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DRIVING FORCE

M&K; MPS Speaker System By Hugh Robjohns
Published July 2001

DRIVING FORCE

Hugh Robjohns tests an innovative full‑range speaker system, which somehow manages to get 12 separate drivers working in harmony.

Miller & Kreisel Sound were founded more than a quarter of a century ago, and they now manufacture a range of both consumer and professional speaker systems. Their new MPS series comprises speakers for a broad range of listening environments, from small editing suites up to large theatres and cinemas. The individual units of the system are designed to be used within multi‑speaker configurations, such as those required for surround mixing, but they can also be used to create a more traditional full‑range stereo setup with two satellite speakers and a subwoofer, and it is such a system which is under evaluation here. M&K are unusual in specifying their speakers in terms of the capacity of the listening room, and the review system — namely a pair of MPS2510 powered satellite monitors, a matching MPS5310 powered subwoofer and M&K's bespoke LFE4 Bass Management Controller — is designed for listening rooms with a capacity of around 3500 cubic feet.

MPS2510 Powered Midfield Monitor

The balanced and unbalanced inputs of the MPS2510 each have linked outputs for directly feeding a separate subwoofer unit.The balanced and unbalanced inputs of the MPS2510 each have linked outputs for directly feeding a separate subwoofer unit.

The MPS2510 is available in both passive and active versions, and is designed for midfield use at a distance of at least six to eight feet from the listener. The speaker is magnetically shielded and has received approval for use in THX pm3 monitoring rooms, when used with the dedicated subwoofer and bass controller.

The active version measures roughly 320 x 270 x 410mm (hwd). This is around half the height of most other pm3‑compliant speakers, which could be useful in locations with vertical positioning limitations. The arrangement of drive units within the box is unusual, with twin mid‑range drivers and a column of three tweeters — M&K specify that the tweeters should be on the inside edges of the stereo pair. The bass/mid‑range units are 110mm in diameter, while the soft‑dome tweeters are 25mm units, set in a face plate which is slightly dished to act as a waveguide. A removable front grille offers some protection to the tweeters, and small foam baffles mounted directly above and below the two outer tweeters play an important role in controlling high‑frequency dispersion. Two sets of four threaded inserts in the base of the speaker allow it to be mounted onto a suitable support bracket.

The rear panel of the MPS2510 features a comprehensive selection of controls, including a unique facility for user‑selectable vertical directivity, which allows optimisation of the speaker for different monitoring environments. The Narrow position provides a tightly controlled high‑frequency directivity, helping to keep HF energy from splashing off the ceiling or mixing console surfaces, while the Wide position is intended to provide better coverage for a larger listening area.

A very brief examination with my Audio Toolbox test set suggested that the three tweeters operate at different levels, with the central one being around 9dB louder at 10 kHz than the top and bottom units. Switching to the Wide mode seemed to increase the centre drive level by a further 3dB. As all three tweeters are driven by the same amplifier it seems unlikely that there is any clever interspeaker phasing going on to produce the claimed directional characteristics.

The speaker includes a switchable 24dB/octave high‑pass filter for matching it with a separate subwoofer, should you want your system to accurately portray information below 80Hz. With the filter switched out, the energy level drops off smoothly below around 70Hz (this is a sealed cabinet, remember), but is still generating a useful audible output below 60Hz. Though a subwoofer can be used with the MPS2510s directly, M&K recommend using their dedicated LFE4 Bass Management Controller for the best results, and this option would become a necessity if creating a surround monitoring system (see 'LFE4 Bass Management Controller' box for more details).

The MPS2510's rear panel is dominated by a large heat sink for the two discrete 150W amplifiers — one driving the low/mid‑range speakers and the other driving the tweeters. Above this, balanced and unbalanced audio inputs are provided on XLR and phono sockets respectively, with linked outputs for feeding a subwoofer. Power is delivered to the unit via a fused IEC connector, with associated switch and status LED. A second power status LED is recessed into the front panel of the monitor in such a way that it is only visible when the main axis of the speaker is directed accurately at the listener — a useful aid for physically aligning the system.

MPS5310 Powered Subwoofer

The MPS2510s are substantial units to heave around, but the subwoofer is definitely a job for two! It weighs a substantial 37kg, and measures roughly 590 x 390 x 430mm (hwd). As with the satellite speakers, the front grille of the MPS5310 is removable, although I guess that there may be little desire to take it off given that the cone has the M&K logo printed on it in large white letters, along with the words 'Discover Deep Bass'! The sealed‑box design boasts an in‑room response which is claimed to be flat to 20Hz and, unlike subwoofers with vented cabinets which exhibit a sharp roll‑off below the limit of their flat response, the MPS5310's curve rolls off much more gently below this.

The main panel of the subwoofer's amplifier unit hosts a pair of phono connectors which receive the left and right inputs from a pair of satellite speakers. A single balanced input is provided on an XLR socket, and this can be used for connecting an external bass management system, such as M&K's own LFE4, when working with multi‑channel monitoring setups. User facilities include a polarity switch and a rotary control for setting the subwoofer gain — there are calibrated positions marked for unity, +3dB and +6dB. A switch provides a THX reference input level instead of the variable gain option, and further switch allows the EQ curve to be set to the THX standard.

There are three low‑pass filtering options available, selected using a three‑way toggle switch. For a simple stereo system using MPS2510 satellites there's a fixed 80Hz low‑pass filter. For more complex installations, or for incorporating the MPS5310 with equipment from other manufacturers, the turnover frequency can also be adjusted manually to be anywhere between 50 and 125Hz, with a 24dB/octave slope. The THX mode bypasses the low‑pass filtering altogether, relying instead on an external bass management system to filter the signal feed.

The bottom of the panel carries the IEC mains inlet and fuse holder, with a power switch at the top of the rear panel for ease of access. A 350W amplifier chassis drives the two 12‑inch bass speakers, one of which faces the front while the other is mounted in the base of the cabinet with its magnet assembly on the outside. This dual‑speaker arrangement is designed to maintain the internal volume of the main sealed cabinet, irrespective of the movement of the cone. In this application, as the front driver moves out to generate a compression wave in the room, the base driver moves into the cabinet keeping the cabinet volume constant and thereby reducing the degree to which unequal pressures on the back of the speaker diaphragm might create second harmonic distortion.

Listening Test

With a complete system consisting of a pair of MPS2510s and an MPS5310 with the LFE4 controller, my first observation was of the sheer detail extracted by these speakers. Reverberation, room ambiences, and mechanical noises of acoustic instruments being played were all very apparent, but in a perfectly natural and correct proportion. This is the hallmark of a true monitor speaker — acoustic information being presented accurately, not glossed over to seem hi‑fi or overblown to the point of fatigue.

The second point I noticed was the near‑perfect integration between satellites and subwoofer. Though, it took quite a bit of experimentation to locate the optimal site for the single MPS5310 in my listening room, the whole system sounded extremely smooth and well‑integrated once it had been located and balanced carefully. The crossover frequency is quite low compared to many systems and this probably helps the integration, with the subwoofer adding just the right amount of weight to bass instruments, yet without affecting the stereo imaging or clouding the lower mid‑range in any significant way. The bass was tuneful, although not quite as fast as with some integrated monitors — a common side‑effect of many subwoofers, in my experience.

The stereo imaging was very wide and spacious, extending well beyond the speakers with the right material, and providing good left‑right stability over a reasonable working area in the Narrow setting. Switching to the Wide mode brought a perceptible high‑frequency lift, with an edginess becoming apparent on otherwise silky‑smooth vocals, and percussion becoming noticeably sharper. To my ears it sounded like a small but deliberate EQ change, though without affecting the stereo imaging particularly — I was unable to confirm any convincing and worthwhile extension to the stereo listening area, anyway. However, this may, to a large extent, be down to the acoustic properties of my listening room.

As M&K indicated, using the speakers on their sides or with the tweeters on the outside both had a damaging effect on the stereo imaging. I also noticed that moving my head along a vertical axis close in front of the speakers resulted in some very obvious phasing and lobing, particularly between the tweeters, although at a typical working distance of, say, eight feet this is unlikely to be a significant problem.

Male and female voices were naturally portrayed in both speech and singing, a testament to the neutrality of these speakers. Acoustic instruments were also rendered very well and with accurate dynamics and believable scale. I felt at times that there was a touch of congestion or mild clouding in the mid‑range — the 500‑1500Hz region — but that the high and low frequency areas were very detailed and precise. I don't want to overemphasise this hint of mid‑range congestion, though, because only the very best full‑range three‑way monitors would probably better it.

In terms of power handling, these speakers were more than sufficient for my listening room (capacity 3200 cubic feet), demonstrating almost real‑life dynamics on percussion and without any evidence of power‑compression problems. They seemed to have plenty of headroom too, and even listening at high levels for extended periods I did not suffer any listening fatigue at all, which is another very good sign!

On Balance

Overall, the combination of MPS2510s and the MPS5310 subwoofer makes impressive listening. It is a powerful, well‑balanced system with excellent integration between the satellites and the subwoofer. I must admit to being highly sceptical of the use of so many drivers (particularly the three tweeters) when I started this review, but I have to say that the arrangement does seem to work well, as long as you stay close to the 'sweet spot'. I would imagine a full 5.1 surround rig based on this system would be highly impressive, accurate, and conveniently compact.

In fact, the relatively small size of the MPS2510 satellites, their THX pm3 accreditation, their ability to deliver high sound levels and natural dynamics, their imaging and tonal accuracy, and the associated bass‑management facilities should all help to place this system near the top of anyone's short‑list for high‑quality surround monitoring.

LFE4 Bass Management Controller

The LFE4 Bass Management Controller is a 1U rackmount unit with no front‑panel controls at all. Its function is to redirect bass frequencies from up to six inputs to one or more dedicated subwoofers, with filtering circuitry optimised specifically for M&K studio monitoring speakers.

Designed primarily for 5.1 surround setups, the unit is also sufficiently flexible to be used for simple stereo (LR or 2.0), Dolby Pro Logic (LCRS or 4.0), Dolby Digital (5.1), and DTS (5.1) applications. Surround systems using even more channels can be accommodated by a sister product, the LFE6, which provides bass management for up to 10 channels. The rear panel of the controller has balanced XLR inputs for five input channels from the individual surround speaker feeds — appropriately high‑pass filtered versions of these signals are then fed to an associated bank of five outputs. In addition, there are two LFE channel inputs, one at +4dBu nominal level and one with 10dB more gain to comply with the extra headroom requirements of Dolby Digital. All the input signals are combined, low‑pass filtered and then routed to a pair of identical subwoofer outputs. A wall‑wart PSU powers the unit via a screw‑locking four‑pole connector. Although there is no power switch at all, a front‑panel LED indicates when the unit is powered up. A pair of 4mm binding posts on the rear panel allow chassis and signal earths to be linked or separated, as required.

The crossover point is at 80Hz, and fourth‑order (24dB/octave) Linkwitz‑Riley filters are used. Though signals in the individual speaker feeds are passed through the LFE4 at unity gain, the input sensitivity of each signal can be adjusted over a ±12dB range, if necessary, using 270 degree trimmers. These trimmers, while useful, are a little fiddly to set up precisely compared to the more conventional multi‑turn trimmers used in much other professional audio equipment. The subwoofer output operates at a level 15.5dB below that of the main inputs, as defined in the THX specification.

Aligning the whole system for stereo use was quick and easy, only requiring a pink noise source at +4dBu nominal level routed to each of two main inputs in turn. With the monitors switched to their calibrated gain setting, each satellite speaker's level trimmer was adjusted until the sound pressure level at the listening position reached the required level — pukka studios, mastering suites or dubbing suites would use the recommended theatrical calibration level of 85dBC (with slow averaging), though I personally find 79dBC a more comfortable nominal monitoring level for working within typical semi‑domestic listening rooms.

Once the satellite speakers were aligned, I simply reconnected the noise source to the zero‑level LFE input to drive the subwoofer directly, trimming its input gain such that its output SPL was 3dB less than that for the satellites. This was in recognition of the limited bandwidth involved and the correspondingly lower energy measurement on a broad‑band SPL meter. Aligning the subwoofer was actually an iterative thing, as its level was dependent on its position in the room — minimisation of modal standing waves can only be found by dragging a subwoofer around the floor to find the position in which it gives the flattest bass presentation.

Pros

  • Very high standard of monitoring accuracy.
  • Designed to cope with a range of different multi‑speaker monitoring configurations.
  • LFE4 provides excellent integration of satellites with subwoofer.

Cons

  • The UK price of such high quality...

Summary

High calibre professional monitoring system with approval for THX pm3 rooms. With the optional MPS5310 subwoofer, these speakers make a very well‑integrated system, but the MPS2510 is also sufficiently flexible to use on its own or with subwoofers from other manufacturers.

Published July 2001