This impressive setup combines point‑source technology, advanced loudspeaker management DSP and a powerful new bass extension system. Is this the state of the art in studio monitoring?

The 8351A was the first of the technologically advanced Genelec The Ones series of three‑way, dual‑coincident, ‘point‑source’ monitors to be introduced, and Bob Thomas gave it a glowing review in SOS August 2015. Bob has also more recently (in SOS September 2021) written, again in glowing terms, about the larger 8361A. Since the launch of the 8351A Genelec have expanded the series to include both smaller and larger models, and some of the know‑how and newer technology developed for those products has been fed into the first subject of this review; the 8351B.

There’s more than just a revised and updated monitor to describe here, so the plan is to cover quite a big parcel of Genelec land along with the 8351B. That’s because Genelec have significantly refreshed and upgrared their GLM (Genelec Loudspeaker Manager) optimisation and SAM (Smart Active Monitor) control technology, and also introduced the W371A Woofer System. There are, by the way, some very good and technically fascinating reasons why I didn’t, and Genelec don’t, describe the W371A as a subwoofer. I’ll get around to explaining that later on. First I’ll offer a few paragraphs on the electro‑acoustic fundamentals of the 8351B.

To The Point

As with a few other dual‑coincident monitor designs of recent years, Genelec’s opportunity to design and introduce dual‑coincident technology came about with the lapse of KEF Electronics’ original patents, which effectively protected the idea of a small tweeter mounted concentrically at the apex of a substantially conical bass/midrange diaphragm. With The Ones series, however, Genelec chose not just to borrow the KEF idea and apply it to an otherwise conventional two‑way monitor design, but to develop it much further and extend the idea to a three‑way ‘point source’ (meaning that low, mid and tweeter elements all effectively radiate from the same location in space) monitor format, and to integrate the mid/tweeter compound driver with the curved form of the enclosure front panel. At a quick glance it’s not really obvious where the midrange driver diaphragm ends and the enclosure front panel begins. And as I’m mentioning the front panel, it’s probably a good time to say that the whole 8351B enclosure is created from two immensely rigid aluminium die‑cast components.

Also cleverly incorporated within the enclosure design is Genelec’s unique three‑way ‘point‑source’ solution to integrating low‑frequency reproduction with dual‑coincident mid and high frequencies. A fundamental issue with low frequencies and dual‑coincident drivers is that the output of a tweeter mounted at the apex of a bass/midrange diaphragm will suffer significant frequency modulation distortion if that diaphragm is required to move beyond a millimeter or two. This is because the bass/midrange diaphragm effectively has a secondary role as a tweeter waveguide, and the last thing you need in that scenario is the waveguide moving significantly when the bass player hits a low B, just as the drummer’s playing some delicate brushed ride cymbal. The obvious solution is to take the responsibility for bass reproduction away from the midrange driver so that its diaphragm is not required to move significantly — but then, where do you locate the bass driver and still retain the point‑source principles?

Genelec’s solution is to go to a three‑way format and split responsibility for low frequencies between a pair of bass drivers located symmetrically about the compound mid/tweeter axis and loaded by a single rear‑panel reflex port. The bass drivers are oval in form and all but hidden behind the profiled front panel. They radiate through slots formed between the front panel and the top and bottom surfaces of the enclosure. With the bass‑to‑midrange crossover frequency at 320Hz, the physical spacing from the bass driver slots to the mid/tweeter driver is small enough a proportion of the one‑metre wavelength for the point‑source principle to remain valid.

The Drivers

While I’m on the subject of the bass drivers, not only is their architecture and location unusual in the 8351B, they also display an interesting constructional feature in that their rubber roll surround is corrugated around the curved section of the oval. I asked Genelec’s R&D Director Aki Mäkivirta about the surround and he explained that its corrugations and curved sections work together to optimise the force distribution around the perimeter of the glass‑fibre‑reinforced paper driver diaphragm. Diaphragm stability is important in enabling the driver to retain linerarity at high excursions, and to achieve that, the surround force needs to be equal around the perimeter of the driver. Genelec optimise the surround in this respect by using variation in its height as a factor to adjust its flexibility, hence the corrugations. Finally on the bass drivers, they are loaded by a shared reflex port located around the back of the enclosure that’s very generously flared at its exit. The flare will help keep the airflow laminar and so delay the onset of obvious chuffing noises or more insidious port compression effects.

I wrote earlier that it’s not really obvious where the midrange driver diaphragm ends and the enclosure front panel starts, and that’s because, relieved of the need to play any bass, the midrange driver of the 8351B (and the other The Ones‑series monitors) can be fitted with an almost flat surround. It doesn’t need the generous roll that would otherwise enable the diaphragm to move more significantly. Designing a surround that needs only to deal with midrange energy also means that its material properties can be optimised to work over a much narrower band of frequencies. Dual‑coincident or not, this is one of the big wins that can come with the decision to go with a three‑way monitor format: the midrange driver can be designed specifically for midrange and doesn’t suffer compromise by also having to play bass. With a dual‑coincident driver, however, a flat midrange surround brings a second benefit: it doesn’t result in a significant high‑frequency diffraction feature.

Before I leave my basic description of the 8351B, I’ll just mention that the mid driver diaphragm not only features an unusual two‑piece aluminium construction, it also has an inner surround along with the outer surround that I’ve already described. The inner surround joins the apex of the midrange diaphragm to the outer part of the central tweeter housing, and in doing so cleans up a few potential sources of diffraction. And again, it’s the three‑way format and the fact that the midrange diaphragm isn’t required to move significantly that makes the inner surround feasible. Finally, the 8351B tweeter, nestled down at the apex of the midrange diaphragm, is a 25mm aluminium dome. It’s quite possibly the most conventional‑looking element of the 8351B.

From A To B

A simple change of codicil letter from A to B, and the fact that the fundamental architecture and external enclosure design of the 8351B remains the same, perhaps suggests that not too much has changed since the 8351A. The reality is that there are numerous revisions. One of the most significant is that Genelec have moved from a conventional, linear internal power supply to a switched‑mode device. This not only results in a monitor that’s a significant 4.7kg lighter, but enables a substantial increase in amplifier power. Where the 8351A was rated at 150W, 120W and 90W for bass, midrange and tweeter respectively, the 8351B is rated at 250W, 150W and 150W. This increase in amplifier power helps the 8351B achieve a 2dB increase in maximum output level. However, it’s not just more power that results in increased maximum volume; all the 8351B drivers are slightly larger than their 8351A predecessors. The slightly larger midrange driver has also made possible a drop in the bass‑to‑midrange crossover frequency: from 470Hz to 320Hz. This ought to help a little with vertical off‑axis consistency at large angles.

A further refinement on the 8351B over the 8351A is that its DSP incorporates phase equalisation from around 500Hz upwards. Phase equalisation corrects for the frequency‑dependent delay effects that are fundamental to the processes of electro‑acoustics, and although it results in slightly increased overall in/out latency, Genelec say it can provide a subtle but worthwhile gain in subjective performance.

...perhaps even more significant DSP revision in the 8351B is that it incorporates significantly more filter ‘horsepower’ than the 8351A in terms of the number of individual notch and shelf filters...

One perhaps even more significant DSP revision in the 8351B is that it incorporates significantly more filter ‘horsepower’ than the 8351A in terms of the number of individual notch and shelf filters than can be accessed and deployed by Genelec’s GLM room optimisation package. Where the 8351A offered a total of 10 filters (six notch and four shelf), the 8351B increases the total to 20 (16 notch and four shelf). The notch and shelf filters are accessible for manual selection through banks of DIP switches on the 8351B’s rear panel, adjacent to its balanced XLR analogue and AES3 digital input sockets, but to my mind, manually selecting EQ options for the 8351B borders on the daft when the power of Genelec’s GLM app is so easily and, in the context of the cost of the 8351B, relatively inexpensively, available.

GLM 4.1

We’ve written about GLM a few times since its launch in 2006 so I’ll not spend too many words covering old ground, but to recap a little, there are two fundamental elements to it: the hardware, comprising a measuring microphone, a compact USB interface and a bunch of RJ45 cables to connect the monitors to the interface; and the software, comprising a Mac OS or Windows app that handles both monitor and room optimisation and monitor system configuration and management. Once a monitoring system is up and running, GLM can also operate as a very handy on‑screen monitor controller too.

The recently launched 64‑bit architecture, 4.1 version of GLM marks the 15th anniversary of Genelec’s room optimisation technology, and incorporates a re‑engineered AutoCal 2 routine that, Genelec say, results in quicker and more accurate optimisation data. In particular, AutoCal 2 is claimed to produce better optimisation results in rooms that are more reverberant in character, and also in setups that employ extreme nearfield monitoring (as close as, say, 50cm), either necessarily due to an ultra‑compact listening space, or through a desire to emulate a more headphone‑like feel to monitoring. GLM 4.1 also adds further to the 500Hz and above phase compensation inherent to the 8351B that I mentioned a few paragraphs ago. The new Extended Phase Linearity option reduces low‑frequency group delay (at the cost of an additional 7.5ms overall system latency) such that, for example, an 8351B displays group delay that’s comparable to that typical of closed‑box monitors: less than 5ms down to 70Hz.

The decision to implement positive‑gain EQ in GLM 4.1 was partly, say Genelec, a result of the data collected since GLM 3 began to employ the Genelec cloud server for AutoCal processing.

Another new development in GLM 4.1 is that it allows for localised regions of positive gain EQ to be applied where a significant notch in the in‑room response can be feasibly equalised without the monitor running into headroom problems. Equalising notches by adding localised gain is something that previous versions of GLM were not designed to do, for two reasons. Firstly, any notch in a room response that’s primarily caused by destructive interference between two signals (direct and back wall reflected sound for example) fundamentally cannot be filled in by adding localised gain. The destructive interference between two signals will always occur, never mind how much extra local gain is applied. The second reason for avoiding extra localised gain is simply that it can potentially result in a monitor running out of amplifier headroom. Every 3dB of gain demands twice the amplifier power, so even relatively modest positive‑gain EQ can quickly ask significant questions of an amp. The decision to implement positive‑gain EQ in GLM 4.1 was partly, say Genelec, a result of the data collected since GLM 3 began to employ the Genelec cloud server for AutoCal processing. The resulting dataset of 20,000 examples of monitor optimisation curves gave Genelec the confidence to know in which frequency bands, and to what degree, positive EQ could be both safely and effectively implemented.

In use, GLM 4.1 is fundamentally straightforward and intuitive, but its ability to manage and optimise systems comprising very large numbers of monitors and channels, and to create optimisation profiles for multiple listening positions and multiple monitoring setups, means things can quickly become complex. To provide a flavour of just how complex, GLM 4.1 can manage systems comprising over 80 monitors and subwoofers, creating an individual response optimisation profile for each one while also enabling monitors to be grouped in different format arrangements (stereo, 5.1 or Dolby Atmos, for example) and also offering multiple optimised listening positions for each group. GLM 4.1 imposes very few limitations in terms of the practical application of even the largest monitoring systems. The decision I think to endow GLM 4.1 with the capability to optimise and manage so many monitor and subwoofer channels reflects Genelec’s increasing success in equipping very high‑channel‑count immersive performance and production spaces.

A significant element of GLM 4.1’s ability to manage such complex systems is the combined architecture of the software and monitors, which puts the DSP hardware needed to handle the room compensation EQ in the monitor. The GLM software processes no audio itself, so in terms of doing the maths it cares little how many monitors are involved — it ‘simply’ manages the optimisation process and uploads the response optimisation data to the appropriate monitor. Similarly, the remote cloud server location of the AutoCal 2 optimisation calculations helps GLM manage extremely complex systems without imposing any significant processing load on the local computer (which quite possibly already has its hands full running a massive, multi‑output DAW session).

Room Optimisation Calibration

Regardless of how many monitor or subwoofer channels a GLM system comprises, the process for creating room optimisation data for upload to the appropriate monitors is the same. The GLM 4.1 launch screen displays a hexagonal grid graphic that represents the monitoring space, as illustrated in Screen 1. Monitors connected (via the proprietary Genelec Ethernet‑based network) to the Genelec GLM USB interface appear in a list at the side of the hexagonal graphic and can be dragged into one of the boxes to represent its monitoring role (left, right, centre, surround, and so on).

When the monitors are positioned, optimising each one is simply a case of placing the GLM measuring mic at the preferred listening position and pressing the AutoCal button. GLM will route a sine sweep test signal to each monitor or subwoofer in turn and upload the results from the measuring mic to the GLM cloud server, which intelligently decides on the appropriate EQ settings. GLM then uploads the EQ settings to each monitor taking into account the number of DSP‑based filters available in each. Screens 2 and 3 respectively illustrate the GLM correction EQ for the left‑channel 8351B alone and then the composite 8351B/W371A system. Being a room‑mode effect, the low‑frequency suck‑out between 40Hz and 50Hz on the 8351B alone wouldn’t be fixable by adding targeted gain, but is corrected perfectly when the W371A is added.

If the studio space incorporates multiple listening positions (mix engineer, client sofa, producer desk...) then the measuring mic can be moved to a new position, the AutoCal process repeated and the new optimisation profiles saved. GLM 4.1 then makes it very easy to switch between listening positions. Similarly, in complex multichannel systems, monitors can be saved as groups so that if, for example, the same audio programme is being mixed for multiple formats (maybe stereo, 5.1 and Dolby Atmos), it’s a simple matter to create a group of monitors for each and switch between them. Once calibration is complete, GLM can then take on the role of a software‑based monitor controller where it offers pretty much all the functionality you’d expect of a hardware device.

The W371A Woofer System

Moving away from GLM 4.1 for a moment, I’ll spend a few paragraphs describing the new W371A Woofer System. While, thanks to its sub‑25Hz low‑frequency roll‑off, it’s so very tempting to describe the W371A as a subwoofer, it’s really a very different animal. To begin with, rather than just fill in the lowest octave, the W371A can actually operate all the way up to 500Hz — well over two octaves higher than you’d normally expect the job of a subwoofer to be done and dusted. And furthermore, the W371A, thanks to its two widely spaced drivers, brings a significant element of low‑frequency dispersion control to the party. Conventional subwoofers are almost always exclusively omnidirectional devices.

Having mentioned the widely spaced drivers of the W371A I’ll now add a little flesh to those bones. The W371A is not small: it’s a 0.4m deep and wide rectangular black box that stands just over 1.1m tall and weighs a not insignificant 61kg. Use of the terms ‘stands’ is appropriate because in many installations the W371A is an appropriate height on which to place the 8351B (or the equally compatible 8341A/8361A). In being plain, black, and obstinately rectilinear in form, the W371A has little of the lavish industrial design style of the 8351B, but part of the justification for that I suspect is that maximising internal volume for electro‑acoustic needs trumps any softening of appearance.

Facing forward at the top of the W371A cabinet is a 365mm (14‑inch) diameter bass driver, and facing backwards at the bottom of the cabinet is a 305mm (12‑inch) bass driver accompanied by an adjacent flared slot reflex port. The two drivers operate in separate enclosures and are driven by 400W Class‑D amplifiers. Their combined role is to turn the 8351B (or again, 8341A/8361A) into a four‑way system, with their specific responsibilities, in terms of low bass to upper bass crossover integration and room optimisation, managed intelligently by GLM depending on the needs of the room optimisation and dispersion targets at each optimised listening position — hence the W371A being able to operate up to 500Hz. The result is that systems comprising the W371A and 8351B, (or 8341A/8361A), in addition to offering a remarkably flat and very wide‑bandwidth in‑room frequency response at multiple listening positions, can also offer multiple dispersion profiles all the way from around 60Hz up to frequencies where the 8351B itself begins to display cardioid characteristics.

The system dispersion control profiles I mentioned can be chosen to, for example, suppress floor or side wall reflections, or simply to continue, all the way down to low frequencies, the dispersion characteristics of the main speakers. The combination of GLM with the W371A and 8351B makes all this possible across multiple channels, with GLM doing all the difficult sums and making the decisions concerning exactly how, and at what frequency, the crossover between the 8351B and the W371A is best handled. It’s pretty much as if the composite speaker system of 8351B and W371A is intelligently designed by GLM on the spot to suit the specific room acoustics and needs of the user.

The system is undoubtedly a triumph of electro‑acoustics...

Home & Away

I mentioned earlier that the 8351B, along with the majority of Genelec’s monitoring products, incorporates an enclosure constructed from aluminium die‑castings. The die‑cast construction undoubtedly helps ensure that the enclosure makes minimal acoustic contribution in terms of panel resonance, but it also represents a pretty eye‑watering investment in terms of tooling costs, and that I think has some significant implication in terms of the market sectors and applications Genelec pitch their monitors towards. Once a decision has been made to invest huge sums of cash into tooling, it’s no good then aiming the product at a niche — rock & roll or EDM mix monitoring, for example. You need to attract customers from as broad a church as possible; from bedroom indie guitar pop bedroom studios to major, multichannel immersive experience stages. And as if to reinforce this idea, I had two contrasting opportunities to spend time listening to the 8351B and W371A. Firstly, a few weeks at home with just a stereo pair of 8351Bs and GLM, and secondly, a few hours in the control room of Studio B at London’s Metropolis Studios with a system comprising a stereo pair of 8351Bs, the W371A, and of course again with GLM.

Home listening first. The 8351B loan period coincided with a house move that left me working temporarily in a pretty small (3 x 3.5m) and minimally treated room, and for some monitors, especially those like the 8351B blessed with significant low‑frequency bandwidth, that would likely be a significant problem. Thanks to GLM and the point‑source nature of the 8351B, however, the small size of the room turned out to be relatively benign. Firstly, GLM effectively suppressed the low‑frequency room modes, and secondly, one of the advantages of point‑source monitors is that they don’t really care about listening distance so can be used effectively in the extreme nearfield. There comes a point with conventional multi‑way monitors where a really close listening distance can begin to render individual drivers subjectively apparent (mainly through the off‑axis cancellation nulls in the crossover region becoming more audibly significant), but with all the audio emanating from a single point in space that problem doesn’t occur.

My overwhelming subjective response to the 8351B, optimised for the room and primary listening position by GLM, was one of tonal neutrality and bomb‑proof professional competence. The 8351B exudes a sense of trustworthiness in that its subjective performance is completely without quirks or any particularly noticeable character — if it were an Instagram post there’d be no filter. Bass, despite the small room, but aided no doubt by GLM, was informative and clear with no obvious ported monitor traits. Midrange and high‑frequency performance was similarly satisfying, with great image focus and detail portrayal without any monitor‑borne artefacts. Those midrange mix details that we tend to get obsessed with — reverb tails and compression character, for example — were all easily audible and satisfyingly focused in the space between the monitors. The combination of a completely trustworthy and neutral tonal balance and outstanding midrange mix detail is, to my mind, one of the ultimate signs of a great monitor. You can often have one or the other, but both at the same time is much more unusual.

My overwhelming subjective response to the 8351B was one of tonal neutrality and bomb‑proof professional competence.

Metropolis Studios

Following my time with the 8351B at home, I decamped to Metropolis Studios to hear the combination of the 8351B and W371A in the Studio B control room. The system had been previously set up by Genelec, with GLM 4.1 configured to provide a few system response and dispersion options. Of course, being dropped into a less familiar environment to listen to an unusual monitoring system makes any definitive conclusion difficult to draw. Having said that, however, the experience left me with little doubt that the 8351B/W371A system is extraordinary. Bass bandwidth and level available from the W371A seemed subjectively unlimited, perfectly integrated with the midrange, and flawless in terms of pitch and dynamics. I listened to a wide variety of old favourites via Tidal, a couple of which I’d both mixed and played bass on, and heard countless elements that I’d simply never previously noticed: everything from new perspectives on how, say, reverbs integrate with the stereo image, to hearing significant instrumental or vocal performance details that I’d simply never been aware of before. It was seriously addictive.

As I described previously, GLM provides the opportunity to select from various pre‑configured monitoring response and dispersion presets, and in Screen 3 some can be seen listed on the right. The presets include those that employ the dispersion control capabilities of the 8351B/W371A composite to suppress low/mid‑frequency floor, back or side wall reflections, and these in particular made for fascinating listening. The subjective differences between dispersion options weren’t apparent so much in tonal terms as they were in the way the system presented stereo focus and imaging. With side reflections suppressed, for example, the image seemed less expansive in terms of width but more explicit in terms of depth. But while the comparison of different presets was fascinating, I had some trouble deciding which one I preferred or which would offer the most value in terms of mix work. I think I’d need longer with the system, and probably an actual mix job to do, before I settled on a preference. I also suspect that 8351B/W371A dispersion control options might become somewhat more relevant in less well‑controlled listening spaces than a Metropolis control room.

Back to the more fundamental performance of the 8351B/W371A at Metropolis. The system is undoubtedly a triumph of electro‑acoustics and if I were lucky enough to be able to afford such a system I’d probably only hesitate for as long as it took to experience its few equally impressive competitors. I was left with a couple of questions, however. Firstly, if I were working in Metropolis Studio B with the 8351B/W371A, I’m not sure I’d ever feel the need to use the main monitors. And secondly, I wonder, when a monitoring system is so hugely capable in terms of revealing detail over such a wide bandwidth, how I’d ever be able to conclude that a mix is finished? I’m pretty sure I’d never know when to stop fiddling with it.