Jumpin'. Until Sean goes live, I ought to spell out personal questions. In the past Sean had been firm. His so-called Griewe loading doesn't behave like classic ports. Yet John Atkinson's Stereophile measurements had shown a textbook saddle response. That meant two high impedance spikes around the tuning frequency to behave like ports. Combined with Zu's earlier penchant for 16Ω speakers, this reflected in unusually high resistive swings in music's most power-demanding region. Particularly with transistor amps it meant compromised power transfer in the bass. That was likely cause for the long journeys past Zu owners made to identify their perfect amp. To illustrate what makes Soul VI less fussy, I asked Sean for an impedance plot.
My own Zu exposure centers on various Druid incarnations. Their tall mid/woofer-above-tweeter layout naturally casts a high stage. Performers stand not sit. With the coax center far lower, would stage perspective follow, subjective airiness and sheen dim? The tweeter of our Audio Physic Codex sits 105cm off the floor, the bipole horn tweeter of Aurai's Lieutenant 108cm. Off axis, tweeters attenuate rapidly. Larger drivers like Zu's signature widebander asked to play unusually high beam as well though the whizzer creates a counter transition.
Doesn't this whizzer cone look like a steep (vibrating!) quasi horn for the tweeter?
Sean's finger ports are small floor vents without preceding port tubes. They rely on spike clearance to breathe as intended. The widebander's rear wave sees the floor through them. The gap between cabinet bottom and floor determines the reflected acoustic impedance. A short gap raises it and with it, driver cone damping and control. A taller gap lowers it and with it, ups the driver's bass power. Should Soul VI image relatively low, was it allowable to build in rake with taller front and lower rear spikes? That would angle the driver more at the listener. Finally, during the Druid VI reveal, much had been made of Zu's ongoing R&D into nano treatments for their favored paper-pulp cone. How much nano tech factors in the Soul VI widebander? Such coatings aren't visible to the naked eye after all. As you can tell, I had questions. Time for Sean to put them to rest.
But first, one final bit of good review housekeeping. Sean's video kicked off with tone. It then covered more efficient transfer of input amp power to output acoustic energy so less loss in physical driver motion and heat sunk into the voice coil. Hello higher sensitivity. It also mentioned lower group delay. That neatly extrapolates his design focus. It leaves us free to disagree; or flock like a moth to light. Either way expectations set clearly on what Soul VI goes after. Its holy trinity is tone, timing and dynamic expression.
Bits of Soul VI cabinetry
If your focus differs, blip off. This speaker isn't about making everyone happy. It's about making those happy who agree with its premise. If Sean Casey judged that right, it could suit a lot of listeners. For a reminder of Soul VI's roots, there's John Darko's 2013 review of the $3'500/pr MkII precursor. So today's isn't a story from zero to hero in 3 seconds. It's a tale going from II to VI after a solid eight years. But then 8 minus 2 equals 6. For other math of 21-inch woofers and 20'000-watt amplifiers, there's a Steve Guttenberg interview with Sean.
"Shipping for regular finishes with three weeks of burn-in (you really want three weeks but standard is two) is a month out. Custom finishes if you go crazy add an extra month." Again, I just asked for the standard teal over Okoume finish to take good photographs in our settings. Here's more on Sean's headspace before we get to his thinking on Soul VI.
"Right on, looks like a great start, thanks. We're doing your set with 'filled grain' to make grain and candy color pop. As it's still satin not gloss, it's easy to photograph with no hard glare. Your set hit burn-in Friday. On Soul Six two weeks are mandatory. I want to put three on yours. I'll hit you back in 10 hours with a response to your previous questions." I added another. Sean often calls out the abysmally low power conversion efficiency of modern loudspeakers. A powerful flux in the magnetic gap coupled to low moving mass can improve voltage sensitivity. The Soul VI driver claims 100dB. Strategic venting in its makeup will minimize heating up the voice coil to better resist driving up impedance which lowers dynamic linearity. But without the impedance converter of a horn, how can one still improve a direct radiator's power conversion ratio? How can more amplifier signal at its voice coil turn into acoustic ear pressure rather than shed as a 95% loss of heat and ineffective motion that doesn't couple to the air? Soul VI claims some small advances in this area to 3.1% efficiency. Curious cats want to know how. Now Sean jumps into the act.