“The allure of single drivers is enticing as it can do things no other speaker can attempt: perfect impulse response, time and phase correct, single point source imaging, filterless connection to the voice coil, extreme efficiency.”
So says Birch Acoustics’ website, and I agree. But single-driver speakers can have some less appealing characteristics, too: restricted frequency extension, limited power handling, and a need for horn or other enclosure designs that try to circumvent the driver’s limits. Still, I’ve found wonderfully appealing the directness of sound from a speaker whose single driver is connected directly to the amplifier without any intervening crossover network, and so have pursued several such speakers. All of these have had significant drawbacks that I’ve had to live with or try to minimize. For me, their attractions have outweighed their drawbacks, but I realize that others won’t be willing to live with their shortfalls.
Birch Acoustics’ Raven ($7500 USD per pair) isn’t really a single-driver loudspeaker -- each cabinet has four 5” paper cones. However, all of these are driven full range; there is no tweeter, and therefore no crossover. Birch gets its name from the fact that their enclosures are made of birch plywood. It looks as if they take sheets of birch plywood, cut out many cross sections of the cabinet’s desired inner and outer shapes, then glue a stack of these slices together until the desired height is created -- in the case of the Raven, 42" (by 9"W by 11.5"D). The completed speaker weighs only 35 pounds, a real lightweight compared to the massive designs from Magico and Wilson Audio Specialties. The polished enclosure sides reminded me of early Magico speakers, before they abandoned wood for aluminum. I thought the Ravens looked quite handsome, and so did several visitors to my listening room.
Birch Acoustics makes every part of the enclosure from wood: the crossbar footer in front, the end of each foot, the dowel that extends to the rear of the footer to support the rear of the enclosure -- even the terminal that holds the speaker wire. Only the ribbon conductor that connects the terminal to the speakers is metal. The terminal block looks a little like Cardas’s patented binding posts, but has a wooden clamp to hold the speaker wires, which must either be bare wires or terminated with spade lugs. There’s a port in the cabinet’s bottom panel; its opening depends on how high the speaker’s feet raise its bottom front edge above the floor.
Birch specifies the Raven’s frequency response as 40Hz-20kHz -- quite respectable, if not suitable for playing pipe-organ recordings. With a claimed sensitivity of 96dB, the Raven is claimed to need only 1W of tube power or 10W of solid-state power. If this seems a bit odd, recall that some people think tube amps sound more powerful than solid-state amps of the same power rating. The Raven’s flat 8-ohm impedance should be easy for most amps to drive.
Birch sells its speakers direct to users, with a 40-day, money-back trial period. A generous five-year warranty assures you that the speakers will perform properly for a long time. If a company is going to sell direct, these are the types of customer support they should have in place, in my opinion.
Setup and use
The Raven’s light weight made it easy to move the pair of them around to try different positions. I wound up with the speakers positioned about 7’ apart, 3’ from the front wall, and at least 10’ from the sidewalls.
I was concerned that, even with the Ravens’ feet fully extended, their downfiring ports might not be raised far enough above my carpet. So I set the feet on marble floor tiles, which gave the ports adequate clearance and made the speakers more stable, and their sound a bit more open and dynamic. Still, because neither the tiles nor the speakers’ flat-bottomed feet could penetrate my carpet and pad, the Ravens weren’t firmly coupled to the floor. I’d be reluctant to use them directly on carpet.
I used Clarity Cables’ Organic speaker cables, terminated with spade lugs. Although made of copper wire, the Organic cables have a very extended claimed frequency response.
I tried three quite different amplifiers with the Birch Ravens: the First Watt J2, a 25Wpc all-JFET amp; the Octave Audio V70SE, a 70Wpc tubed integrated; and the David Berning ZH-230, a 30Wpc tubed design. All three sounded good, but the Berning proved a synergistic match with the Ravens. In particular, the ZH-230 seemed to supercharge the Ravens’ bass, adding weight and extension. All of my comments on the Ravens’ sound are based on what I heard with the Berning. The ZH-230 costs $8360; that’s not cheap, but it’s not unrealistic to consider for an amplifier to be used with $7500/pair speakers.
I listened to several sources during the review, but for critical listening I used the Auraliti PK100 music player, since it’s a repeatable source. By that, I mean that every time I play a selection it sounds exactly the same, which is essential when reviewing.
I’d been told that my review samples were already broken in, but I heard a high-frequency peak that I thought might be tamed by additional break-in. So I played the Ravens an additional 200 hours before doing any serious listening. I’m glad I did -- that HF peak smoothed out a bit. I don’t think it ever went away completely, but it became listenable.
The Ravens produced a robust, full-bodied sound, but rolled off the highest frequencies a bit. In Jennifer Warnes’s “The Panther,” from her The Well (16-bit/44.1kHz AIFF, Sin-Drome), the assorted percussion instruments that open the track produce a variety of high frequencies that sounded a smidgen rolled off through the Ravens -- not absent, just attenuated. At first I thought the bass was also slightly rolled off, but after I’d hooked up the Berning ZH-230, the Ravens lived up to their specification of extending down to 40Hz. The Berning also produced more bass detail and dynamics -- something it did throughout the entire audioband. “Folia Rodrigo Martinez,” from Jordi Savall and his group’s La Folia 1490-1701 (16/44.1 FLAC, Alia Vox), has a bass drum that extends down into the mid-20Hz range, and while the Ravens didn’t go that low, they did reproduce the drum with surprising depth and impact -- I thought at first that I’d forgotten to turn off my subwoofers. But the bass sounded just a tiny bit loose, which added to the sense of impact, if not of accuracy.
Somewhat offsetting the rolloff of the highest frequencies was an emphasis of the mid-treble, which made the sound a bit bright. I know, it sounds weird to claim that the highest frequencies were attenuated, while at the same time saying the Ravens had a high-frequency peak. But it’s just a matter of which part of the highs we’re talking about. On soprano Patricia Petibon’s Rosso (16/44.1 AIFF, Deutsche Grammophon), a collection of Italian baroque arias, her incredibly agile voice sounded just a bit hot. But the higher frequencies on The Well were slightly attenuated.
To return to that opening statement by Birch Acoustics: Did the Ravens demonstrate any of the advantages of a crossoverless design? They did. The reproduction of both macrodynamics and microdynamics was just splendid: fast and uncompressed. Clearly, no crossover was dulling the transient response. “Folia Rodrigo Martinez” varies continuously in volume level, and the Ravens flawlessly tracked its dynamic swings and range. Some audio components portray these volume changes as a series of steps instead of as a continuous, unbroken range of variation. Several times, the sound virtually explodes as the players emphasize the melodic line, and the Ravens never compressed those explosions at all. Leading-edge transients from wood blocks and castanets were sharply defined. One oddity I noticed with this recording was that Savall’s viola da gamba sounded a bit odd; I thought it was tonally a bit squawky, the instrument’s usually rich harmonics a bit congested. This had to be a narrowband phenomenon -- most harmonics sounded rich and full.
A new disc of Elgar’s Enigma Variations and Vaughan Williams’s The Wasps and Greensleeves, with Michael Stern conducting the Kansas City Symphony, illustrated the Raven’s prowess with harmonics (24/176.4 FLAC, Reference/HDtracks) -- the sound positively glowed with orchestral color. The Raven’s lack of a crossover let the dense harmonics shine through unscathed without temporal smearing. In other words, the right harmonic frequencies showed up at the right time. Even with this wide-ranging recording, the Ravens sounded quite full range, and even though they rolled off the highest highs, I really didn’t miss them.
The audiophile fave “Spanish Harlem,” from Rebecca Pidgeon’s The Raven (24/176.4 FLAC, Chesky/HDtracks, remastered by Bob Katz), sounded unusually three-dimensional, as if Pidgeon were standing squarely between the two Ravens. Her voice had a particularly solid texture, as I could hear her enunciate each syllable. I kept hoping that Pidgeon, who is not at all hard on the eyes, would pop into view, but I guess I’d need a theater system and a Blu-ray for that. In the Tallis Scholars’ recording of Allegri’s a cappella Miserere (24/96 FLAC, Gimell), the main chorus is in the foreground, a smaller group of singers some distance in the background. The larger chorus sounded very focused and firmly placed at the front of the very reverberant soundstage, the solo group very distant. Through the Ravens, sometimes, the reverberant part of the soundstage just didn’t show up, making it hard to tell that the two groups are standing in different places.
My Affirm Audio Lumination speakers cost nearly four times as much as the Birch Acoustics Ravens, so I’m not sure it’s fair to compare them. The Lumination does, however, embody the advantages (and disadvantages) of single-driver speakers enumerated in the opening paragraph. Its single 5” Feastrex driver uses a whizzer cone to produce high frequencies; a huge alnico magnet drives an extremely light paper cone incredibly fast to produce amazingly detailed sound. Like most horn-loaded speakers, the Lumination is pretty sensitive: 103dB. And since the horn loads the cone, it doesn’t need an amplifier with a high damping factor -- in fact, such amplifiers tend to produce rather lean bass with this speaker.
The first thing I noticed about the Lumination in comparison with the Birch Raven was the smoothness of the Affirm’s treble response. It’s not the last word in high-frequency extension, but with Warnes’s “The Panther,” the highs from the percussion instruments were more extended than through the Ravens. Yet Patricia Petibon’s soprano was smoother through the Affirms, and free from any high-frequency emphasis.
The bass in “Folia Rodrigo Martinez” was less powerful than through the Raven, but it was tight and well controlled. Bass seemed to extend as deep as with the Birch, but the latter seemed to have more impact. Above the bass, the Lumination provided more musical detail, allowing me to hear deeper into the performance. Jordi Savall’s viola da gamba sounded smooth and refined.
On the disc of Elgar and Vaughan Williams, the Lumination’s tonality was just as rich as the Raven’s -- both were sublime. The Luminations made Allegri’s Miserere sound slightly more detailed, but the reverberant field surrounding the smaller, more distant chorus was not as prominent, though still evident. Which portrayal was correct? I guess you’d have to be present at the recording event to answer that.
All in all, the Lumination was more detailed and smooth than the Raven -- but at four times the price, it darn well should be.
The Birch Acoustics Ravens demonstrated the strengths of full-range-driver speakers claimed in the opening sentence. They sounded very dynamic and direct, with excellent soundstage reproduction. Further, their transient response and harmonic accuracy illustrated the advantages of having no crossover. There were a couple of minor anomalies, but nothing major.
All speakers are collections of compromises. In the Raven, the Birch designers have compromised on high-frequency extension (no tweeter) in favor of a direct-sounding midrange and high sensitivity. I seldom missed the highest highs, but when I played music that extended into that region, I could tell that the Raven’s response there was rolled off. So is the Raven a good value for $7500? I’ve done my best to describe its strengths and weaknesses -- if that combination sounds appealing to you, the Raven may be worth trying. The $7000-$8000 price range is very competitive; I recommend auditioning several candidates before making a decision. I liked the Ravens; you may too.
. . . Vade Forrester
- Speakers -- Affirm Audio Lumination
- Amplifiers -- Octave Audio V70SE, David Berning ZH-230, First Watt J2
- Preamplifier -- Audio Research PH5 phono stage, Audio Research LS27 line stage
- Analog sources -- Linn LP12 turntable on custom isolation base, Graham Engineering 2.2 tonearm, van den Hul Platinum Frog cartridge, Sony XDR-F1HD tuner (modified)
- Digital source -- Auraliti PK100 music player connected to Audio Research DAC8
- Interconnects -- Clarity Cables Organic, Audience Au24 e (balanced), Purist Audio Design Venustas (unbalanced)
- Speaker cables -- Purist Audio Design Venustas, Audience Au24 e, Clarity Cables Organic
- Power cords -- Purist Audio Design Venustas, Clarity Cables Vortex, Audience powerChord e
- Digital cable -- Wireworld Gold Starlight 6 S/PDIF
Birch Acoustics Raven Loudspeakers
Price: $7500 USD per pair.
Warranty: Five years parts and labor.
1317 Scott Rd.
Papillion, NE 68046
Phone: (402) 578-6930