Tweeters can be troublesome things. The smaller they are, the more broadly they disperse high-frequency sound - but the more they also tend to distort at lower frequencies. With a typical one-inch tweeter, the speaker engineer usually has to specify a crossover point somewhere around 2.5 kHz; anything lower will stress the tweeter. But that's right in the range where the human ear is most sensitive and where a lot of the defining characteristics of the human voice lie. The engineer would rather push the crossover point a lot lower, into a less critical range, but then the tweeter will distort like crazy - until it completely fries. Sure, you could add a midrange driver, but then your costs go way up.
The Balanced Mode Radiator (BMR) – a technology licensed by NXT and popularized largely through Cambridge Audio's Minx speakers – seeks to solve this problem with a unique driver that works like both a midrange and a tweeter. At lower frequencies, a BMR operates like any other 2.25-inch midrange driver, working as a piston that moves back and forth to produce sound. At higher frequencies, though, the BMR diaphragm works more like an electrostatic or planar magnetic speaker: the center portion of the diaphragm vibrates on its own in a bending motion that's independent of the driver's back-and-forth pistonic motion. Because only the flexing middle part of the diaphragm reproduces high frequencies, the BMR has broader dispersion than conventional 2.25-inch drivers, yet its larger size allows it to be crossed over to a woofer at 250 Hz, in a frequency range that's not as critical to sound reproduction. So says Cambridge Audio, anyway.
The Aero line marks Cambridge Audio's first use of the BMR in a conventional speaker. The $1,099 per pair Aero 6 tower and $549 per pair Aero 2 bookshelf speaker both use a BMR to cover most of the audio range. The Aero 2 augments the BMR with one 6.5-inch woofer, while the Aero 6 has two 6.5-inch woofers. For this review, I'll focus on the Aero 6, although I'll toss in a few comments about the Aero 2 as well. You can easily expand either the Aero 6 or the Aero 2 into a full home theater system by adding the $449 Aero 5 center speaker, the $549 Aero 3 surround speaker, and the $899 Aero 9 subwoofer. The Aero 5 has a single two-inch BMR flanked by two 5.25-inch woofers. The Aero 3 has dual four-inch BMRs, which can be run together in a bipole configuration for 5.1-channel surround sound or run separately for 7.1-channel sound. The Aero 9 has a 10-inch woofer powered by a 500-watt amp, plus a 10-inch passive radiator to reinforce the bass. Of course, you could use pretty much any subwoofer you want with the Aero speakers.
Other than the BMRs and the low crossover points, there's nothing unusual about the Aeros. They're handsome enough, but they're basically just plain, front-ported box speakers, available in either a black or walnut finish.
The Aero 6 towers sat in the place where I put most tower speakers, with the front baffles about 36 inches from the wall behind them, the speakers about eight feet apart and 10 feet from my listening chair. When auditioning the Aero 2s in the front, I placed them atop my 28-inch-high, kitty-litter-filled Target metal stands and set them in the same spot – except when I was comparing them with the Aero 6s, in which case they sat side-by-side.
So what was that little twist? Both Aero models initially sounded a little mellow in the upper treble, and I found that toeing them in to point straight at my listening chair - something I accomplished with the aid of a laser pointer - was critical to getting good high-frequency output. Likewise, I leaned the magnetic grilles in the corners behind the speakers and never used them. Granted, this is what I do with most of the speakers I review, but maximizing the treble output is especially critical to getting the best sound from the Aero speakers.
By the way, I also did full measurements of the Aero 6 and Aero 2, which you can see on the About.com Stereos page or by clicking on the images below:
Click on over to page 2 for the Performance, the Downside, Comparison and Competition, and The Conclusion . . .
The Aero 6 delivered a much different experience than I would expect from a $1,100 per pair speaker. Normally, I expect a speaker in this price range - which isn't a lot to pay for a decent tower speaker - to sound pretty good, but to also have some readily audible flaws in the midrange. Typically, those flaws are a result of an imperfect transition between the woofer(s) and the tweeter. With the Aero 6, these flaws are nearly absent, but I would also discover that the BMR design is a trade-off, not a miracle. The Aero 6 does have a sonic weakness that its competitors generally don't, which I'll get to in a moment.
The coolest thing about the Aero 6 is that the midrange is so much cleaner and less colored than I expect in a speaker at this price. You can hear this if you play tenor saxophonist Gene Ammons' rendition of "Willow Weep for Me" (from the wonderful collection Gentle Jug, recommended to me by reader Bruce Erwin). When I heard what the Aero 6 did with this track, portraying Jug's full, romantic tone and his spitty-sounding upper midrange with world-class neutrality and detail, I wondered how much better this recording could sound. So I quickly substituted my reference speakers, the $3,500 per pair Revel Performa3 F206 towers, to find out. Turns out this recording couldn't sound all that much better. Sure, the F206 outperformed the Aero 6, but not in the mids or the bass. The only difference - and it was a shockingly subtle one - was a little less sense of air and space, and a tad less detail in the mid and upper treble. Everything considered, I felt the Aero 6 speakers got about 98 percent of Jug's sound, which for a $1,100 per pair tower is pretty amazing.
Likewise, "The Blue Whale" from alto saxophonist David Binney's Lifted Land showed the Aero 6 at its best. The dual woofers combined with the BMR to deliver an extremely detailed and powerful rendition of upright bassist Eivind Opsvik's introductory solo. The punchy resonance of the bass's sound box and the forceful pluck of Opsvik's right-hand fingers on the strings gave the passage an immediacy that reminded me of sessions at the Collective in New York City, where I often sat just a few feet from the upright bass players when we were jamming. Again, the F206 outperformed the Aero 6 on this cut, but still, the difference was mild: a little more snap in Opsvik's slaps, a little more stick on drummer Tyshawn Sorey's ride cymbal.
Singer/songwriter Ron Sexsmith's coarse voice tends to brutalize affordable speakers. If the drivers are second-rate or the crossover's not well-executed, Sexsmith sounds too raspy. If the tweeter sucks, he sounds too dull. If the speaker's bass is exaggerated, he sounds bloated. Through the Aero 6, Sexsmith's "Words We Never Use", from his debut CD, sounded smooth even with the volume cranked up, yet not one bit of Sexsmith's unique character was lost. The BMR sounded totally at ease with Sexsmith's voice, in a way that few speakers with conventional woofer/tweeter arrays do.
The Aero 6 played loud with ease – at least when I was playing music. The relentless pounding of Band of Skulls' "Hoochie Coochie" from Himalayan didn't faze the Aero 6 at all, even when I got the level up to an average of 101 dB measured from my listening chair at a distance of about 10 feet. I didn't hear a lot of deep-bass power, but I also didn't hear any real sense of strain.
The BMR driver also avoids the flaw I so often hear in affordable speakers with conventional tweeters: harshness in the highs. Listening to cuts from L.A. saxophonist Terry Landry's Amazonas, I noticed that the cymbals, brushed snare, and various Latin percussion instruments all sounded completely smooth and natural, with no edginess or blare at all.
Not surprisingly, the Aero 2 sounds almost just like the Aero 6. Obviously, it has a lot less bass. When I played David Binney's "The Blue Whale," the bass solo still had all its definition and precision, but lost most of its weight and much of its power. Even though the Aero 2's BMR driver is, apparently, the same as the one used in the Aero 6, the Aero 2's mids and treble sound a little more present. This is a psychoacoustic effect caused by the Aero 2's reduced bass output. So in ways, I like the Aero 2 a little better than the Aero 6, but of course the Aero 2 requires a subwoofer to achieve full-range sound.
The more I got into treble recordings, the more I realized that the BMR isn't the equivalent of a good tweeter when it comes to extended treble reproduction. The Aero 6 didn't bloat the voice of Hawaiian slack key guitarist and singer Reverend Dennis Kamakahi on "Kaua'i O Mano" (from the Pua'ena CD), but Kamakahi's voice and guitar sounded clearer through the F206. The Aero 6's treble on this cut sounded slightly rolled-off, lacking a couple decibels of energy above 10 kHz, and it also sounded somewhat garbled and unclear in comparison to what I heard from the F206's one-inch aluminum tweeter.
Here's another case: On percussionist Trilok Gurtu's "Once I Wished a Tree Upside Down" from Living Magic, the ambient sounds of the bell trees swirled around my listening room as they're supposed to, but the upper harmonics of the bells sounded almost as if they were emerging from inside a shoebox – i.e., the high-frequency sound was more focused and less directional than I'd have liked.
I also found that the Aero 6 really needs a subwoofer when used for home theater. The sound is adequately full for character-driven, dialogue-intensive dramas and comedies, but full-throttle action movies are too much for the woofers. The scene in the Terminator: Salvation Blu-ray disc in which a pair of moto-terminators (basically robotized motorcycles with a nasty grudge) chase a tow truck caused the Aero 6's bass to distort pretty badly. The midrange and treble, though, played loudly and clearly, so just add a decent subwoofer, cross it over at 50 Hz or so, and you should be good to go.
Likewise, the Aero 6 really isn't a heavy-rock speaker. Mötley Crüe's "Kickstart My Heart" couldn't kickstart my feet because the kick drum's power was lost – although the guitars, snare, cymbals, and vocals sang out loud'n'clear.
Comparison and Competition
There's a lot of serious competition in tower speakers priced from $1,000 to $1,400/pair. The toughest, arguably, comes from the $1,298/pair PSB Image T6, which has a 5.25-inch midrange, a one-inch tweeter, and two 6.5-inch woofers. It has received nothing but rave reviews. There's also GoldenEar Technology's $1,399/pair Triton Seven tower, with its ultra-spacious-sounding HVFR folded-ribbon tweeter, dual 5.25-inch midwoofers, and dual passive radiators. Plus Monitor Audio's $999/pair Bronze BX-6, with dual 6.5-inch woofers, a 6.5-inch midrange, and a one-inch tweeter.
I didn't have a chance to compare any of these directly with the Aero 6, but based on my memory plus listening notes and measurements I've done on some of them, I'd guess that the Image T6 would equal the midrange smoothness of the Aero 6, and the Triton Seven would come pretty darned close. I think all of these speakers would deliver more treble energy – and thus, a greater sense of perceived high-frequency detail – than the Aero 6. Where the Aero 6 might beat them all is in its total lack of edginess. To my ears, it simply never sounded harsh or fatiguing, and it's hard to say that about any speaker with a good conventional tweeter.
Some audiophiles crave the ultimate in treble presence and detail. They're the guys who usually seek out Grado or AKG headphones, and speakers with ribbon tweeters. That's the kind of buyer who I expect won't like the Aero 6 or the Aero 2 all that much. But other audiophiles crave a smooth sound. They hate harshness. They're the guys who usually seek out old-school tube amps and speakers with softer-sounding fabric-dome tweeters. I think that kind of audiophile will absolutely, positively love the Aeros.