Media
Opal
AUSTRALIAN HI-FI October, 1998

EQUIPMENT REVIEW - Written by Greg Borrowman

Duntech Audio is the company that stamped the word 'Australia' on the world's map of high-end loudspeaker manufacturers, for which all other Australian hi-fi manufacturers should by eternally grateful. The company also assumed the high ground in terms of price in this country, with its best-known designs, such as the Sovereign, commanding sums that deterred all but the most committed audiophiles. However, unlike many of its competitors, Duntech has always refused to chase the so-called 'budget' end of the loudspeaker market, where compromises in component quality (and, therefore, sound quality) are inevitable. The Gemstone range to which the Opal belongs, is said to have been designed "to provide the most accurate sound at a more affordable price."  What sets Duntech's Opal design apart from most other speakers that sell for around the same price is the fact that Duntech pre-tests and pre-pairs all the bass/midrange drivers prior to systems being built, and then left/right pair matches after completion - not to mention the application of the various Duntech philosophies and patents...

The Equipment

This new design from Duntech is an all-Morel design, using two of Morel's MW166 double-magnet woofers. These drivers use a massive 75mm diameter aluminium voice-coil former, on which is wound hexagonally-drawn aluminium wire. Nominally rated at 8ohms, this driver is rear-vented, the vent being protected by a layer of coarse fibrous material, similar to the material used as a filter in domestic air-conditioning systems. The cone itself is made from polypropylene, which is attached to a butyl rubber roll surround. Unlike normal roll surrounds, which use a 'half-roll' configuration, the MW166 surround is so sharply pleated that it almost resembles a 'V'. Duntech has modified the mass of the driver by attaching three adhesive-backed circles or felt to the central dustcap of each driver. Although the adhesive used is like a 3M 'sticky note', so the pads can be easily removed and reattached. I wouldn't recommend you do this if you want to maintain the original performance of the loudspeakers. The chassis of the driver is made from pressed steel, but the basket is very shallow, so structural integrity is extremely high, and ringing is very low. Four star-headed bolts and captive nuts attach each bass driver to the baffle, and the driver is rebated into the baffle. Each driver is sealed with a triple rubber/felt/rubber gasket. I discovered that the fit between the driver and the cabinet is so tight that these seals are a little bit of overkill. I managed to remove the bottom-most bass/midrange driver for inspection only with the utmost difficulty, and couldn't remove the top one at all! (I don't suggest owners attempt this, even for interest's  sake, because doing so would almost certainly void the warranty!) The overall diameter of the bass driver is 160mm, buy the moving part of the driver (the cone and roll surround) is only 132mm in diameter. Actual piston diameter (from which Theile/Small parameters are derived) is 116mm. This gives an Effective Cone Area (ECA) of 105.7cm, for a system total of 211.4cm. Equating this ECA back to a single driver, that driver would have an equivalent piston diameter of 164mm and an overall diameter of around 214mm.

The tweeter is a Morel MDT-32-S, a 32mm soft-dome made with doped fabric. The rear of the tweeter appears to operate into a very small chamber formed by a plastic back-plate, but I could not remove the plastic back-plate, but I could not remove the plastic cover to determine the exact construction.The tweeter is recessed, to ensure correct time alignment with the bass/midrange drivers and, in typical Duntech fashion, the edges of the cut-out have been protected from creating early reflections by a star-shaped felt cut-out, somewhat less complex than I seem to recall seeing on some more expensive models from Duntech. As I have mentioned in previous reviews, Duntech claims this design is protected by a US Patent (No. 4,167,985) which does not seem to have deterred any number of loudspeaker manufacturers around the world from copying it.

Internal wiring is all loomed using Van den Hul M.C. CS-12 Halogen-Free cable. At the crossover, wires are terminated by silver-solder, but at the driver end, the wires are terminated in spade connectors, which slide over the driver terminals. However\ver, unlike most driver terminals, which are made of some base metal, the terminals on the Morel drivers used in the Opal are gold-plated, presumably to Duntech's specification.

The inside of the cabinet is fairly unusual. It's divided into top and bottom chambers. The top chamber is totally sealed, and contains the upper mid/woofer and the tweeter. The bottom chamber contains the crossover network and the lower of the two mid/woofers and is vented through the front baffle, through two circular bass-reflex vents. Both chambers are filled with non-allergenic open-cell foam. The ports are standard plastic types, with a heavy flare at the outer end to help reduce chuffing noises. The other (internal) end of the port, which is slightly narrower (38mm ID) than the outside opening (44mm ID) is not flared at all. Overall port length is 145mm. (At the absolute end of the flare, the port diameter is 57mm.) The cabinet is internally braced by 'B' sections of Meranti.

Duntech provides a very elegant 'Classic Series' manual with the Opal that introduces the reader to the basic Duntech philosophies, including the use of aligned path-lengths between individual drivers and the listening position (phase coherence), symmetrical radiation patterns, simulated point-source radiation, the use of first-order crossover networks with air-cored inductors and polypropylene capacitors, and minimisation of diffraction absorption by the use of sound-absorption materials on the front baffle. This is despite the fact that the Opal is part of the Duntech's 'Gemstone' series, rather that the 'Classic' series.

The manual goes into considerable detail about the difficulties of room placement, the effects room placement will have on sound quality and gives examples of placement options, room treatments and so on. It's an excellent manual. Duntech provides a form that new owners can fill in should they wish to become a member of the 'Duntech Owners Club'. Membership entitles the owner to a regular copy of the club's newsletter to a regular copy of the club's newsletter, 'Sound Down Under.'

Unlike the first Duntech loudspeakers, which were designed by John Dunleavy, the new Duntech Opal was designed by Simon Wilde. Wilde is one of Duntech's longest-serving employees. Following Dunleavy's departure from Duntech, the company has applied itself even more-rigorously to quality control and the use of state-of-the-art components. All incoming electrical components for use in crossovers, for example, are measured- capacitators, resistors and inductors - and are accepted only if they are within two percent of the original design specification. It's also nice to see that as much attention goes into the cabinet as into the design of the speakers themselves. The enclosures are made from 18mm MDF that is finished in a selection of Australian veneers - usually Jarrah or Queensland Walnut. Whatever veneer you prefer, it's hand-rubbed to give a perfect finish.

The crossover in our sample was hard-wired, and consisted of one large inductor, two Solen capacitors and two Noble wire-wound ceramic resistors. All the components are mounted on a section of MDF attached to the inside wall of the cabinet, adjacent to the terminal panel on the rear panel. The reason for this handy positioning became evident when  I peered in - there's a tiny two-position microswitch mounted to the bottom edge of the board with positions for 3.3F and 2.7F. After looking through the manual in vain to see the purpose of this switch, I finally contacted Duntech, only to be informed that I had received one of the early production pairs that had been used for final crossover tweaking prior to full production and that full production models did not have this switch fitted. (According to designer Simon Wilde, the switch was "an adjustment to tailor the bandwidth and directivity of the tweeter to study the effects of room boundary interaction.")

It is also possible to access the crossover by removing the base plate of the speaker (which also forms the plinth). Do this, and you'll find that in order to improve the stability of this rather tall and narrow design, Duntech has attached four layers of lead sheet to the inside of the base. Although this works, tipping the speaker 220mm sideways is sufficient to cause it to topple. In a forward direction, this distance increases to 300mm.

The rear-panel terminal plate is a conventional plastic moulding, with two sets of gold-plated terminals that can be separated should you wish to bi-wire.

LISTENING SESSIONS

Although I had become somewhat used to the fact these speakers were narrow when examining them in my office, nothing quite prepared me for how they disappeared into the listening room when I finally got them home. The narrow profile and the light wood veneer finish lets them blend into the background - even when they're positioned a little distance out from the wall.

I found the Duntechs were not fussy about positioning, giving good results almost everywhere I tried, except the usual no-no's, such as corners, or with their backs pressed right up against the wall. I did, however, find that I definitely preferred both tweeters to be aimed directly at the listening position and that the optimum listening position was exactly 3.2metres from a baseline drawn between the two speakers. At this listening distance, I also preferred the rear spikes to be set 2mm lower than the front spikes.

After I have established a feel for a speaker, I generally look for a single word that can sum up the speakers' performance, or their greatest strength. With the Opals, I decided that that word would have to be 'melodious'. I was impressed  by the overall performance - the bass, the midrange, the treble - but what stuck in my mind were the way melodies sang through the music when I listened to the Opals. It's particularly interesting when listening to more subtle melodies, such as those Robert Schumann was fond of, for example, which are made more difficult to hear by the way they wander from treble to bass clef, and meander in between. Listening to the Opals, I could hear Schumann's beautiful melodies tripping through the surrounding notes, always perfectly in balance with the surrounding harmonies. Mindful of the fact that so-called classical music is a minority interest these days, I had to make absolutely certain the melodic nature of the Opals' performance was not constrained to this one genre. It wasn't Fed an eclectic diet of music ranging from rap, hip-hop, heavy metal, and hard rock right through to country, bluegrass, blues and jazz, the Duntechs' essential character remained truly melodic. This was accompanied by a sense of 'easy' listening, where there was never any sense of the listener having to work to hear what was going on. The Opals are truly musical creations.

Given that  I had decided on the word melodious, I have to point out that it was a toss-up whether imaging would get a gong instead, because the imaging of the Duntech Opals is in a class of its own. I suspect this is something of a combination between the handmade Morel drivers used in the Opals and Duntech's own factory procedures, but whatever it is  - and whoever is responsible for it - it works, because the stereo imaging of these speakers is fabulous. One example of how good it is, is that when listening to Holly Cole, I didn't only hear her voice perfectly positioned in the mix, but could also tell she was clicking her fingers of her right hand, 40cm away, and hear as she raised and lowered it. And it isn't only just the left/right imaging, we're talking the whole box and dice here, with full floor-ceiling height and depths approaching that of a live stage.

Deep bass is very good. Listening to Larry Melton's bass on Time Is A Healer (from Eva Cassidy's Songbird) it was so easy and effortless to follow the bass patterns that I was never once lost, or lost that eerie sense of knowing in advance where  the music was coming from, and going to. On the minus side, the bass is so very revealing that the drum programming on this track was also rather cruelly exposed for what it was - second rate. I decided to give the bass a real workout with GVSB's 'Freak on ICA' at terrifyingly high volume. No problem. The Opals handled Black Hole, Pleasurized, and One Firecracker as if there were born to highpower grunge. I was a little worried that the extremely high-power synthesised 'noises' on this disc might cook the drivers, but I need not have worried, because they didn't even compress after multiple back-to-back high volume listening sessions.

I auditioned the greater part of the midrange mostly with music, most particularly solo piano in jazz trios and with both male and female vocals, but I also used a test CD recording of an 88 note piano run and a BBC radio play (Under Milkwood). The  Duntech Opals proved to be superbly accurate, with excellent control over level and a great ability to retain harmonics, such that it's easy to hear an opened string on a piano resonate when another key is struck - something that's very obvious or Kevin Hunt's jazz version of J.S.Bach (ABC Jazz). But the clarity of the midrange is also evident even on such technically less-than-perfect discs as the soundtrack to Fear and Loathing in Las Vegas, which contains a lot of (often less than salubrious dialogue, but also some great music, vis For Your Love, White Rabbit, Stuck Inside a Mobile with Memphis Blues Again, Time is Tight - but I guess you had to be there (and it probably helped if your ears were chemically enhanced). The Opals caught Tracy Chapman's hard-edged voice perfectly - many speakers tend to take the hardness off, negating that perfectly real voice (I listened to The Thrill is Gone, but any Chapman track would serve as well.)

The tweeter was very pure, with a transparent crystalline sound and not a trace of harshness. Again, the tweeter was so clean that it could be cruelly revealing at times. Listening to the title track from 'Songbird', for example, you could hear the phase errors and dissonance's that result from Cassidy multitracking her own background vocals. But listening to Barbara Morrison sing the blues on 'I Know How To Do It' (Larrikin), I could hear every subtle nuance of her unique voice...great stuff...I don't think Don't Explain has been done as well since Billi's original version. (John Merola's brushed cymbals on this track are a treat, by the way.) The extended treble of the tweeter, however, means that listening to older re-masters, such as Jimi Hendrix's BBC Sessions (MCA) means enduring spectrally pure white noise at irritatingly high levels (the intro to Day Tripper is almost all tape hiss, for example, but how you could be without a track like Driving South, hiss 'n all?)

But in the end, irrespective of how I analysed the sound of the Opals, I always came back to that word melodious, as if the speakers were trying to tell me something, so I finally forgot about the analysis, and just settled back to enjoy the music.

Conclusion

An impeccable pedigree, a pure and realistic sound quality and attractively styled. Duntech's Opal is indeed a gem!

Fig 1 Pink noise frequency response on/off axis (30) measured at 1metre 2.83-V input

Fig 2 Gated sine response on-axis (solid) : 30 off-axis horizontal (dotted) : 45 off-axis horizontal (dashed)
Fig 3 Gated sine response on-axis (solid) : 30 above vertical axis (dot-dash) : 30 below vertical axis (dashed) Fig 4 Near-field bass response showing woofer (solid line) and port (dashed line) [Note that the output of the port has not been compensated for area]
Fig 5 Impedance vs. Frequency Fig 6 Nearfield woofer response and gated on-axis sine response plotted on the same graph (see copy)