Monitor Audio Platinum PL 500 II Floorstanding Speakers (Pair)

In keeping with Monitor Audio tradition, the PL500 II contains a wealth of innovative technologies—specifically in its drivers and crossovers. According to the manufacturer’s white paper on the Platinum II line, these new tech developments are the fruit of extensive FEA modeling and measurement (prior to extensive listening testing, naturally). In addition, Monitor Audio builds all of its drivers and crossovers in-house.

The PL500 II is a three-way, seven-driver floorstander in a D’Appolito configuration. The tweeter, a micro-pleated diaphragm (MPD), was created by Monitor Audio as an improved version of Dr. Oskar Heil’s Air Motion Transformer (AMT). Typical AMTs have a null in frequency response at around 40kHz, but with the help of FEA modeling Monitor engineers figured a way around this issue. As explained in the white paper, the larger rolls (or pleats) in the AMT diaphragm were causing phase cancellations at progressively higher frequencies. The resulting null, which reached a –3dB point at roughly 28kHz, could be eliminated by reducing pleat height and increasing the number of pleats. Incorporated for the very first time in a Monitor speaker, this new MPD driver reportedly functions with uniform output to over 100kHz.

Another advantage of this advanced transducer is its low mass, lower inertia, and larger radiating surface area (eight times the area of a typical dome tweeter), which together produce transient response that’s more similar to an electrostatic driver than to a dynamic design. Indeed, I found the speaker possessed a satisfying sense of speed of attack as well as snappy overall energy and pacing (traits which of course are also linked to the electronics in the chain powering the speaker, more on which later). The MPD has a pair of neodymium/iron/boron magnets front and rear to reduce distortion, provide greater uniformity of response, and increase efficiency; the micro-pleated diaphragm only needs to move one-eighth of the distance of your average dome tweeter to produce the same output. These factors contribute to the PL500 II’s power handling and high sensitivity of 91dB @ 1W. (This surprising sensitivity allow to drive the PL500s with a relatively low-powered tube amp—to very ear-pleasing effect.)

Monitor’s newly upgraded Platinum II technologies have also resolved the coherence issues that plague large-scale multiways. For starters, the crossover networks have been redesigned using air core inductors for the tweeter and midrange, and laminated steel cores for the woofer. All cone drivers in the Platinum II line also use underhung voice coils for lower distortion. For more efficient driver and voice-coil coupling, the speaker’s drivers feature Monitor’s new patented Dynamic Coupling Filter (or DCF) mechanism, which is a pliable nylon ring that is calibrated to stay rigid up to the crossover frequency, but above that wavelength to act like a spring to dampen excess HF energy.