speaker systems is not the only way to stay connected!

    ¤ [DoPA] - Which way do you see the industry going on in the future?
    ¤ [FD] - As in many other industries, customer requirement for service and therefore service value will keep on increasing.

    ¤ [DoPA] - Which way do you see Nexo going on in the future?
    ¤ [FD] - We will follow the same route that led us to success: continuously impressing and satisfying customers beyond their expectations.

    ¤ [DoPA] - Any other thoughts you would like to share with our readership?
    ¤ [FD] - Nexo’s success in Latin America means something special to me. Thanks to Celso Papadopoulos, Roberto Tschopp and our Latam distribution network for making that happen.