Superficially similar to the Lowther, with their cream paper composite cone/whizzer construction, the BD4B (AX) was specially adapted for the AXjet Pro, using a polycarbonate central ‘point’. But what makes the AXjet horn topology unique is the Afterburner, a spun aluminium ‘bucket’ that fits into the throat of the forward firing horn. Carefully profiled front and back, it mates with the driver basket and the driver’s central ‘point’ to produce a geometrically and volumetrically identical cavity on either side of the drive unit, thus creating a truly balanced arrangement, equally loading front and rear. In the centre of the Afterburner there is a polished polycarbonate treble horn to extend and augment the high-frequency output up to 20kHz, without the characteristic honking or hot-spots that afflicted the Lowther drivers.
The bass driver, mounted in the upper face of the low-frequency horn deserves special mention. An addition to the original AXsuperjet design, this is no simple sub-woofer hung on the end of a Low-pass filter. Theis is a ‘tapped’ arrangement, where the driver’s rear wave is transmitted via a pair of quarter-wave, exponential tubes to interface with the low-frequency horn’s output, an arrangement that helps significantly when it comes to integration. Compare the ‘tub’ of the AXsuperjet in the pictures to the AXjet Pro and you can see the humped contours of those bass tubes wrapped around the rear horn. The low-profile 250mm aluminium cone employs a special shallow magnet assembly and is driven by an internal Class D amp, delivering output down to 30Hz, with user adjustable output level, low-pass setting and phase controls, although the latter is largely redundant as the horn length from driver rear to mouth is identical for both the AER and the bass unit. Certainly, there was no musical benefit to be had in adjusting it in my situation. It allowed you to dial in depth and space – but at the expense of timing and pace. That’s not a trade-off I’m prepared to make, as it undermines the speakers’ expressive integrity in the name of presentational manipulation.
Easy Driver…
System sensitivity is an impressive 106dB from a relatively compact enclosure, with a 6Ω nominal load – however, like all speakers that divest themselves of the electrical indignities imposed by passive crossovers, the AXjet has a friendly face to show almost any amplifier. I used the speakers with the CH Precision A1.5 (a surprising and surprisingly successful pairing), the TEAD Linear A and the diminutive Icon Audio Stereo 20 – all of 10Watts/side from a pair of push-pull EL84s. Which raises another important point when it comes to the thinking behind the AXjet Pros. Hang this speaker on the end of the full GPA/Wadax/CH set up that I use more often than not and it is completely, impressively, spectacularly at home. But you don’t need to throw electronics costing in the high six-figure range at these speakers. You can run them on the end of a basic streaming set up and a modestly priced and powered amp. Pay attention to the fundamentals and the results will likely astonish and delight in equal measure.
