Harbeth HL5 Bookshelf speakers
The predecessor of this version of ex-BBC designer Dudley Harwood's monitor loudspeaker, the HL Mk4, rated very highly for its wide-ranging neutrality and smart appearance. However I see that the Mk4 cost £475 per pair back in 1987, whereas the HL5 is listed at £825. We can blame inflation for a good deal of this increase but it seems fair to investigate the physical changes and final sound quality in terms of perceived value for money.
Well the enclosure seems little changed. Birchwood ply thin-wall panels are again used- the material originally chosen from 19 others as producing least coloration. Double thickness Bitumen pads are now applied to damp out resonances and the polyurethane foam filling has had part of its surface modified to improve the suppression of internal standing waves. The front baffle thickness has been increased to 18mm and veneered to match the rest of the cabinet. The reflex-loading circular vent hole is set towards the bottom right hand corner of the baffle and is dimensioned to best BBC principles for resonance-free bass extension with minimum vent coloration. The grille is a simple modified foam sheet held on to the baffle by no fewer than 16 Velcro pads.
The two drive units are centrally aligned, the stereo pair being closely matched on test and checked against the in-house Harbeth standard model. A test certificate is supplied, and the factory keeps the Bruel & Kjaer frequency sweep for each serial number on file for reference in case a replacement driver is ever needed. The evolution of this HL design has owed much to the choice of the plastics cone material used for the all-important 200mm bass/midrange driver. When the company was first founded in 1977, the original HL moved away from Bextrene to Dudley Harwood's patented polypropylene copolymer cone. This had much higher internal damping so that the need to add a damping layer, and so increase cone mass, was avoided. With the Mk4, another change was made to a new plastic called TPX. This is said to be the lightest known thermoplastic and provides high efficiency, high power handling and improved transient performance.
The HL5 again uses TPX but with a special half-roll surround to optimize the edge damping. There has been a change of tweeter to a 25mm aluminium dome unit resembling that used in the HL Compact. It has a 25mm voice-coil and ferrofluid damping. The designer states that he has contoured the extreme high-frequency response on-axis for optimum energy balance in the room and avoidance of listener fatigue. The crossover network has 28 high-quality components mounted on a fibreglass pcb, reflecting the traditional BBC concentration on proper seamless crossover performance for natural midrange reproduction of speech as well as music-and in marked contrast to the minimalist crossovers used elsewhere.
The cabinetwork is of very high quality, and finished in carefully matched real-wood veneers. The input panel is recessed and supports two pairs of high-grade terminals accepting either 4mm plugs or bare wires. The HF and LF crossover inputs are connected individually to permit bi-wiring and the loudspeakers are supplied with robust spade-terminal linking wires already fitted for normal single-cable operation.
How they performed
Forward-facing vented loudspeakers need just as much care in room placement as any other type, particularly when they lay claim to an extended bass response. Harbeth suggest keeping at least one metre away from the walls, with substantial floor stands to raise the height by up to 45cm (18 inches) depending on ear height in one's chosen chair. I obeyed these instructions and was still left with one variable, the extent to which I turned the loudspeakers inwards to direct the principal axis towards my ears. In the event this did produce a very small degree of treble rise, compared with the pointing straight ahead arrangement, and I would recommend some experimentation to suit one's taste within the particular (more or less HF-absorbing) room.
When I settled down to serious listening, I soon identified this design's virtues. The bass end has indeed been extended and firmed up to give orchestras, choirs, organs and pop ensembles of all kinds a satisfying depth and solidity. At the same time, careful balancing of the high-frequency end and smooth crossover characteristics have produced an integrated sound devoid of any telltale peaks or troughs. Reproducing pink noise confirmed this overall smoothness, and incidentally revealed the slightly narrowed HF 'window'. Male speech sounded natural enough to make it seem that the talker was in the room.
Aural memory is notoriously fickle but I felt that the HL5 scored over the Mk4 at both ends of the spectrum. For corroboration I resorted to Harbeth's own trick of referring to individual response plots, and looked out my Mk4 in-room frequency graph of two years ago.
Although these are by no means precision measurements, a' straight comparison could be made with the HL5 graph made using identical microphone and speaker positions. Sure enough, the two graphs kept nicely within ± 1dB tramlines from about 100Hz to 10kHz showing no bumps at the crossover frequency (around 3.5kHz). Below 100Hz the HL5 had a substantially delayed roll-off whilst the graph above 10kHz no longer indicated the Mk4's slight 'brightness' rise around 12-15kHz.
With smoother treble, the HL5 also possessed a sharp attack on transients and stereo imaging was exemplary. Professionals and home enthusiasts will surely warm to this natural, almost anonymous, sound monitor. It can handle reasonably high signal levels without distress, but mayor may not be accepted by rock fans who like their loudspeakers to go very loud indeed and show 'character' rather than neutrality. For natural reproduction of classical music - so necessary for professional monitors - the Harbeth HL5 well deserves an audition. The price is fairly high, but you get a lot of civilized loudspeaker for the money.
