SPECIFICATION

Frequency response; 45-20,000Hz

Drive units; 150mm bass, 25mm tweeter

Sensitivity; 88dB SPL at I metre for I watt

Power handling; suitable for amplifiers rated at 20 watts minimum Nominal impedance; 8 ohms

Dimensions (H x W x D); 512 x 200 x 270mm (202 x 79 ii 10.6 inches) Weight; 0kg(221b)

Manufacturer; Monitor Audio Ltd., 34 Clinton Road, Cambridge CBI 4ZW UK retail price; £345 per pair, in a wide range of real wood finishes

ONE notable feature of Monitor Audio loudspeakers, apart from the fact that they generally sound pretty good, has always been their superb cabinet construction and finish. Indeed they manufacture enclosures for quite a few other loudspeaker brand names, and so have an extensive woodworking facility.

This R552 model is in a range of "System R" designs and can be supplied in a variety of attractive realwood veneer finishes: the usual teak, walnut and black—but also rosewood, yew, pine, oak and mahogany to order. The price includes a custom-designed stand (of which more later) which is veneered to match and contributes both to the handsome appearance and the quality of reproduction. The review pair came in nicely grained yew veneer, with a dark brown grille fitted on a light frame with stud fastenings. Even the front baffle is veneered, so that some users might well decide to leave the grilles off.

The internal volume must be no more than about 25 litres, yet the tall slimline shape makes this enclosure seem larger than it is, and of course has the incidental advantage of broadening the horizontal dispersion to make the listening position less critical. The cabinet is sealed, with the longer sides braced to reduce low-frequency panel resonance effects. Internal treatment also includes slabs of plastic foam and bitumen pads for damping.

The narrow profile has been made possible by electing to use a smallish (150mm) bass/midrange drive unit.

This has a weighty diecast chassis and 32mm voice-coil claimed to possess improved heat dissipation and power handling capacity. The cone is formed from synthetic PVC material called Cobex, combining rigidity with the required low mass. The cone surround, mass, etc. have been designed to give controlled highfrequency roll-off which permits a very simple crossover network to be used—just one component in series with the bass driver". Internal wiring uses Monitor Audio's own 100strand cable, the crossover components being fixed to the back panel. The tweeter (coming in nominatty above 25kF-Iz) is a 25mm soft dome type made by SEAS to Monitor Audio's requirements. The two drive units are mounted vertically in line and as close together as possible, with flush facings. All these factors should improve Stereo imaging and minimize diffraction at the unit edges.

Back panel fixings are colourcoded screw terminals on a wellrecessed sub-panel. A more than usually helpful instruction booklet is supplied which points out that 3mm banana plugs can be inserted into these terminals—but strongly advises screw fixing, and the use of special loudspeaker cables in preference to, say, 5-amp electrical flex. There are also useful tips on loudspeaker positioning, room conditions, ancillary equipment and normal care and operation.

The special stands screw firmly into threaded inserts in the bottom panel. They raise the loudspeakers about 325mm above the floor and introduce a few degrees of backward tilt. This should line up the tweeter Centres for optimum height in relation to a seated listener. The stands have been designed for avoidance of ringing or odd resonances, and are fabricated from a lossy composite material called 'medite'. They come with holes already fitted to take floor spikes (which Monitor Audio can supply). The idea is to provide a rock steady floor support, which very thick carpets might not. Any wobble that a carpet or loose castors allowed to take place could theoretically diminish the attack on powerful bass notes. I subscribe to this idea only where tall light structures are concerned (the R552 just about comes in this category) but, considering the massive weight of most high-fidelity loudspeakers, I should think that the forces acting on the cone are most unlikely to set the whole system rocking back and forth to any appreciable extent. Having said that, floor spikes can do no harm (they actually damage the carpet less than castors or ordinary furniture legs do) and they just might tighten up the bass reproduction of rock music and percussion generally.

How they performed

Since the R552 loudspeakers are delivered with their floor stands included in the price, t naturally fitted the stands promptly and carried Out most of the tests and listening in this way. However, Out of curiosity, I first switched my system to mono and did some A/B comparisons with single speakers first. Placing one R552 straight on a carpeted floor was a disaster. The plummy sound, combined with a kind of ringing like a kettle-drum, was almost comic and ruled out direct floor-standing completely. Moving up to a fairly traditional square-section steel stand on castors restored my sanity and, by cleaning up the bottom couple of octaves, let me hear a more balanced sound in which voices, brass and strings were more naturally differentiated. There was still a slight veil between me and the performers and some box coloration.

With the Monitor Audio stands properly fitted (stn easy task using 12 screws per speaker) this veil disappeared and the kind of detailed reproduction which I like to hear on music of all types could be enjoyed. The bass end was naturally rolled off—well, the small enclosure can hold up low frequencies only so far down the scale—but boxiness was now greatly reduced. The sort of one-note bass we get from inferior cabinet designs (of any size) was eliminated and no serious peaks or dips remained. If I say that I could never quite forget that I was listening to a pair of boxes and that a faint edge was imparted to some upper middle sounds, this is no more than I would expect from any compact twoway loudspeaker outside of the exotic unaffordable category.

The same picture emerged when I ran an in-room plot with warble tones. Output began to slip from about 100Hz downwards and was around —6dB at 80Hz. Response elsewhere was unusually held to within ± 2dB and helped to explain the lack of awkward attention-drawing middle or upper frequency peaks. Sensitivity was average, or a little higher, at a measured 87dB SPL for I watt at I metre. The impedance varied no more than usual with frequency and never fell appreciably below the nominal 8 ohms. This is good news for amplifier matching, and I would agree with the manufacturer's suggestion that any reasonable amplifier rated at 20 watts or more should drive the R552s to their optimum performance.

These are also good loudspeakers from the point of view of stereo spread (something I often find associated with a narrow baffle width) provided they are kept at a reasonable distance from the side and rear walls. With an overall quality that is pleasantly free of sonic excesses or unevenness, I can recommend these units to any sensitive listener. They are well constructed and well worth the price of £345 per pair including the excellent matching stands.

JOHN BoRwicK.