Stereo Amplifier

Review: Harbeth HL-K6 Speakers

This brand-new loudspeaker from Harbeth, together with a big brother, the HL-S8 floor-stander costing twice as much, forms part of the steady expansion which has raised the profile of this traditional British company among its rivals.

The HL-K6 costs £975 per pair in standard real-wood veneers including a handsome new cherry, and £1,075 in the so-called ‘exotic’ veneers of rosewood or yew. It comes between the Compact 7 and the HL-P3ES 'shoebox' model both with regard to price and to physical size. I seem to have been on a run of reviewing mini loudspeakers of late so I was quite pleased to extract this sizeable model from its immaculate packing and heave its 10.4kg on to substantial floor stands.

At 440 x 250 x 308mm, the HL-K6 is big enough to allow the designer more freedom in his quest for low frequency extension but is not really tall enough to suit floor standing. Harbeth market handsome real-wood veneered stands at £ 199 (or £299 in the exotic veneers) and their height of 520mm would seem to be ideal, bringing the tweeter centers to about 830mm above floor level.

The system is two-way in a vented enclosure, showing numerous signs of the Harbeth perfectionist approach. The construclion is something that they call SuperTunedStructure (one word!). Basically the extra-thick 15mm front baffle is married to top, bottom and side MDF panels which are double veneered but only 9mm thick. However, these in turn have a bitumen lining to which are attached four fibre-board panels, to achieve a calculated balance between mass and compliance. An all-round lining of 16mm thick absorbent fibre helps to reduce internal standing waves. The dense MDF back panel is inset and secured to an inner framework by no fewer than 12 woodscrews. Four gold-plated terminals on a recessed plywood panel permit bi-wiring but are supplied with solid metal Jinks in position for normal wiring as ‘default’.

Crossovers are taken very seriously at Harbeth, reflecting the BBC background or the founder, Dudley Harwood. Here we have a complex 18-element network using individually tested and selected components mounted on a high quality printed circuit board. The 18dB/octave slopes are centred on 3-6 kHz and critically damped, a circuit arrived at with the aid of special acoustic modeling computer software. Loudspeaker pairs are level- and response-matched to within 0.75dB against a master reference loudspeaker. Individual results are kept on file and all loudspeaker pairs leave the factory with an Owner’s Certificate.

The two drive units are set in vertical alignment and each is ‘borrowed’ from an earlier model. The 200mm woofer is also used in the Compact 7 and employs Harbeth patented ’’Radial” technology. It has a special rubber surround, a phase plug, a 25mm vented aluminium voice-coil and a rigid glass-reinforced chassis which is bolted at the back of the baffle board. The 19mm tweeter is also used in the HL-P3ES. It has a profiled black anodized aluminium dome diaphragm, is Ferro-fluid damped and set in a flared faceplate for smooth high-frequency dispersion. Both drivers have ‘anti-magnets’ to allow placement near a television or computer screen without causing color distortion.

The reflex vent consists of a 54mm long by 49mm diameter plastics cylinder and is located near the left or right bottom corner of the front baffle, the loudspeakers being ‘handed’. The review samples were finished in the new cherry veneer whose light, smooth-grained appearance came as a pleasant change from black or the more common wood effects. The black grille cloth is kept in place by Harbeth’s own FramelessFrame technique. The fabric is wrapped round a thin metal frame which slots into a channel in the baffle itself so that it effectively ‘disappears’ so far as sound waves are concerned and thus avoids the diffraction irregularities which the conventional projecting frame can produce.


The first thing to say about this latest Harbeth creation is that it produces smooth, wide-ranging sound quality. My in-room response check showed almost unvarying output (certainly well within the claimed ±3dB limits) from 20kHz all the way down to 63Hz. Useful output extended to beyond 40Hz. Subjectively this smoothness made a vital contribution to instrumental color and vocal fidelity.

The high frequency sparkle was highlighted on percussion and brass. I could differentiate between instruments and voices with ease, and loud transients made me sit up. This clinical aspect could cruelly expose over-bright recordings, giving an edge to strings and cymbals, for example. However, this is just the sort of detailed response that professional engineers and broadcasters look for in a monitor, and well-engineered recordings have nothing to fear. They sounded ideally transparent at the top end. It then became a question of sorting out the sheep from the goats in terms of the partnering hardware - a loudspeaker of this caliber certainly deserves something significantly above average in one’s choice of CD player, tuner, tape machine, pickup cartridge and even amplifier.

Bass response had more depth and solidity than we can ever expect to hear from the mini monitors which currently hold centre stage in the marketplace. Piano recordings demonstrated this most effectively and one could easily imagine the instrument ideally placed just behind the loudspeakers, producing that special resonance that identifies a Steinway or Bosendorfer after hearing just a few notes. Nonetheless, I was aware that the bottom octave did roll off ever so slightly.

Room placement should be given due care and attention. I found that treble dispersion was reasonably wide, and angling the loudspeakers in towards the listening position produced only a subtle change which could be tuned to suit personal taste. When loudspeakers have a good bass extension, however, as here, they do tend to be more room-dependent. Harbeth’s well-written owner’s guide states that their loudspeakers are "optimised for so-called ‘free-space’ use”, and that the best sound will be obtained with the loudspeakers away from room boundaries and other hard reflective surfaces.

My experiments certainly bear this out. The unusually extended high-frequency response does naturally call for comparable bass extension which I am bound to say was not quite achieved in the free-space position. However, within the bounds of typical living-room dimensions, the HL-K6 treble/bass balance is probably about optimum. Attempts to boost bass by moving the loudspeakers closer to the rear wall were more liable to introduce unwanted muddling of the response and were soon abandoned. Male and female speech is always a good test of loudspeaker accuracy and, no doubt due to the company's earlier BBC influences, voices were extremely well balanced in the ‘free-space’ placement.

Dynamically these speakers were again impressive. The 86dB sensitivity is only about average, making an amplifier rating of at least 40W per channel desirable. However, given this amplifier capability, the volume could be raised to nearly public address levels without signs of audible stress. Indeed the bass response took on extra punch and depth at what we might call ‘realistic’ sound levels, encouraging me to do much of my listening that way (I have no immediate neighbors!).

The Harbeth HL-K6 surpasses all the marquee’s smaller models in smoothness, bandwidth and high-volume confidence. It is not cheap but, where good quality source material, amplification and environment can be provided, it should be given a high position on any shopping short-list.