Monitor Audio was to be congratulated for its decision to use ribbon tweeters in its flagship Platinum series, launched back in 2007. The PL100 – which cost £2,300 – ran a very nice ceramic coated aluminium/magnesium ribbon HF unit riding shotgun with a single 6.5 inch Rigid Diaphragm Technology bass-mid driver. Designer Dean Hartley saw the mass of conventional dome tweeter as a problem, restricting both speed and overall bandwidth. He told me, “the ribbon tweeter does not have a voice coil or suspension mass, and in this case the moving mass is the same as the ribbon mass which is 18mg.”
This worked down to 2.5kHz, where it crossed over to the mid/bass driver – the crossover boasts specially made metalised polypropylene film capacitors, graded to 1% tolerance. Air cored inductors gave low distortion, and internal wiring was pure silver. Hartley said the mid/bass driver was, “a new in house development which we call RDT, made from bonding very thin skins (40uM thick) of C-CAM alloy to a Nomex honeycomb core. This forms a laminated sandwich type construction and is incredibly strong. The concave design has an un-interrupted surface to provide smooth response. RDT cones are directly driven by the voice coil and have no dust cap or joints to interfere with the driver response.”
The PL100 was beautifully built and finished, especially by mid-noughties standards. The superbly sculpted, heavily braced cabinets were ﬁnished in exotic, hand-selected Santos Rosewood and Ebony natural wood veneers coated in eleven layers of lacquer, while the front baffles delighted with their soft Strathspey leather upholstery. The cabinet had multiple laminations of wood veneers shaped to form a rigid plywood shell, and irregular internal sides to counter internal standing waves and rigid ‘Pin-hole’ type bracing to provide further rigidity. Tie-bolts were screwed into the brace from the back and front of the cabinet, tightened to specific torque to further tune out any resonance, and Bitumen internal sound deadening material was applied to all internal walls. The front baffle was an ‘anti-resonance composite’, a thermo-set composite resin with organic fillers. “It possesses a high degree of structural rigidity and damping properties, which is acoustically excellent,” said Hartley.
It’s a distinctive sounding loudspeaker, in the sense that it doesn’t suffer a lot of the woes of most rivals. That lovely ribbon makes it different to every dome tweetered design, and it proffers an unfettered, open window on what’s happening in the upper midband and treble. By comparison any dome tweeter – with the exception of certain ultra-light Beryllium dome perhaps – sounds fuzzy and sat-upon. The feeling of space the PL100 confers is exceptional, taking you right into the recording.
This wee speaker sounds so fast, and is beautifully textured and timed with majestic precision – making a song bound along when on lesser loudspeakers it merely plods. Fortunately the mid/bass units are sufficiently well integrated to keep up, giving low frequencies a wonderfully propulsive gait. In absolute terms, you can hear the mid/bass unit running ever so slightly behind the tweeters – there’s no way that any cones can move in and out as fast as gossamer-thin ribbons, and the ported cabinets introduce very slight time-smear too, as any infinite baffle enthusiast will tell you. But still they’re excellent at the price, and in the great scheme of mid-price loudspeaker things. Properly set up and matched to a smooth, open source and amplifier, I can think of few better small boxes at the price – and never tire of that distinctively warm, sweet and svelte sound.