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Tannoy System 600A

Active Monitor By Hugh Robjohns
Published April 1998

Tannoy System 600A

Throughout the years, Tannoy have determinedly supported their successful dual‑concentric driver concept in the fierce cut and thrust of the monitor marketplace, and the 600A is their latest mid‑priced champion. Hugh Robjohns enters the fray...

Tannoy are amongst the oldest of the British loudspeaker manufacturers and have an enviable reputation. One aspect of loudspeaker technology which many automatically associate with Tannoy is their long and keen interest in dual‑concentric drive unit designs — the mounting of the tweeter assembly within the bass‑mid unit. Theoretically, this approach has some very significant benefits over conventionally spaced drive units, because all frequencies are effectively generated from the same point in space.

System 600A

Tannoy System 600A

Tannoy's new System 600A incorporates their latest generation of dual‑concentric drive units, and the new loudspeaker has been coupled to a pair of integrated amplifiers and an active crossover, to provide a self‑contained active nearfield monitoring system — all in a remarkably compact and attractive package.

The bass‑reflex cabinet is constructed from dense MDF panels (the front panel is an inch thick) and is built in an octagonal arrangement. Besides making the loudspeaker visually appealing, this unusual design is intended to minimise the sizes of the side panels and thus reduce their potential for low‑frequency resonances. Other benefits of this design are claimed to be an improvement in the damping of internal energy (the extra joints in the cabinet help here), and a reduction in the diffraction and reflection of sounds around the cabinet compared with a traditional rectangular loudspeaker cabinet. Internally, the cabinet is damped with high‑density polyurethane foam.

There's no grille or drive unit protection of any kind, as none is needed. Unlike conventional loudspeakers, where the delicate tweeter is mounted flush on the front panel, the Tannoy dual‑concentric system employed here has the tweeter mounted inside and at the base of the bass‑mid driver. The cabinet is primarily intended to be used on console meter bridges in 'landscape' format (ie. wide rather than tall), although either arrangement is acceptable. The only caveat is that the degree of magnetic shielding varies on the different sides of the cabinet. TVs and computer monitors can be placed immediately adjacent to the ported end of the enclosure, but must be at least 150mm away from the opposite end and 80mm away from either of the long sides. This is something to also bear in mind if there are moving‑coil meters in your console; as these are magnetic devices, external fields from loudspeakers will influence their readings and could even cause them permanent damage.

Besides carrying the co‑axial drive unit, the front‑panel woodwork also contains a pair of forward‑firing ports which employ plastic tubes roughly 140mm long and 30mm in diameter. A 'Tannoy Active' badge between the ports can be rotated to suit landscape or portrait orientation, and an extraordinarily bright blue LED illuminates when the system is powered (it's so bright, in fact, that several people commented on its resemblance to an "incoming photon torpedo"!).

Drive Units

The drive units employed in the System 600A look most unusual — almost as if the central dust cap has been left off! At first glance it appears that there are three concentric brass tubes at the centre of the relatively conventional bass‑mid diaphragm. The outer one defines the edge of the bass‑mid driver, while the inner pair form a 'tulip' waveguide for the treble driver.

The 165mm (6.5‑inch) bass‑mid cone is supported by a nitrile‑rubber surround on the outside edge, with an inner suspension arranged to allow the cone to slide up and down on the outer of the three brass tubes. The user manual proudly professes that the motor system (ie. the magnet and voice‑coil assembly) has been "computer optimised" in terms of coil‑winding parameters and magnetic flux strength in the air gap.

The HF diaphragm is made from aluminium and magnesium alloy, supported on another nitrile rubber suspension. The voice coil uses high‑temperature copper wiring bonded to a kapton former attached to the outer edges of the diaphragm skirt, and the magnetic gap is filled with ferrofluid to improve thermal power handling.

Rear Panel

The rear of the loudspeaker features a large metal panel which carries the signal and power connections, user controls, and a large area of heatsink for the power amplifiers. The latter is mounted in such a way that the greatest convection cooling will occur with the loudspeaker in landscape orientation.

The panel is effectively divided vertically by the heatsinks, and the left side houses the IEC mains connector (with integral fuseholder), a rocker switch to power the unit, and a mains voltage selector. The right‑hand side carries the audio input on a combi‑jack connector (which accepts both 3‑pole XLRs and 3‑pole quarter‑inch jacks) wired for balanced operation, although unbalanced connections can also be made by shorting the cold and screen connections in the usual way.

Above the XLR connector are three chromed toggle switches. The lowest sets input sensitivity between +4dBu and ‑10dBu (although it is obviously intended for use with ‑10dBV equipment and works well enough in practice). The other two switches provide HF and LF contour adjustment of +2dB, 0 and ‑2dB for the HF control and 'half space' or 'free space' (whether the speaker is mounted close to a wall or not) for the LF control.

In practice, owners of these monitors will probably just play with the switches until they get a sound they like, but for the technically minded, free‑space mode introduces a 12dB/octave high‑pass filter into the signal path, arranged to boost slightly the levels of low‑frequency signals between 45 and 100Hz, but remove everything below 40Hz or so. The idea is to compensate for the lack of natural low‑frequency enhancement when the speaker is mounted on stands or a console monitor bridge well away from walls. Below 45Hz, the second‑order slope of the filter removes unwanted LF energy which could damage the drive unit and reduce amplifier headroom. If the speaker is placed close to rear or side walls (ie. in half‑space) there's no need to boost the speaker's LF output, since it will be boosted through natural acoustic behaviour anyway.

The System 600A is claimed to have a frequency response which extends down to 52Hz (‑3dB point in an anechoic measurement) with the filter switched out (half‑space mode) and the reflex cabinet imparts a fourth‑order roll‑off below that. In free‑space mode, the bass is extended down to 44Hz (‑3dB) but then rolls off much more quickly, with a sixth‑order slope (36dB/octave)

When I was running some test tones through the system I discovered an interesting side effect of the LF contour switch. Between 40 and 150Hz, switching to half‑space mode reduced the level of low frequencies slightly compared to the free‑space mode — exactly as expected. However, below about 40Hz, the half‑space mode has considerably more subsonic energy than the free‑space mode (as there is no high‑pass filter in the audio circuit to remove it). Potentially this means that in half‑space mode a lack of amplifier headroom could be more of a problem, although I experienced no such difficulties during my auditioning!

Listening

The System 600A is no slouch in the performance stakes. Transients are crisp and stereo imaging is pin‑sharp. The frequency range is well extended at both extremes, although I found I preferred the quality of the lower register when the speakers were switched to half‑space mode, even when mounted well clear of walls. To my ears, the sound of bass instruments was more natural and acceptable, and the high‑pass filter associated with the free‑space mode seemed to impart a bloated and slightly harder sound quality. At the upper extremity, I found the unity gain position on the HF contour control best suited my listening environment, but the 2dB of lift would be beneficial in an over‑damped room and the 2dB cut quite handy in an over‑reflective one. The range of adjustment available here seems to be very well judged.

Going back to the stereo imaging, although positional information is commendably precise left to right — explicit, even — everything appeared to be on much the same level, and there was less depth to the image than I'm used to hearing from my other regular nearfield monitors (mainly PMC and Dynaudio Acoustics). Tonal balance is on the warm side of neutral, but this is dependent to some extent on the setting of the contour switches and the precise positioning of the speakers.

The most revealing test for any loudspeaker is a well recorded human voice, especially the spoken word — simply because we all have many years experience of knowing what a real voice sounds like, and any resonances or distortions which the human vocal chords simply can't produce tend to become obvious. I found that spoken and singing voices were slightly 'warmed' by the 600As, but in general the sound balance was usably accurate and consistent. I certainly had no difficulties forming a repeatable frame of reference with the Tannoys, and my mixes transferred well to other monitors.

The Tannoys are capable of handling a surprisingly wide dynamic range in nearfield conditions, although the sound hardens dramatically when the limits are approached. I also found that high levels of very low frequencies (synth basslines being a good example) can generate a lot of 'chuffing' noises from the front‑facing ports, which shift an extraordinary volume of air under these conditions. Percussive instruments are also handled well — due largely to the combination of the wide dynamic range and the time‑coincident nature of the dual‑concentric driver design.

Verdict

All in all, the new Tannoys are certainly worthy of extended auditioning and should be on anyone's shortlist of active nearfields, acquitting themselves well in a fiercely contested sector of the market. They're clearly built to a price, but they retain the professional characteristics of typical Tannoy monitor systems in a very elegant and effective package.

Loud & Proud: The Amplifiers

Installed in the rear of the 600A cabinet with eight allen bolts, the amplifier pack is very modest but is optimised to the drive units, and the whole forms a very capable system. It uses a pair of diminutive TDA7294 amplifier chips, providing 70Watts each, coupled directly to the two drivers. The input buffer and active crossover are based around a pair of TL074 chips, and the whole lot is mounted on a single circuit board. The torroidal mains transformer is bolted directly to the back of the panel, the whole of which acts as a heatsink, although the addition of additional cooling fins increases its efficiency significantly.

Pros

  • Elegant design.
  • High‑quality build.
  • Explicit stereo imaging.
  • Wide dynamic range.
  • Typical Tannoy sound character.
  • Flexible tonal adjustment.
  • Excellent connectivity.

Cons

  • Potential for sub‑sonic problems in half‑space mode.
  • Little depth to stereo imaging.

Summary

The 600As constitute a high‑quality nearfield active monitoring system with Tannoy's latest dual‑concentric driver technology, and are well engineered, with sufficiently good sound quality to compete strongly.