Active Crossover: Even if you don't purchase the Dvorak's optional dipole subwoofers, the external active crossover/equalizer is employed to extend the low-frequency rolloff of the main panels to 40Hz. With the subwoofers in the system, however, the crossover between the main panels and the big woofers is set to 100Hz. This significantly reduces the excursion demands on the 8" drivers, allowing them to operate in a more linear fashion. Specific equalization is also applied to both the feed to the main-panel amplifier and that for the subwoofer. This equalization compensates for the natural dipole 6dB/octave rolloff below 100Hz for the subwoofer's 12" drivers and above 100Hz for the rolloff of the 8" drivers. (This rolloff occurs for all frequencies where a half-wavelength is greater than the separation between the center of the front and rear radiating elements.)
The active crossover is contained in a black sheetmetal enclosure. A blue LED shines from a 1/2"-thick, black-anodized aluminum faceplate. One input and two output RCA jacks per channel are mounted on its rear panel. Pushbutton switches allow each main panel and subwoofer to be turned on or off independently. If you don't buy the subwoofers, you simply turn the crossover's woofer circuit off and connect the pair of main outputs to a single stereo amplifier. Otherwise, two stereo amplifiers are used.
There is also a separate woofer-level adjustment control knob for each channel. These potentiometers provide a 12dB range to precisely match the system's bass response to a given room and/or balance any inherent level differences between the two amplifiers -- should there be a difference. A front-mounted "video" button prevents the subwoofers from bottoming-out when playing the occasional excessive soundtrack explosion by adding a gentle, 6dB/octave high-pass attenuation from around 50Hz downward.
Inside the active crossover a single circuit board occupies the chassis' full width and more than half its depth. This board contains an addition +/-12dB bass-level switch that, along with the external woofer-attenuation knob, provides as much flexibility as one could ask for in optimizing low-frequency performance. While the design of the electronic crossover is clean and straightforward, the Dvorak is built to a relatively affordable price point, so you won't find a "Who's Who's" list of audiophile-approved passive parts. On the other hand, circuit design -- by far the most important consideration in determining overall performance of electronic gear -- is well executed, and the parts used in the Dvorak crossover are of good quality.
Inputs and outputs are AC-coupled using polypropylene capacitors. Along with 1% metal-film resistors, the same type of caps are used to implement the filter and EQ circuits. Four op-amps are used for each channel, these the excellent Burr-Brown OPA-2604. Burr-Brown dedicates a whole page of their data sheet to a description of the special sonic qualities of this modern FET-input op-amp -- an unusual step for a mainstream semiconductor company. The OPA-2604 is used with carefully optimized support circuitry in some of the best-sounding high-end gear in today's market, such as the Mark Levinson No.38S preamp.
Audio Artistry has developed an ultra-quiet balanced crossover to accommodate their new flagship Beethoven speaker. A revised version of the crossover for the Dvorak incorporating some of the same refinements will likely follow in the near future. One of the nice things about an external active crossover is how much easier it is to upgrade: you don't have to send the entire speaker back to the factory to take advantage of inevitable progress.
The 180mA, +/-12V "wall-wart" power supply shipped with the Dvorak's crossover was selected to keep the speaker affordable and to avoid hassles when exporting the system to foreign markets, not to provide ultimate performance. Alternative power supplies are available that may provide some subtle refinements, yet the stock supply is certainly adequate. Also, keep in mind that the sonic impressions rendered in this review were based largely on the stock supply.
With a retail price of $5990 for the entire five-piece system, the Dvorak is reasonably priced. (The Dvorak subwoofers are also available with an unequalized version of the crossover for use with other speakers that could use the benefits of dipole bass. Price: $3590.)
setup
The Dvoraks may be less sensitive to room placement than panel dipoles and most box speakers, but some care and experimentation will certainly pay off. I recommend placing the speakers at least 3' to 4' from the back wall, and a minimum of 2' from the side walls. Toe-in the main panels so that the tweeters are nearly on-axis with your ears, then place the two subwoofer cabinets slightly in front and on the outer side of each main panel so that the center point of each subwoofer cabinet is the same distance as the nearest tweeter from your respective ear.
This time-aligns the woofer voice-coils with those in the main panels with respect to your ears. You can experiment by sliding the woofers along an imaginary arc that connects the center of the two cabinets and intersects the tweeters in both panels. The ideal spot for each will vary with your room's dimensions and your sonic preferences. If you have the space, try a tweeter-to-tweeter spread of 8' or more. And be sure to carefully level the panels from left to right and from front to back.
Those who use speaker-placement softward or formulas for smoothing the bass response in a given room should keep in mind that, where an omnidirectional woofer will give its smoothest response when located at the nodes of a room's modal profile, a dipole is just the opposite with respect to the front-to-back axial modes. The relationship of side-wall and ceiling axial modes is similar for the two types, but because dipoles have a null at 90o, less off-axis interaction will occur in these two planes, particularly if the speakers are at least a couple of feet from the walls. Therefore, if you wish to further smooth the Dvorak's bass response, try placing the panels and subs in the anti-node nearest the node you would normally choose to place a box speaker.
Whether the final woofer placement is nearer the panels or the side walls, I do suggest you toe them in a bit as well -- though not necessarily on-axis like the main panels. Some degree of toe-in, however, will give you increased focus from the directional bass. It's also possible to move your listening position much farther back than you would with most box speakers and still get good imaging. This is due to the reduced amplitude of the overall reverberant field and the weak side-wall/ceiling reflections which, in turn, expand the "near-field" response window compared with a monopole.
Watch the woofer level: Though the marriage between the dipole woofers and main panels is seamless, as the balance is partially in the hands of the user, the flexibility afforded by the wide range of bass-level adjustments makes defining a specific sonic character for the Dvorak's bass and midrange response difficult. The most common mistake people make with the speaker is to turn the woofer levels up too high -- they misinterpret the resultant thumping quality as "good" bass. Don't do it! The owner's manual gives a thorough guideline for dialing-in the woofers for your particular room and associated amplifiers, so I'll just highlight a few tips. It's not difficult to do, but it does take a little time and is best accomplished with the help of a friend.
When following the woofer-adjustment instructions, pay attention to the timbre or tonal character. If the balance gets leaner with the woofers in the circuit, turn the level up on the crossover. Be careful, because adjusting the level knob by one "hour" changes the bass level by 1.2dB; even a small step in low-frequency output can produce a surprisingly big sonic change.
If the sound becomes thicker, more "tubby," with the woofers on, turn it down. With the bass levels set too high, dynamics are curtailed, midrange focus and definition degraded, kick drums will sound as if the drumskins are damped with pillows, and bass guitars can sound like someone's playing with leather gloves on.
When you've got it right, the system's overall tonal balance should be the same with or without the woofers engaged. However, with the subwoofers, the midrange has greater presence, the focus improves, and the soundstage is better defined. The effect can be awe-inspiring: bass is conveyed with a correct mix of transient snap and weight while improving resolution of midrange harmonics. In addition, you simply cannot hear the woofers as a discrete sound source. I've found that the final woofer-level adjustment will range between 11:00am and 1:30pm for most average-sized rooms when both amplifiers have the same amount of gain. The best setting may differ in larger or smaller rooms or when dissimilar amps are used.