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Powered Monitors
Published May 2005
By Hugh Robjohns

The TB2SA (outside) and DB1SA (inside) monitors, complete with their Flying Mole amplifier packs.The TB2SA (outside) and DB1SA (inside) monitors, complete with their Flying Mole amplifier packs.Photo: Mark Ewing

Pioneering digital amplifiers are combined with PMC's proven transmission-line cabinet designs to deliver spectacular monitoring performance at a project-studio price.

The Professional Monitor Company — now known more simply as just PMC — have built up a phenomenal reputation for their entire range of monitors, from the massive BB5/XBD system down to the tiny DB1. These products can be found in mastering houses, film dubbing suites, recording and broadcast studios, and outside broadcast trucks, and are increasingly making inroads into the homes of well-heeled hi-fi buffs.

Many of these products have already been reviewed in the pages of Sound On Sound, including the DB1, TB2, FB1, and AML1, and all employ highly sophisticated transmission-line loading principles unique to PMC. The majority of PMC's products are passive, meaning that they employ high-level crossovers constructed from passive components — albeit highly specified components laid out with enormous care on huge and complex circuit boards behind the terminal panels. Only the largest systems — the BB5 and MB2 speakers — and the compact AML1 are available in fully active configurations.

PMC have long argued that while the active approach has some significant advantages over a passive design, it is an expensive solution requiring high-quality active components — filters and amplifiers. The large active BB5 and MB2 systems, for example, employ specially modified Bryston active crossovers and Bryston amplifiers throughout. Even the AML1 employs Bryston circuitry built under licence.

Making active speakers to suit the budgets of the home-studio market while still meeting the quality threshold demanded by Peter Thomas, Managing Director and Chief Designer of PMC, has so far proved impossible — not, apparently, through lack of trying! To date, Peter has simply not found a way of incorporating active crossovers and amplifiers of sufficient quality at a low enough price to make this dream a reality, and the company has long recommended instead partnering their passive speakers with a top-quality amplifier to achieve the product's performance potential.

To that end, they have long offered the neat solution of the Bryston Powerpac amplifiers — single-channel self-contained units, available in a range of powers from 60W to 240W, which can be bolted to the rear panels of the speakers to produce a convenient 'powered speaker' — an approach PMC like to call Activated. While this solution lacks the 'tweakability' featured in many active designs, and it is relatively expensive, it works very well indeed and the resolution and quality surpasses many similarly priced active designs.

Regular Sound On Sound readers will already know that I have used a pair of TB1s, Activated by Bryston Powerpac 120s, for many years with no complaints whatever. The sound quality and resolution are superb given the system's size, although the combination is relatively heavy and quite expensive. However, these criticisms have now been addressed with the launch of the TB2SA and its diminutive brother the DB1SA. Essentially these are standard TB2 and DB1 speakers with re-engineered cabinets to incorporate Flying Mole monobloc digital amplifiers in a very neat package. The amplifier is incredibly lightweight and highly cost-effective, while giving remarkably little away in sound quality terms to the heavy and expensive Bryston. It may sound too good to be true, but the proof is in the listening!

The Mystery Of Model Names

First off, it might be useful to explain the logic behind the model names and some of the recent developments, which have left some potential purchasers a little confused. The TB2 is named as the second generation of the 'tiny box' loudspeaker — it's older and discontinued sibling being the TB1. The newer model introduced improvements to the transmission line and crossover, as well as rounded baffle edges to enhance stereo imaging. The 'S' in the model name refers to the Studio version — the most cost-effective model in the range, with a painted black cabinet rather than the more expensive range of real wood veneers favoured by up-market studios and hi-fi types. Finally, the 'A' suffix points to the Activated status of the model, with the incorporated Flying Mole amplifier.

Interested parties may become confused by another suffix — the '+' model. Recently, PMC decided that economies of scale would allow the original metal-dome tweeters fitted to several models — including the DB1 and TB2 — to be upgraded to the soft-dome tweeters used across the board in the more expensive models. This upgrade was indicated by the '+' suffix, and the current production models of the passive speakers are marketed as the DB1S+ and TB2S+ (older metal-dome systems can be upgraded — contact your dealer for details). However, in the interests of simplicity, the Activated models, which all employ the same soft-dome tweeter, don't include the '+' suffix.

Last but not least, is the 'M' version, which means that the monitor is Magnetically Corrected — this is only available as an option, rather than being built in as standard. Given the almost universal use of LCD computer monitors, and the growing use of LCD and Plasma TV screens, magnetic shielding is far less important than it once was, and hence many will enjoy the reduction in cost that derives from making the shielding an optional extra.

Phew! Hope you were paying attention, because I'll be testing you later...

Technical Specifications

Supplied for review were pairs of both DB1SA and TB2SA monitors. The TB2S and DB1S have both been reviewed before (in SOS November 2001 and January 2003 respectively), so rather than go over exactly the same ground here, I'll concentrate mainly on the differences. First, though, it might be worth giving the outline specs of each model as a reference point.

The Flying Mole's simple controls are provided on the top panel of the amplifier pack for ease of access — this picture was taken from directly above the monitor.The Flying Mole's simple controls are provided on the top panel of the amplifier pack for ease of access — this picture was taken from directly above the monitor.Photo: Mark Ewing

The TB2 measures 400 x 200 x 350mm (hwd) and weighs just over 9kg. The amplifier is mounted vertically in a cabinet extension from the upper half of the rear of the speaker, and the connection between amp and speaker is courtesy of a right-angled Speakon connector that protrudes from the foam of the transmission-line port at the bottom of the rear panel. It is a very neat solution, and the integration of amp and speaker is elegant and practical. The new rear panel is equipped to accept an Omnimount bracket for wall mounting, if required. PMC claim the usable frequency range for the TB2 to be 40Hz-25kHz, with a peak SPL (at one metre) of 111dB. The bass driver employs a doped-paper cone in a 170mm cast-alloy chassis, coupled at 2kHz to a 27mm fabric soft dome.

The DB1 and its amplifier housing are constructed in a very similar way to those of the TB2, but with scaled-down dimensions. Again, the new rear panel is equipped for wall mounting, but rather than a standard Omnimount system PMC supply an optional bespoke wall bracket. This tiny speaker measures 290 x 155 x 283mm (hwd) and weighs just 5kg. The soft-dome tweeter and crossover frequency are the same, but the doped-paper bass driver is mounted in a 140mm cast-alloy chassis. As you would expect, the low-frequency extension is not as great, and neither is the power handling, with specifications of 50Hz and 108dBSPL, respectively.

The Flying Mole amplifier unit is fitted so that its power switch and volume control are both at the top, while the bottom panel provides an XLR input, IEC mains inlet, and the pre-connected Speakon output. The amplifier power output is quoted as 120W when coupled to the PMC monitors, and the manufacturer claims a power conversion efficiency of over 85 percent — hence a power consumption of just 25W (6W when in standby mode with no input signal) and no heat to worry about!

The amplifier's audio I/O and mains connectors are on the underside of the amplifier pack, and a sturdy right-angled Speakon connector links the amplifier output with the speaker's crossover.The amplifier's audio I/O and mains connectors are on the underside of the amplifier pack, and a sturdy right-angled Speakon connector links the amplifier output with the speaker's crossover.Photo: Mark Ewing

Flying Mole Amplifier

The name Flying Mole seems an odd one for a Japanese amplifier manufacturer. Apparently it derives from the notion that the greatest goal in life for a mole scurrying around underground might be to fly — well, it always has been hard for Westerners to understand the Oriental mind-set! But regardless of the company name, the products are impressive.

Digital amplifiers — Class-D amps — are nothing new, and lots of active loudspeakers already use Class-D amplifier designs. However, most leave something to be desired when auditioned; Class-D amps are often harsh-sounding and lack the resolution and 'inky black' silences that a good analogue amp can deliver. However, the technology has improved significantly in recent years, and Flying Mole's unique Bi-phase Fusion Technology certainly seems to be able to deliver the goods. In some ingenious but secretive way, this technology integrates the amplifier's switched-mode power supply with the switching amplifier circuitry, resulting in unusually high power efficiency and no audible artefacts. Most analogue amps struggle to better 30 percent power efficiency and typical Class-D amps are about 65 percent efficient. The impressive 85 percent performance figure of the Flying Mole amps means that they always run cool and don't require external heat sinks — they're just simple plain boxes the size of paperbacks, but they drive loudspeakers very nicely indeed!

Strangely, the distortion figure given in the specifications (0.03 percent at 50W output) appears rather unimpressive, yet auditioning the amp suggests it compares very favourably to a Bryston — which quotes distortion figures with several more zeros before the digit. The logical conclusion is that what we hear and what we measure are not necessarily the same thing! In many ways, the Flying Mole amps can be compared to a really good valve triode design — which would share a similar, yet equally inaudible, distortion figure.

The DADM100pro reviewed here is available in three main versions with different input and output connectors. The DADM100pro BI version used with the Activated PMCs features a balanced XLR input and Speakon output, while the BB version retains the XLR input but uses 4mm binding posts for the outputs. The last version is the HT model, which couples an unbalanced phono input socket with 4mm binding posts for the output. The last two models measure 43 x 132 x 238mm (hwd), while the BI model isn't quite as deep (223mm). All weigh a ridiculous 650g. In fact, the amplifier is so lightweight that during the review a heavy speaker cable was easily able to pull it off the desk!

In addition, there are dual AC/DC versions of each of the above, equipped with a 12V DC power input in addition to the standard IEC mains inlet. The DC input is useful for portable and outside-broadcast applications, and the amp draws a modest 5A of current at full power! There are also various brackets and mounting kits available to fix the amps to the rear of any speaker, to a 1U rackmount shelf, or in a six-pack lump!

Listening Tests

I have owned a pair of TB1S speakers for many years and use them when recording on location. Recently they were upgraded to the TB2+ spec with the soft-dome tweeters and crossovers. As already mentioned, Bryston Powerpac 120 amplifiers are bolted to their back panels and provide plenty of clean, articulate 'welly' to allow the monitors to deliver their best. As it happens, I also have a pair of DB1S speakers (with the original metal-dome tweeters) and a pair of stand-alone Flying Mole amplifiers which I use when editing — so all in all, there are sufficient elements to hand to provide valuable references and comparisons.

The first thing to mention is the significant improvement wrought by the new tweeter and amended crossovers — to both the TB2 and DB1. The old metal-dome tweeter was certainly no slouch, but the soft dome — which is admittedly a much more expensive device — has clear advantages in terms of the precision and naturalness of the high frequencies. The crossover changes that the new tweeter required have improved the mid-range resolution too. If the TB2 speaker rated at an eight out of 10 before, it's the full 10 out of 10 now, and the DB1 has benefited from a similar improvement in resolution.

Furthermore, the matching of timbre and imaging is now almost flawless across the entire PMC range. I was able to compare the DB1SA and TB2SA not only with each other, but also directly against the larger LB1 two-way and huge IB1 three-way monitors. Aside from the inherent increases in headroom/SPL and bass extension (and the additional resolution of the three-way design), the sound character barely changed at all — which is a praiseworthy achievement.

The Flying Mole amplifiers appear to defy the laws of physics — I can think of no other explanation! I compared the Flying Mole DADM100pro BI monobloc amplifier (see the 'Flying Mole Amplifier' box for more details) directly with the Bryston Powerpac 120 and found it hard to tell the difference! The Bryston is large, heavy, and very expensive, while the Flying Mole is none of those things — and yet they produced near identical sound. Okay, so in the final analysis the Bryston retained the edge, with more headroom, better bass control and sustain, and the ability to convey transients and dynamic changes with an effortless ease that the Flying Mole couldn't quite equal. But without a direct A/B comparison it would be very hard to tell them apart. Not all Class-D designs are equal, and I share the view expressed by Peter Thomas that the Flying Mole amps are in a class of their own — the first switching amp that comes within a whisker of equalling the best analogue designs.

Overall, then, the new Activated versions of the DB1 and TB2 are unqualified successes. All of the qualities of the original monitors have been retained — the superb bass extension and control, the consistent sound balance regardless of monitoring level, the vast three-dimensional sound stages, the wide sweet spot, and the neutral presentation with high levels of resolution. The '+' updates with the better tweeter and revised crossovers have improved mid-range and high-frequency resolution and accuracy, and have also made the sound character more consistent across the entire PMC range. The Flying Mole amps are the icing on the cake, matching a powerful, high-performance, high-resolution amplifier to the speaker to form a convenient, effective, and affordable package.

The problem with passive speakers as good as PMC's is that they can reveal the failings of inadequate amplifiers just as easily as they can poor mixes or mic placement issues. Unfortunately, the cost of a really good amplifier often matches or exceeds that of the monitors, so the complete package can appear very expensive when compared to some of the active monitors aimed at the home-studio market. The Flying Mole amplifiers, whether in stand-alone form or fitted to the DB1SA and TB2SA, redress that balance very well, and allow the PMC monitors to deliver a superlative performance at a far more reachable price. It is hard to find fault with the combination in any way at all, and if you are in the market for good nearfield studio monitors, these Activated monitors make ideal reference points.

Published May 2005