PresentDayProduction MUM-8

Can a direct sales model and high‑tech components make top‑level monitoring affordable? PresentDayProduction believe so.

People get into designing speakers for all sorts of reasons. Sometimes, there’s a family connection. Sometimes it starts off as a hobby or a teenage obsession (as in my case). Sometimes a choice made in education leads directly to a career. The subject of this review, however, doesn’t really fit any of those narratives. The MUM‑8 active monitor is the brainchild of Mark Ashfield and James Nugent who, along with running a successful mix and mastering business, also create and present the PresentDayProduction YouTube pro‑audio review channel.

Mark and James’ decision to design and manufacture a monitor was driven partly by a desire to install Atmos monitoring in their studio, and the realisation that this wouldn’t be affordable using their preferred ATC monitors. So they adpoted the radical solution of building their own monitor, and after a year or two spent learning and developing, the MUM‑8 was introduced to an unsuspecting world. A further respect in which PresentDayProduction are unusual is that rather than doing business via dealers or distributors, they sell direct to end users. This business model offers a significant advantage in terms of costs, but it also potentially leaves distant end users without local support. PresentDayProduction say they overcome that issue by offering online help that can even extend to the remote configuration of monitor EQ.

MUM’s The Word

The MUM‑8 is a three‑way closed‑box active monitor of dimensions that put it, to my way of thinking, somewhere between a large nearfield and a compact midfield. At 19.25kg the MUM‑8 isn’t light, but not so heavy that weight is likely to become a significant installation issue. The three drivers comprise a nominally 200mm (8‑inch) aluminium‑diaphragm bass driver, a 75mm (3‑inch) silk‑dome midrange driver and a 25mm (1‑inch) silk‑dome tweeter. The drivers are all bought‑in OEM devices; from Purifi of Denmark in the case of the bass driver and Bliesma of Germany in the case of the midrange driver and tweeter, and they’re all impressive examples of the driver designer’s art.

Take three of the best drivers available, put them in a well engineered, rigid enclosure, drive them with powerful and high‑quality amplification, and you get the MUM‑8.

Rather than being the affectionate yet respectful term for a female parent, MUM stands for Modular Upgradeable Monitor. The ‘8’, if you hadn’t already guessed, refers to the bass driver diameter. The MUM‑8 is modular in that its rear‑panel‑mounted amplification module can be detached and connected by speaker and control cables to enable, for example, the monitor itself to be soffit‑mounted. And the MUM‑8 is upgradeable in respect of its midrange and tweeter drivers. The standard‑issue silk‑diaphragm drivers can be swapped out for beryllium‑diaphragm units. Mark and James say that doing so brings a significant performance upgrade, but for review purposes it seemed to make most sense to look at the standard version.

The MUM‑8 occupies a conventional format, with a tall and narrow cabinet that has drivers stacked asymmetrically one above the other on the front panel. However, in some nearfield installations the stacked driver arrangement is likely to leave the tweeter located somewhat above a seated nearfield listening position. So the MUM‑8 provides the facility to swap its tweeters, with a similarly dimensioned circular blanking plate located to the side of the midrange driver to enable the monitors to be installed in landscape orientation yet still have the midrange driver and tweeter stacked vertically. This means landscape orientation doesn’t suffer from the potentially compromised horizontal dispersion in the mid/tweeter crossover band of laterally arrayed drivers. It’s a simple solution to a very real problem. Most of my listening to the MUM‑8 was done with tweeters arranged for landscape orientation.

Rigid Thinking

In expressing an almost entirely functional aesthetic, the MUM‑8 won’t win prizes for looks. Its cabinet is extremely inert, and in monitors built primarily to do a professional job, panel rigidity probably trumps beauty. The Valchromat from which it’s made inhabits the same kind of material world as MDF but offers a few advantages: it’s stiffer than MDF, can be machined more effectively, and is coloured all the way through (its base fibres are dyed before being pressed into panel form). It can therefore be used without need for any final finishing, which how it’s employed in the the MUM‑8.

The MUM‑8 rear‑panel connection facilities, along with mains power, comprise balanced and unbalanced analogue, and S/PDIF, optical and AES digital inputs. Input selection is carried out using a compact remote control handset supplied with the monitors. Channel selection for digital inputs is preconfigured so that installing a pair of monitors with their midrange and tweeter drivers positioned towards the inside results in the correct left/right channel routing. This principle also holds for landscape orientation.

With three Hypex Class‑D modules rated at 250 Watts each for the bass and midrange drivers and 100 Watts for the tweeter, the MUM‑8 is not short of power. Along with power amplification, the MUM‑8 Hypex module also incorporates a DSP element that provides analogue‑to‑digital conversion (at 24‑bit/192kHz), crossover filtering, three preset EQ profiles and, potentially, the option for user‑defined global EQ to be configured and applied.

The MUM‑8’s amplifier module can be removed and mounted independently of the speakers if desired.

As I mentioned in an earlier paragraph, the MUM‑8 amplification module can be detached from the back of the monitors and located remotely. When attached to the monitor, the module is connected to the drivers and front‑panel display using short Speakon‑terminated speaker and multi‑pin XLR‑style‑terminated comms cables; when it is to be located remotely, these need to be swapped out for extended cables. The comms cable drives a front‑panel OLED display that shows input gain setting, input selection and EQ preset. Three EQ presets are available: P1 is the default, wide‑bandwidth (extended bass) option. P2 offers less low‑frequency bandwidth but consequently higher maximum volume. And P3 offers a low‑frequency roll‑off suitable for integration with a subwoofer. Presets are selected, as are inputs, using the remote‑control handset. The MUM‑8 DSP also enables wide‑band EQ to be configured and applied to the monitor to suit personal preferences, and even perhaps to provide some rudimentary room optimisation. However, this needs to be done from a PC running a proprietary Hypex DSP configuration app connected to a service USB socket on the amplifier module, so is perhaps not something for the inexperienced.

Driving Forces

I promised a little more detail on the drivers, and I’ll start with the bass driver. Its unusual roll‑surround is the result of a complete reappraisal undertaken by Purifi of the sources of distortion inherent in the traditional moving‑coil driver architecture. One of those distortion sources, which has gone unnoticed for decades, is that conventional roll‑surrounds tend to behave asymmetrically. Put simply, the radiating area of the surround is different depending on the direction of diaphragm movement, and that leads to distortion. So the surround of the MUM‑8 bass driver is designed not only to do the job of terminating the diaphragm while freely allowing axial movement over large displacements, but to do so without behaving asymmetrically. It’s the combination of those two requirements that results in the surround’s highly unusual and complex shape. While the surround is the most visible result of Purifi’s analysis of driver distortion mechanisms, there are numerous other innovations hidden within the driver’s motor system (its magnet and voice coil). Its pole‑piece, for example, rather than being a simple steel component, is also a secondary flux‑control magnet, and the driver voice‑coil is wound variably, rather than linearly, in order to compensate for non‑linearities that occur with diaphragm movement.

One of the benefits of the Purifi approach is that their drivers are able to retain linearity over extreme diaphragm displacement. The driver employed in the MUM‑8, for example, is generally linear to ±9.5mm displacement — almost twice as much as conventional drivers. This means it’s possible to engineer extended low‑frequency bandwidth in an active monitor without having to employ reflex loading, with its inherent time‑domain and compression issues. As a result, the MUM‑8 low‑frequency cutoff specification is ‑3dB at 26Hz, which is pretty much subwoofer territory. There’s currently little else around quite like Purifi’s driver technology, and its use in the MUM‑8 constitutes a notable differentiator (the only other pro monitor company currently employing Purifi drivers that I’m aware of are Wayne Jones Audio).

The midrange driver and tweeter are sourced from Bliesma in Germany. Like Purifi, the Bliesma company are relative newcomers to the high‑performance driver business, but founder Stanislav Malikov has a long and distinguished career in driver design and manufacture with companies such as Morel and Accuton. The Bliesma product range comprises just dome tweeter and midrange drivers, offered in a range of sizes with a variety of diaphragm materials: from silk at the entry level via magnesium and diamond to beryllium. Bliesma drivers, like those from Purifi, are meticulously engineered within their motor systems to minimise distortion and any non‑linear behaviour.

On The Bench

I took a MUM‑8 to my large measuring space, fired up FuzzMeasure, and captured some acoustic data to investigate its electro‑acoustic performance. The data was taken with the measuring mic 1.5m distant on an axis aligned midway between the MUM‑8 tweeter and midrange driver. The nominal sound pressure level was 90dB at 1m: not particularly loud, but loud enough to have the MUM‑8 flexing its muscles. Volume level is significant when measuring speakers, because distortion mechanisms become significantly more apparent, and potentially more audible, as volume increases.

Diagram 1. MUM‑8 axial frequency response (red ), and second/third harmonic distortion (green and blue, respectively). All curves 1/48th octave smoothed.

Diagram 1 shows the axial frequency response along with its second‑ and third‑harmonic distortion, and there’s a few things to consider. Firstly, the axial response isn’t the flattest I’ve ever measured. It displays gentle dips centred on 200Hz and 750Hz, and then between 2kHz and 7kHz there’s some general untidiness. It’s hard to know for sure what is responsible for these features, but the dip at 750Hz could well be a crossover artefact (the crossover between bass and mid drivers is nominally at 500Hz). Online reviews of the midrange driver suggest that the dip at 6kHz might be inherent to it, rather than to the MUM‑8’s design. However, with the crossover frequency specified at 3.5kHz, I’d expect a 6kHz midrange driver dip to be less apparent — although that does depend on the crossover filter roll‑off rates used.

A ‘flat’ response might seem to be one of the prime requirements of a loudspeaker, especially a monitor. However, even leaving aside the extremely un‑flat frequency response we’re likely to perceive thanks to the influence of the listening environment, the idea of a flat frequency response at source (the speaker) becomes increasingly nebulous the more you examine it. For example, the MUM‑8 axial frequency response I measured would have looked somewhat different if I’d chosen a different microphone position or distance (see Diagram 2). Similarly, I’ve chosen to display the response with a bit of curve smoothing applied to make it a little easier to comprehend. I chose 1/48th‑octave smoothing (not much), but if I’d gone with 1/6th‑octave smoothing (which psychoacoustics tells us is more representative of how we hear), the curve would look different again. So, while frequency response measurements give us a handle on the baseline characteristics of a speaker, and measuring one that’s really flat always gives me a buzz (get a life, Phil), measuring a frequency response that raises questions doesn’t necessarily mean the speaker is fatally flawed. Far from it.

And if you wanted an example of why that’s the case, the green and blue curves in Diagram 1 provide it. These respectively show second‑ and third‑harmonic distortion, and both are low, but the more subjectively problematic third harmonic is really very low — generally better than 60dB or more down above 100Hz. ‑60dB is equivalent to 0.1%, which is more like an amplifier distortion specification than it is typical of a loudspeaker, and I’d swap a few undulations in the frequency response for such low distortion any day of the week.

Ups And Downs

Diagram 2 shows the variation in frequency response 20 degrees vertically above (blue) and below (green) axis. The red curve is a repeat of the axial response. Moving the measuring microphone to an off‑axis location vertically introduces relative time delays between the drivers, because the path lengths from each driver to the mic change. This means that audio from, for example, the midrange driver and tweeter that were in phase on‑axis are slightly out of phase off‑axis, and that’s revealed in the extra level of untidiness in the off‑axis frequency response curves. The dip around 750Hz in the ‑20 degree (green) off‑axis curve is also perhaps due to the relative phase of the bass and midrange drivers changing, although the naturally increasing directivity of the bass driver as frequency rises may also be a factor. Overall, the off‑axis response curves are generally typical of a speaker with spaced drivers — although, as with the axial curves, they are a little untidy. If I’d made the measurements with the alternative (landscape) driver arrangement in place, the results would be slightly different.

Diagram 2. MUM‑8 on‑axis frequency response (red), with +20° (blue) and ‑20° (green) vertically off axis. All curves 1/48th octave smoothed.

Diagram 3 illustrates the low‑frequency bandwidth characteristics of the MUM‑8. The data was captured by placing the measuring mic less than half a centimetre from the bass driver. The three curves illustrate not only the overall bandwidth achieved by the MUM‑8 but also its preset options. The red curve shows Preset 1, the green curve Preset 2, and the purple curve Preset 3. The first spot is that the 26Hz/‑3dB low frequency cutoff specified by Preset Day Productions looks reasonably genuine, although this does depend a little on where you choose to place 0dB. The other preset options result in ‑3dB at around 55Hz and 90Hz — the latter, I think, a sensible choice for integration with a subwoofer. A slightly strange feature of Diagram 3 is that the bass driver appears to show a gentle peak in response around 100Hz followed by a down‑shelved region between 200Hz and 400Hz, above which the low to mid crossover filter begins to become apparent. The down shelf above 100Hz appears to tie in with the 200Hz dip revealed in the axial frequency response in Diagram 1.

Diagram 3. MUM‑8 close mic LF frequency response. Red — Preset 1, Green — Preset 2, Purple — Preset 3. All curves 1/48th octave smoothed.

Into The Detail

Monitors are of course primarily for listening rather than measuring, and I began my tests with the MUM‑8s set up in landscape orientation on my monitor shelf. I had really high hopes for the bass. With one of the world’s highest‑performance bass drivers, in a closed‑box enclosure and with generous amplifier power available, what could possibly go wrong? As it turns out, nothing. The bass is perhaps even better than I hoped it would be, combining fabulous bandwidth with outrageously seductive speed and detail. But it was the explicit communication of pitch that really caught my attention. The sometimes hazy reproduction of, for example, double‑bass pitch and kick‑drum tuning that we kind of accept as inevitable in so many monitors, small ones especially, is completely absent with the MUM‑8. No double‑bass player will ever again get away with dodgy ‘E’ string intonation because the monitors can’t resolve it. This element of the MUM‑8 is all but worth the ticket price alone (and I say that as a double‑bass player who sometimes struggles to stay in tune).

The bass is perhaps even better than I hoped it would be, combining fabulous bandwidth with outrageously seductive speed and detail.

The MUM‑8 is more than a one‑trick donkey, though. Further up the band, the quality of the Bliesma midrange driver and tweeter are instantly apparent with their immense clarity, inaudible noise floor and uncannily sharp stereo image focus. The MUM‑8 is an incredibly revealing and analytical monitor that immediately lays all the elements of a mix naked and exposed. You almost feel you ought to be able to reach into the stereo image and touch things, and the level of detail occasionally borders on the unsettling. I do have a gripe, though, which is that I found the overall tonal character a little unbalanced. The 200Hz dip revealed in the measurements is subjectively noticeable, leaving male voices and lower‑register acoustic instruments lacking in body and warmth. Cellos sounded somewhat viola‑like, for example. At the same time, the upper presence band (say, 2kHz to 4kHz) is, I think, a little over‑emphasised, as is the tweeter band generally. The MUM‑8 takes no prisoners tonally, which could result in mix translation challenges and can make it a slightly tiring listen. Some in‑room response measurements I made, illustrated in Diagram 4, confirmed both the 200Hz dip and a couple of dB too much upper midrange compared to my reference (and room optimised) Neumann KH150s.

Diagram 4. MUM‑8 (red ), and Neumann KH150 (blue, room optimised) in‑room response. All curves 1/6th octave smoothed.

My tonal balance doubts about the MUM‑8 might appear to be a significant flaw, but I refer you to an earlier paragraph where I wrote that the MUM‑8 has some significant DSP power embedded within its electronics that includes comprehensive EQ facilities. PresentDayProduction also say that they are perfectly happy to work with customers to tweak the EQ to suit needs and preferences. So my tonal balance doubts could be easily fixed, and I proved that to my own satisfaction simply by applying some EQ from a DAW plug‑in; +2.5dB at 200Hz and ‑2.0dB from between 2kHz and 6kHz did the trick for me. It left me with a more comfortable tonal balance but cost none of the MUM‑8’s fundamental quality. And it’s that phrase, “fundamental quality”, that sums up the MUM‑8 for me. Take three of the best drivers available, put them in a well engineered, rigid enclosure, drive them with powerful and high‑quality amplification, and you get the MUM‑8. I’ve just made it sound really simple, but in reality it takes huge commitment, hard work and not a little skill. Mark and James ought to feel very proud of what they’ve achieved.