Combining high output, extended low end and remarkable affordability, Fluid's newest point–source speakers offer a compelling option for engineers who need a bit of 'oomph'.
A couple of years ago I reviewed Fluid Audio's FPX7 nearfield monitor. Once a few early sample teething problems had been overcome, that monitor, the dual-concentric ribbon–tweeter–equipped FPX7, turned out to be a capable and engaging one. The subject of this review is somewhat more conventional than the FPX7 in sporting a dome tweeter, however it retains Fluid Audio's implementation of the dual-concentric driver concept. I'll write a bit about the history of dual-concentric drivers a few paragraphs down, but first a bit of description.
The FX80 is the larger of two new entry level-priced, US–designed and Far East–manufactured active monitors. The other model in the range, the FX50, is slightly smaller and slightly cheaper. As perhaps hinted at by the model names, the FX80 incorporates a nominally eight–inch (200mm) bass/mid driver, and the FX50 a five–inch (130mm) unit. The bass/mid driver diaphragms in both drivers are a relatively unusual composite of paper with a thin thermoplastic skin on the front surface. The idea behind the composite is that the paper foundation provides rigidity while the thermoplastic layer provides damping, and perhaps a more high-tech, engineered appearance (paper is a fabulous driver cone material, but it doesn't look particularly 21st century). In other respects, the bass/mid drivers appear to be of entirely conventional manufacture. The FX80 (and FX50) tweeter is mounted slightly forward of the bass/mid driver apex, effectively on an extension of the pole piece. It's a 30mm silk–dome device covered by a metal protection grille and surrounded by a gently profiled waveguide component of around 75mm diameter. The waveguide will help modify the tweeter directivity and aid its acoustic integration with the bass/mid driver, however with the crossover frequency set at 2.4kHz, where the wavelength is around 140mm, the effect of the waveguide will only begin to come significantly into play acoustically from, say, 6kHz upwards. So, below that frequency the tweeter will radiate significant energy backwards towards the bass/mid driver cone where it will reflect and unavoidably cause a degree of disruption to the system response in both time and frequency domains. I'll cover that with a few FuzzMeasure curves later in the review, but first, here's the promised bit on dual-concentric drivers.
The first and probably best-known exponent of dual-concentric drivers is of course Tannoy. However, the Tannoy dual-concentric principle, where a compression–style tweeter is located behind the bass/mid driver magnet and radiates through its pole-piece, is these days the exception rather than the rule. Contemporary dual-concentric designs, where the tweeter is mounted in front of the bass/mid driver, were to a significant extent made possible by the development of rare-earth magnet materials such as neodymium-iron-boron (NdFeB). Before NdFeB, it simply wasn't possibly to position a viable tweeter in front of the bass/mid driver without significant compromise to the bass/mid driver performance — magnet technology powerful enough to enable a small tweeter to reach the required sensitivity simply...