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  KEF KHT-3005 Home Theater System

      Date posted: December 16, 2007

KHT-3005 Home Theater SystemSugg. Retail: $2000 (CAN) including wall brackets Distributor: KEF Canada Division, KEF America & Celestion America Inc., 10 Timber Lane, Marlboro NJ 07746 USA (732) 683-2356 FAX 683-9790 KEF Canada 416-233-6421 www.kef.com

Round, organic, egg-styled, baby-like, modern…there are so many things you can call KEF’s current series of home theatre loudspeakers, the main adjective being, of course, small. Available in glossy black and sleek silver, they definitely make a modernist statement. But, unlike other B-system brands affecting style out there which I shall not name for fear of incurring the wrath of the Dreaded “Mark” (that’s a Tronna joke), these actually make nice, high fidelity music and have some very credible and genuine engineering behind them.

Often, when he came to Canada, I used to have dinner or lunch with KEF founder Raymond Cooke (and later with his equally affable son, Martin), and got to know some of the speaker engineering behind the great line of speakers he founded and designed. From the pioneering active-bass enhanced small tower designs to the
oddly shaped DIY-favourite woofers to the mighty Reference 107, KEF speakers have pushed the envelope of dynamic speaker design like those of few other British companies. Now allied with another great name from ’over ’ome, Celestion, the company seems to be building on its heritage rather than riding on it like some other once fabled marques.

KHT-3005 Home Theater System

I say that as a prelude to some technical comments about these new, oddly-but-organically shaped speakers that strive to stand out in spare modern interiors. This will be accompanied by cutaway diagrams and discussion of various concepts of physics and electrical engineering, so keep your slide rule handy (oh well, if it has to be a scientific calculator, all right!).

Let’s start with the Uni-Q concept. There is always a compromise in a loudspeaker where one part of the musical spectrum comes from one driver in one place and the rest from another driver (or more) in another place. In all sound, and audio signals analagous to sound, higher frequencies are “piggy-backed” on lower ones. That’s why a signal at a single frequency, especially a lower one (also called a sine wave) looks quite smooth in shape; when you add all the higher fundamentals and harmonics, it gets quite messy, but the point is, when you separate these in a loudspeaker or the crossover network in it, these tied-together musical signal relationships are broken apart, and have to be re-tied together acoustically, either on the way to your ears, or by them.

The best way, according to Cooke and his engineering team, was to radiate all frequencies above the deepest bass from the same driver in each speaker system/channel, and their way to do it is called Uni-Q, used with the HTS3001, in which the tweeter is an integral part of the mid/bass driver, using its mechanical system but with its own voice coil electrical motor system, and situated at centre to move in complete concert with this driver as a part of it. That way, the sound is radiated in the same way as it would have been from the original musical instruments, or as much so as can be properly approximated in a reproducing system.

Satellite cutaway

Of course, other things acoustical fall into place too, by doing this. One is the dispersion of sound into the room, which is very even and timbrally correct, because that’s how the frequencies are radiated spatially by Uni-Q. In the exploded diagram above you can see how the driver is constructed, the tweeter being at centre of the long throw mid-bass unit.

In a more recent design innovation, the HTB3B2 subwoofer employs a “Heavy weight long-throw motor design with aluminium Faraday ring for reduced distortion. Magnetically shielded”, with “4-layer copper coil for high power capacity, FEA [Finite Element Analysis computer program] optimised coil and magnet design to give a linear BL profile. [BL Profile = measurement of the motor force factor on the speaker driver over the working displacement of the magnetic coil]” All this from the KEF website.

It is driven by a “Highly-efficient Class D amplifier. Thermal and overcurrent protection built into the amp and power supply unit ensuring ultra reliable performance. Sophisticated limiter system to prevent voltage overload - optimised for maximum audio quality. [Optocoupled LED and light sensitive resistor senses and automatically limits to prevent damage to the unit]”.

With respect to the Auxiliary Bass Radiator (ABR) seen below in the cutaway drawing, it is a “Balanced symmetrical low profile ABR design for more linear excursion and reduced distortion” with an “Internally vented ABR air cavity resulting in less compliance damping giving better LF performance.”

KEF Subwoofer Cutaway

The HTC3001 centre channel is a dedicated design, rather than identical to the satellites, because the designers saw it as especially important: “Carrying up 60% of the sound, the centre channel is vital in any home theatre system.” The extra flanking 3″ bass/mid drivers “give the necessary frontal impact; all important when watching a movie.” “‘Sit anywhere’ Uni-Q technology assures perfect timbre matching to the HTS3001 satellites”.

Looking at the measurements, we see some pretty impressive curves, particularly with the subwoofer. Well, actually, it’s one curve, but that’s enough for me. You see, the HTB2 has no crossover or level adjustments: it simply attaches, either by line input or speaker passthrough, to the rest of the system, so no adjustment, hence no further measurements, are necessary. The whole story is told in that single +/-2 dB trace from 150 Hz down to about 23 Hz. This sub is flat, flat, flat, and smooth, smooth, smooth.

But there is more story to tell. The HTB2 is also very quick and dynamic, with a lot of power punch at the lowest frequencies from the active and passive driver KHT-3005 Home Theater System Frequency Responsecombination, driven by a Class D (digital) 250-watt internal amplifier (which leads me to comment on its resemblance to the Sunfire series of subs, which claim ‘2700 watts’ of power; but, then, them’s Bob Carver watts, which differ in impedance as well as numerically; let’s just say that the sonic results suggest that both have plenty of balls!). The curve is so good that I didn’t even bother to smooth it at top, though it is, as always, the average of 4 or more individual actual measurements for utmost accuracy. It can be seen at right in a smoothed version.

Turning to the satellites and centre, the former are at top, and show well controlled uniform dispersion, the top 2 traces the PNS (Pink Noise Sweep, the spikier unsmoothed one), and the other overlaid one being the SAR (Summed Axial Response, that is, the 3 curves below added together). We do see in all of these a sloping tendency with rising frequency, a good thing in the smaller acoustic spaces where this system will live.

The combination of the 5 drivers and closer listening distances makes this down-tilted response a necessity for natural sound, and the key is smoothness, which we do see here, with 10 kHz just 4 dB down from 1 kHz response, and 3 dB increments per octave between 1 and 4 kHz, with shelving above for clear highs.

This response is followed by the HTC3001 centre, with a little more linearity in the slope (bottom), matching seen to be very close at 0 and 30 degrees off axis, with just a little less mids and top at the ends of the couch. With a slope of only 3 dB between 1 and 10 kHz, the centre channel will provide a little greater articulation of speech and musical detail, which will be underlined by its 2 extra drivers in addition to the pefectly matching central Uni-Q.

This is a really nice system to listen to, easy and powerful at the same time, though in my big room I missed the extra subwoofing I normally live with. That said, the compact KEF is one of the most amazing low-end reproducers in my experience, and, frankly, I wouldn’t mind having 3 or 4 of them around, with their entirely predictable dynamic, quick, and smooth performance up to very high levels. Just keep ’em out of the corners, and crank ’em up! And they can also be fine tuned with an electronic crossover like my reference Energy EAC.

The KEF HTS3005 HT speaker system is definitely a true high end audio system that happens to be multichannel, and I think many buyers of plasma and other big flat-screen displays will see it as the perfect match, especially in the high-gloss black, but also in its shimmering silver version. In both performance and styling, this one is the real thing.

(Further thoughts from the Summary of HT Systems from Vol. 23 #1)

Integrated technology is definitely a byword with the KEF 3005 system, which has some resemblances to the Klipsch in concept, but goes to a new plateau of matching of satellites and subwoofer, with just about the most instinctive and user friendly setup I’ve seen. This system is absolute high end HTIB (Home Theatre-In-a-Box). I liked the subwoofer so much that I chose it to temporarily replace the Sunfire in my own HT system after the latter developed a nasty repeated thump after one of our more abrupt AC power outages (actually, it was the “innage” that did it in; ie, the AC-on transient). Here the KEF 3000 sub has proved appropriately unobtrusive but authoritative, its exemplary deep bass power (especially for its size) heard when required. Imaging of the complete KEF system is seamless in surround, and I liked its easy acoustic and visual elegance, though it may not handle quite the SPLs of some of other systems.

Andrew Marshall

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