HEDD’s impressive Mk2‑series speakers let you choose between ported and unported formats. Which works best?
My previous experience of HEDD monitors was the three‑way Type 20 Mk1, which I reviewed back in the March 2018 issue of this magazine. I admired the Type 20 greatly, not only for its very high level of both objective and subjective performance, but also for its innovative ‘Lineariser’ plug‑in approach to correcting the time‑domain errors inherent to all electro‑acoustic transducers. The Lineariser seemed, to my ears, to add an extra polish and finesse to the Type 20’s performance, however its plug‑in format meant that it was only accessible when the monitors were being driven from a suitable DAW session. Now, with the Mk2 versions of their monitor range, HEDD have fixed that issue by incorporating the technology within the speakers’ on‑board DSP. But that’s not all. The Mk2 versions of the HEDD monitor range introduce quite a few refinements, improvements and new ideas. Read on and I’ll tell all.
Rather than simply looking at the Mk2 version of the Type 20, I decided for this review to step one rung down in the HEDD product range and examine the two‑way Type 07.
Before I get on to the specifics, though, a little refresher regarding the company. HEDD is an acronym for Heinz Electro‑Dynamic Designs, and the Heinz in question is Klaus Heinz, who previously played the role of R&D director at ADAM Audio. Heinz, and his mastering engineer and musicologist son Frederik Knop, founded HEDD in Berlin in 2015 specifically to offer a new range of technologically advanced monitoring and headphone options for pro audio applications. The full HEDD range now includes four monitor models ranging from compact nearfield to large‑scale midfield; an ambitious main monitor ‘tower’ system; two subwoofer products; and a headphone. Our editor, Sam Inglis, wrote in glowing terms about the HEDDphones back in the July 2020 issue.
Back to the Type 07 Mk2, at first sight it appears to be a relatively conventional two‑way ported active nearfield monitor, with perhaps the only obviously notable feature being its use of a Heil AMT‑type folded ribbon tweeter (monitor geeks might notice that use of an AMT‑type ribbon tweeter is customary in ADAM monitors; this I guess is no coincidence considering Klaus Heinz’s previous employ). The Type 07 Mk2 is a convenient size for nearfield installation, and although relatively heavy its weight shouldn’t cause any sleepless nights. The MDF cabinet is finished in a silk/matte black paint. Beneath the ribbon tweeter is a nominally 18cm‑diameter composite‑diaphragm bass/midrange driver, and beneath that live a couple of decently flared reflex ports. It’s with the ports that the unusual stuff begins, because the Type 07 Mk2 actually offers ported (reflex loaded) and non‑ported (closed‑box) operational modes.
There’s two aspects to converting the Type 07 Mk2 to and from reflex loaded to closed: the acoustic and the electro‑acoustic. The acoustic element involves the physical insertion of plugs, supplied with the monitors, in the ports to seal the enclosures. The plugs are short metal cylinders fitted with foam peripheral sections that provide a comfortable yet tight interference fit in the port diameter. On one face of each metal cylinder is a tapped hole that fits a small, machined screw tool supplied with the monitors. Screwing the tool into a cylinder enables its removal from the port. I can’t help thinking HEDD would be well advised to have a tapped hole on both faces of the cylinders because, as things stand, I’m not sure how easy it would be to remove a plug if it were inserted the wrong way. The reason I’m not sure is that I didn’t make that mistake, but it was an extremely close run thing.
Before I move on to the electro‑acoustic aspect, a bit of background. It is perfectly feasible with a passive monitor (that can’t incorporate DSP or even conventional analogue EQ) to contrive a low‑frequency system that works in both ported and closed‑box modes. In fact, quite a few hi‑fi speakers ship with optional foam port bungs. You just have to engineer the various electro‑mechanical parameters of the bass driver to produce a workable low‑frequency and time‑domain response with a fixed enclosure volume for the closed option and a fixed combination of enclosure volume and port tuning frequency for the ported option. Such arrangements can work, however they’ll always involve a hint of frequency response compromise — neither ported nor closed modes is likely to be optimal. But with a DSP‑enabled active monitor, where the opportunities for equalising in both time and frequency domains are almost unlimited, it’s perfectly possible to engineer a speaker that can operate equally optimally both ported and closed (actually it’s not quite so clean cut as that; see the ‘Ports & Stuff’ box).
So when the Type 07 Mk2 morphs from ported to closed (or the other way around) through the addition (or removal) of its port plugs, a switch on the rear panel also needs to be moved to select a ported or closed EQ profile. If the optional Lineariser is also engaged, selecting the ported or closed option will also implement alternative time‑domain compensation profiles, because not only does adding or removing a port change a monitor’s frequency response, it’ll change its group delay (frequency‑dependent latency) too.
So that’s the nuts and bolts of the ported or closed configurations of the Type 07 Mk2. But, I hear you ask, why would you want the option? The ported versus closed‑box question has been mulled over many times in the pages of Sound On Sound and, believe me, if you were to rank electro‑acoustic topics in terms of hours spent on discussion during a speaker design career, the topic would probably come top.
To recap: the point of a reflex port is to extend the bandwidth and/or increase the maximum volume level of a moving‑coil speaker by employing the otherwise unemployed acoustic energy that radiates from the rear of the bass driver diaphragm. A port does this by using a tuned resonance to reverse the phase of that rear radiation over a narrow range of frequencies so that it reinforces, rather than cancels, the forward radiation of the driver.
There’s no free lunch though, so port loading brings with it some snags that many who give this kind of thing a second thought believe are potentially damaging. Firstly, reversing the phase of the driver’s rear radiation unavoidably implies a time delay. If, for example, a port is tuned to 40Hz, one complete cycle takes 25ms, so a half cycle flip (180 degrees) implies a delay of 12.5ms. All other things being equal then, when the speaker plays 40Hz, the output will be delayed by a minimum of 12.5ms. Secondly, one fundamental characteristic of a resonant system, such as a reflex port, is that not only does it take a finite time to get going, it takes a finite time to stop too. So back to our 40Hz port, if the driving signal stops suddenly, the output won’t. And the higher the Q of the port resonance (and much of the point of a port is lost if you don’t maximise its Q), the longer it will take to stop. It’s not unusual to find output continuing for multiple cycles after a stimulus signal has ceased. At 40Hz, for example, that could be as much as, say, 75ms.
The final snag introduced by port loading is that port performance is highly sensitive to its mechanical architecture. The Q of the port resonance will only remain suitably high if the airflow in the port remains laminar. If the airflow becomes turbulent (and that’s jointly a function of its velocity, the port diameter and length, and degree of exit and entrance flaring), the Q will collapse and, rather than reinforcing low‑frequency output, the port will behave more like a leak that contributes nothing but compression and noise. Ports are also prone to ‘organ‑pipe’ resonance, where they effectively become a wind instrument in their own right and, driven by the upper‑bass and lower‑midrange acoustic energy bouncing around inside the enclosure, generate a high‑Q pipe tone that can make an audible contribution to a monitor’s midrange.
Having read that paragraph of reflex port demolition, you’re probably wondering why any monitor designer would ever bother with a port. There are two answers. Firstly, the benefits that ports offer in terms of low‑frequency bandwidth and volume level, especially when a monitor has to hit a manufacturing budget that can’t afford the extra bass driver costs that a closed‑box format of equal bandwidth and volume performance would demand, are too great to ignore. A hole and a plastic tube is a lot less expensive than, say, a bass driver magnet that’s twice the size. And secondly, skilful and knowledgeable design can undoubtedly minimise the problems that ports introduce and render them acceptably benign.
Before I start measuring and listening, I’ll finish the job of describing the rest of the switches. Firstly, the Type 07 Mk2 is unusual in offering both input sensitivity and gain options. Both are on detented knobs so there’s no problem in ensuring that the two monitors of a pair are matched. Having both sensitivity and gain control leaves no stone unturned in the search for optimising monitoring gain structure, but considering how DAW and interface output levels all tend to be very similar these days, I’m not sure how much genuine use it will be to the majority of users. Having said that, I did nudge the input sensitivity up a notch in my system.
Along with input sensitivity and gain, the Type 07 Mk2 includes low‑ and high‑shelving EQ options that offer ±4dB of adjustment in 1dB steps at 200Hz and 3kHz respectively; low‑frequency bandwidth options that offer extended, normal and subwoofer (80Hz high‑pass filter) settings, and three desk EQ presets. I’ll investigate the desk EQ options a little further down the page.
While I’m still on the rear panel, as far as inputs are concerned the Type 07 Mk2 offers balanced analogue and AES3 connections. Internally the Type 07 Mk2 signal flow is digital, running at 32‑bit/96kHz, and at the downstream end of that signal flow, the Type 07 Mk2’s Class‑D amplification is rated at 100 Watts for both the bass/mid driver and tweeter. The crossover frequency sits at a conventional 2.3kHz.
And so to the promised FuzzMeasure data. Diagram 1 shows the Type 07 Mk2’s forward axial frequency response from 200Hz to 20kHz, along with measurements taken 20 degrees above and below. The axial response is suitably flat and tidy, and the vertical dispersion is also well managed. The sharp suck‑out at around 2.5kHz on the lower axis curve (purple) is typical of vertically arranged two‑way speaker systems, and is caused by destructive interference between the two drivers in the crossover overlap band. A vertical off‑axis crossover suck‑out is all but unavoidable in two‑way speakers, however designers do have some freedom (through choices in crossover filter design) to decide in detail how it is managed and whether it is better engineered into the above‑ or below‑axis frequency response. The usual and sensible decision — which the Type 07 Mk2 clearly adheres to — is that it’s better not to compromise the above‑axis response, as a below axis listening position is less likely. Back to the Diagram 1 off‑axis curves, the gentle off‑axis droop at high frequencies is typical of ribbon drivers, however it is relatively mild on the Type 07 Mk2 and, especially in the context of nearfield listening, unlikely to be a major issue.
The impulse response plots of Diagram 2 illustrate the result of engaging and disengaging the Lineariser processing. The most obvious result is that the Lineariser adds around 10.5ms of extra latency to the system, but it also clearly tightens the impulse response shape, making it more compact and, well, more impulsive. The 12.5ms latency of the non‑Linearised impulse, by the way, reflects that of my measurement signal chain and the signal ‘flight time’ from monitor to measuring mic.
Finally, Diagram 3 illustrates the action of the Type 07 Mk2’s desk EQ feature. The desk EQ introduces a gentle suck‑out centred on 180Hz that increases in depth from a subtle 1dB or so to a more significant 4dB. I’ve found similar desk EQ options quite useful in the past and in combination with the shelf EQ options there really ought to be few listening spaces that the Type 07 Mk2 can’t be adapted to suit. And that brings me to one of the significant positives of the Type 07 Mk2. The multiple EQ options, ported or closed format, and linear or ‘natural’ time‑domain response mean a huge variety of possibilities for adapting the monitoring character to meet the needs of personal preference, room acoustics and programme material. The Type 07 Mk2 is a genuinely impressive proposition in that respect.
Monitoring adaptability would of course mean nothing without great fundamental performance, but the Type 07 Mk2 has that too. I remember being immensely impressed with the core electro‑acoustic character of the original Type 20 in terms of its tonal balance, imaging and detail portrayal, and lack of coloration. The Type 07 Mk2 pulls off the same trick in that there’s something immediately satisfying about the way it presents material: everything is fundamentally in the right place, with the appropriate tonal character, image focus, pitch and dynamics. Vocals in particular sound properly focused and convincing with a ‘high‑end monitoring’ level of quality. For example, I found myself listening to Jesca Hoop’s, ‘The Lost Sky’, a track I know well (and love), on repeat and becoming fascinated anew by how it’s put together in mix and arrangement terms, while simultaneously being completely seduced by the vocal performance.
For what it’s worth (because your mileage will vary), the EQ options I settled on in my studio space were 1dB of desk EQ combined with 2dB of LF shelving attenuation and 1dB of HF shelving attenuation. But I guess the elephant questions in the room are, “ported or closed” and “Linearised or natural”? My preference on the second of those questions was for Linearised. As with my previous experience of the Type 20, the Lineariser seemed to add an extra degree of image focus and precision. Mix elements appear to live somehow more separately in their own space. It’s subtle, but once you become tuned into the effect, I think it’s worthwhile.
There’s something immediately satisfying about the way it presents material...
The question of ported or closed is a more complex one. The subjective difference between the two options is significant, and my preference was generally for the closed option — if forced to choose I’ve always preferred precision and accuracy of bass over bandwidth. Monitors are tools of a trade, however, and personal preference is an unaffordable luxury if it impedes getting a job done. So in use there will be times when the extra low‑frequency bandwidth and maximum volume level offered by the ported option will be of crucial importance because, on a very basic level, it could render audible some mix elements that the restrictions of the closed‑box option cause to remain hidden. And even then, it’s not as if the quality of bass that the Type 07 Mk2 is capable of in ported mode isn’t extremely high, because it is.
My time with the HEDD Type 07 Mk2 was characterised by increasing respect. To begin with I felt it was predominantly a very well‑engineered but conventional two‑way nearfield monitor. But as I used the Type 07 Mk2 more and experimented with its many EQ and format options, my admiration grew significantly. And now, at the end of the review period, I’ll be sorry to see the back of them. As is my usual practice, when I get towards the end of a monitor review, I do a bit of research to remind myself of the price, and when I did that with the Type 07 Mk2 I had to check I wasn’t looking at the cost of a single monitor rather than a pair, because I’d imagined it to be significantly more expensive than it is in reality. So bearing in mind just how much I came to admire the Type 07 Mk2, I think it’s a steal.
There’s one compromise in optionally ported and closed two‑way monitors that can’t be managed with DSP, and it arises because each type of monitor ideally demands different quantities and types of internal damping in the enclosure. In a ported enclosure it’s important not to stuff the bulk of the cabinet with wadding, because doing so will significantly decrease the reflex port’s Q and damp the very resonance it is installed to exploit. So the usual strategy is to line only the internal enclosure surfaces with acoustic foam.
In a closed‑box enclosure, however, there’s no port resonance to worry about so the entire volume of the enclosure can be lightly stuffed with wadding (usually polyester but sometimes natural wool), often to the benefit of reduced midrange coloration. Now, you may have noticed that I qualified this whole discourse by specifying two‑way monitors in the first sentence. That’s because three‑way monitors dodge this particular compromise: the midrange driver enclosure can be bulk filled with wadding to more effectively dissipate the driver’s rear radiation and minimise coloration, while the separate bass driver enclosure can be internal surface‑lined so that a port, if one is used, isn’t compromised.
The Type 07 Mk2 finds itself in a competitive niche where there are some very capable alternatives. For example, the Focal Shape Twin, Genelec 8040A, Reproducer Audio Epic 5 and Dynaudio Lyd 8 can all be had for around the same price.
- Exceptionally high fundamental electro‑acoustic performance.
- Adaptability through EQ and port options.
- Lineariser option.
The HEDD Type 07 Mk2 is a seriously high‑performance nearfield monitor that incorporates some genuinely useful and interesting extras. Apart from the other models in the Type Mk2 range, there’s really nothing else quite like it.