This review page is supported in part by the sponsors whose ad banners are displayed below

Sven Boenicke: "Frederik Ahlm is a very smart young designer who asked me to help him with his graduation project. It was to be a speaker so we made the Björn together. The basic concept was mine, he did all the fine work. It spread so quickly on Facebook that after 4 days he got job offers from design bureaus!"

"Pity you couldn't make it. It was literally the first time I had much better sound at a show than at home. You'll agree that means a lot. I think you would have loved it deeply. As for the tweeter, that's a gold-anodized 25mm Titanium Supravox TG1 with just the right type of 95dB sensitivity and ultra-smooth response I needed. The suspended widebander is another Supravox. It's their 165GMF unit with 1.4 Tesla field strength, 35 watts power handling, 64Hz self resonance and my own phase plug. The special suspension I designed for it works great. You just can't hear the box even though it's so big. That suspension works by seating the widebander inside an 11-ply wood cylinder which is demarcated by the aluminum ring. If you undo its 16 outer bolts the entire assembly slips out. The inner bolts affix the leather suspension between driver and ring. On the other end of the driver I have a string suspension on the magnet. It looks a bit like five spokes of a wheel. These spokes support the motor inside the cylinder which opens into a chamber accessible from the rear with a magnetically secured latch. Here you can remove the fiber fill bundle to alter midband damping depending on your amplifier of choice.


Widebander inside Plywood cylinder facing chamber to trap door, bundled fiber fill removed for photo.

"All inside walls are lined with either a rubbery 5mm composite layer or a porous cross-cut cardboard with thousands of fine air cavities for rear-wave exhaustion.

"I'm bringing in the main tweeter at a low 2.000Hz. This avoids having the widebander beam too much. The protruding tweeter mount is for physical time alignment of course. There's no resistor on the TG1—its published 98dB spec is really a full 3dB lower—but the widebander gets padded down with an Audio Consulting step-down transformer for output matching. I angled the midrange unit up to give it a bit less directivity and a slightly more 'omni' aspect. This creates more soundstage depth particularly if you sit closer as many folks will at home.

Frequency response of Supravox 165GMF.

Step response of Supravox 165GMF.
"The rear-firing ambiance tweeter comes in above 7.000kHz and is off-centered to create unequal edge distances. The sidefiring hard-hung 12-inch woofer loads into the entire solid Ash enclosure. Its internal cavity tunnels around the inset midrange tube to also utilize the air space behind the tweeter for the bass driver which then vents out the back through a massive slot beneath the binding posts.


Deep inside the bass slot showing thick cardboard lining and cotton-sleeved hookup wiring.
"The side walls are 15mm and 10mm respectively (the thicker wall is on the woofer side). This creates nicely asymmetrical resonance modes. In strategic spots between the side walls I've then installed three transverse solid 5kg/ea. lead barrels. These absorb remaining resonance modes for a really very quiet cabinet you can't hear.


Mundorf Zero-ohm coil
  "The 4-driver three-way W20—this replaces my former W20-SE model—is obviously centered on a high-efficiency paper-cone widebander. Even so the latter isn't used full-range to optimize its performance and bandwidth. At the edges of its desired pass band I augment it with two tweeters (one main, one ambient) and a woofer which fronts quite substantial inner air volume. Even so this speaker only uses five crossover components. There's a Duelund paper-in-oil cast capacitor on the tweeter; a 0.68uF Obbligato foil capacitor on the SB Acoustics SB29 rear-firing tweeter; a Mundorf copper-foil coil and Audio Consulting step-down transformer on the midrange; and a Mundorf Zero-ohm Feron-based coil on the bass driver (an Eighteen Sound 12" paper cone woofer with pleated surround). As for tuning there's a special sound-enhancing series module on one tweeter leg. I also use David's Black Wonder acoustic phase linearization device, Steinmusic speaker matches, Steinmusic e-pads, the latest generation Bybee quantum purifiers, WBT NextGen terminals and my on on.high cable for internal wiring."


W20 next to my B10 for size comparison.
Enlarge!