Audience Au24 SE interconnect
A recent e-mail exchange with John McDonald, the president and CEO of Audience, got me wondering if it was time to hear their latest and greatest cables. He said that the $220 upgrade from the standard Au24e to the Au24 SE ($1190/1m pair) was "three times as big as the upgrade from Au24 to Au24e" (footnote 1). I was skeptical. But on the other hand, I've followed Audience's products over the years, and have learned that when they make a change, it's a significant one.
McDonald's e-mail caught my attention for another reason. He said that the only difference between the Au24e and the Au24 SE is the latter's new RCA plug, whose center pin is made of a tellurium-copper alloythe cable itself is the same as in the Au24e.
His tellurium-copper hook was set. For a metallurgist like me, what could be more interesting than a jump in a cable's performance due to the use of a new alloy?
What makes a good electrical connector?
Pure copper and silver are excellent conductors of electricity; gold is pretty good, with an electrical conductivity about 25% lower. All three, however, lack the stiffness and strength to support enough clamping force to make a solid connection and minimize contact resistance. They're also expensive and, worst of all, very difficult to machine. On a scale of 0100, copper's machinability is about 25.
At the other end of the spectrum are brass and beryllium-copper, the materials most widely used in connectors. They're cheap, their mechanical properties are adequate, and they're much easier to machine than copper or the other noble metals. Unfortunately, their conductivity is only 2530% that of copper or silver. Plating with silver or gold over an interlayer of equally low-conductivity nickel reduces contact resistance without affecting overall conductivity, but creates severe discontinuities in electrical and magnetic properties.
C14500, the tellurium-copper alloy that Audience uses in their SE connectors, is 99.492% copper, 0.5% tellurium, and 0.008% phosphorous. The use of C14500 has become relatively common in high-end electrical connectors, and compared to the other choices, it looks awfully good: It has 93% of copper's electrical conductivity, along with mechanical properties similar to those of brass or beryllium-copper. With a machinability of 85, it's easily and inexpensively made into complex shapes. Most tellurium-copper contacts are plated with silver or gold, but without the nickel interlayer. Because there's no interlayer, and the conductivities of the plating and the underlying alloys are very similar, the discontinuities between the two are very small.
One of Audience's design goals is to minimize the creation of eddy currents, which are caused by just such physical or electrical discontinuities. The smaller electrical discontinuity between tellurium-copper and the gold or silver plating reduces the formation of eddy currents, which should lower the noise floor and improve low-level linearity, detail, and clarity.
As much as I'd like to claim that any audible improvement from Au24e to Au24 SE was due solely to metallurgical factors, I can'tbecause Audience has also changed the design of their conductor. In the Au24e, the ground connection is made by formed tabs that encircle the entire jack. In contrast, the SE connectors are similar to the Bullet Plugs from Eichmann, which use a single, small contact point for the ground connection. Although the SE plugs actually have two small contact pads, only one of them is used, so the configuration is essentially the same as in the Bullet Plug. The reasons for using a single, small contact point are to emulate a star-grounding concept andyou guessed itreduce the formation of eddy currents.
It's all about context
Not surprisingly, given my reader friend's observation, the system I used for this review is tried, true, and well understood. (See the equipment sidebar.)
Rather than my usual approach, which is to cable my entire system with the review product, I decided to instead insert a single 1m run of Au24 SE. Since the Au24e and Au24 SE interconnects are also used as Audience's Low-Z phono cable (footnote 2), I first installed the Au24 SE between my turntable and phono preamp. Later, to see how the Au24 SE worked with line-level signals, I used it between my Primare CD31 CD player and line stage. In both cases, the rest of the system was wired with Au24e. I threw other cables into the mix, but because I was most interested in the tellurium-copper plugs, I spent the bulk of my time alternating between Au24e and Au24 SE. Before installing the Au24 SEs, I burned them in for about a week using a Duo-Tech Cable Enhancer.
And in this context . . .
While the Cable Enhancer was cooking the Audience Au24 SEs, I worked through my reference cables to thoroughly refamiliarize myself with the sound of the Au24e. Ears and system dialed in, I spun Roy Orbison's Mystery Girl (LP, Virgin 91058-1). My analog system had a balanced, natural sound, with all of the things that have made the Au24e one of my reference cables: smooth and flowing, yet with enough immediacy and detail to draw me inbut with not so much of either that a hyperawareness of the sound intruded on my connection with the music.
My vinyl-playing system also passed the audiophile checklist with flying colors. The frequency response was extended and flat, the dynamic transients were large and clean, and the notes started and stopped quickly, yet flowed naturally from one to the next. All of the other, smaller things we obsess overimaging, detail, focus, transparency, etc.were excellent, and consistently reproduced across the audioband and loudness range. All good.
I installed the Au24 SEs, sat back, psyched myself up, and turned my reviewer radar up to High. I was determined to listen even more carefully to the areas that, per Audience's theory, should most benefit from the change to tellurium-copper and reduced eddy-current formation: image focus and resolution of detail. I also concentrated on detecting any electronic artifacts or textures that might be woven into the music or the open spaces when no sounds are being made by musicians.
Footnote 1: Click here for my review of the Audience Au24e in the June 2010 issue of Stereophile and here for my review of the original Au24 in the August 2002 issue.
Footnote 2: This turned out to be incorrect; see the "Follow-Up."Ed.