Loudspeakers

In this era of DSP room correction systems, surprisingly few loudspeaker manufacturers seem to be looking at the issue of room interaction from the speaker design angle, trying to find ways to quell the room’s influence and thus, potentially, render DSP assistance redundant. Danish company Dali is an exception, although to look at the Helicon 400 Mk2 you could be forgiven for thinking that it is an entirely conventional direct-radiating floorstander.
   The giveaway, although its significance may not be immediately obvious, is the trademark Dali twin tweeter module which combines a 25mm soft-dome unit with a leaf supertweeter whose diaphragm is 10mm wide by 55mm high. Supertweeters are normally deployed these days to extend response out to low ultrasonic frequencies but the Dali supertweeter also has an important function within the audible range, where it takes over from the dome tweeter at 13kHz. Key to this role is its tall but narrow aspect ratio, which endows it with better extreme treble off-axis dispersion than the dome unit. This is important because Dali speakers are not designed to be toed-in towards the listening position: rather, Dali intends them to be aligned parallel, firing straight down the room.

ON REFLECTION
What this has to do with room acoustics becomes apparent when you consider its effect on the lateral early reflection from the nearest side wall. With a toed-in speaker, the direct sound to the listener is the speaker’s on-axis output, whereas the first reflection arrives from a large angle off-axis. Because most speakers have frequency dependent sound dispersion, there is consequently a large spectral disparity between the direct and reflected sound.
   I’ve been trying to persuade readers for over 20 years that this is bad thing, and recently Siegfried Linkwitz (famous for the Linkwitz-Riley crossover alignment) has formed the same opinion. Dali obviously thinks likewise because its recommended speaker alignment is specifically intended to arrange for the direct and reflected sound to come from similar angles off-axis, so reducing the spectral differences between them.
   Of course, you can position any speaker this way and benefit from the bigger sound – spatially and dynamically – that results. But unless a speaker is designed to be used in this fashion you will typically experience reduced upper midrange and extreme treble output, which can rob the sound of impact and detail.
   In other respects the Helicon 400 Mk2 is indeed fairly conventional, although distinctively styled with its large, gently curved side panels, well finished in a high gloss cherry or rosenut veneer and solidly constructed. Apart from the twin tweeters there are two other drivers: identical 6.5in reflex-loaded bass-mid units which work in parallel below 700Hz. Above that frequency the lower unit is rolled off, leaving the upper driver to continue to the 3kHz crossover to the dome tweeter. A split crossover allows bi-wiring or bi-amping, the bottom pair of terminals driving the two bass-mid units and the upper pair the twin tweeter module.
   Meanwhile, M10 spikes are provided which screw into tapped inserts in the cabinet plinth but these are ineffective on thick carpet because their wide cone angle prevents them penetrating to the floor beneath – a nonsense that Dali would do well to correct.

BROAD AND BALANCED
For the listening I drove the Helicons bi-amped from four Exposure XVIII Mono power amplifiers and bi-wired from a Musical Fidelity A5cr power amplifier, using a DACT stepped attenuator passive preamp for volume adjustment in both cases.
   From the outset the revised Helicon 400 (I never heard its predecessor) struck me as a well-balanced performer, comfortably reproducing a broad range of musical styles. For a start, it has – when positioned as Dali recommends – a pretty neutral tonal balance, without the get-you-noticed upper-mid/lower treble forwardness that I experienced recently from the smaller, cheaper Ikon 2. The Helicon occupies a quite different sector of the market and behaves accordingly.
   This was evident when, in a fit of nostalgia, I put on the CD of the digitally remastered ‘One Night in Paris’ by 10cc. Whoever did this remastering sure likes hot treble, to the extent that this track can be unbearable on speakers with any high-frequency emphasis or grittiness. The Helicon didn’t disguise the blatant overcooking of cymbal sounds but held it in check while separating the many strands of this early example of rock operetta.
   What’s more, there was no evidence of a lack of bass weight, despite the modest measured bass extension. Low frequencies were full and well controlled, something I confirmed with quick bursts of Burlap To Cashmere’s ‘Digee Dime’ and Brian Bromberg’s The Saga of Harrison Crabfeathers.

SWITCHING TO CLASSICAL
It was on classical music that I really got to grips with what the Helicon does well – and where its shortcomings lie. I dug out two of the recordings I often turn to for insight into how products image and how effectively they resolve the minutiae that make all the difference between a living, breathing performance and a cardboard cut-out: the Weber Clarinet Quintet, with Musical Fidelity’s Antony Michaelson the soloist, and Classic Records’ 24/96 remastering of the Rachmaninov Symphonic Dances conducted by Johanos.
   On the Weber I hope to hear a wide, deep, natural soundstage with the clarinet to the right of centre sounding airy, dynamically unconstrained and not too shouty in its upper range, where this recording always sounds a little edgy. As far as imaging was concerned, the Helicon delivered. Strong, full-spectrum side wall reflections usually generate a wide, deep image and that was the case here, the Helicon maintaining depth perspective to the edges of the soundstage, where many speakers foreshorten it. It also did a fine job of preventing the clarinet becoming overly harsh.
   Yet the overall sound was less well etched than I’m used to, and that’s a characteristic you have to be comfortable with if the Helicon is to win a place in your affections. I felt it didn’t quite tell me enough about the playing to grab and hold my attention.
   There’s some odd imaging on the Rachmaninov but, in compensation, it conveys the full spectrum of orchestral tonal colour with a rare vividness and, on the right system, has a dynamic punch that has me tensing and twitching as if I were watching a rugby international. Again the Helicon did a good job of conveying the spatial scale of the piece but the
micro- and macro-dynamics of the playing weren’t conveyed as explicitly as I’d hoped – and my listening chair escaped a mauling.

VERDICT
The revised Helicon delivers a neutral tonal balance without exaggerations that become annoying or emphasise recording foibles. Coupled with large-scale imaging, this makes it easy to live with across a broad range of recordings. But those who place resolving power above all may find it lacks the insightfulness they crave.

Originally published in the March 2008 edition