Avantgarde Acoustic Uno Series Two loudspeaker Page 2

The Avantgarde Uno is technically a hybrid: a sealed-box cone subwoofer supplements the horn-loaded midrange and tweeter modules. The midrange driver is a 4" unit with a 2.5" dome, covering the range from 220Hz to 3500Hz, and was developed especially for the Uno. In the original Uno, the tweeter's sensitivity was lower than that of the midrange, which required a network to lower the midrange sensitivity by 1.5dB.

The Uno Series Two has a new tweeter that matches the midrange in sensitivity, so that the midrange is now driven directly by the amplifier, with no electrical crossover. The midrange driver's physical design produces an acoustical rolloff of 12dB/octave above 3.5kHz and 18dB/octave below 220Hz. The tweeter's response potentially extends down to 1kHz, but it's rolled-off by a 12dB/octave crossover at 3.5kHz so that it matches the midrange. The crossover uses high-quality polypropylene-foil capacitors, air coils, and metal-oxide resistors. The tweeter has an oversized 6.5-lb magnet, and its claimed power-handling capacity is more than 100W.

The new SUB225 CTRL PRO subwoofer, optional with the Uno Series Two (the speaker is also available with the 217 PRO subwoofer, at a $1000 saving, but Jim Smith strongly recommends the 225 CTRL PRO), represents a major design effort to have a subwoofer that matches the horn drivers in efficiency and sonic character. The two 10" subwoofer drivers are apparently quite special: 3" voice-coils, 15-lb high-energy magnets (BL-force factor of more than 19 newtons per ampere, if that means anything to you), 0.71" excursion, each driver with a power-handling capacity of 250W (RMS), and a sensitivity of 95.0dB. The subwoofer drivers are connected in parallel, yielding an efficiency of over 100dB, thus matching the horns' efficiency. The enclosure is of 1.2"-thick MDF, with very rigid construction.

Integrated with the rear panel of each subwoofer is the PA101 power amplifier/crossover. The amplifier puts out 200W and is optimized for bass reproduction, with a high damping factor to control the drivers. The PA101 also features what Avantgarde refers to as a velocity-controlled driver feedback system. This is not a conventional servo control using an acceleration sensor on the driver, but a type of equalization that varies with changes in signal level and frequency.

The final step in the production of each 225 CTRL PRO is the tweaking of the driver control circuit, taking into account variations in the characteristics of the specific drivers. User controls include potentiometers for subwoofer level and crossover frequency (variable from 90 to 220Hz, 12dB/octave), and a switch that allows selection of 20, 25, or 30Hz as the low-frequency extension point (12dB/octave), with an additional constant 6dB/octave filter at 18Hz to protect the system from damage. I'll take bass quality over quantity any time, so I used the 20Hz setting. The PA101 takes the signal from the amplifier speaker output rather than the preamplifier, which is said to preserve the main amplifier's tonal and dynamic characteristics, enhancing the integration of the subwoofer with the rest of the range. (REL subwoofers use the same approach.) The subwoofer amplifier presents a high impedance load, so driving it draws a negligible amount of power from the main amplifier.

When it comes to describing the Uno's appearance, I'll forgo taking up a thousand words and leave the task to the photo accompanying this review. Although the Uno is the smallest Avantgarde, it's still a pretty big speaker that takes up a considerable amount of floor space, and it's not exactly visually unobtrusive. I find the form-follows-function honesty of its industrial design quite appealing; the Uno looks like a speaker, not a speaker masquerading as a piece of French Provincial furniture.

The finish on the review sample was the standard white polished ABS, with the subwoofers in gray Nextel. The speaker is also available with the horns and sub in matching automotive metallic lacquer finishes, which boosts the price by as much as $2000—a bit steep, if you ask me. I quite like the standard white ABS—even if the midrange horn does bear a certain resemblance to a Yamaha Sousaphone. The quality of fit'n'finish is exceptional, confirming Avantgarde's claim that their products have much in common with Porsche, Leica, Mercedes-Benz, and other examples of German craftsmanship.

Setup
Given the Uno's size and unusual dimensions, unpacking and setting up a pair of them was not as much of a chore as I had anticipated—once I figured out that the midrange and tweeter have to be switched around from the way they're shipped, a fact the instructions fail to point out. The speaker consists of three parts: midrange horn, tweeter horn, and subwoofer, which are all attached by long bolts to three metal posts. There are three sets of holes in the posts, allowing the horns to be mounted at different levels depending on the height of the listening seat. The highest mounting position is recommended unless the listening seat is very low, and this worked well in my situation. As delivered, the weight of the entire speaker, including the subwoofer, is supported by the posts, which have feet that allow the speaker to be moved around with relatively little difficulty.

Once the speakers are optimally positioned, a set of four supplied spikes can be screwed into the bottom of each subwoofer, and the posts' feet removed, which gives the speaker more solid support. I followed this procedure, and found that the installation of spikes improved general focus and tightened the bass. The Uno can be single-, bi-, or tri-wired; short pieces of cable are supplied for joining the different modules if single- or biwiring is used. For all my serious listening, I used Nordost SPM biwire speaker cable, one pair connected to the midrange and the other to the tweeter, with the supplied Avantgarde wire linking the midrange and the subwoofer.

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