Rogers LS7 & Studio 1 Speakers
The LS7 is a two-way speaker; and the bass/mid driver is notable on two counts. First, the voice coil is claimed to handle temperatures (and therefore power) well above the norm for domestic speakers. Second, the speaker cone is made from polypropylene. This has rather bizarre cosmetic ramifications, for the cone is transparent, and (perhaps for the first time) you can see the guts in action. The real reasons for Rogers' choice of polypropylene are more sober though.
Paper (or, more strictly pulp) cones are by no means inherently useless, but it does take skill to coax accurate sound from this material. Consistency is another problem, particularly when we're concerned with accurate speaker matching, for good stereo. Imagine the problems in trying to match up hundreds of pulp cones, all slightly different, into (identical) stereo pairs! Thanks to the BBC - and various luminaries - the emphasis in this country has long been on tonal neutrality and stereo imaging (in the US, other qualities receive priority attention), and this lead the BBC influenced manufacturers, such as Rogers, to get into plastic cone technology at an early stage.
The first successful material used was Bextrene, a rubbery mixture of polystyrene and neoprene. Good as it is in the bass and low-midrange, (up to around 600Hz), the response above 1 kHz has long been a problem area, often needing equalisation. In a passive system, that requires a complex crossover network and inevitable power losses or, alternatively, just accepting the problem area. These obstacles can be side-stepped by making cones from polypropylene, which is well damped - like Bextrene - yet much lighter, and needing little or no EQ. The main drawback here, as with pulp cones, is consistency. Or rather, was: In recent years, the technical problems have been solved by the careful addition of subsidiary materials (eg. Polyethylene), so today we have a cone material that's superior to pulp (at least on paper!), apparently without any of the drawbacks. One positive attribute for our purposes, is the levity of polypropylene. With less weight, the cone should respond accurately up to higher frequencies. Levity should also aid sensitivity, but ironically, the LS7 is below average, at 88dB (@ 1 watt, @ 1 metre). That's equivalent to increasing the amplifier power twofold, for the same sound level. This is the price we pay for polypropylene's key advantage - a very smooth frequency response.
The tweeter is a Celestion HF1001 unit, coming in above 3kHz. This driver also boasts an unusually flat response, up to 20kHz and beyond, and should be viewed on a par with the ubiquitous Scanspeak.
In the supplied literature, 'Thirteen precision elements...' are extolled. What we actually get is 4 inductors, 3 resistors and two capacitors - that's nine elements, and not quite the level of complexity advertised! (Unless Rogers count each driver also). The bass crossover is -18dB/octave, and there's a zobel network at the output, across the driver. This helps the crossover to see a sensibly constant impedance above 3kHz. Otherwise, the rising inductance at this point (common to most drive units) would upset the crossover slope, and phase relationships. Conversely, the tweeter features inductive compensation (a series inductor), presumably to cancel the driver's capacitative reactance below its crossover point. The actual crossover slope is -18dB/octave again. Both the compensation networks discussed above can also be looked upon as passive EQ networks, in the sense that they help to smooth out the amplitude response; but they're not equalising the drivers directly.
The enclosure isn't constructed of especially thick chipboard, but nevertheless, it's surprisingly dead. Considerable assistance comes from the bituminous panels, glued and stapled over most of the inside. This is a well proven way of reducing the potential colouration of sound, brought on by noisy panels at high playback levels.
This discipline is widely practised by DIY builders, but few manufacturers go to these lengths, at least in this price range. At the same time, it's fair to note that the LS7 enclosure lacks internal bracing, which is just as useful an addition, and no more expensive to contrive.
Inside, there's extensive foam - perhaps more than is usually recommended in Thiele-loaded enclosures. This does nothing to improve the sensitivity, but cleans up the finer details of the sound by absorbing sound coming from the rear of the cone, before it's able to bounce around and emerge out-of-phase with the legitimate outfront signal.
All the crossover components are PCB-mounted. Out of the other speakers reviewed in HSR, only the Kord models had this feature. Mounting components on plywood, 1930's style is fine, but PCB-mounted inductors tend to be securely tie-wrapped, rather than glued. This suggests they're less likely to come astray if subjected to nasty 'g' forces, on the road say. Secondly, a PCB lessens the headaches if the crossover is suspected of being faulty; the job of repair/replacement is made a whole lot quicker and easier.
The bass/mid driver's connections are soldered, and the tweeter has a Molex snap-on connector which won't come astray easily. But the connections coming from the input terminals are simply clamped with unlocked nuts. Any experienced professional manufacturer should know better than this. Okay, on the sample reviewed, these were certainly tight, but that means little. Rogers should invest in a phial of nail-varnish.
The last niggle concerns the bass/mid driver's fixing. The machine screws used here mate with metal threads (T-nuts), and given that lockwashers are a non-starter - because they'll doubtless be missed out if the driver is subsequently removed and replaced - high torque is desirable to prevent the screws working loose. Sadly, the pozidrive head employed doesn't readily align with this requirement; Allen head screws would be a much better choice. (Most drive units have pozidrive screws, but of the self-tapping variety, going direct into chipboard, which is generally a snug enough fit of its own accord).
The Roger's exterior is not quite utilitarian; an unexceptional 'veneer', and a glossy plastic grille are used. So these are not the speakers for you if you exhibit any aesthetic sensibilities, particularly if you're working in the home environment. Put simply, the level of decor befits the ilk of Amstrad, and fails to shout "Hi, I'm a professional monitor" in dulcet Alexis Korner tones!
On the rear panel, amplifier connection is via the usual 4 mm terminals. But these aren't recessed - unlike most - so it's easier by far to thread bare wires, prior to clamping. At the same time, the lack of recess in no way aggravates the chances of damage, because the terminals Rogers use are unusually rugged. They also offer a good, tight mating with 4mm plugs, so full marks here.
The LS7s were set up on stands, at least one metre from adjacent walls, but Rogers wisely recommend that 'before the final position of the loudspeakers is decided upon, some experimentation with mounting and positioning is done...'
In view of the BBC influence, one would expect a neutral tonal balance, and this was indeed the case - at least on serious BBC broadcast material. On rock material, however, several problems were evident. To begin with, there was a distinct lack of bite on percussive sounds, especially snaredrums. But the big problem area was the bass end. Kick drums suffered from overhang - a tendency to 'boooom' instead of 'boooof'.
This is one symptom of a badly designed/implemented Thiele alignment; the 'Q' is wrong, and the driver's diaphragm gets into serious over-excursion trouble in the all-important 60-70Hz region. There's a certain minimum SPL before synthesised bass happening in this region begins to occur properly, and when we commenced testing at high levels, one of the bass/mid drivers promptly committed Hari-Kari when confronted with a Malcolm X record. But more seriously, the problem is compounded by (i) the absence of any warning noise when the cones bottom and (ii), the low sensitivity, which makes it deceptively easy to clip the power amp, along the lines of 'surely it can't be at full power yet?'
With rock material, the low frequency incapacity makes a mockery of the voice coil's acclaimed power handling capacity (PHC), which seems unlikely to have its (midband) muscles flexed: There's no doubt cast upon the quoted 200 to 300W PHC on music programme, but this must come with the proviso that any amount of low bass energy will reduce PHC to a lower level - say 50 watts.
The stereo was disappointing too - fortunately this was assessed early in the proceedings - depth was average, but there were no 3D qualities, nor any height in the image, and moreover the integration was poor in that the tweeters are perceived as discrete sound sources.
This is Rogers' senior model, and unlike the LS7, it's a three-way system. The mid/bass driver is again one of Rogers' own units, but with a bextrene cone. The extra cone weight partially explains the sensitivity, which is actually lower (by ½dB) than the LS7, rather than the 1 or 2dB higher that the larger enclosure would lead us to expect. To a small extent, this is made up for with moderate bass extension - the bass roll-off being some 10Hz lower on this model.
The 3kHz crossover point and -18dB/octave slope is retained, going over to a Celestion 1300 driver up to 14kHz. The 1300 rolls off abruptly here, so a second crossover (also of the -18dB/octave variety), brings in a KEF T27, which extends up to 28kHz. In view of the Studio 1's poor sensitivity, it's notable that both HF drivers are attenuated by 3dB or so. So a useful increase in sensitivity could have been attained by choosing a different bass/mid driver. This is not a unique point - most direct-radiator speakers are held back by insensitive bass/mid drivers. But when competing companies can achieve 7dB more SPL (equal to having 5 times the power) from a speaker cabinet two thirds the size, with equal bass extension and better PHC below 100Hz, there is something wrong.
The Studio 1's exterior is mostly similar to the LS7, but with greater finesse in the cosmetics. This is particularly evident when the snap-on front grille is removed - a recommended procedure in any case. Oddly, the bass/mid driver is rear-mounted, 1960's style. This exposes the baffle's edge, but it's neatly bevelled and extremely smooth, to prevent any mild diffraction effects above 800Hz.
A more important ramification of rearmounting is that it entails a removable rear panel (again, 60's style), instead of it being an integral part of the cabinet, as with all but one of the speakers we've previously reviewed. This arrangement is fine, so long as the back panel's fixing is firm and airtight. There are doubts on the latter point, as there's no foam or other sealing around the edge of the rear panel. Noisy air-leaks are thus possible. Another apparently suspect area is the cabinet's overall acoustic properties. Like the LS7, bitumen-covered damping pads are generously displayed on the interior surfaces, but the Studio 1's cabinet is noticeably resonant, particularly in the centre of the side and rear panels. In practice though, there is no audible effect, because the damping pads shift the resonant modes downwards out of the critical midrange region.
In addition to the LS7's 4mm terminals, the Studio 1 has a parallel XLR socket. Following the BBC's requirements, this is of the male variety, which is wholly non-standard for most of us, but better than no XLR at all. (XLR inputs are conventionally always female, be they at mic, line or speaker level).
Listening tests commenced with the Turner B502 amp (reviewed this month), but the below average sensitivity of the speakers meant clipping was inevitable if we made any attempt to listen at high SPLs. So we switched over to the higher powered Yamaha PC2002M (see February 84 HSR}. Even this amplifier had to be driven close to its limits (300 watts) to achieve a satisfactory SPL, which at 107dB, also happens to be the maximum available.
In contrast to the LS7 the bass end is much improved, having none of the overhang, but cone bottoming still occurs too readily, and without adequate warning. The 300 watts handling is all soaked up by the low sensitivity, and even using the PC2002M's in bridge mode (750 watts) is no panacea, for the cone bottoming on normal rock programme sets an effective 300 watt limit. The imaging was also an improvement over the LS7, but not special in any sense.
The successful integration of three drive units is no easy task, but there were no obvious problems in this area - the 3 drivers work well together. Rogers don't explain why they feel two tweeters are necessary to cover 3kHz to 28kHz, especially when one alone can happily cover all the audible frequencies in this range. There is certainly potential here for extra power handling - by splitting up the high frequency (HF) content (and hence signal energy) between two drivers, but this would be best done by crossing over around 6kHz or even lower.
I suspect these speakers have been designed with attention focused exclusively on gaining a ruler-flat response in the anechoic chamber, and with little or no references to the requirements of Rock material. But even from a Jazz or Classical perspective, the undeniably accurate tonality is let down by no more than average stereo imaging on the LS7. Put simply, competing speakers, with better performance and/or a lower price are made at home by other UK companies, (ie. without the benefit of cheap labour). Because Rogers are more of a specialist manufacturer, perhaps without the benefits of high volume production, we shouldn't expect a low price, but for the price asked, a higher standard of overall performance could reasonably be sought.
In mitigation, if high SPLs, and bass end performance (especially re. LS7) are not high on your list of priorities, but you need something serviceable, and with accurate midrange and HF performance, the LS7 and Studio 1 should be carefully auditioned.
Further details concerning the Rogers monitors can be obtained from Michael Stevens & Partners, (Contact Details).
Gear in this article:
Review by Ben Duncan
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