PMC AML1

Hugh Robjohns tests the AML1, and discovers that PMC can actually get a quart from a pint pot.

Although PMC are no strangers to active monitoring — their highly praised BB5 flagship and smaller MB1 systems are both active — the AML1 is the company's first 'compact' active monitor. Like all PMC speakers, it uses the transmission‑line principle, but it also incorporates much ground‑breaking technology, and took three years to develop.

Measuring just 400 x 200 x 316mm (hwd) and weighing 16kg, this is a true reference‑grade monitor. Not only is it able to resolve considerable detail and portray huge stereo sound stages with pinpoint accuracy, it is also capable of astonishing volumes with no hint of compression or distortion. The real surprise is a usable frequency range extending from 33Hz to 22kHz — and that bottom end is not an optimistic paper specification, as these boxes really shake the floorboards in a manner that would have anyone unfamiliar with PMC's extraordinary abilities searching for the subwoofer!

Technology

The rear panel of the AML1 features a substantial, arched heatsink with an internal chimney to aid the amplifier cooling. All of the electronics are mounted behind this panel, and reside within a sealed rebate in the substantial MDF cabinet, with only an IEC mains inlet and an XLR audio input being visible from the rear. The amplifier and crossover circuitry is built under licence from Bryston — a well‑regarded Canadian manufacturer who are so confident of their products that they provide a 20‑year warranty!

The crossover is tuned to a very low 1.4kHz, with 24dB/octave slopes, and drives two all‑discrete amplifiers — 100W for the bass and 80W for the treble driver. In true Bryston manner, these powers are very conservative figures, as are the distortion specs of under 0.009 percent at full output power! With a 0dBu input signal the AML1s will produce 106dB SPL at one metre, and can go substantially louder as well, with a phenomenal peak capability.

The AML1's three frequency‑tailoring controls have a useful global bypass button for checking the efficacy of settings.PMC have provided comprehensive calibration controls but, rather than placing these on the rear panel where access is often difficult, they are tastefully hidden away under a magnetically latched cover at the rear of the top panel. Three rotary switches provide HF Tilt of ‑5, ‑2.5, 0 and +2.5dB (above 1kHz); LF Tilt of ‑9, ‑6, ‑3, 0, +1.5 and +3dB (below 500Hz); and LF Roll‑off at 160, 80 or 50Hz, with an 'off' position. An EQ In switch, with status LED, allows instant comparison of user settings with the original factory response — a very sensible facility. A conventional volume control is also provided, but with no calibrated setting.

The high driver is an unusually large 32mm soft‑dome unit made by Audax, and is fitted with a drilled dispersion plate. This is the same unit PMC uses its monster MB1 and BB5 monitors, so its characteristics are very well known. The 165mm low driver is a custom‑designed unit optimised for transmission‑line loading. The flat, piston‑like diaphragm is constructed from a honeycomb of carbon‑fibre and Nomex which is extremely light, but incredibly stiff. The concept of this innovative driver was first established in the three‑way passive IB1 monitor — albeit with a larger and more powerful 250mm version. It should come as no surprise, then, that the folded transmission line of the AML1 is a scaled‑down replica of that in the IB1, providing an effective length of 1.7m.

PMC claim the only drawback of the bespoke piston driver is its limited high‑frequency range. Although not an issue in the three‑way IB1, the solution in the AML1 has been to use an oversized tweeter to allow an unusually low crossover frequency. This ensures that any nasty bass driver break‑up modes are kept out of harm's way, and the larger tweeter has the added advantage of greater power handling.

Both high and low drive units employ substantial, large‑diameter coil motor assemblies — the bass driver's being virtually as large as the cone itself! The drivers are matched by hand for precise stereo pairing, and calibration plots are archived, so that if replacement units are required they can be matched perfectly to the rest of the system's components. Magnetic shielding is incorporated as standard, allowing the speakers to be used close to monitors and console meters.

Model Looks

PMC have introduced some very attractive styling into their range following the acquisition of their own cabinet manufacturing facility. The AML1 has a custom plastic moulding which covers the entire front of the MDF cabinet. Carefully damped and secured to avoid resonances, this front panel not only hides the driver fixings, but also incorporates wave guides to ensure accurate dispersion, helped by the large‑radius outer edges, which prevent secondary radiation from cabinet corners. The transmission line vents at the bottom of the front baffle, through a perforated plastic grille.

Set into the front plate are six shiny magnets, originally intended to secure a front grille, although none is supplied as standard. Whilst the speakers look great au naturel, the tweeter is rather exposed and might be easily damaged by careless handling.

Listening

The PMC family resemblance in the AML1s was obvious on first audition, although they required a considerable amount of running‑in to loosen‑up that bass driver. Perseverance paid off though, as the speaker then reproduced astonishingly low‑frequencies, presenting precise and tuneful bass lines with superb resolution and detail, and with negligible mid‑range masking distortion.

Comparing the AML1 with several other well‑known active and powered monitors of similar physical size resulted in a landslide victory for the PMCs — in terms of resolution, accuracy, dynamics, and bass extension. However, these speakers come at a substantial UK price, and perhaps fairer comparisons would come from systems of a more similar cost. At this level, most competitors are three‑way designs and the advantages of a dedicated mid‑range driver are readily apparent, although the AML1 is far from outranked even in company of this calibre.

The sound is always well‑balanced and with accurate weight in bass instruments and percussion, with superb speed and attack and certainly no hint of the lag that used to be the bane of transmission lines two decades ago. Imaging is absolutely sharp and totally stable over a very wide listening area, while the see‑through clarity more than justifies the 'reference monitor' title. Voices are portrayed with stunning realism and precision, and the speaker easily reproduces real‑life dynamics in a nearfield situation, without any hint of strain.

This intriguing speaker redefines perceptions, and has to be heard to be believed. If your budget can take the strain, the AML1 makes an ideal monitor choice for any high‑end application where space is limited — small control rooms, dubbing theatres, or outside‑broadcast trucks, for example. Provided that care is taken to protect the drivers during transportation, the AML1 would also be ideal for location recording setups too.