TMD diaphragm surround with harmonic damper

An innovation to enhance the value of mediums.

OBSESSION WITH THE MIDRANGE

The midrange register is undoubtedly the most complex to master in an acoustic system. On the one hand, it must ensure a harmonious energy junction with the bass channel. On the other, it must be coherent with the tweeter in terms of dispersion and acceleration. Timbre homogeneity and spatialization depend on it.

Over the last twenty years, Focal has been working to control diaphragm "break-up" (the frequency at which the cone deforms and causes distortion) with 3rd generation "W" composite diaphragms, and to drastically reduce tweeter resonance with the IAL 2. Today, thanks to the power of numerical finite element analysis, our teams have developed a simulation tool to visualize the dynamic behavior of the surround that links the cone to the saladier, revealing the dysfunctions on which progress can be made.

THE TMD HARMONIC DAMPER

Following the discovery of these malfunctions, the challenge was to design a device that would enable them to be controlled. Known solutions for increasing surround damping lead to an increase in mass, which in turn affects definition. The answer was found in a technique used in anti-seismic systems for skyscrapers, and also found in the surrounds of racing vehicles! This is the Tuned Mass Damper technique: an additional mass oscillates in opposition to the resonance to control it.

Applied to the loudspeakers, the solution simply consists of two circular "beads" molded into the surround mass and judiciously sized and positioned. They constitute our harmonic damper (TMD) and stabilize the surround's behavior at resonance to avoid cone deformation and not penalize dynamics. This innovation is patented.

VISUAL ANALOGY OF A SURROUND WITH OR WITHOUT HARMONIC DAMPER

Two circular "beads" molded into the surround mass constitute our harmonic damper (TMD). Above, a conventional surround, below, a TMD suspension. This simple solution, developed thanks to our new software, stabilizes the surround's behavior at resonance, avoiding cone deformation without penalizing dynamics.

THE "TMD" HARMONIC DAMPER PRINCIPLE

The principle of the "TMD" harmonic damper: in red, an m1/k1 system with a very pronounced resonance. The addition of a m2/k2 mass-spring device (upper part of the central diagram) will result in a behavior showing two resonance peaks as on the blue curve. The trough, or anti-resonance, having been set to the resonance of the main device, we obtain the green curve and finally, by judiciously dosing the damping, we end up with the purple curve. Resonance has all but disappeared!

In the case of the Sopra line of loudspeakers, we've combined this innovation with an exponentially-shaped cone to extend its frequency response, and therefore its impulse response. Another argument in favor of even greater definition.

MEASUREMENTS AND ANALYSIS

Improved linearity between 1 and 2 kHz and frequency extension brought about in part by the cone's exponential profile.

In blue, our latest-generation midrange. In red, a previous-generation W midrange. Improvements to the magnetic circuit also make their contribution. NB: the dip at 3 kHz is due to the absence of a core cover on the test unit.