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Focal Shape Twin

Active Monitors
Published September 2018
By Phil Ward

Focal’s newest Shape‑series speaker boasts a host of unusual design features — which combine to make an unusually good monitor!

The Focal Shape range of active nearfield monitors seems to have been well received since its introduction around two years ago, and now the existing three Shapes have been joined by the subject of this review: the Shape Twin. The Shape Twin continues the unusual industrial design of the earlier models and continues also the unusual use of twin, side‑mounted auxiliary bass radiators (ABRs). The Shape Twin, however, adds a second bass/mid driver and dedicated amplifier, a more powerful tweeter amplifier, and a significant increase in the height dimension.

Shape Twin’s ‘MTM’ driver arrangement.Shape Twin’s ‘MTM’ driver arrangement.On first glance you might expect the Shape Twin’s ‘MTM’ driver arrangement (mid‑tweeter‑mid; a bass/mid unit either side of a tweeter) to be configured in a classic and acoustically symmetrical D’Appolito array, but somewhat surprisingly it’s not. The Shape Twin is in fact what’s known as a 2.5‑way system. One of the bass/mid drivers, the upper one in this case, extends up to 2.5kHz where it hands over to the tweeter, while the other bass/mid driver is slowly attenuated from around 180Hz as bass becomes mid‑range. I’ll describe and discuss in more detail Focal’s nearfield take on the MTM 2.5‑way configuration shortly, but first, a little more general description of the monitor is probably in order.

French Curves

As somebody who’s spent a long career in and around speaker design, I know just how hard it is to come up with a new aesthetic that doesn’t frighten the horses, is affordable in terms of tooling or material costs, and is workable in terms of manufacturing. So I think Focal are to be congratulated on the look and style of the Shape range. I admired it from the moment I saw the launch pictures, and now I’ve got a pair in front of me, I’ve not changed my mind. Focal are to be congratulated too for manufacturing the Shape range in Europe, where the majority of potential customers are likely to be located, rather than in the Far East, like probably the majority of competing products. I say this not through any cultural or racial prejudice, but because it always seems to me to be a particularly special environmental madness that so many boxes full of air are routinely shipped half‑way across the world.

Focal Shape TwinWhile I admire the unconventional industrial design of the Shape Twin it does raise a couple of quirks that deserve a little contemplation. Firstly, I’ve found in recent reviews of conventional D’Appolito configuration monitors that switching between landscape and portrait use has the potential for altering the way the dispersion of the monitor interacts with the room and nearby reflective surfaces. This effect occurs because the D’Appolito configuration (in portrait mode) results in relatively wide horizontal dispersion combined with relatively narrow vertical dispersion, and I’ve found that this is potentially useful in terms of suppressing either desk or side‑wall reflections. Now, while the Shape Twin won’t have the full‑fat narrow vertical dispersion of a conventional D’Appolito configuration, its vertical dispersion will be asymmetric, so a similar advantage might have been available from installation in portrait mode or upside down. The design of the Shape Twin, however, makes those options unfeasible.

The second slight quirk of the Shape Twin arises through its adjustable, rubber‑tipped feet. The feet, four of them in the underside of the enclosure, enable the Shape Twin cabinet to be angled upwards or downwards by around five degrees, so that the mid‑range and tweeter drivers can be more accurately directed towards the listening position. The 10‑degree total adjustment range is not really hugely significant in terms of vertical dispersion, but the adjustable feet are a nice little touch. However, if like me you mount your monitors on a couple of typically monitor‑width shelves either side of the DAW, using the feet while also angling the monitors inwards isn’t possible. My monitor shelves are 20cm wide and would have to grow to around 35cm to enable both inward angling and the slight down‑tilt that might have been ideal. This is by no means a deal‑breaker of course, but something to factor in to your thoughts if you’re tempted by the Shape Twins.

Le Back Panel

The Shape Twin offers a lot of frequency‑response adjustment options. In addition to the HF and LF shelving filters, there are four high‑pass filter settings (including ‘off’), and a ±3dB peaking filter, intended to compensate for desktop, console or wall proximity.The Shape Twin offers a lot of frequency‑response adjustment options. In addition to the HF and LF shelving filters, there are four high‑pass filter settings (including ‘off’), and a ±3dB peaking filter, intended to compensate for desktop, console or wall proximity.Moving around to the back of the Shape Twin, there’s the usual amplifier heatsink and connection panel. Interestingly, despite the use of conventional Class‑A/B amplification, rather than the increasingly common and more thermally efficient Class D, there are no obvious heatsink fins. Presumably the relatively large metallic connection panel makes fins unnecessary. Amplifier power specifications are 80 Watts each of the bass/mid drivers and 50 Watts for the tweeter. Input connection facilities are analogue only, with just balanced XLR and unbalanced phono sockets provided. If the Shape Twin is slightly limited on input sockets, however, it’s blessed with a useful variety of EQ facilities, although unusually it’s missing any input sensitivity adjustment. There’s optional 45, 60 and 90 Hz high‑pass filters, a shelving LF option that provides ±6dB from 250Hz downwards, a shelving HF option that offers ±3dB from 4.5kHz upwards, and a mid‑range cut/boost that offers ±3dB at 160Hz. The intention behind the 160Hz option is to provide some compensation for the specific effects of desk or wall boost. I’ve illustrated the effect of the HF EQ in the FuzzMeasure curve in Diagram 1.

Before I leave the EQ options behind and move on to more weighty matters, my usual disappointment was triggered by the EQ knobs being variable rather than detented. So, as ever, it’s hard to be entirely confident that each monitor of a pair is configured identically. The defence in Focal’s favour here is that the relatively limited range of adjustment provided by the knobs is combined with generous knob travel, but even so: please, nearfield monitor manufacturers, make an old man happy and fit detented knobs.

Diagram 1: the effect of the HF control when set at +3dB (purple trace), 0dB (orange) and ‑3dB (red).Diagram 1: the effect of the HF control when set at +3dB (purple trace), 0dB (orange) and ‑3dB (red).Despite appearances, the Shape Twin enclosure is a relatively conventional box constructed from MDF panels. The enclosure doesn’t feel entirely inert in the way some do and, when given the low‑tech ‘knuckle rap’ test, reveals a slightly resonant nature. It’s no worse in this respect than many other monitors, however, and a knuckle rap is of course not a fool‑proof indicator of performance. I did find myself wondering if the holes cut in the side panels for the ABRs leave the enclosure less rigid than it otherwise would be.

Auxiliary Bass Radiators

I’ve already mentioned the side‑mounted auxiliary bass radiators of the Shape Twin, so it’s maybe a good time to revisit the hows and whys of the ABR. The ABR technique is related to port loading in its fundamental principle of employing a resonance to shift the phase of the rear radiation from the bass driver, but ABRs can offer some distinct advantages. Firstly, a limiting factor of port tubes is often that, to achieve a low enough tuning frequency and also physically to fit length‑wise inside the enclosure, the port needs to be relatively small in diameter, which means it will become non‑linear at surprisingly low volume levels. By contrast, the tuning frequency of an ABR can be lowered simply by adding mass to the moving diaphragm. So a carefully designed ABR can be both tuned to a low frequency and remain linear to significantly higher volume levels than even the most generously flared and streamlined port tube. Reflecting this, the rubber surrounds on the Shape Twin ABRs are noticeably generous of radius in order that the diaphragms can move a long way before non‑linearity rears its frightful noggin.

Diagram 2: The output measured at the passive radiator. Note the fundamental resonance around 45Hz and the absence of further resonances higher up the range (the erratic response above 200Hz is simply ‘noise’ from the bass/mid drivers around the front of the cabinet).Diagram 2: The output measured at the passive radiator. Note the fundamental resonance around 45Hz and the absence of further resonances higher up the range (the erratic response above 200Hz is simply ‘noise’ from the bass/mid drivers around the front of the cabinet).A further advantage of ABRs is that they are not prone to the organ‑pipe resonances that can afflict ports, and which typically occur in the voice region where ears are most sensitive. ABRs also generally result in less audio energy inside the enclosure escaping to the outside world. Diagram 2 illustrates the Shape Twin ABR output measured using a microphone very close to the diaphragm. The first feature to note is the fundamental resonance, where the output peaks at around 45Hz, while the second thing to notice is the absence of any resonant features as the output decays with rising frequency into the noise floor (the noise being that of the bass/mid drivers, as there’s no way of measuring the ABR without the bass/mid drivers working too).

So why, you might ask, do we not see more ABRs than ports in contemporary speaker and monitor design? There are three reasons, I think. Firstly, ABRs introduce additional variables so are more challenging to design and optimise. Secondly, there’s no getting away from the fact that a hole backed by a length of tube is very significantly cheaper to implement than any ABR (which in terms of cost is a driver without the magnet and voice coil). And thirdly, there’s enclosure real estate: ABRs take up much more space than ports — as witnessed by Focal fitting the Shape ARBs on the side of the enclosures.

Flax Time

The Shape Twin’s slightly off‑piste appearance and Focal’s unusual decision to employ ABRs is matched by its use of some atypical driver technology. I’ll start with the tweeter. Focal have long evangelised the benefits of inverted dome tweeters. I may be wrong, but off the top of my head I can’t think any other significant speaker manufacturer that has remained so resolutely on the inverted dome path. Focal say that the inverted dome has two fundamental advantages over the conventional format. Firstly, they claim that the inversion and consequent ‘fold’ at the dome periphery results in more rigidity in the aluminium/magnesium diaphragm than would otherwise be the case. And secondly, they argue that the dispersion of an inverted dome remains wider than a conventional dome up to higher frequencies. It is of course not at all easy to prove either of Focal’s claims for the inverted dome, but to my mind such an exercise would be somewhat academic anyway — there is much more to designing an effective dome tweeter than whether it sports an ‘innie’ or an ‘outie’.

The bass/mid driver cones are made from a material called ‘Flax Sandwich’, which comprises a core of flax within outer layers of glass fibre.The bass/mid driver cones are made from a material called ‘Flax Sandwich’, which comprises a core of flax within outer layers of glass fibre.The bass/mid drivers of the Shape Twin appear to be relatively conventional units in all respects other than their diaphragm material. Focal call the material Flax Sandwich, and it’s created by enclosing a core of flax within two thin layers of glass fibre. I did a bit of research on ‘flax’ after I’d written that last sentence so you may as well now benefit from what I discovered. Flax is otherwise known as linseed, and, apart from its use as a livestock feed and for its seed oil used in applications such as traditional glazier’s putty and coating cricket bats, it is most familiar in its linen fabric form. That linen shirt you have, washed but un‑ironed, in the wardrobe? Well, that’s made out of similar stuff to the Shape Twin driver cones. Focal say that flax used as the filling in a glass‑fibre sandwich provides a unique combination of light weight, rigidity and damping. It looks pretty good too I think.

While the flax cone is the most obviously unusual feature of the Shape Twin bass/mid driver, I suspect that a couple of rather more subtle features are at least equally significant. Firstly, the magnet and voice‑coil design incorporates what Focal call Neutral Inductance Technology, which aims to stabilise the natural variation of magnetic flux with frequency and voice‑coil position. The result, say Focal, is significantly lower distortion. Secondly, the rubber surround of the bass/mid driver incorporates some circumferential step features that provide a mass damping effect to help dissipate the vibrational energy moving outward through the cone. Focal call this technique TMD (Tuned Mass Damper) and I’ve described some of the background to it in the ’Material World’ sidebar.

Diagram 3: The tweeter output, with grille (green) and without (orange).Diagram 3: The tweeter output, with grille (green) and without (orange).Before I get around to my experiences of actually using the Shape Twin there’s a couple more elements to describe and cogitate on. Firstly, the Shape Twin is supplied with optional perforated metal grilles that slot‑fit over each driver. My preference was to fit the tweeter grille but leave the bass/mid drivers uncovered. Partly this was the appearance I preferred, partly it was because the naked tweeter diaphragm is decidedly exposed and I didn’t want to have to make an embarrassing phone call to Focal, and partly because I measured the frequency response of a Shape Twin with grilles on and off, and at high frequencies the effect of the grille is appreciable. Diagram 3 shows the tweeter grille on/off comparison, and the response with the tweeter grille fitted is clearly a little more linear. The bass/mid driver grilles have little or no measurable effect.

Diagram 4: The Shape Twin’s vertical dispersion. The red trace shows the on‑axis response, and the yellow and green traces show measurements 20 degrees above and below the tweeter, respectively.Diagram 4: The Shape Twin’s vertical dispersion. The red trace shows the on‑axis response, and the yellow and green traces show measurements 20 degrees above and below the tweeter, respectively.Finally, I mentioned right at the start that the Shape Twin will have asymmetric vertical dispersion due to its 2.5‑way configuration, and Diagram 4 illustrates the phenomenon. The dispersion remains relatively linear at 20 degrees below the horizontal, however a measurement made upwards at the same angle reveals some response errors caused by the outputs of the drivers going out of phase due to path length differences between driver and mic. Based on these measurements, Focal’s decision to locate the bass/mid‑range driver at the top (remember, the lower driver radiates bass only) of a relatively tall enclosure, and engineer the dispersion to be more linear in the downward direction, makes perfect sense. The logic of Focal’s decision to steer clear of a full‑fat D’Appolito configuration can also be seen, as it helps ensure a relatively wide vertical dispersion lobe that’s directed slightly downward.

Twin Peaks

There’s been a mine of interesting stuff to write about with the Shape Twin, which is very much the way I like things because it speaks of a monitor that potentially offers something more than the conventional. Of course, none of the Shape Twin’s unconventional nature would be worth a jot if it didn’t deliver the goods, but thankfully there’s no need to go down that road because there’s no question for me that the Shape Twin is excellent. To begin with, the Shape Twin displays a usefully neutral tonality that will help make balancing decisions easier. It also plays loud with ease and has good low‑frequency extension for its size. But perhaps the Shape Twin’s most notable quality is its genuinely exceptional sense of hear‑through clarity, image depth and low‑level detail in the mid‑range.

It’s a bit of a tired old cliché to write this, I guess, and perhaps self‑evident also, but if a monitor can reproduce a really natural and unaffected human voice, with all its nuance and detail, it’s probably ticked the most important box. The Shape Twin undoubtedly has that covered (it seems my enclosure resonance concerns were unfounded). Those subtleties of mid‑range tonality and detail that can be so important in defining the character of a mix are revealed really explicitly on the Shape Twin. And all the processing and ‘production’ that regularly earns its crust in the mid‑range is explicitly and easily audible. I was genuinely surprised how many ‘new’ elements of familiar material I was hearing with the Shape Twin and in this respect I think it punches significantly above its price range.

If the Shape Twin displayed its stand‑out abilities in the mid‑range alone it would still fall into the ‘success’ category, but its qualities extend also to either end of the bandwidth. The tweeter pulls off the difficult trick of being revealing and detailed while at the same time restrained and delicate (I tended to use the Shape Twin with the HF EQ at ‑2dB), and at low frequencies the Shape Twin ABR system offers nicely extended bandwidth with none of the port character that’s often audible on reflex‑loaded monitors. Having said that, my only doubts about the Shape Twin concerned a slightly soft and marginally lazy character of bass transients. I had a pair of closed‑box Neumann KH310A monitors temporarily in residence at the same time as the Shape Twin, and to my ears the Neumann displayed a faster and more convincingly accurate LF character (it should, though, at twice the price!). The Shape Twin’s bass response is by no means a deal‑breaker, however. It’s an innocent characteristic more than a fault.

There are effectively two separate audible elements to the problems of ported monitors: firstly, the slower attack that results from increased LF latency (known technically as group delay) and the associated longer decay time, and secondly the distortion and compression that results from turbulent air flow in the port. In employing ABRs, the Shape Twin may well display levels of group delay and decay time significantly higher than would be typical of a closed‑box monitor (unfortunately Focal were unable to supply numbers for this, and without a huge space I am unable to measure low frequencies accurately); however, clearly the Shape Twin won’t display any port air‑flow issues. Perhaps the subjective upshot of this is just what I heard?

Conclusion

It’s time to wrap up. I really like the Shape Twin and there’s no doubt in my mind that it is a fine monitor. It displays the odd quirk of design, but fundamentally that’s because, with the Shape Twin, Focal have tried to bring something a little bit different to the nearfield monitor market. If the Shape Twin turned out to be the last monitor ever to grace my workstation, I’d have no problem with that.  

Alternatives

Monitors offering similar features and performance at a similar price are not that easy to find. A couple of options are the Eve Audio SC307 and the ADAM A77X. If the vertical format appeals, there’s also the rather more expensive Unity Audio Boulder MkII.

Material World

The surround component on a bass/mid driver fundamentally has two jobs. The first is that at low frequencies, the surround has to enable the diaphragm to move significant distances with minimal resistance. The second job, however, is that at higher, mid‑range frequencies, especially as the diaphragm begins to move more chaotically, the surround has to damp and dissipate the vibrational energy. Unfortunately, one of the problems often thrown up by the mechanical properties of feasible driver diaphragm and surround materials is that successfully doing both jobs simultaneously is a problem, and that’s typically reflected in a significant surround resonance, usually somewhere between 750 and 1500 Hz (depending on the diaphragm diameter).

Curing such diaphragm/surround resonance ills in decades past would sometimes result in narrow beads of damping compound applied to the inside of the surround roll, or even in surrounds made in two parts; one floppy, one stiffer. These days, however, with the benefits of computer‑based FEA (Finite Element Analysis) modelling available, surround components with complex profiles that simultaneously offer both flexibility at low frequencies and damping at targeted mid‑range frequencies can be created. Focal’s TMD technique is a perfect example of this.

About The Author: Phil Ward’s loudspeaker career began in 1982 when he joined UK hi-fi company Mordaunt-Short in a junior design role. After leaving Mordaunt-Short in 1987 for a spell in audio PR, Phil joined Canon as Design Manager for the Japanese multinational’s range of consumer and custom install speakers, and then Naim Audio as speaker design and project manager. Since 2001 Phil has worked as a freelance consultant and writer across both the pro and consumer audio sectors. Phil plays electric and double bass and has recorded, produced and mixed numerous bands and artists. Phil's blog can be found at http://musicandmiscellany.com   

Published September 2018