POSITIVE FEEDBACK ONLINE - ISSUE 31
as reviewed by Akhilesh Bajaj
For over seven years, I have been building and listening to a wide variety of loudspeakers, from horn to bass reflex to sealed box to open-baffle designs, in single- and multi-driver configurations and with both active and passive crossovers, always attempting to learn by listening. While this has made me familiar with most of the loudspeaker options available today, my preference is for high-efficiency speakers driven by tube amplification, usually single-ended triode (SET).
In the open-baffle (OB), or dipole, speaker, a design that exists on the do-it-yourself hobbyist fringe, the speaker has no box, simply an open baffle. To picture this, think of two identical single-driver speakers, in boxes, one on top of the other, wired in phase. When one driver pumps forward, the other pumps backward, so the bass cancels out, but not the higher frequencies, since the baffles beam them directionally. The bigger the baffle, the longer the wavelength (i.e., the lower the bass) that can be "beamed." An equalization bump of 6 dB per octave below the cancellation frequency of the baffle needs to be applied, since the frequency response theoretically falls at that rate. This equalization can be applied in several ways—with a passive component, by using a driver that gives out more bass than treble, or by electronic compensation, as Linkwitz does in his Orion OB loudspeaker (www.linkwitzlab.com).
Why bother with an OB design? The main advantages are (1) there are no box colorations, and (2) the sound is less susceptible to room effects, including standing waves. A well-executed OB speaker system will have smooth frequency response, extremely natural-sounding bass, and a very organic presentation of the music, with natural depth and imaging. The lessening of room effects and box colorations can also offer greater clarity and transparency. OB designs are primarily in the realm of DIYers, but kit offerings do exit. Most, including the Bastanis Prometheus Mark II (www.bastanis.com/us/prometheus+mkii.htm) and the Basszilla by Dick Olsher, use enclosed woofers. The Orion by Linkwitz is one of the very few OB designs that has OB bass. Several DIYers have designed dipole subwoofers (an example is here), but many of these lack efficiency, which prohibits the use of low-powered tube amplifiers. Until now, there was no reasonably full-range, high-efficiency driver that could be used in an open baffle.
In 2005, Darrel and Diana Hawthorne, the principals of Hawthorne Audio (www.hawthorneaudio.com) approached Eminence (www.eminence.com), one of the world's leading professional driver manufacturers, with the idea of building a driver that would fulfill these needs. The Hawthorne Audio Silver Iris is a 15-inch coaxial driver with a compression tweeter that fires from the center of the larger driver. The Silver Iris offers response down to an impressive 40Hz, and up to the high trebles in the open-baffle setup offered by Hawthorne.
The sensitivity of the midrange driver is 96dB/W/m, allowing the use of SET amplifiers. The sensitivity of the tweeter, which uses the midrange driver's cone as a horn, is 105 dB/W/m, but since the mid and tweeter drivers are passively crossed, the overall efficiency of the Silver Iris is around 96dB. If the Silver Iris is to be used to the full extent of its 96dB efficiency, an active crossover is needed. The driver can handle 150 RMS watts of power, which means that (like most pro drivers) it offers very impressive dynamic handling. For those who need OB bass that goes even lower, Hawthorne Audio has also partnered with Eminence to create the Augie (short for Augmentation?), an 89dB/W/m driver that goes down to approximately 30Hz in Hawthorne's OB design. The Augie can handle 225 RMS watts of power. The drivers have a seven-year warranty.
After reading about the Hawthorne drivers in several DIY forums and corresponding with Dave Leonard, who builds the crossovers for the Silver Iris drivers, I became very interested in hearing them, so I emailed Darrel and Diana Hawthorne to see if a review could be arranged. I learned that several driver/cabinet combinations are available. They include:
The Solos and Duets come as ready-to-play units, with drivers, binding posts, etc., already installed. I requested a pair of Duets, each of which consists of an Augie and a Silver Iris coaxial driver mounted on an open baffle. The Hawthornes also sent the plate amplifier used by Darrel to play his own Augies. The Duets allow the user to play just the Silver Irises, just the Augies (for OB bass only), or both together. It is worth noting how much value for money is represented by the Duets. With most commercial offerings, the cost of the parts is often only a small fraction of the total cost. That is definitely not the case here. Given these margins, the Hawthornes must have day jobs!
As might be expected, the Duets have no boxes to speak of. Instead, as the pictures show, the drivers are installed in well-finished baffles that are mounted onto wooden bases. The baffles measure about 24 by 38 by 11 inches. Several colors and wood grains are available. The backs of the drivers are encased by simple frames covered with acoustically transparent cloth. The passive crossover between the Silver Iris' midrange and tweeter drivers is mounted toward the back of this wooden frame. The fit and finish of the Duets is excellent, and definitely worth the amount of money charged by the Hawthornes. The packaging is also excellent. Each speaker arrived in its own large box, well padded with Styrofoam,™ and the packaging includes a lint roller to get the Styrofoam™ lint off the grille cloths. This is just one example of the thought and care that the Hawthornes devote to every aspect of the construction and delivery of their speakers.
It was easy to pull the speakers out of the boxes. Though they are relatively light (no heavy cabinets), the speakers require two people to maneuver them, as the mounting of the baffles to the bases is somewhat delicate. Once in the room, moving the speakers requires little effort. Sliding the backs off displays the kind of high-quality crossover parts that a DIYer would use if building their own speakers. The binding posts are also of high quality, and are able to accommodate 10-gauge speaker wire. The solder joints look excellent. Another example of the care taken by the Hawthornes is the fact that different wires are used for the midrange and tweeter drivers, which makes it easy to disconnect and reconnect them. (This would happen, for example, if the user wanted to disconnect the crossover in order to test a different one.)
The manual is rudimentary, and spends more time discussing the benefits of open-baffle design than it does explaining how to set up and use the speakers. While setup is simple, Darrel encourages every customer to consult him. When placing OB speakers, it is necessary to have at least three feet between the speakers and any wall. I first tried the Duets in a 12-foot-wide room. Given the need to have three feet between the speakers and the side walls, the two-foot width of each speaker left only about two feet between them. While the sound had potential, this was not the best setup for imaging or depth, so I moved the speakers into a 15-foot-wide room that would allow about five feet between them. Imaging and depth improved significantly, leading me to conclude that five feet is the minimum spacing suitable for the Duets. In this room, my listening position was about 5.5 feet away from an imaginary line drawn perpendicular to the speakers. After some experimentation, the speakers sounded best with around a 30-degree toe-in from straight ahead. The room was about 8 feet high by 11 feet long by 15 feet wide, and quite well damped. My source was a Berendsen CDP-1 CD player. I first used a Vista Audio il84 push-pull amplifier (www.positive-feedback.com/Issue30/vistaaudio_i84.htm), then the Ultrafi I'O 845 SET, which has about ten watts per channel. I used well-shielded interconnects and kept them as short as possible.
Even though the Duets are ready to play right out of the box, they also represent a platform to test different permutations of the speaker. (In other words, they satisfy the DIY beast inside you.) Several possibilities exist. First, you may listen to the Silver Irises and Augies with a plate amplifier driving the Augies full range (the out-of-the-box approach). Second, you may listen only to the two-way Silver Irises, using the passive crossover that comes with the speakers. Third, it is possible to listen only to the Augies along with other drivers of one's own choosing, in a situation where OB bass is required. Finally, you can use an active crossover to send line-level signals to separate amplifiers driving the Augies, the Silver Iris midrange and tweeter drivers, or even a two-way active crossover for just the Silver Iris mids and tweeters without the Augies.
I first listened to the system using just the Silver Iris drivers with the built-in passive crossover. With the Vista amplifier, the bass was sufficient for most music, especially acoustic instruments and voices. There was no congestion, even with large orchestral pieces, and the drivers threw a good soundstage. I used the Chesky Ultimate Demonstration disc to evaluate various aspects of music reproduction, including transparency, depth, imaging, bass impact, dynamics, midrange purity, and so on. I also listened to female vocalists (Sinead O'Connor, Eva Cassidy, etc.), rock music with heavy beats (Heart, etc.), and a wide variety of classical music. Like every speaker system, this one had its strengths and weaknesses. Its strengths were imaging, depth, and an organic cohesiveness. The midbass was very clean. I could hear the lack of the lowest octave only occasionally—with kick drums, for instance. Areas in need of improvement included the low treble, where I could hear some coloration. While the system could have been improved, I was really impressed. When I switched to the Ultrafi amplifier, a high-end SET with excellent bass impact, transparency, and musicality (at a cost of $6200, compared to the $729 Vista), I heard more transparency and a better midrange. I recommend listening to the Duets with just the Silver Iris drivers (essentially, the same as listening to a pair of Solos) for listeners whose priorities include depth, imaging, and overall coherence, and who don't listen to much bass-heavy music. I should add that, because of their pro-sound heritage, the Silver Iris were able to handle dynamic shifts easily, so big orchestral pieces sounded really nice (and keep in mind that I am used to listening to horn speakers).
It was now time to add the Augies into the mix, and hear the basic Duets. One way to drive the Augies is to use a plate amplifier with a built-in crossover that accepts line level inputs, plus either a splitter or a preamplifier with multiple outputs, like my passive Mod Squad Line Drive. Darrel Hawthorne was kind enough to send me his own plate amp, and I connected the Augies to it via the Mod Squad preamp. After some experimentation, I set the subwoofer crossover to a hair above 40Hz, and adjusted the volume to blend it in as seamlessly as possible. In my smaller listening room, the bass was definitely augmented. The Augies brought the bass up smoothly from 30Hz, and the extra half-octave or so was most welcome, especially for bass-heavy music. Still, with most music I preferred the cleaner bass quality of the Silver Iris drivers alone. Careful listening revealed that the problem was caused by a certain amount of overlap between the Silver Iris mids and the Augies. Since the crossover of the plate amplifier did not allow a crossover point below 40Hz, and since the Silver Irises run freely down to 40 Hz, there was no way to solve this problem except to split the signal in two, with one portion going to the Augies and the other to the Silver Irises (although a larger listening space may have allowed a better blending).
I then installed a DBX 234 analog crossover that can split the signal into three different bands, at a 24-dB-per-octave slope. I disconnected the Silver Iris drivers from the passive crossover, and used the DBX unit to split the signal to the Augies, the Silver Iris mids, and the Silver Iris tweeters. After some experimentation, I set the splits at 80Hz and 2300Hz. With the three-way crossover, I needed to use separate amplifiers for each pair of drivers, and in this setup, I drove the Augies with the plate amplifier (with the built-in crossover shut off), the mids with the Ultrafi amplifier, and the highly efficient tweeters with a .75-watt Abraxas Audio SET amplifier that delivers very clean highs. With this setup, the bass became a lot cleaner, with very good extension, a relaxed presentation, and excellent depth resolution. I did hear some slight colorations in the lower treble, which made some instruments sound a little louder than they should. Email exchanges with Darrel Hawthorne revealed that the passive crossover supplied with the Silver Iris drivers takes care of some peaks inherent to the drivers, so I reconnected the passive crossover to the Silver Irises, switched the DBX to two-way mode, and supplied signals over 80Hz to the Silver Irises, with those below 80 going to the Augies. This setup sounded the best to me. The high-frequency colorations were significantly reduced, and I heard none of the bass overlap that was audible with the one-way plate-amp crossover. Music ranging from Pink Floyd's The Wall to Patricia Barber's Café Blue to Beethoven symphonies all sounded excellent. Especially rewarding was the depth and placement of instruments and the overall musicality.
The Hawthorne Audio Duet loudspeakers represent extraordinary value in the world of audio. They are chameleon-like speakers that allow the user to create a system tailored to his or her personal requirements. For listeners who listen to vocal/acoustic music and are not inclined to experiment, the Solo system (the Silver Iris speakers by themselves) will be sufficient. For larger rooms, and more bass-heavy music, the Duets make more sense. Of course, one can buy the Duets and run them as Solos by not using the Augies. (The baffles are identical.) If running the Augies, my experience indicates that using an active crossover to split the signal between the Augies and the Silver Irises is the best method. The passive crossover does a good job of handling driver peaks and integrating the mids and tweeters.
Like any speaker system, the Duets are not perfect. A possible area of improvement is a higher-quality tweeter. The current one sounds like a pro tweeter (which it is), and I am used to the smoother sound of tweeters geared toward home listening. However, this is a small quibble, and other people who have heard the Silver Irises have not been bothered by the treble. The Duets perform very much above their price class. As I said earlier, they are also unique, in that they provide a full-range, open-baffle system (except for the compression tweeter) with high efficiency and very good sonic performance.
If you want the imaging, depth, and organic presentation of an OB speaker system, but also want high efficiency in order to use low-power tube amplifiers, and finally, also want the dynamic range usually possible only with horn-based or pro-sound systems, there is really nowhere else to go. I take my hat off to Darrel and Diana Hawthorne for noticing a gap in today's commercial speaker offerings, and for producing such a well-thought-out product, not to mention providing friendly support to boot. In my opinion, this is exactly the kind of product (and attitude) that can revive interest in the possibilities of well-reproduced audio in the home. Akhilesh Bajaj