The Tannoy 700 Dual Concentric

Historical Review: Martin Colloms April 1993

Tannoy has made steady progress on the studio monitor market over decades. Medium sized monitors are required to have a performance envelope which reaches beyond the capability of most domestic speaker designs. Low coloration, subtlety and transparency may be the provenance of high quality domestic speakers; the professional monitor must be capable of very high standards in terms of dynamics, ‘speed’, power handling and loudness as well as outright sound quality. Furthermore it must be highly analytical. It does not have to sound ‘nice’; rather it must faithfully reveal both flaws and qualities in the monitored signal source.

​The Definition 700 project emerged from this studio background,. The brief was to domesticate a studio monitor in this size and price range, clothe it, smooth it and balance it for domestic rooms as well as for the intended floor mounted location, but at the same time retain its fundamental monitoring qualities.

The D700 has occupied some of the best brains at Tannoy for some time now and this shows both in the design details and the performance level the company has achieved. At close on £2,000 a pair, this is a sizeable floor standing loudspeaker of sufficient width to accommodate the 250mm, 10″ bass -mid drivers used. It stands tall at 99cm high including the substantial floor spikes, and with the neat grilles installed it certainly looks the part. The prismatic rear outline helps to reduce the impression of depth and visually the speaker does not appear too broad. A clean expanse of mahogany veneer was evident on the review pair, which were very well finished.

The system may be bi -wired; the transition is placed between the mid and treble ranges. Power handling is upwards of 200W with impedance claim an optimistic 6 ohms. The sensitivity is way above the norm at 93dB/W [an 8 ohm watt.]

A bass response down to 35Hz is claimed together with a very high maximum spl of 118db at 1 metre for a 300W peak input. This translates to a very substantial 110dBA for a stereo pair in a typical listening room with 200W per channel of amplification.

Such a system should be capable both of good power and bass delivery since the ‘700 uses two 250mm bass -mid drivers per enclosure, equivalent to a single 350mm bass driver. Moreover the bass drivers are reflex loaded by two substantial ports 70mm in diameter by 160mm long, tuning an internal volume of 72 litres to a well damped 40Hz or so.

The lower unit mainly covers the range up to 300-400Hz while the upper unit is a full range concentric with the so called ‘Tulip’ wave guide at the throat driven by a rear mounted, forward facing 25mm alloy dome transducer, here with its own magnet system.

The Tannoy concentric principle has benefited from some serious development in recent years, As regards cone technology this is bang up to date and uses the latest injection moulded, tapered profile polypropylene, mineral filled for damping and reinforcement. The units are built on rigid die- cast alloy frames. Being concentric the crossover design is greatly eased and the mid- treble crossover is true 1st order, 6dB per octave, the horn tweeter coupled via a single mechanically damped polypropylene capacitor, a mixed value composite component, which has been the subject of extensive auditioning. The bass to lower mid unit has a quasi second order network to help improve its rolloff rate. Compression free air-core inductors are used.

Great care was taken with box stuffing using dense, stable mineral wool packing resulting in a well damped Bessel alignment in the bass and the almost complete suppression of the upper driver resonance and also the higher order box modes. Likewise the enclosure is braced by multiple partitions in all directions and has a very low panel ‘read out’. This large tall box has been successfully tamed!

Sound quality

​Trials were undertaken using several listening stations and particular care was taken to ensure that the designer’s claims for good dynamics and rhythm were explored. In particular rhythm can show a temperature dependency due to a stiffening of the driver surround suspensions. For example below 19 C the 700s were definitely less free and rhythmic in the bass compared with their operation in the 20-24 C range. Nothing awful happened at the lower temperatures – quite simply the speaker was better sounding when reasonably warm!

It also showed some dependence on amplifier type and clearly presented a significant load. Modest amplifiers of medium output current capability could sound well enough at low volume levels but when turned up the end result was increased tonal hardness with a ‘ringing’ presence range. Neither an Musical Fidelity P140 or an ARC V70 were really happy here Moving to amplifiers with an appetite for 4 ohm loads, but still of subtlety and refinement, the ‘700 really came to life. The Naim NAP250 was awaiting formal test and I hooked it up to the Tannoys via a direct connection to the Accuphase DP70-V with its digital volume control. I have never heard this player sound so clean, fast, dynamic and rhythmic as it did now. The NAP250 took firm command of the Tannoys and they responded in kind, delivering an exceptional, tight punch. This was not restricted to the low bass but extended to the mid bass and on through the mid range and into the treble.

The ‘700 has a big heart. Its dynamic authority was not achieved at the expense of impaired tonal balance. If anything, it has an authentically strong lower mid range, an area where classic BBC monitors are so right, but one which few designers recognise or understand.

When you install a speaker of this size in your living room you hope for a decent bass, and here the ‘700 certainly satisfies. It went deep – subjectively to a low 27Hz or so – but it did this without false emphasis, boom, uncertainty or unevenness. It can deliver real bass transient slam, the kind one gets from a real sub woofer system or costly specials such as the Watt/Puppy arrangement. In fact in terms of bass power and extension I reckon it surpasses my own Watt-Puppy, which is no mean feat. Moreover its rhythmic resolution was only a little backward through the bass and lower mid range.

Headroom was the keynote of the ‘700. It never sounded stressed. There was no doubt that not only would it play loud, but it would also play loudly enough to drive bigger rooms. Up to 110cubic metres should be permissible.

Allied to the high dynamic peak levels were the fine dynamics. Soft to loud transitions were handled without perceptible compression; percussive attack was portrayed properly and in this respect I was reminded of the equally remarkable attainment achieved by the Naim SBL passive.

However, the news is not uniformly wonderful. Care is needed with positioning if the mid is not to sound too forward, or the stereo to sound diffuse and phasey, the treble distinctly spiky and grainy. As regards the latter, here the Naim SBL ‘tweeter and decoupled cabinet’ system demonstrated its mastery. The coaxial horn tweeter used for the Tannoy horn series is still something of an acquired taste. It is necessary to outline just how I arrived at a well balanced and satisfactorily convincing treble.

To begin, the mid range balance hinges on the spacing from the rear wall. 0.6m suited me, but feel free to experiment according to room acoustics and your favourite listening position. Secondly, the tweeter should not face you directly – these little spikes in the treble are axisymmetric, as KEF would put it when discussing their own concentric Uni Q systems. They blend in when the speakers are set 5 to 7 degrees off axis. This means toeing in the ‘700 so the axes cross 0.5 to l m in front of the listener. Magically , the stereo image then comes into focus and the rating then lifts from average to ‘good plus’.

This speaker reproduced complex detail well, and did not ‘ring’ or ‘shout’ on piano. It also showed quite good transparency. Both stage width and depth were fine, and coloration was moderate.

Capable of reading the driving system clearly, it proved easy to differentiate between different cables and there was no doubt that slam and dynamics were at their best with a rigid, low resistance link. Naim NAC-5 was the most effective we tried, while the speaker quality also justified Siltech ribbon FT12 or van den Hul Revelation, using short runs to keep the price down. The NAIM 250 was found to be surprisingly compatible with these moderately inductive spaced conductor type of cables and also with the D700. Other power amplifiers which are worth trying include the Krell KST 100 and the Meridian 605m.

Also capable of accepting a bi-wire connection, in this mode the ‘700 rewarded us with greater clarity, finer bass and cleaner treble. All in all it comes firmly recommended.

Conclusions

​With the proviso that its high sensitivity will be partially compromised with less muscular amplifiers due to its poorer than average load impedance, the D700 is seen to be a highly accomplished design.

This is a full blooded, full range loudspeaker capable of really high sound levels and for like reasons, is capable of driving large rooms. Much of the competition is rendered puny and anaemic by comparison.

The bass was first rate and free from boom. It went deep, and was both articulate and tuneful, packing a real punch; very fine dynamics and dynamic expression characterise the broad sweep of this speaker’s output.

Tannoy have every reason to be proud of the Definition 700 which approaches the performance of the Wilson Watt 3 Puppy 2 system in a number of respects. The treble range has its advantages and drawbacks while the system as whole is confidently recommended. It is entertaining and musically involving and too few such examples are around at present.

Lab report

Sensitivity was high – well above average and close to the specification. On test it measured 92.5dB/W [8 ohm watt] versus the claimed 93dB. This high sensitivity assures high sound levels with amplifiers of a generous load current rating and helps offset the harder than usual demands that its low impedance places on an amplifier. Valve/ tube amps of variable matching should be used on their 4 ohm setting if possible.

The speaker has an unusual impedance characteristic. Certainly it was predominantly resistive but its mean value was fairly low at 5 ohms. Moreover it fell to around 3.1 ohms over a broad high power region of the spectrum, 100 to 300Hz. The interior was so heavily damped that the upper system resonance was entirely suppressed, this is normally expected at 60-70Hz. Despite its bass reflex design the two humped impedance curve did not arise. The visible hump only rose to 7 ohms and was also heavily damped. This is the reflex resonance in the 45Hz , the peak spread and shifted due to the high resistive damping. As a result you get a smooth, resonance free bass extension.

With that 3.1 ohm worst case loading the weaker amplifiers are best avoided. Conversely a 93dB/W sensitivity and 200 watt programme capacity means that in a typical 80 cubic meter room high 110dBA sound levels can be achieved. This system will drive big rooms well when asked.

The bass extended to 33Hz -6dB and continued to a low 27Hz under normal room loading. A sub woofer is not really worthwhile with this model.

On axis at 1 metre the response [1] was well integrated, slightly rising on axis which it typical for a a dual concentric of this size. This is done to preserve the target power response in the room volume.

Noting the expanded, magnified vertical scale the response on the listening axis was essentially +/-2dB 50Hz to 10kHz which was a fine achievement., Exactly on axis, [dotted] the response extended out to 20kHz together with a mild axisymmetric peak at 10kHz. At 5 degrees off axis the response was maintained to 16kHz, almost to the edge of audibility.

Concentricity endows such a system with excellent crossover integration. The evidence is in the off axis set of graphs, successively 15 degrees 30 degrees and 45 degrees off axis. These are classic high uniformity responses and show no significant diffraction or reflective anomalies, [2].

Sine wave testing resulted in no rattles or premature overload and the bass power handling was also unusually good, for example, 40w at 50Hz with no significant distortion.

The energy time curve was most presentable, it had decayed to 45dB by 2 milliseconds but was skewed a little by the tweeter delay.

Analysed for decay response on a waterfall presentation, the first 30dB [3] dynamic range, 0.l millisecond filtered graph showed a good result for early decay. The horn tweeter cleared very quickly at the back and the performance of the two bass -mid drivers were also quite good. Turning to the 60dB scale, 0.2 millisecond presentation [4] the picture was more complex – lower level stored energy was evident in the treble range, these are secondary ripples in the acoustic structure of the whole horn assembly. More detailed behaviour was also evident in the mid range though this did not appear to significantly affect subjective transparency or clarity.

Measured by multiple position room averaging, the powerful extended bass was recorded, free from lumps or boom, and even with a floor standing position its output held within +/- 3.5dB, 25Hz to 8kHz. The slow rolloff above 10kHz was typical of this multi axis room measurement. The D700 clearly integrated well with the room environment and this is further evidence of the great care which has been taken in its voicing and balancing.