KEF XQ40 Review
Coaxially Cool
March 08, 2010 by EH Staff

The most common type of speaker design has a tweeter towards the top of the speaker and a woofer below it. Some speakers mix it up with a woofer above too, or maybe a mid-range in there somewhere.

The XQ40 from KEF, like most of their speakers, does something a little different. The tweeter is inside the woofer.

Called a concentric tweeter, there are acoustic benefits and of course, potential negatives. KEF calls the design “Uni-Q” (say it out loud, it’s kinda clever), and claims it “disperses an accurate sound image evenly throughout the room.” In other words, because the sound waves are emanating from the tweeter and the mid-range from the same “point” in space, the sound gets to your ear “time aligned.”

This means the sound is theoretically more accurate, and has the potential to have better frequency response off-axis. The potential downside is a shouty, horn like sound. Have a friend cup their hands over their mouth and say something, and you’ll get the idea.

But those are just the potentials. Let’s take a look at the actuals.

The tweeter in question is a 0.75-inch aluminum dome, residing in the center of a 6.5-inch mid-range where you’d normally find a dust cap. The tweeter crosses over to the midrange at 2.5 kHz. Bass comes from two more 6.5 inch woofers that come into play below 400 Hz. KEF claims a sensitivity of 90 dB with 2.83 volts at 1 meter. The XQ40s can bi-wire/bi-amped.

The curvy cabinet design is solidly built. My review samples had the Birdseye Maple finish, which I found quite attractive.

To start I hooked my laptop up to the Simaudio Moon i3.3 and went through my music library on random, to get a feel for the sound of the XQ40s. One character readily came across: a razor sharp center image. Vocal tracks benefitted from this the most, with a rock solid image between the speakers.

This isn’t to say there was no stereo imaging, which there was. On one end of the spectrum you have speakers like electrostats that can create a diffuse sound, but often at the expense of accurate imaging. Think of the XQ40s as the opposite of that. Not a judgment call either way, both have their proponents and fans.

Moving away from the center, there wasn’t the usual drop-off found with many other speakers. So if you have a wide room or a lot of seats, the XQ40s would be a good choice to ensure those seated at the edges of your theater still get decent sound.

KEF claims the XQ40s are 3 dB down at 45 Hz, and that wouldn’t surprise me. Depending on your room and usage, if you don’t want a sub you certainly don’t need it. The XQ40s go deep, but it’s not overwhelming or out of balance with the rest of the sound.

While I love the sound of the i3.3, I like to try different amps with each set of speakers I review. Not every amp sounds good with every speaker, and vice versa. I swapped in a Sunfire Cinema Seven, a 400 watt per channel monster. Even at low volumes, the KEF’s came alive. There was more vibrancy to the sound. Now before you assume that this was just a matter of giving the XQ40s more power, I also tried them out on the Wadia 151PowerDAC mini. They sounded great, and that only has 25 watts per channel.

Returning to the Sunfire, I cued up Emmylou Harris’ DVD-Audio Producers Cut, the 2-channel 24/96 track portion of course. Track 2 is her standby, “Boulder to Birmingham.” The strong bass and clean treble were welcome, though her voice was a little more forward than I’ve heard on other speakers. At higher volumes, it got a touch shouty. Some tweaking was needed.

Normally I start with speakers toed in towards the main listening position, then adjust as needed. So I moved them so they were straight on. Because the off-axis response of the XQ40s is so good, this hardly had any effect on the treble. In fact, it seemed to even out the sound even more. In my room anyway, this setup resulted in a more natural sound. Never forget that your room is part of your system. The soundstage also got wider, as you’d expect, but the razor sharp imaging remained.

Up next was Bon Iver, track 8 “For Emma” from For Emma, Forever Ago on CD. The KEFs did a fantastic job filling my room with the layered ethereal sounds on this album. Trumpets were suitably brassy, the rhythmic guitar strums never harsh or biting.

The trumpets sounded so good, I moved on to one of my favorite jazz albums: Cannonball Adderly Somethin’ Else on 24/96 DAD. With track 3, the title track, the KEFs really came into their own. The imaging placed the instruments precisely across the soundstage. The strong bass of Sam Jones’ bass filled the room. The sax and trumpet played vibrantly with no coloration. Art Blakely distinctly pounded away keeping time, his cymbals airy while retaining definition. The XQ40s, powered by the Cinema Seven with the i3.3 doing the decoding, came together to create a fantastic little system.

Just to be sure they could rock out, I put in the incomparable Rolling Stones with Through the Past Darkly and the growling guitars of “Honk Tonk Woman” on SACD. There was some great growl, and when I turned it up, well past where I’d want to be in the room, the XQ40s impressively never fell apart.  This, for sure, was thanks in part to the 400 watts of the Cinema Seven beast. But even with that much power, many other speakers fall apart with volume (hopefully not literally).

All told the XQ40s offer excellent imaging, a wide sweet spot, and strong bass. They took a little more fiddling than some other speakers I’ve reviewed, but that’s all part of the fun with speakers, in my book. The only negative I found was toed in (facing the listening position) they were a little shouty, but it was minimal and alleviated by positioning them straight on. If you’re in the market for some tower speakers, these beauties should be on your audition list. Just don’t forget to take off the magnetic grill to check out the cool concentric tweeters.

XQ40: $4,000/pair


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