PMC FB1

Developing their TB1 nearfield into a floor‑standing loudspeaker, PMC have come up with a full‑range monitor which nicely balances studio performance with the cosmetics of quality domestic hi‑fi.

Monitoring loudspeakers are not what they used to be. There was a time when they were the size of small brick outbuildings and looked as if they were made out of rough‑hewn railway sleepers. But these days tonal accuracy isn't the only consideration — engineers also demand compact dimensions with the aesthetic appeal of nice wood veneer!

Although large soffit‑mounted monitors (installed to be flush with the wall) are still popular in the biggest studios, for most smaller rooms, more modest systems supported on stands behind the console are preferred. Apparently there is also a trend towards floor‑standing units, which are often seen as being aesthetically better than heavy metal stands, particularly in some mastering and post‑production suites where the high chairs at the console have been discarded in favour of comfy sofas and an altogether more relaxed atmosphere.

It is with this background that PMC were persuaded to develop a new budget floor‑standing monitor speaker to satisfy the needs of the post‑production, home‑studio, quality hi‑fi and home‑theatre markets — the relatively high sales volume in this last sector helping to justify the development costs. It should be said, though, that PMC are no strangers to floor‑standing monitors, as their top‑of‑the‑range BB5 system, found in mastering rooms and recording studios around the world, can be configured as a gargantuan floor‑stander of around seven feet in height!

The FB1 Investigator

The FB1 (Floor Box 1) project started out purely as an experimental modification of the highly successful TB1 (Tiny Box 1) nearfield monitor. Designer Pete Thomas hadn't been able to try such a small bass driver in a true transmission‑line system before, because the TB1 used a hybrid arrangement which he calls 'Transflex' — a combination of reflex and short transmission‑line elements (see 'The Transmission Line' box for an explanation of these designs). However, the additional cabinet volume gained through redesigning the TB1 as a floor‑stander has enabled a proper transmission line to be constructed.

The FB1's cabinet shares the TB1's width and depth, but is obviously much taller, with overall dimensions of 1000 x 200 x 300mm (hwd). Although the FB1 looks quite large it remains sufficiently well proportioned for domestic approval, but is big enough to allow some typical PMC magic at the bottom end!

Independent driver connections on the rear panel of the FB1 allow it to be bi‑wired or bi‑amplified should you require.Most floor‑standers (most speakers, in fact) are reflex designs and, because of the physics of reflex‑loading, the full volume of the box is often more a hindrance than a blessing due to unwanted standing waves and resonances. However, in the case of the FB1 the additional volume has enabled the inclusion of a transmission line with an effective length of around three metres. The bass driver is positioned around a third of the way along the line and, through skilful balance of the numerous parameters involved, the FB1 has been blessed with a frequency response which extends between 22Hz and 20kHz at the ‑3dB points. In fact, it is substantially flat above 27Hz, and I am not aware of any other full‑range monitor speaker of this size and at this price point which shares the same degree of bass extension.

The cabinet is a little more 'designed' than those of many professional loudspeakers, featuring rounded front corners and an optional black plinth base. It is also available in a selection of real wood veneers including Light Oak, Walnut, Cherry, Black Ash and Rosewood (this last at extra cost). Such detailing is mainly intended to gain the FB1 acceptance within the domestic hi‑fi marketplace, but also helps to make the speaker stand out amongst its professional monitor peers.

The optional plinth is a worthwhile accessory as it not only increases the stability of the tall cabinet, but also provides a visual 'full stop' to the design. Fitting it is simply a case of unscrewing the spikes from the base of the cabinet, securing the plinth using the supplied Allen bolts in the old spike threads, and then refitting the spikes to the newly installed plinth.

The end of the transmission line vents to the front of the cabinet through black acoustic foam, which is visually balanced by a removable black fabric grille over the drive units at the top of the baffle. However, I'm sure many users will prefer to take these covers off to reveal the shiny metal tweeter.

Vifa 2000

The drive units employed in the FB1 are the same Vifa components as those in its diminutive sibling. A 170mm doped‑paper‑cone mid/bass unit on a cast magnesium‑alloy chassis is coupled with a phase‑corrected, aluminium‑alloy‑dome tweeter with Ferrofluid cooling.

Not surprisingly, the crossover is very similar to that in the TB1 and retains its gentle 12dB/octave slopes, integrating the two drive units at 3kHz. However, it has been tweaked slightly to rebalance the mid and top end of the frequency spectrum to take into account the extended bass response.

The rear connection panel is equipped with a pair of binding posts and gold‑plated linking bars. Removing the links allows the speakers to be bi‑wired or bi‑amplified, while four threaded inserts above the connection panel provide mounting points for a Bryston 'Powerpac' amplifier module to be fitted if required. Available in either 60 or 120W versions, the Powerpac has been designed to turn the FB1 into a powered monitor which uses the internal passive crossover.

The passive crossover design presents a very easy 8Ω nominal load and the speaker has a sensitivity of 90dB per Watt at 1 metre, permitting quite modest amplifiers to generate impressive volumes. The peak SPL output is quoted at greater than 110dB at 1 metre, which is more than sufficient for most mastering, post‑production and home studio applications.

Finding Your Sweet Spot

The FB1s were delivered for this review by Pete Thomas himself and, after moving my own PMC AB1 monitors out of the room, he set about finding the best position for the new boxes. Pete's approach is to concentrate initially on the bass, moving the speakers a few inches at a time to find the position in the room where the bass response is as smooth and uniform as possible. Once satisfied that the best compromise had been found, he adjusted the relative angle of the speakers — the toe‑in — to maximise the precision of the stereo image.

Whether you are spending a few hundred or several thousand pounds on your monitors, you really should take the time and effort to experiment in this way and not just plonk the monitors where they look good! It is surprising what a difference just a few inches of movement can make to the balance and imaging of the speakers. It was also interesting to note that although we started with the FB1s in the positions occupied previously by the AB1s, they ended up quite a bit closer together, slightly further forward, and much more toed‑in — so just because a position works for one speaker it doesn't mean it will be right for another!

For this review the FB1s were driven by a Bryston 4B amplifier, although at 250W per channel they were, perhaps, a little overpowered — PMC recommend around 100W for general monitoring duties with reasonable headroom. However, I am very familiar with both the big AB1s and the tiny TB1s driven from the 4B, so it allowed fair comparison to be made.

Listening

My first point of reference were the compact TB1s which provide almost an extra octave of bass extension compared to most equivalently sized nearfield monitors. They also possess excellent levels of neutrality, detail and imaging for the asking price, so I was not surprised to find similar qualities in the FB1s. However, I was completely bowled over by the sheer scale of sound these modest boxes created.

I was simply astonished that, using exactly the same drivers, the FB1s could sound so much bigger than their siblings and I would not have believed it possible to generate powerful, trouser‑flapping bass from a six‑inch driver! These relatively compact speakers were actually standing closer comparison with the much larger AB1s — which is very impressive indeed given the price differential.

As might be expected from the metal tweeter, the high end is crisp, detailed and revealing, but it was not fatiguing at all. I was able to listen for many hours at a time without feeling the need to take a break, which is always the sign of a good low‑distortion monitor. The usual recording anomalies, such as clicks and dropouts, were exposed clearly but without being unduly distracting. The metal‑dome tweeter is recognisable, but doesn't seem to suffer any obvious resonances and works well in this design.

The mid‑range is just as neutral and transparent as the TB1 which shares its excellent Vifa paper‑coned driver. I find mid‑range quality is quickly revealed with well‑recorded voices and the FB1, whilst not matching the best three‑way designs, certainly stands up extremely well against any equivalent two‑way monitor. I also found the integration with the tweeter to be natural, both on‑axis and off‑axis — the phase response and dispersion seemed to have been blended very well.

The bottom end, as I have already mentioned, is solid and weighty, but without any hint of boominess or monotonicity. Complex bass lines come across with both melody and dynamics perfectly intact and remain distinct from bass drums. The system, as a whole, is also very fast, with the transients and LF thud of a kick drum arriving together as a single sonic event.

Combining a narrow baffle with small, wide‑dispersion drivers provides stereo imaging which is razor‑sharp on appropriate material. It is also extremely stable, although I found that the 'sweet spot' is at its widest if the axes of the two speakers are arranged to cross slightly behind the listening position — if they cross in front, the image tends to collapse into the nearer speaker as you move from side to side.

I was simply astonished that the FB1s could sound so big, and I would not have believed it possible to generate powerful, trouser‑flapping bass from a six‑inch driver!

Unlike reflex‑loaded speakers, the transmission‑line design tends to retain its frequency balance irrespective of listening volume, and the FB1 demonstrated this quality very well. Even with the level turned right down, the low end was still present and correct, with bass guitars and kick drums retaining their fundamental components rather then being relegated to a few weedy harmonics! I particularly appreciate this aspect of the transmission‑line system, as I'm sure would many who end up mixing late at night or in close proximity to neighbours.

For those involved in mixing in surround sound, the FB1 would also make an ideal component — its role depending on the application and on the size of room. For example, it can be used as a full‑range rear speaker in larger systems, or for the main left and right monitors in more modest installations. A complementary subwoofer (the XB1) and matching centre‑channel versions of the FB1 are also available.

The bottom line is that a pair of FB1s are playing in the same ball park as the ATC SCM10, Mackie HR824, or Genelec 1029s with the 1091 subwoofer. You can't put them on the meter bridge as you can with the ATCs, Mackies or Genelecs, but they will produce a wider window on the audio signal than all of these contenders, produce similar levels of resolution and sound a lot more 'together' than the separate subwoofer approach. As always, there are horses for courses, but if domestically acceptable styling and installation in the midfield is appropriate, I would strongly recommend the FB1s.