Tannoy Stratford Speakers
Few readers will need reminding that the more sophisticated Tannoy models are widely used in UK studios, in some areas almost to the exclusion of their competitors. The situation here is confused to some extent, in that the famous Tannoy dual-concentric drivers are also used by competing system manufacturers, Lockwood being perhaps the best known. Tannoy are a long established, all British company, founded by Guy Fountain in 1926, and along with a dozen or so other British manufacturers, they share responsibility for maintaining the pre-eminence of British loudspeaker technology and design thinking that's legendary throughout the world!
The Stratford is a low cost, two-way speaker aimed at domestic hi-fi, and, of course, home studio monitoring. Both of the drive units are designed and manufactured by Tannoy in the UK. The bass/mid driver is an 8", long-throw unit, Thiele loaded in conjunction with the vented enclosure. This arrangement provides a flat response down to 53Hz (± 3dB) although it should be noted that the bottom octave for any Thiele alignment (ie. Vented enclosure) is subject to power limitations. A horn loaded tweeter handles all frequencies above 3.5 kHz, the response of which is unusually smooth, and is only down marginally at 20kHz.
Although 2 way systems have several advantages over speakers with 3 or more drive units — most notably the avoidance of extra crossover points, there are naturally trade-offs as well. It's generally difficult to make a horn-loaded tweeter operate satisfactorily below 3 to 4kHz, especially without sacrificing the last octave (10 to 20kHz), so the bass/mid unit has to cope with the remaining 6 octaves, which is no small task. To a great extent, the problems of handling such a wide bandwidth are down to a judicious cone design (to prevent cone 'breakup' at high frequencies) and the use of a small diameter driver — in this instance, eight inches. A driver of this size inevitably lacks bass performance, but in this system, as in many others, this is compensated for by (a) a long throw cone, and (b) the vented enclosure. Cone 'breakup' is successfully combated by using a suitable plastic, as opposed to the paper cones of indifferent drivers.
Compared to purely domestic systems in the same price range, the Stratford's horn-loaded tweeter is novel, particularly in view of the widespread vilification of horns in UK hi-fi circles. In the £70 price bracket, this is perhaps not entirely unjustified, but at the top end of the market, amongst the world's best speakers, there are more horn-loaded systems than moving-coil direct radiators. Manufacturing a decent, yet low cost horn loaded tweeter is quite a challenge, but Tannoy — with many years of experience in horn design — have succeeded admirably in an area where even the Japanese (who also have a penchant for horns) are either too pricey or simply abominable!
So what are the advantages of the horn-loaded top end? Perhaps the most important is the sound dispersion which is tightly controlled for stable stereo imagery, and also relatively independent of frequency, producing 'constant directivity'. At the same time, with the diaphragm being efficiently coupled to the air, via the horn, there's a decent transient response, which is particularly noticeable in the low treble region, where it really counts — on snare drums, say. And lastly, all these characteristics are largely independent of room acoustics, whilst the siting of the tweeter in the cabinet, vis-a-vis diffraction effects, is much less critical than with direct-radiator counterparts.
Undoubtedly the place where the Stratford — in common with any other Tannoy design — scores over speakers intended primarily for domestic purposes is the high sensitivity, coupled with fair power handling capabilities. For 1 watt of signal level at one metre, you get 93dB; for a pair, this indicates a maximum SPL (sound pressure level) of 113dB at the maximum rated power (100 watts) at a distance of six feet. In practice, the actual SPL will be 2 or 3dB down — say 11OdB — due to inevitable compression effects.
Listening tests were conducted in a 12' x 14' room with good high frequency (HF) absorption, but a fairly poor bass acoustic — a feature not uncommon to home studios lacking the expensive treatments needed to control LF reverberation. Test sources included a variety of discs, high quality broadcast material, and, of course, master cassette tapes.
The preamplifier in all cases was of audiophile minimalist design, with no EQ, and with the RIAA replay curve corrected to within 0.2dB. For amplification, we used a Quad 405-2 (reviewed in this issue) and a Pantechnic MOSFET amplifier to ensure that any power amplifier problems — such as the operation of protection circuitry — could be correctly ascribed.
At 'normal' listening levels (70 to 80dBA), sound colouration and distortion were both very low, as was evidenced respectively by the neutral balance on serious broadcast material and the audibility of an overloaded SM58 vocals mic, and other 'errors at source', such as sibilance.
The very acceptable rendition of a live recording, a Mikey Campbell mix of Aswad, was also revealing; Reggae being a near impossible diet for most speakers in this class. At higher levels the sound on rock material was slightly harsh and a little proud in the presence region (2 to 5kHz), but to a great extent, this proved to be down to the source; a lot of records are (very naughtily) mixed this way, and of course, it's easily equalised out.
Nevertheless, the horn tweeter is partly to blame, most notably at high levels, this being confirmed by the fact that the harshness was more noticeable off-axis, where the tweeter's relative contribution is enhanced around the crossover point owing to its wide dispersion. In common with most horn tweeters, it's not at its best in the first octave (3.5k to 5k), but on the other hand, it did provide outstanding reproduction of bells and similar percussion instruments. At this point, it must be stressed that no equalisation was used, and many people do find a slight dip — say 2dB — in the presence region more realistic, and often preferable to a dead flat response;, so with suitable EQ there should be no problems.
Imaging was not exceptional at a conventional listening position of around 3 metres — but it sprang to life at close range, and was especially spectacular at high levels, becoming plausibly three dimensional on some material. Image stability was also good under these conditions. Also, with a view to poor acoustics, close listening means more direct sound, and is therefore to be recommended for the accurate assessment of balance when monitoring in a less than ideal acoustic.
This is exemplary. Tannoy have a good reputation in this respect, and no corners have been cut just because it's a model at the bottom of their range. In particular, full marks are due for the passive crossover, which features a top quality plastic film capacitor and an air-wound inductor, instead of the more commonly encountered electrolytic and ferrite-cored coil, which can give rise to audible non-linearities at low and high levels respectively.
The Stratfords are nominally rated at 100 watts and 8 ohms. All speakers, however, exhibit impedance variations, and it's important to know the minimum impedance — in this instance 5 ohms — and then ensure that the amplifier can handle this without the protection circuitry leaping in prematurely.
Provided you heed any signs of distress, speakers can be driven from nominally overpowered amplifiers, and the Stratfords were quite at home with the 250 watt MOSFET amplifier. In most instances, tweeters are blown up by clipped signals from overdriven, underpowered amplifiers. At this point, it should be stressed that the Tannoy tweeter is less susceptible to vapourisation than most, because it's 'ferro-fluid cooled', but nonetheless, for monitoring, where we can assume that high levels will be the rule, 100 watts is perhaps best regarded as a minimum figure for power-amping.
For it's price, the Stratford is strongly recommended. To begin with, unlike some 'here today, gone tomorrow' Japanese units, it'll remain serviceable for a long time. Few other manufacturers have the skill and expertise to produce a £70 speaker which will handle 110dB SPLs with little detriment to the other qualities. The horn tweeter is its biggest strength, and at the same time, the only area of reservation, but perhaps only if your ears are used to hearing horn-loading in more exotic and elaborate tri-amped systems.
Finally, do bear in mind that all speakers are dependent on room acoustics, and to get best results from them, some experimentation with siting and listening positions is essential. In our own evaluation, the Stratfords were best — indeed spectacular — at close range, and also when spaced away from the wall (as recommended by Tannoy). So mounting them on either side of a largish mixing console is worth trying.
The recommended retail price of the Tannoy Stratford speakers is £140 inc. VAT (per pair).
Review by Ben Duncan
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