Simply impressive. The definition of the AML1 combined with the power of the SB100. ISP Música magazine continues its tour of 5.1 systems, and this time it's the turn of PMC, a manufacturer that is already becoming an old friend of the magazine.
Not for nothing have several monitors from the Professional Monitor Company passed through our test benches, such as the AML1 (in a stereo setup, April 2006), the DB1S-A (March 2007) and, most recently, the RM2 (co-designed with Digidesign, September 2007).
On every occasion, PMC products have received very good reviews, and at the time the AML1s stood out in their stereo configuration. This time, they come as part of a surround system, with the SB100 subwoofer handling the LFE channel.
Transmission lines
Talking about PMC means talking about its Advanced Transmission Line (ATL). Although the use of transmission lines in loudspeaker design was first described in 1965, the truth is that few manufacturers use it today.
The ATL, the manufacturer's proprietary design, is based on this concept of an acoustic transmission line, in which the energy radiated backward by the speaker is captured in a "labyrinth" built inside the cabinet itself.
Suitably damped, this energy is radiated outward again, in phase with the energy coming from the front of the driver. The result is less coloration in the low-mid frequencies, greater power and definition, and improved bass extension.
The downside of all this is that both the design and the construction are considerably more expensive than with bass reflex models, which explains why this system isn't very widespread, despite its better response.
(More details on how the ATL works can be found in the ISP articles mentioned at the beginning of the text.)
PMC AML1 monitor
Although PMC already had passive monitors that could be "activated" with amplifiers added to the cabinets, the AML1 was the company's first active monitor, designed from the start together with its amplifier. It soon earned a very good reputation, gaining ground on other classic PMC combinations, such as the IB2 monitors powered by Bryston's 7B SST.
The two-way AML1s stand out both for their definition and for their bass extension, especially considering their size. This is largely due to the ATL, whose length (1.7 m) lets the monitors' response extend from 25 kHz down to 33 Hz.
The bass driver (6.5") is a "flat piston" design made of carbon fiber and Nomex®, materials whose stiffness and lightness allow large speaker excursions without flexing. This quality is essential in a transmission line woofer, since for the line to be effective, the speaker has to withstand high pressure on its rear side. These qualities do mean, however, that the driver's midrange response isn't as good.
To make up for this, a somewhat larger than usual tweeter (1.33") is used, which allows the crossover point to be lowered to 1.4 kHz. This silk dome high-frequency driver is protected by a metal sheet, perforated to help the waveguide with dispersion.
The drivers are powered by two Bryston amplifiers of 100 W and 80 W RMS (lows/highs), which deliver a maximum SPL of 106 dB at one meter (distortion <0.009%). The frequency split is handled by a 24 dB/octave active crossover.
On top of the monitors is the EQ section, which can be switched on or off. This EQ includes a high-pass filter (0, 50, 80 or 160 Hz), a low shelf (-9 dB, -6 dB, -3 dB, +3 dB at 30 Hz, with the turnover point at 500 Hz) and a high shelf (-5 dB, -2.5 dB, +2.5 dB at 10 kHz, with the turnover point at 1 kHz).
SB100
The (passive) subwoofer also uses a flat piston made of carbon fiber and Nomex®, but in this case with a 10" ferrofluid-cooled driver. Combined with the 2.8-meter transmission line, this driver lets the SB100 reach down to 25 Hz at the low end, with a maximum SPL of 116 dB at one meter.
Despite these figures, the subwoofer cabinet isn't excessively large, especially when it comes to depth (350 mm), which means the SB100 can be placed under any desk without problems. The connectors are 4" sockets, although Neutrik NL4 connectors can be requested when ordering the SB100. The nominal impedance is 4 ohms, with a recommended power of between 120 W and 500 W.
As mentioned at the start of the article, this setup is designed for the SB100 to handle the LFE channel directly, so the subwoofer has no bass management or filters of any kind.
Setup and calibration
As with any other audio playback system, the placement and setup of the speakers is paramount.
The simplest way to position monitors correctly in a surround configuration is to mark a listening position and, from there, draw an imaginary circle on which the monitors are placed at the various angles (0º for the center satellite, +/-30º for the fronts and +/-110º for the rears, according to the International Telecommunication Union's ITU-R BS.775 standard).
So, before setting the monitor levels, several layouts were tried, varying the listening position and the distance between speakers (the radius of the circle), until a suitable placement was found in which both the distance from the monitors to the listening position and each monitor's position relative to the room's walls were balanced.
Levels: 85, 83, 79, 77…
Recommendation RP 200 from the Society of Motion Picture and Television Engineers (SMPTE) specifies SPL levels for surround setups for film or television.
In the first case, the reference level is 85 dB SPL, while in the second it drops to 79 dB SPL, since television mixes translate better when they're done at a lower level.
However, calibration levels for music program material aren't as clear. Many music studios follow the RP 200 standard, but with one small variation: the recommendation specifies that the rear satellites be 3 dB below the fronts, whereas for music playback all the satellites are set to the same level.
The problem is that 85 dB SPL can be a somewhat high level for mixing music, so some authors recommend calibrating the system with this reference and then using the master volume control to reduce the level by a known amount, between 6 and 10 dB.
Since the aim of this test was to evaluate the system with different types of program material, we chose to calibrate the system at 85 dB, using pink noise at -20 dBFS RMS and a one-third-octave RTA (five-second integration time, Hanning window).
According to the standard, if each satellite emits pink noise at 70 dB SPL, the sum of all of them should produce 85 dB SPL (in theory, and provided the sources emit uncorrelated pink noise).
The five
Once the satellites were calibrated, we could start evaluating the system, and the truth is that, even before integrating the SB100, our first impressions were excellent.
The word "satellite" seems to carry the implicit image of a small speaker with a limited response, but we mustn't forget that in this case the satellites were five AML1 monitors.
As was the case when we tested these monitors in a stereo configuration, listening through them is impressive. Powerful, well defined, with great dynamics.
The way the AML1s behave makes them virtually disappear (a trait of high-end monitors), and in their place the musical scene appears.
The monitors' accuracy in revealing the smallest details, reverbs and other auditory localization cues heightens the sense of envelopment typical of a surround system, creating a sharp image around the listening position.
They show no trace of compression, even when pushed to high levels. The monitors seem to work effortlessly, even making you forget the mere fact that they're there.
Mixing
Taking advantage of the band Havalina's visit to the studio (they were recording their fourth album, soon to be released), we chose the song "Septiembre" to do a surround mix.
The concept of this song is perfect for a mix like this, with long guitars with reverb and delay creating big spaces, solid drums that build the rhythm around the toms, a punchy bass supporting the drums, and a melancholy (yearning) vocal that sits in the middle ground, close yet distant at the same time.
When approaching the mix, two possibilities came up: one route was to place the instruments around the listener, including the rear speakers, so that it would seem as if the listener were in the middle of the band. Although somewhat unrealistic, many users enjoy this type of mix.
The other way was to use the five speakers to create an "enveloping stereo image," in which the main instruments are placed in the front monitors but opened up toward the rears, either with the divergence control, by panning their reverbs to the Ls and Rs channels, or a combination of both. Something like recreating the experience of seeing the band in a concert hall.
The latter was the route chosen, being more in keeping with the album's overall concept. So the mix sought to enlarge the instruments through the rear monitors, creating a "big stereo image."
The result was really good and, in fact, once you got used to listening this way, going back to normal stereo seemed small and poor by comparison.
The subwoofer
Someone may be wondering what happened to the subwoofer, since nothing has been said about calibrating it yet. That's because the first part of the tests was done using only the AML1s.
As already mentioned, these monitors' bass extension is really good, and the music mix worked well without the subwoofer (keep in mind that this particular style of music doesn't demand as much sub-bass as other types).
However, when we moved on to evaluating the system with another type of program material (a movie trailer), the lack of low end became obvious. That's when we added the subwoofer to the system, again using the spectrum analyzer and pink noise.
Once integrated, the lack of low end was solved, giving way to full-spectrum listening. The improvement on the trailer was obvious, and the second mix of "Septiembre," done with the subwoofer, also demonstrated the SB100's good work.
While on the trailer the subwoofer's contribution was evident in some parts (explosions and other effects), in the music mix the SB100 provided a poise that the mix without it lacked. It didn't stand out for being there; rather, you missed it when it wasn't, because of its solidity, support and definition at the bottom of the spectrum.
Like its teammates, the SB100 seemed to work effortlessly, and the more you asked of it, the more it gave.
Conclusions
The PMC system is truly impressive. With other monitors, the sense of envelopment is created by the perception that the sound comes from different sources.
In the case of the team made up of the AML1s and the SB100, the sense of envelopment is created by the image the monitors produce. You aren't aware of five discrete speakers at work.
This is no accident; it's the result of meticulous work in which every detail is taken care of: the design of the transmission lines and absorbent materials, special drivers tested and matched by hand, high-end amplifiers with OS-CON capacitors, fully bypassable EQ… All these aspects together shape the system's response.
Unfortunately, as is often the case with this company's products, the price is a drawback, possibly the only one. This surround setup is expensive, and depending on the case you'll need to add the cost of a power amp for the subwoofer and external bass management.
In return, however, you get a system that is far above average. Clarity, definition, reliability, solidity, power… are just some of the adjectives that come to mind to describe the AML1-SB100 tandem.
If budget isn't a constraint, it's undoubtedly a "must have."
