John Darko
Wharfedale has this week announced a new series of loudspeakers called Aura that is intended to sit between the company’s entry-level EVO and its flagship Elysian. Aura comprises two standmounts (Aura 1 and 2), two floorstanders (Aura 3 and 4) and two centre channels (Aura C and CS).
The press release tells us that the Aura’s high gloss cabinets are slightly larger than those seen with EVO but that the drivers and crossover components are closer to those used for Elysian.
To wit, all bass and midrange drivers are made from a “proprietary woven glass fibre matrix” that’s been trickled down from Elysian. The 2-way Aura 1 comes fitted with a 13cm mid/bass unit whereas the 3-way Aura 2 lands with a 10cm midranger and a 15cm bass unit. The Aura 3 and Aura 4 each feature the same 10cm midrange driver as the Aura 2 with the Aura 3’s bottom end augmented by a pair of 13cm bass drivers and the Aura 4 extended its tinw bass drivers’ diameter to 15cm.
Like Elysian and EVO, The tweeter in all Aura models is an Air Motion Transformer (AMT). An AMT driver uses folded pleats to squeeze air forward like an accordion instead of relying on the less efficient push/pull motion of a domed unit. I hit up Aura designer Peter Comeau via email to ask “Why AMT?”. His extremely detailed reply is as follows:
“The problem of domes is that they are, in essence, pressure drivers and the dome therefore needs a fairly large diaphragm. Conversely, the diaphragm needs to be very lightweight in order to respond to very high frequencies. This makes it prone to various resonances that we hear as spitty or zingy or excessive sibilance. If we make the dome very stiff we can move some of these resonances into the ultrasonic, but we can still see reflections of these resonances at audible frequencies unfortunately. It is very difficult to keep the whole of the dome diaphragm under control with a voice coil attached to its outer circumference.”
“The AMT is a velocity driver. The diaphragm is pleated and squeezes the air between the pleats, expelling the air from each pleat at 5.3 times the velocity of the diaphragm. In total, from all the pleats, the expelled air forms the desired pressure wave with minimal distortion from the diaphragm. With careful design and use of advanced thermoplastics, we can make the pleats with a high level of stiffness and control their velocity accurately by embedding a conductive aluminium foil circuit that carries the music signal. Like any piece of advanced engineering, none of this is easy to do and the differences in materials used, linearity of magnetic flux distribution and resolving the pressure wave correctly will always mean that AMTs from different manufacturers will vary widely in their sound.”
“Coming back to our frequency response discussion, the ear is actually very insensitive to amplitude variations. It is very difficult even to detect a change in sound pressure level of 1dB, which is a 26% power difference. By contrast, the ear IS very sensitive to frequency variation – a shift in frequency caused by a violinist adding vibrato to a note is of the order of 0.5%. So, really, we should be far more critical of frequency variation – the fluttering of tones and the distortion added by extraneous tones – than we should of amplitude response. In that respect the AMT, when correctly designed, exhibits far lower frequency distortion than a dome.”
“We instituted a three-year program of development for the Wharfedale AMT and I believe that we have developed a unit that outperforms domes in its resolution of musical detail and a superior rendering of the upper harmonics of instruments.”
But the designer talk doesn’t end there. Inside all but the 2-way Aura 1, Comeau has spread the crossover over two boards to reduce electromagnetic cross-pollution. Once again, via email, Comeau explains why:
“Crossover coils are big generators of alternating magnetic fields. As such, each coil will react with other coils near it and induce signals where they are not wanted. It is easy to test this. Just disconnect the drive to the treble unit input to the crossover and play a 1kHz tone through the bass crossover. If you hear the tone from the treble unit it is because the coil(s) used in the bass circuit are inducing a signal in the coil used in the treble circuit.”
“Of course, we can reduce this by two methods. One is to physically put the coils at right angles, which moves their magnetic fields of influence away from each other. The other is to space the coils as far away from each other as possible. The latter is easier to arrange by spacing two PCBs at a distance. This is more important in a 3-way speaker where the midrange and treble coils have to be rotated and spaced away from each other, so adding a bass coil on the PCB is asking for trouble! Incidentally having the bass section on its own PCB means we can keep the copper tracks as wide as possible, and therefore of high current carrying capacity, without having them interfere with the layout of the midrange and treble circuits.”
The Wharfedale Aura series is shipping now. Pricing is as follows:
Aura 1: £1499/pair Aura 1 stands: £899/pair
Aura 2: £1999/pair Aura 2 stands: £999/pair
Aura 3: £2999/pair
Aura 4: £3999/pair
Aura CS: £1099
Aura C: £1299
Your choice of piano-lacquered black, white or walnut wood veneer.
Further information. Wharfedale
Specs…
