Ironically, the two prime criteria for a recording studio monitoring loudspeaker system are beautifully fulfilled by a Challenger tank.

First it should go loud enough to make your ears bleed, and at the same time it needs to be as bulletproof as Chobham armour. However illogical, it is only after these two factors are under control that the designer can add the luxury touches that constitute accuracy, in all its many forms.

This is a key foundation of Neil Grant's Boxer monitor systems, which are just beginning to creep into some of the top studios. Fundamentally conventional, the Boxers break new ground in charging serious money for a monitor system — £14,000 for the big Boxer Four and £11,650 tor the smaller Boxer Two. Yet looked at in the context of the price of other studio gear, not to mention the cost of getting the acoustics right in the first place, monitor systems have always been comparatively small beer.

They don't look expensive compared to many an electronic box of tricks, or for that matter various domestic hi-fi speaker systems. But the fact that control room monitors are increasingly ignored in favour of cheap transportable nearfield systems is itself evidence that all is not well in the world of full size monitors. The Boxer is part of an honest and justifiable attempt to reverse this trend.

Having acquired a healthy disrespect for the limitations of generally available commercial monitor systems, setting out to do it better yourself is a natural path to follow. This is the route Neil Grant set out on two years ago under the DRL (Discrete Research Ltd) banner, alongside his architectural/acoustic consultancy, now known as Harris Grant Associates, which seeks to carry the revolution into the control room environment.

OF CHICKENS AND EGGS

Neil is the brains behind DRL/Harris Grant, and his main task is attempting to turn the sow's ear acoustics of many even reputable studios into the silk purses that are increasingly needed to produce recordings to the standards required for steadily improving domestic reproduction.

The Boxer programme started out peripheral to the main consultancy work. But there is necessarily an intimate interdependency between the acoustics of a studio and the monitoring used therein. And having created a control room with known acoustic behaviour, it makes a lot of sense to fit a known entity therein in order to achieve the right final result.

Neil's work in existing control rooms has brought disenchantment with both the generally prevailing acoustics standards and the state of the monitoring loudspeaker art. Where efforts have been made to cut down unwanted reflection effects by absorption, the net effect has often been to soak up enormous amounts of midrange and high frequency energy. In order to achieve the required levels and "fight" the dead acoustics, there has then been no alternative but resort to horn-loaded compression units.

At the same time, the difficult task of tailoring low frequency characteristics to achieve smooth extension has been left largely to luck, with the odds, inevitably, stacked heavily against the studio. Measurements have shown that so-called low frequency absorbers are largely ineffective, and that only the actual walls, floor and ceilings have sufficient mass to influence the end result significantly.

Required to use PA midrange techniques to provide PA levels in a dead environment, the upper part of the main monitor's range suffers all the endemic problems of compression units, lacking linearity and adding substantial coloration; a phase response resembling a cross-section of the Himalayas ensures that stereophony is essentially random.

Interacting with the aforementioned sow's ear at low frequencies, any real bass extension in the monitors themselves is more likely to be a source of embarrassment than worth. If the speaker is inherently good, the room will get upset as often as not, and hence upset the sound; if the speaker is not good then none will be any the wiser, and the results will be even less predictable.

Under such all too common conditions, the engineer and producer may be better off avoiding the control room acoustics as far as possible. Hence the popularity of nearfield monitoring: small loudspeakers are sited on top of the console, well away from the reflections of the room (if not the desk), and their limited bandwidth and energy output causes less grief to the room acoustics than the big soffit units. (This explains why the bass extension of the Boxers make no attempt to win any specmanship race: -3dB at 34Hz makes an excellent compromise between programme content and the monitoring environment.)

BACK TO BOXING

In many senses the strength of the Boxer will only be revealed when coupled with careful alignment in a sympathetic environment. But the ingredients themselves are impressive enough, in their own understated way. The exterior is severely functional, finished in fashionable battleship grey. The box itself is constructed from a combination of 24 and 36mm MDF (medium density fibreboard) panels, internally riddled with bracing and struts, some 50mm sq hardwood, others 50 x 18mm ply. The panels are then damped by a 3M semi-setting compound attached to lead vinyl sheeting. A forklift truck was one of the more visible items of capital expenditure seen in the factory, leaving Neil's back sufficiently intact to carry the TEF-10 around.

Over-engineering is one of the orders of the day, and an essential ingredient in a system designed to withstand continuous high level output. Yet at the same time there are the sort of acoustic subtleties that are already de rigeur in the high end hi-fi market, so the Boxer is by no means just brute strength (with or without ignorance).

Going for maximum cabinet rigidity is the only sensible starting point when designing for operation at these levels, but scattered around the factory were several development carcases as evidence of two years' work done in refining the construction of the cabinetwork for the best sound quality.

The bass unit frames are recessed, and clamped in place by four M6 machine screws. The midrange and treble units are mounted on a removable sub-baffle, to cover the unlikely need for service/replacement. Seventy nine-strand cabling is used throughout, with heavy duty terminal and junction boxes.

So far, so sensible, but the real trick the Boxer has up its sleeve is its drive units, and the midrange home in particular. This was developed specifically with high level studio applications in mind, and is certainly the largest dome radiator this writer has ever seen, both in terms of voice coil diameter (100mm) and magnet size. You don't attempt to hold it in one hand, unless your name is Geoff Capes, and you put it down very carefully to avoid crushing a digit or two.

There is no tougher trick in the loudspeaker engineer's book than the large, high SPL midrange dome, trying to preserve pistonic motion while avoiding rocking and flexure in the various planes and degrees of freedom. Get it working mechanically at all, and you begin with a head start, because power handling is prodigious and dispersion very favourable. The large diameter and (comparatively) large excursion allow this unit to operate from as low as 250Hz, so that this single driver covers a complete decade over the most musically important part of the spectrum.

Careful experimentation with damping materials and TEF analysis has resulted in a dome which is neither hard nor soft, but sort of "firm". The response is smooth, and time domain analysis shows even, rapid decay without significant resonance. While the TEF played its part, the real secret weapon is probably Stan Kelly, hi-fi and audio engineer/guru whose years of experience in the field is longer than the average age of London's recording engineers. Stan has forgotten more about loudspeakers than most of us ever suspected there was to know. His strength has always been in design and development rather than the business side, yet the Kelly/Decca ribbon units made him a legend 30 years ago, and there is arguably no one in the world more capable of getting a macho midrange dome to deliver the goods.

The tweeter is a derivation of the midrange, but the 37mm voice coil is naturally a rather easier prospect. Once again this is a "firm" dome, with a similar viscous damping. An interesting touch is a special porous plug — derived from an industrial filter — which eliminates cavity resonance between pole piece and dome, and is essentially resistive rather than reactive in nature. Here again a massive magnet gives the necessarily very high sensitivity without resorting to horn loading.

The bass arrangements constitute the only differences between the two Boxers. Logically, the Two has two 310mm bass units while the Four has four of the same. In each case the drivers are reflex-loaded by the single ported enclosure, the port itself being large with chamfered exits to reduce turbulence. The bass drivers are reasonably conventional, but use a short voice coil within a longer magnet gap to maintain linearity under excursion.

Inevitably such a costly system is actively driven, the EAA amplifiers and DRL active filter unit being supplied, complete with floor-standing rack, as an integral part of the system. There are no plans to offer a passive alternative, as the constraints in terms of phase response, driver control and protection are considered unacceptable.

These French power amplifiers are modified slightly to meet the system requirements. Like the drivers they represent a high quality execution along traditionally accepted lines, with high speed bi-polar output transistors and a conventional 2x2kVA power supply. Negative feedback is low, the transistors are carefully matched and balanced within each amplifier and connected with high definition signal cable, and a two speed fan ensures thermal stability. Advanced protection circuitry monitors a number of parameters such as output current, heatsink temperature, voltage, and load impedance, computing the power delivery and comparing to the SOA (safe operating area) of the amplifier and drive units.

The crossover is a dedicated DRL unit, fully balanced and with switch on delay. The slopes are fourth order, modified to compensate for the amplitude and phase responses of the drivers. A factory adjusted phase set ensures the phase alignment of the different drive units through the crossover regions. FET overvoltage protection prevents any signal from clipping the following amplifier.

The basic specification reflects the high quality of the ingredients. The response is quoted within ±2dB limits from 44Hz-14kHz, and within ±3dB from 34Hz-17kHz. High dynamic linearity is claimed at all power levels, while SPL maxima are quoted at 123dB mean, 133dB peak (1m) — levels which are rarely normally achieved without resort to compression drivers.

Fashion plays an embarrassingly large part in the popularity of studio equipment, so it is encouraging that the Boxer word seems to be getting around. A number of prestige installations have been made or are in prospect (helped, to be sure, by the consultancy activities and the integrated room/monitor concept).

Clients include Baby Records (Milan), Welks Music Group (Nashville), Red Bus (London), and Tennessee State University (first one installed and four more scheduled). Two systems are due to be installed in Swanyard (London) in October. More installations could well be confirmed by the end of the year.

This is a pretty impressive roster for a design which has so far received very little pushing, and has yet to build a track record. Neil is garrulously confident that the product speaks for itself, and comes far closer than rivals to the ideal of a giant hi-fi speaker, capable of real stereo (height, depth, phantom images and all), accurate dynamic linearity, and low coloration, while at the same time operating at real rock studio levels with reliability. So far, touch MDF, they haven't had a single failure.

Pursuing the circular argument further around the circumference, a monitoring system of the quality of the Boxer is only really appropriate to a control room with acoustics that are pretty well sorted, at low frequencies as well as midrange and treble. Traditional techniques of controlled absorption and reflection management are quite effective at the higher frequencies, but LF has always been the troublespot. Large heavy membrane absorbers do work and are controllable, but Neil has become particularly enamoured of a new tool in the acoustician's trade, the diffuser — specifically the RPG Diffusor, for which DRL act as UK distributors.

The reflection phase grating diffusers have been developed from mathematical number theory by Dr. Peter D'Antonio, and represent an acoustic equivalent to the diffraction grating of spectroscopy. In simplest terms they reflect rather than absorb an incident sound wave. But they do so in such a way as to neutralise the undesirable coherence of the incident wave, by disturbing the phase relationships across a broad frequency spectrum. As a result, the diffuser breaks up the ordered nature of an arriving sound, but doesn't actually absorb much energy in the process, merely re-radiating in a diffuse form.

These diffusers started out as devices for midrange treatment, but recent experimental work into the development of low frequency devices shows considerable promise. Neil is particularly excited about the prospects of providing an alternative approach to dealing with the inevitable and pernicious standing wave phenomena. Certainly the addition of a practical and effective diffusing capability to existing techniques of absorption and reflection should dramatically enhance the capability to create an optimum acoustic environment.

Furthermore, the coincidental development of the TEF-10 computer system, which has powerful acoustical analysis software, has provided the tool necessary to determine cause and effect of changes both to the room acoustics and to the monitoring loudspeakers therein, so that the end result can be a monitoring environment able to give far more accurate and repeatable results than hitherto.

The commissioning part of a Boxer purchase includes the personal appearance of Neil Grant plus TEF-10, ready to do battle with your particular control room until the best setup results are obtained. The customer is then presented with copies of all the TEF curves taken in the room. Alternatively, if you're starting to have second thoughts about your current soft dome system you put in six months ago, Neil will happily don his Harris Grant Associates hat and come and check out the phase sets of that system for you, carrying out whatever tweaks may be necessary to finetune system and environment.