Gradient Helsinki 1.5 loudspeaker John Atkinson, November 2010

John Atkinson reviewed the Gradient Helsinki 1.5 in November 2010 (Vol.33 No.11)

Art Dudley reviewed the Gradient Helsinki 1.5 in August 2010 (Vol.33 No.8). This unusual floorstanding loudspeaker combines a metal-dome tweeter and a 5" paper-cone midrange, each mounted in its own subenclosure, with a side-firing 12" paper-cone woofer. There is no enclosure for the woofer, giving it a dipole radiating pattern. "The Gradient Helsinki 1.5 is a remarkable product whose execution seems to lag only slightly behind its conception—and its conception is both original and, in its way, ingenious," concluded AD.

However, Art had immense difficulty setting up the Helsinkis in his listening room. Finally, "I threw up my hands and made yet another drastic change in course, bringing the Helsinkis back against the wall, but with each speaker toed-in about 45°—their on-axis treble response now crossed well in front of the main listening seat . . . —and each placed about 30" from its respective sidewall. Each woofer faced the wall nearest it, leaving the magnets to bicker across the room. From there, the bass measured acceptably well, and sounded okay. Center fill wasn't at its best, but most instruments and voices sounded timbrally right. And every iota of the Gradients' remarkable spaciousness was back."

I couldn't travel to Art's place in upstate New York before the review was published, so it wasn't possible to measure the Gradient speaker's interactions with his room. However, as I had both review samples in my possession following their being photographed for the August issue's cover, I set them up in my own listening room.

Fig.1 Gradient Helsinki 1.5, anechoic response on optimal axis at 50", averaged across 30° horizontal window and corrected for microphone response, with nearfield responses of midrange unit (red) and woofer (blue) plotted below 300Hz and 600Hz, respectively.

Fig.1 shows the individual outputs of the woofer (blue trace) and upper-frequency section (red). The woofer's nearfield output is scaled in the ratio of its radiating diameter to that of the midrange unit. It covers the octave between 30 and 300Hz and, as AD found in his review, the integration of its output and that of the midrange unit will depend on the proximity of the listening-room walls and the angle of toe-in.

Gradient publishes two recommended setups in the Helsinki 1.5's manual. In one, both speakers are positioned against the wall behind them and fire straight ahead. This wasn't possible in my room (see photo), so I started out with the speakers in the other recommended positions: well away from the rear wall, each speaker a couple of feet from its sidewall, with its woofer facing away from the listening position, and toed in 45°. The sound was a little threadbare, so I ended up with the speakers against the sidewalls (again see photo linked to above), which brought the midbass region into balance with the upper frequencies. I then experimented with both toe-in and the distance of each speaker to the wall behind it, to get what sounded like the most neutral sound. The soundstage was very wide, however, which, even with the excellent imaging specificity and focus offered by the Helsinkis, took some getting used to. When Ginger Baker rolled round his toms in "N.S.U." (DVD, Royal Albert Hall, London May 2-3-5-6 2005, Reprise/Rhino R2 970421), the kit occupied the full width of London's Albert Hall!

Fig.2 Gradient Helsinki 1.5, spatially averaged, 1/6-octave response in JA's listening room.

Fig.2 shows the Gradients' spatially averaged response in their final positions in my room. (To generate this graph, I average twenty 1/6-octave–smoothed responses taken for each speaker individually in a vertical rectangular grid measuring 36" by 18" and centered on the positions of my ears in my listening chair. I used an Earthworks omni microphone and a Metric Halo ULN-2 FireWire audio interface, in conjunction with SMUGSoftware's Fuzzmeasure 2.0 running on my Apple laptop.) The speakers extend quite low in the bass, rolling off below 30Hz, while at the other end of the spectrum, the top-octave rolloff is a little steeper than usual in my room and there is an excess of energy at the bottom of the tweeter's passband. Though the midrange is generally flat, it doesn't quite meet the standard set by the last Gradient speaker reviewed by Stereophile, the full-range dipole Revolution (see fig.5 in its measurements).

In general, the small peaks below 300Hz are due to the effects of room modes that had not been eliminated by the spatial averaging. The broad suckout between 70 and 110Hz, however, is due to destructive interference between each speaker's front- and backwaves. The suckout was more sharply defined for each speaker individually, its frequency depending on the distance between each speaker and the wall behind it.

When I first set up the Gradient Helsinkis, with only a small amount of toe-in, the low frequencies sounded rather phasey. This was minimized by increasing the toe-in angle to 45°. Once the speakers had been moved next to the sidewalls, I was reminded that there is something very attractive about the sound of low frequencies produced by an aperiodic design—as I had found with the Gradient Revolution, which also has a dipole-mounted 12" woofer. The bass-guitar ID tracks on Editor's Choice (CD, Stereophile STPH016-2) had an appealing combination of bass articulation and fairly good low-frequency extension and weight. The low-bass synth notes on Flanger's interpretation of Miles Davis's "So What," from Midnight Sound (CD, Ntone B00004YLGQ), which reach 36Hz, were very audible, though I must admit that the speakers were being given some help from my room's 32Hz diagonal mode.

Even after I'd measured the Helsinkis' in-room response and knew about the midbass suckout, it didn't sound as if energy was missing in this region. The bass guitar on "North Dakota," from Lyle Lovett's Live in Texas (CD, Curb/MCA MCAD-11964), sounded even; and on my unreleased 1997 live recording of the Marc Copland Quartet playing "Dark Territory," the broken chords played by Austrian double-bass virtuoso Peter Herbert were evenly reproduced without any notes missing.

I listened to the Gradients before performing the in-room measurements, but it was obvious that there was both a little too much presence-region energy and not enough top-octave energy. Eric Johnson's Live in Austin (CD, New West 6084) sounded a little bright and a touch airless, though naturally recorded CDs, such as the late Lorraine Hunt Lieberson singing Peter Lieberson's Rilke Songs (CD, Bridge 9317), sounded thrillingly natural. Keith Jarrett's The Carnegie Hall Concert (CD, ECM 1989/90), for which I was in the audience, was clean and uncolored, with good left-hand weight.

So—a little dark at the top and a little bright in the low treble, but with an uncolored, natural-sounding midrange, well-focused imaging, and an attractive, resonance-free quality to its low frequencies, Gradient's Helsinki 1.5 offers basically excellent sound for a not-unreasonable price. But yes, setup is always going to be more fussy than with a conventional box speaker, and it must be said that this speaker's looks are of the love-it-or-hate-it variety. Art Dudley called it correctly: "The Helsinki 1.5 is a must-hear for anyone with a taste for hi-fi adventure, and quite possibly a must-own for anyone for whom clarity of presence can tip the scale toward ecstasy."—John Atkinson

Gradient Ltd.
US distributor: SimpliFi Audio
California Suites Apt. 1001
5415 Clairmount Mesa Blvd., San Diego, CA 92117
(724) 712-0899