Against this bit of common sense, we have one rational counter attack. With conventional loudspeakers, directivity increases with frequency. Dispersion narrows. In popular parlance that's called beaming. Where the bass frequencies propagate omnidirectionally—in 4pi or full space—the high frequencies focus like a spot light in half space or less. This creates an imbalanced in-room power response. The more broadly radiating bass and mid frequencies benefit from reflective boundary reinforcement aka room gain, the more narrowly dispersed ones less and less so. Whilst measured anechoically at one meter, a conventional speaker might measure flat as designed, in a normally reflective room it no longer does. Now the bass frequencies are too high in output, the high ones too low. Adding a super tweeter which more or less beams like the main tweeter will add output to compensate for treble's natural loss of reflective gain. In a partial fashion, it acts a bit like a vintage tone control.


That general rationale is no bullshit argument but a well-known fact. The only speakers which are fully immune from imbalanced radiation are true omnis like mbl, German Physiks, Duevel & Co. Those are followed by bipoles and dipoles, i.e. electrostatic and planarmagnetic panels which radiate fore and aft; and conventional speakers with rear-, up- or sidefiring drivers. The epidemy of the direct-radiating omni which doesn't involve reflective lenses à la Duevel must be mbl's Radialstrahler. As a trade show regular, many people have heard and commented on the radically different presentation of their speakers. During the early days when his Cylindrical Diaphragm Tweeter still sat mohawk-style atop spun aluminium spheres to radiate a full 360°, Anthony Gallo too had an equivalent tweeter. It also produced an unusually spacious supremely airy sound not achieved by more traditional speakers.

Swapping musical chairs again, we can counter the last argument by saying that since this power-response behaviour is known, proper speaker designers will simply compensate by tailoring their tweeter response accordingly. It may measure hot anechoically but be just right in a standard room. Or—since the relative reflectivity and absorptive index of rooms remains a variable a designer can't predict—they will simply add one or more rear-firing tweeters with an attenuator to let the client fill in as needed. And many in fact clearly go this second route. Obviously a conventional dome tweeter firing backwards remains as directional as its front-firing mate; and the speaker itself becomes a pathway obstruction for some of the intended reflections off the front wall. It's not as effective and truly omni as an mbl but certainly better than nothing.


As my recent review of Elac's 4pi Plus.2 demonstrated, into this discussion we can now bring a 30-year old product which acts as an mbl-style retrofit for conventional speakers. As its name predicts, Elac's super tweeter is an omni radiator. It's a 5µm thin circular aluminium ribbon loaded into a circular waveguide. With a 2nd-order acoustical/electrical high-pass settable at 10, 12 and 15kHz plus adjustable sensitivity between 84 and 92dB in 2dB increments, it is meant to strategically restore 4pi full-space radiation in the mid and upper treble where it usually collapses. It's a bolt-on 360° Gallo CDT if you will. A few days ago I had Nagra's international sales manager and the chief architect for their HD DAC over for some informal listening. For the occasion they'd brought a Nagra MSA amplifier to make for a full front-to-back Nagra system including my personal Nagra Jazz preamplifier; and the HD DAC still in from its recent review and now due for return to their Lausanne factory. With the room and my speakers two unknown variables, it was an opportunity for them to hear their products in an unfamiliar surrounding. For me it was an opportunity to have two very experienced listeners—Matthieu is also a recording engineer whilst Philippe is Nagra's resident golden ear—comment on my setup.

Elac's shiny mushroom tweeters atop my Albedo Aptica two-ways attracted their immediate attention to stimulate multiple with/without auditions to assess their effect. Whilst Philippe instantly embraced the concept mentally because he'd experimented with a dispersion-lens upfiring ribbon super tweeter in the past, Matthieu was a bit skeptical due to the above arguments one and two. But like all veteran listeners will, both could set aside expectations pro and con, get on with sampling things for themselves—i.e. trust their own hearing—and then share their observations regardless of whether they conflicted with or reinforced their initial beliefs. Which segues fluidly into Ayre's irrational but efficacious opener.

And it was precisely in this subjective sphere of believability—of a more convincing somehow more seamless sleight of hand—that the super tweeters improved things. I've already described their exact effects in my formal review. The purpose of this Editorial isn't to repeat it but to reiterate how despite decades worth of experience and very solid engineering credentials, audio remains filled with semi inexplicable, weird but efficacious devices and effects even to true experts. Just because we don't really comprehend them; just because we can more easily find reasons against rather than for them; they're there to enhance our experience if we approach them with curiosity and openness. So what if our eventual fallback must be that yes, we do find such devices weird precisely because according to our understanding, they shouldn't work or worse, produce ill effects but in actuality, work demonstrably and only in the positive? If our hifi pursuit really is about personal satisfaction, not what others think about our choices or tastes, then the embrace of the irrational but efficacious must become part of our comfort zone. With its 30-year availability in various incarnations of ongoing improvements, Elac's 4pi Plus.2 has shown surprising longevity. This same extended term also explains why it's ancient news, hence no longer news at all. It requires deliberate seeking out to revive and undust from the shelves of memory even though it is a perfectly current production item.


For today, I'd simply suggest that for those with otherwise dialled and mature systems, this device could prove very well worth the effort of seeking out. Having two sets of 'pro ears' confirm my own assessment actually prompted this piece. Or as Matthieu Latour put it only exasperated in jest: "Each time I visit you, I gotta go spend money afterwards." Obviously nobody has to do anything when it comes to hifi. The effects of this super tweeter are simply quite addictive. It's also a similar completion albeit on the opposite end of the bandwidth where an infrasonic sub like Zu's Submission works its magic. I'm still on my first Submission. Contributors Marja & Henk in Holland just ordered their second to do 20Hz in full stereo. Obviously these aren't things one worries about whilst the resident hifi is still under construction. Building out the extremes of the bandwidth is for much later. It's when all the other Ts have been crossed off already to one's satisfaction and ability. It's then when such additions can have a surprising impact on the degree of our emotional involvement. That they might leave our heads at a loss to comprehend why and how is simply par for this course. Is it really so much to ask to trust our own God-given pink bits and how our body responds in general? If you rely on reviews, you're in luck with the Elac. Aside from my recent one, Roy Gregory, formerly of Hifi+, has also penned one on it whilst still with that publicaiton. A quick Google search will connect you to it...