Naim NBL loudspeaker Page 2
That mid/treble enclosure operates only above a nominal 270Hz crossover point, and has a generous volume and plenty of depth to absorb rear radiation from the midrange cone. The chamber has a light foam lining and a quite generous "fill" of wool damping. Once the speaker is finally in position, the transit bolts clamping the midrange enclosure in position are removed, and the whole enclosure rests on undamped leaf springs that allows lateral rocking at a few Hz. The mid and treble drivers are then separately decoupled in the fore-and-aft direction from their mounting baffle by more leaf-spring arrangements: the tweeter is mounted on a square metal faceplate with four slits from edge to beyond the center line to provide the compliance; for the midrange, double L-shaped slits are cut through the baffle, then filled with foam strips.
The bass and midrange drivers are manufactured by Naim. The SBL-type bass drivers have nominal 8" cast frames and 6" paper-cone diaphragms, so the NBL has only about half the total radiating area of the DBL's 15" unit. The 5" midrange driver has a 3.5" paper cone and a pole-piece extension or "phase plug"; surprisingly at this price level, its frame is of pressed steel rather than being the more rigid diecast type. The 19mm soft-dome tweeter, a ScanSpeak D2010, has, in various versions, long been a popular choice for upmarket UK speakers.
By popular demand, Naim has ditched its preferred acoustic foam grille in favor of the more conventional cloth. The grille frame is screwed permanently (and very securely) to the edge of the "nest," while the cover itself is held under a tightly fitting O-ring. However, the frame itself looks less than ideal acoustically, despite its inside edge chamfering.
Close inspection reveals another interesting Naim technique: that of applying mass-coupling/damping pads to various elements. Each section of steel tubing around the back has its own little metal counterweight, attached via a rubber pad; more of these are used inside the enclosures, on driver frames, magnets, and box panels.
Naim's hi-fi speaker systems are predicated on an upgrade ladder that culminates in full active drive. Indeed, the NBL was initially available only in active form, but this review concentrates exclusively on the passive version. To enable easy conversion to active drive, separate access is provided to each of the raw drivers via 4mm socket pairs of standard spacing.
The outboard crossover network costs $1200/pair and is a long, slim, elaborate PCB using good-quality components spaced well apart and with inductors mutually arranged at right angles to minimize any cross-coupling. It's housed in a plastic tray affixed snugly into the recess at the back of the speaker, with leads and plugs already attached to feed the drivers, and undoubtedly benefits from being kept clear of internal box vibrations and driver magnetic fields.
A single 4mm socket pair is then set into the crossover case, in an arrangement likely to alienate a good portion of the audiophile community. Naim encourages the use of its own (inexpensive) cable and plugs, precisely specifying the plugs' plating (not gold) and training its dealers to terminate the leads properly.
John Atkinson will discuss the measurements in much more detail in his Sidebar, but my simple farfield, in-room averaging technique revealed some obvious traits that were directly reflected in the perceived sound balance. In my room (14' by 18' by 8.5', solid brick walls, suspended floor and ceiling), the NBL's bass (ie, below 500Hz) was unusually smooth, even, and well-extended, with an average sensitivity of around 89dB/W/m. But it was also a little on the light side, which might be more obvious in larger, more absorbent spaces. The most obvious acoustic characteristic was that the 600Hz-1.2kHz octave was 3-4dB stronger than the lower frequencies and was therefore bound to sound exposed. The presence band (1.5-4kHz) was depressed by a couple of dB, while the treble proper peaked a little at around 5kHz. The net result was an overall in-room balance that held within fine ±5dB limits across the band, but that was lean in the bass, and decidedly forward and rather uneven in the mid and treble.
Although the active version of the NBL promises better dynamic range, as well as potentially useful greater flexibility in setting the gross overall balance, even in passive form this proved an astonishingly good loudspeaker in many respects, most notably its wonderfully wide dynamic range and a remarkable freedom from "boxy" effects.