Mårten Design Coltrane loudspeaker
The Coltrane is the company's "statement" product, and at $50,000/pair, you expect more than a short riff improvised on a familiar theme. Olofsson went for top-of-the-line German Accuton drivers (known as Thiel and Partners elsewhere in the world, but not in the US because of Thiel Audio), including a custom version of Accuton's ultra-expensive, ¾", diamond-diaphragm inverted-dome tweeter, similar to the one used in Avalon's Eidolon Diamond loudspeaker.
How expensive is "ultra-expensive"? For the diamond-tweeter option, Avalon adds $10,000 to the price of the standard Eidolon. Making the synthetic-diamond diaphragm requires a great deal of heat and pressure and a heap of engineering expertise. It's not easy to do, but the resulting stiffness, low mass, and ability to channel heat yield many measured benefits, not least of which is the raising of the tweeter's resonant frequency to well above the audioband.
As this review was being prepared, B&W announced its own diamond tweeter. Press-conference attendees were shown some impressive measurements demonstrating that, while the resonant frequency of B&W's previous best metal-dome tweeter was also out of the audible bandwidth, the rise to the inevitable peak began within it. With diamond offering a much higher-frequency dome resonance than metal, the new tweeter's response appeared to be remarkably flat to well beyond 20kHz; I trust Accuton's will show similarly good behavior. For around $10,000 at retail, it had better!
The Coltrane's midrange driver is a 4" concave ceramic cone made by Accuton to Mårten's specifications. Generating the bottom octaves are two off-the-shelf 9" ceramic cones, also by Accuton.
Adding to the Coltrane's expense is its enclosure, made of carbon fiber and honeycombed Kevlar laminate by a Swedish company that supplies composite structures to the aeronautical and marine industries, and whose owner is an audiophile. A one-piece mold containing two carbon-fiber shells sandwiching a 1"-thick insert of honeycombed Kevlar is baked at 300º in a vacuum oven to produce a curvaceous, lightweight, ultrarigid enclosure weighing about 22 lbs—Mårten goes for stiff and light as opposed to dense and damped. Internal bracing and a downward-firing 4" port are also incorporated into the molding process. The speaker's integrated structure allows the front baffle—made of viscoelastic, constrained-layer-damped, 2"-thick hardwood and MDF—to be bolted securely to the enclosure in three places. The midrange driver is housed in a subenclosure attached to the front baffle but isolated from the composite structure, which is heavily damped with an asphalt-like material.
Given the enclosure's relatively low mass, I asked Leif Mårten Olofsson about its resonant frequency, which I suspected was in the midband. He confirmed that it was around 1kHz, but added that this was easily damped out by the Coltrane's extremely narrow Q factor. I'm as curious as you are to see what John Atkinson's accelerometer measurements show.
Crossover points at 300Hz and 4kHz ensure that fundamental frequencies generated by musical instruments and voices fall comfortably within the midrange driver's passband and away from the driver transition points. The crossover itself features point-to-point wiring, its components secured using a vibration-reducing viscoelastic adhesive. The crossover is inside the speaker, behind the port and close to the two sets of WBT binding posts, to which it is connected using internal cables by Jorma Design, also of Sweden. Mårten recommends biwiring the Coltranes with Jorma cables.
A pair of heavy, polished steel crossbraces fitted with Black Diamond Racing cones support the enclosure and, with the addition of four Black Diamond Racing pucks, provide sufficient clearance for the port's optimal performance.
In short, there's nothing mysterious going on here: just ultra-high-quality drivers and careful attention paid to enclosure construction, with an emphasis on rigidity and vibration control, plus computer-aided crossover design and execution. Like any other modern speaker designer who relies on computer programs such as DRA Labs' MLSSA, Olofsson's ears remain the final arbiters. The designer claims that the Coltrane's frequency response is 20Hz–100kHz, –3dB, with the port tuned to 23Hz, though the specs on the Mårten Design website claim ±2dB with the port tuned to 19Hz.
Despite its price and its promise of ultrahigh performance, the Coltrane is surprisingly compact—not much bigger than my reference Wilson Audio WATT/Puppy 7s—and lacks sex appeal when compared with, say, the stunning-looking Sonus Faber Stradivari Homage. But then, most speakers lose out in that comparison. With its grooved wooden front baffle (available in maple, cherry, oak, or walnut), the Coltrane has an appealingly Scandinavian look. Still, after first reminding me of a sauna door, the baffle's shape then brought a surfboard to mind. Many observers see a resemblance to the Kharma speaker line. Between the carbon-colored enclosure, the grooved baffle, the black-and-white ceramic drivers, and the aluminum cross braces, the Coltrane sends a mixed visual message that some visitors to my listening room found attractive and others didn't.
The Coltranes fit comfortably in my room, where I first placed them on the masking-tape outlines of the WATT/Puppy 7s' positions—not far from the masking-tape outlines used for the just-departed Sonus Faber Stradivaris and Krell Resolution 1s (reviewed in, respectively, the January 2005 and November 2004 issues of Stereophile). Initially, I toed-in the Mårtens so that their tweeter axes crossed just behind my listening position. A multiposition switch next to the speaker terminals allows ±2dB of adjustability, in 0.5dB increments, in the usual "room bump" (or dip) region of 40–80Hz.
So positioned, the Coltranes were a sonic slap in the face compared to the easy-fit, Dockers-like performance of the Stradivari or the Krell Resolution 1. If those speakers were about delivering big, velvety pictures or—to make an automotive analogy—soft, luxurious, shock-absorbing rides, the Coltranes were more forward and about detail, powers of ultra-resolution, and the exhilarating, tightly sprung, road-hugging, steering-wheel-communicating handling of a European sports car.
The Coltranes drew a tighter, more compact picture than either the Sonus Fabers or the Krells, but one with astonishingly sharp focus and weighty image solidity. While those two speakers sounded slightly warm and tended to cushion images in velvet, the Coltrane tended to carve away adjacent space, leaving images free to float in dramatic three-dimensional relief. The Coltrane's musical grip was firm and well-controlled from the midband up, and while it didn't sound etchy or bright, the presentation was revealing of every flaw that preceded it in the recording and reproducing chains. If there was tape hiss, the Coltrane let me know about it. That was fine with me, but the lack of midbass weight wasn't. It produced somewhat skeletal pictures of heads without bodies, orchestras sans venues.
As originally set up, the Coltrane presented a lightweight picture exacerbated by the tweeter's near-infinite high-frequency extension. Getting the speaker to sound good was relatively easy, but getting it to sing for its $50,000 supper was another matter. That's not meant as criticism—any ultra-hi-rez, high-performance speaker will demand an equal amount of attention paid to precise placement and careful choice of associated gear.
Getting the Coltranes in proper tonal and spatial balance required a combination of tiny changes in the speakers' distances from the front and side walls, as well as tweaking their 40–80Hz switch positions. Toe-in was also critical in balancing the tweeters' contribution to the overall picture. While getting the bass locked in lessened the diamond tweeter's overbearing personality, I had to toe the speakers out more than usual (the tweeter axes now crossed farther behind my listening position) to both open the soundstage dimensions and create a smooth, sweet, but still wide-open high-frequency presentation.
One final change was necessary to lock in the Coltrane's sound: using Mårten's cable of choice, the Jorma Design #1. I've used Harmonic Technology's combination of Magic Woofer and Tweeter cables for all of my recent speaker reviews, and have found their performance to be basically "out of the way"; the Harmonic Techs properly expressed the relative warmth and opulence of both the Krell Resolution 1 and the Sonus Faber Stradivari.
Yet when I'd optimized the Coltranes to the best of my abilities, I still found the sound a bit bright and spotlit on top, slightly lean on bottom. The issue wasn't one of "personality"—every speaker's got one—but of balance. A speaker shouldn't impose an imprint on every piece of music it reproduces, or at least it shouldn't be noticeable over time.
Because both Olofsson and his US distributor, Sound Advice, pushed the Jorma Design cables on me and I'd refused the offer—wanna see a room's worth of cables?—I felt I owed it to them to at least try their recommendation, which anyway is what the speakers are wired with internally. The biwired pair of WBT spade lugs protruding from the Jorma Design #1's cylindrical termination housing are marked Highs and Lows; I don't know if some kind of filtering is taking place, but with the Jormas in place, the Coltranes, which had already sounded impressive if somewhat brittle on top and lacking body below, cohered as they hadn't before. The top end, still ultra-extended and detailed, was now transparent and silky-smooth, the midbass more pronounced and fleshed-out, the bass fuller and more tactile. Given the Harmonic Tech cables' outstanding performance in all of the aforementioned parameters, their lack of synergy with the Coltranes remains a puzzle.