Achieving a cardioid response down to low frequencies isn't easy, especially for a 'nearfield' monitor — but Dutch & Dutch have managed exactly that, and the results are impressive.
The Dutch & Dutch 8C is an active nearfield monitor that first came to my attention a couple of years ago, not long after I reviewed the remarkable Kii Three. One reason I particularly noticed the 8C was that it is partly inspired by a similar philosophy to the Kii Three: it aims to reduce the influence of the listening environment through having a cardioid dispersion characteristic. Of course the vast majority of conventional speakers begin to become cardioid at mid and high frequencies — above, say, 500Hz — but Dutch & Dutch claim the 8C is cardioid right down to 100Hz. However, before I explore the hows and whys of the 8C's directivity, there is much more to it than just a cardioid character, so I'll begin by offering a little more general description.
I described the 8C as a 'nearfield' monitor. However, in the flesh, the 8C is physically quite large, and probably pushes the boundaries of that description. The 8C is also very heavy (26kg each) and the combination of size and weight was right on the limit of my monitor shelves. So to begin with, a health warning: the 8C is a big and heavy monitor that's probably best suited to hybrid nearfield/midfield installations.
The generous size and weight of the 8C arise because there's rather more to it than is apparent from the front view of a 200mm bass/mid driver and a 25mm waveguide–loaded tweeter. Around the back of the 8C, along with the obligatory connection panel, there are actually two further 200mm drivers loaded internally by a separate closed-box enclosure, so the 8C is a genuine three-way system. The drivers themselves are of mixed European and Far Eastern origin from highly respected OEM manufacturers and are undoubtedly of sophisticated contemporary design. The mid driver has a 39mm–diameter voice coil with an aluminium diaphragm, rubber surround and a 'phase plug' in place of a dust cap. The two 200mm bass drivers similarly have aluminium diaphragms and even larger (52mm) voice coils, but sport conventional rigid dust caps. Along with ensuring air-tightness (phase plugs almost always introduce a small air leak through the driver), the dust caps will provide significant extra diaphragm rigidity. Finally, the tweeter is a European–manufactured 25mm magnesium/aluminium alloy-dome unit loaded by a deep horn–shaped 'waveguide' that terminates at a diameter approximately the same as that of the mid driver. Apart from being a very high–quality driver generally, it features a usefully low fundamental resonance frequency (550Hz). Dome tweeter fundamental resonance is typically an octave or more higher.
The deep, waveguide–loaded tweeter concept is one that seems to be increasingly finding favour in contemporary nearfield and midfield monitors (the Amphion range of monitors and the Genelec S360 that I wrote about in the April 2019 issue are two such examples). This is because the technique has a couple of significant benefits. Firstly, the dispersion control provided by the waveguide helps match the directivity of the tweeter and mid driver through the crossover region. And secondly, the tweeter efficiency gain provided by the impedance–matching effect of the waveguide means that a lower crossover frequency can be employed without risking tweeter failure or thermal compression. Sure enough, the 8C has its mid/tweeter crossover down at a very low 1250Hz. This is where the tweeter's low fundamental resonance comes in useful. A tweeter with a resonance at 1kHz or higher wouldn't really be viable with such a low crossover frequency.
I've been describing the front–mounted 200mm driver as a mid–range unit, but in truth it also makes a contribution to the 8C's low–frequency output because, like the mid/tweeter crossover, the bass/mid crossover frequency is unusually low, at 100Hz. The bass/mid crossover on more conventional three-way speakers is likely to be al least an octave higher. The low crossover frequency also explains why the 8C mid unit is relatively large: working down to 100Hz, it's required to move some significant air. There are two main reasons for the 8C's low bass/mid crossover frequency. Firstly, the fact that the bass drivers face backwards mean they're definitely not required to make any mid–range contribution, and secondly, as I described in the first paragraph, the 8C aims to offer a cardioid radiation characteristic to as low a frequency as possible, and it's the way the mid driver is loaded by its enclosure that generates the cardioid effect.
Ace Of Hearts
Although I mentioned the Kii Three earlier, the 8C's cardioid-enabling technology has more in common with that of the Geithain RL944K monitors (and the Geithain range in general) that I reviewed back in the SOS February 2016 issue. Rather than employing active circuitry, as on the Kii Three, the approach that Geithain and Dutch & Dutch take is to engineer non-resonant apertures in the enclosure side walls that allow some of the rear radiation of the mid driver to 'escape' and combine with the front radiation. This rear radiation from the mid driver is out of phase with the front radiation, so depending on the exact arrangement and location of the side apertures, the overall result is output that is steered forwards.
This passive cardioid technique is, of course, far easier to describe in print than it is to implement in a real speaker, and a conversation with 8C designer Martijn Mensink suggested that a fair degree of experimental development was involved. One of the biggest problems, it seems, leaving aside the fundamental issue of making measurements at frequencies where the wavelength of sound is several metres, lies in engineering enclosure apertures that radiate sufficient acoustic energy, yet don't result in a tuned enclosure resonance (which would defeat the object because the acoustic phase would reverse). Martijn described the solution to the problem in terms of simply building acoustic resistance into the apertures, but again, I suspect that's far easier said than done and would take no little skill and perseverance to pull off.
Clearly, the C8's cardioid characteristics can't extend to frequencies below the operating band of the mid driver, so its low–frequency radiation, below 100Hz, is fundamentally omnidirectional. However, in all but the largest listening spaces, describing low frequencies as omnidirectional is somewhat academic: even with a monitor located a reasonable distance from the walls, the wavelength is so long that those walls are effectively in the nearfield and therefore reflective. In fact, Dutch & Dutch suggest that 8Cs are best located close to the rear wall (between 10cm and 50cm away). So to all practical purposes, in any real listening room, the 8C's dispersion at low frequencies will effectively cover 180 degrees up to 100Hz. Above 100Hz the 8C's mid-cardioid technology will take over to begin narrowing the dispersion through the upper bass and low mid–range, then at still higher frequencies the inherently narrowing dispersion of the mid driver and waveguide–loaded tweeter takes over.
In The Box
To complete the basic description of the 8C, around the back of the cabinet, beneath the two bass drivers, is a connection panel incorporating the expected mains input along with a balanced analogue XLR input, a balanced XLR subwoofer output, a digital AES3 input and 'through' output, and an RJ45 network socket. A simple push–button and LED interface enables selection of the digital or analogue inputs, +4dBu or -10dBV input sensitivity options, and left/right channel nomination when the AES3 input is in use. Amplification comprises Class–D modules rated at 500 Watts for the low–frequency section and at 250 Watts each for the mid- and high–frequency sections. The 8C is not short of power. The 8C cabinet is constructed of a 19mm solid oak external carcass with 18mm birch ply internal bracing. An injection–moulded, damped ABS trim panel, which also provides the tweeter waveguide, is secured to the front of the cabinet carcass.
You'll perhaps notice that I've not mentioned any EQ options being available on the 8C rear panel, and that's because its network socket provides access to DSP–based equalisation, configured using a browser-based interface. The EQ offers low and high shelving filters plus 24 bands of parametric adjustment, and can be used in combination with room acoustic analysis packages such as Room EQ Wizard or FuzzMeasure to enable pretty comprehensive, albeit manual, compensation for room acoustic effects. Dutch & Dutch technical lead Martijn Mensink delivered the review 8Cs and set them up in my studio room, using Room EQ Wizard to analyse the frequency response of the 8C at my listening position and adjust its parametric EQ to compensate for the major low–frequency anomalies he found (a standing-wave issue at 40Hz and a reflection at 153Hz).
Along with frequency–domain EQ, the 8C's DSP engine also incorporates time–domain processing to compensate for and linearise the monitor's phase response. Linearising phase comes with unavoidable system latency (in a universe where cause precedes effect, there's no option but to delay the quicker frequencies to match the arrival of the slower ones), so there's also a low–latency mode, selectable from the browser interface, that switches off the phase correction. In the default 'full fat' mode that includes phase compensation, the 8C in/out latency is around 30ms. In low–latency mode the in/out delay drops to a perfectly manageable 3ms.
I've illustrated the effect of the two latency modes in Diagrams 1a and 1b. Diagram 1a shows the 8Cs impulse response in both modes, captured using FuzzMeasure with a mic on the central axis of the speaker at 50cm distance. The phase–compensated (high–latency) signal is visibly delayed by around 30ms with respect to uncompensated mode. Diagram 1b shows the 8C step response of the two latency modes overlaid (the step response curve displays effectively the same data as the impulse response curve, but is displayed in a manner that is somewhat easier to interpret). The high–latency mode's step response is clearly tidier and with less overhang than that of the low–latency mode (the pre-echo on the high–latency step response is a DSP artifact). Measuring and demonstrating a difference between the two modes is one thing, however; their audibility is something else. I've describe what I heard in the 'Low Versus High Latency' box.
Diagram 2 illustrates the 8C's frequency response curve from 200Hz up, both on axis and 45 degrees horizontally off axis, again captured with FuzzMeasure. There are three things to note. Firstly, the cardioid character of the 8C is apparent from the full-band attenuation of the off-axis curve. Secondly, the 8C's axial response is unusually linear and fits easily within ±1dB limits all the way from 300Hz to 20kHz (the droop that begins below 300Hz is the first sign of the MF high–pass filter). Making a couple of of vibrating diaphragms generate such a flat amplitude response is no mean feat and not only does it point to a sophisticated understanding of electro-acoustics at Dutch & Dutch, it also points to there being a fair degree of DSP equalisation going on within the 8C, in addition to the those user-accessible filters. The third thing to note, perhaps of academic interest only, is that in common with many similar drivers, the 8C's alloy–dome tweeter has a high-Q diaphragm resonance at around 21kHz. Dogs and bats may be concerned but, to be honest, they rarely have the budget to splash out on high-end monitors.
The final FuzzMeasure curve, Diagram 3, shows the bandwidth of the 8C's low–frequency section, measured with a mic very close to one of the bass drivers (this 'close mic' technique for analysing low–frequency characteristics can't provide data for far-field sensitivity, but it can provide a pretty accurate measure of bandwidth). The most interesting parameter that this curve reveals is just how extended is the 8C's low–frequency performance: it hits -3dB at around 25Hz, with a relatively slow roll-off thereafter. It's a performance that's very much in subwoofer territory and makes me wonder who on earth might find a use for the 8C's subwoofer output socket.
I began, as usual, listening to the 8C play a few old favourite tracks and Pro Tools sessions. It was obvious from the first note that the 8C is an exceptional monitor. It's difficult to know where to start because there is so much to admire about the 8C, but I'll start with the bass. The 8C plays bass in a manner that's truly unusual from a monitor that (just about) falls into the 'nearfield' dimensional category. Its bandwidth extension down to 25Hz, combined with a fundamentally low level of group delay (around 5ms at 50Hz), huge reserves of power and none of the compression or non-linear effects of ports together almost completely remove any of the monitor-borne bass artifacts we're so used to tolerating when using more conventional speakers. I've moved house and changed studio rooms since I reviewed the Kii Three back in January 2017 so it's not an easy comparison to make, but I'm pretty certain I've not heard bass quite like the 8C since then. It's perhaps become a bit of a cliché to write about the vital importance of kick drum and bass guitar timing and balance in those contemporary music genres that are built on such foundations, but the C8's abilities to reproduce bass so accurately make that task an absolute cinch, in a way that so many less capable monitors don't really get close to.
I introduced a comparison between the Kii Three and 8C in the previous paragraph, but it's not just in the low–frequency domain where I suspect the two monitors are toe-to-toe. Up through the mid–range and high frequencies, where the 8C's cardioid nature begins to become subjectively apparent, it displays a similarly natural and explicit quality that makes the traditional subjective language of monitor reviews a bit redundant. I couldn't really identify any inherent mid–range character or obvious coloration from the 8C, and the top end sounded natural, trustworthy and intimately integrated with the rest of the audio band.
The 8C also excels at producing pin–sharp stereo imagery. Vocals, for example, simply hang there, solidly in the space between the speakers. And if a vocal track has been processed in some way, you can hear exactly what's been done to it; but if, on the other hand, the vocal has been recorded naturally, it's uncannily as if there's a disembodied voice in the room. This sense of both individual mix elements and the complete architecture of a mix being laid bare is a fabulous quality in a monitor and it's one that the 8C has to spare. I remember a similar feeling when listening to the Kii Three: that the monitors were all but removed from the equation to leave a near–perfect reproduction of the audio laid out between them.
As with my experience of the Kii Three, I quite soon began to forget about listening to the 8Cs in 'critic' mode and just enjoyed listening to numerous old favourites, continually feeling inspired to dig out old CDs and long forgotten sessions, and then continually noticing things about them that I'd not noticed before. Perhaps that's all you need to know.