Full review and test of the Krix Epicentrix Mk2 Centre-Channel Speaker by Australian Hi-Fi Magazine. Free Download.

Want to know a dirty secret about multi-channel home theatre speaker systems? It’s that most of them are using the wrong centre-channel speaker: one that’s not a tonal match with the front-left and front-right loudspeakers.

Let’s look at what’s required in a centre-channel speaker. In an ideal world, that speaker would be a perfect acoustic match for your main front left and right speakers. That is, it must be not only be made by the same manufacturer, but should also use exactly the same drivers as your main front speakers. And for best effect, it should actually have at least one additional driver, meaning that if your main speakers each have a bass/midrange driver and a tweeter, your centre-channel should have two bass/midrange drivers and a tweeter. If each of your main front-channel speakers has two bass/midrange drivers and a tweeter, your centre channel should have four bass/midrange drivers and a tweeter.

Why are so many drivers required in a centre-channel speaker? It’s all about tonal quality, frequency response and sound-staging.

Think about an ordinary stereo system. You wouldn’t dream of using a three-way floorstander as your left-channel speaker and a small two-way bookshelf as your right speaker, would you? You wouldn’t do it even if they were made by the same manufacturer.

Yet if you look at the centre-channel speaker that’s offered with most home theatre systems, either included in a package, or available as an option, you’ll most often see that the front-left and front-right channel speakers are completely different from the centre-channel. The left and right-channel speakers will usually have more drivers, and often larger ones than the centre-channel.

Does this matter? You bet it does! In a stereo system, sounds that ‘appear’ to come from exactly midway between the left and right speakers are created by those speakers… exactly what the stereo illusion is all about. The better the left and right speakers are matched, the better the illusion that the sound is coming from an imaginary point midway between them. And because both speakers are matched, the tonal character of the sound coming from midway between the speakers will be the same as that coming from either the left or the right speaker alone.

However, in a home theatre speaker system, sounds that come from midway between the left and channel speakers come not from the front left and right speakers, but from the centre-channel speaker. So if the centre-channel speaker is not identical to the left- and right-channel speakers, the tonal character of the centre-channel’s sound will be different.

Let’s look at an extreme example. Imagine a system where the front-left and front-right channel speakers are large, three-way floor-standing models with excellent bass response and the centre-channel speaker is the size of a matchbox, with no bass response at all. You’re watching a movie in which the lead actor is a male, and he’s standing at the left of the screen. As he speaks his lines, his deep, baritone voice will be reproduced by the left speaker. If his image moves across the screen until he’s positioned at the far right, his deep baritone voice will now be reproduced by the right speaker with exactly the same depth and clarity as it was by the left speaker. Now our hero walks to centre stage and, as he speaks, we hear not a deep baritone voice but a squeaky, pip-squeaky sound because the matchbox-sized centre-channel speaker just can’t handle the actor’s voice.

So you can see why the centre-channel speaker should be identical to your left and right speakers. However, it’s actually preferable if the centre channel speaker has more bass/midrange drivers because in a home theatre system the centre-channel is doing almost all the work when images are centred… which they are most of the time. So whereas in a normal two-channel system you have two loudspeakers combining to produce a central image, in a home theatre system, the centre-channel has to do it all on its own. In fact, in most home theatre systems the centre-channel speaker delivers more than 50 per cent of the movie sound track and the majority of the movie’s dialogue.

So why don’t manufacturers offer correctly-matched centre-channel speakers?

In smaller home theatre systems from reputable manufacturers you’ll find they often do. The front-left and front-right speakers will have single bass/midrange driver and a tweeter, and the centre will have two identically-sized bass/midrange drivers and a tweeter. You do have to look carefully at driver size, because some manufacturers still use slightly smaller bass/midrange drivers in their so-called ‘matching’ centre-channel speakers.

However once the left and right channel speakers become larger, almost all manufacturers cut back on the size of the centre-channel cabinet, the number of drivers in it, and the size of those drivers. Why? Because they know that consumers who are given the choice between a system with a small centre-channel and one with a proper-sized centre-channel will mostly opt for the one with the smaller centre-channel… and most especially if they’re buying with their eyes instead of their ears.

All of which is a really, really long explanation as to why Krix’s Epicentrix Mk2 centre-channel speaker is so large, as well as why it costs $2,495. It’s designed to be a perfect sonic match with Krix’s Neuphonix Mk2 stereo loudspeakers.

The Equipment

As you can see, the front panel of the Epicentrix Mk2 has lots of drivers—six to be precise. Four of them are dedicated solely to bass reproduction, each one of these being 130mm in diameter, with a 26mm voice-coil wound on an aluminium former. Four drivers means increased capacity to deliver bass, thanks to a greater cone surface area, but it also means four voice-coils to dissipate heat and thus an increased power-handling capability. Also, because using four drivers means each one has lower cone excursion, they can move in the most linear part of their operating range, where distortion is least.

The four bass drivers cross to a single midrange driver, which is physically and electrically exactly the same design as the bass drivers, so tonal cohesion across the crossover point is perfect, as is the sonic transition from the bass to the midrange.

The tweeter is a 25mm dual-concentric diaphragm model with a neodymium motor system, a non-resonant aluminium rear chamber and a patented phase-plug.

So far as the crossover network is concerned, the Epicentrix Mk2 is a true three-way design, using a hard-wired and hand-soldered crossover network with components that include air-cored cross-mounted inductors, Krix-branded MKP capacitors and high-power cermet resistors that deliver nominal crossover points at 300Hz and 2.5kHz. The midrange driver operates from its own sealed enclosure while the bass drivers operate in a bass reflex environment, with dual symmetrically-positioned reflex ports.

The cabinet of the Epicentrix Mk2 is 233mm high, 910mm wide and 370mm deep and is available in Black Ash, Atlantic Jarrah, Walnut, Blackwood and Cola veneer finishes.

In Use and Listening Sessions

Installed in a 5.1-channel home theatre system comprised exclusively of Krix loudspeakers, including the Neuphonix Mk2s as front-left and front-right speakers, I was completely floored by the front-channel sound: and not just by its out-and-out quality, but also by the seamless way sounds shifted across the front sound-stage. So seamless that I never had a sense of there being a transition at all: images were just precisely placed, and that was that.

The fact that the sound also moved so seamlessly right across the width of the room from extreme left to extreme right, without changing tonal quality as it shifted was remarkable enough, but what was even more remarkable was the performance of the Epicentrix Mk2 when it was delivering its sound almost solus, particularly the silky-smooth highs which have the kind of ‘air’ around the high-frequencies that you usually hear only from high-end stereo hi-fi speakers. But good though the treble sound was, the midrange was at the same high performance level, a level that’s essential for the correct reproduction not only of singing, but also of the spoken voice… not least because when watching movies, after the images themselves, the dialogue is the most important part of the movie, and it’s essential that you hear every word clearly. With every movie I watched, whether it was an old black-and-white movie, rich with dialogue (Raising Baby) or a more modern fare, where background sounds and effects are constantly threatening to obscure the dialogue (The Fifth Element), the dialogue was beautifully articulate and crystal-clear. Our family movie nights, which are notorious for my mother-in-law, who’s hard of hearing, constantly asking ‘what did he say?’ during our movies suddenly became much quieter affairs… though we still did get the occasional query from her.

I also appreciated that the quality and depth of the bass that issued from the Epicentrix Mk2s meant that I could re-tune my subwoofer to roll off somewhat earlier, so that it delivered only the very lowest frequencies, which not only improved its performance, but also gave a greater sense of their being a real surround field in the TV room.

Conclusion

As I said in the introduction, the Epicentrix Mk2 is designed to be used when you’re using Neuphonix Mk2 loudspeakers as the front-left and front-right speakers in your home theatre system. However, it’s also an ‘almost’ perfect match for many other models in Krix’s line-up, so it will also perform brilliantly-well with other Krix loudspeakers.

However, the sound of the Epicentrix Mk2 is so neutral in character that sonically it will also be a great acoustic match with most well-designed high-quality large multi-driver floor-standing speakers.

So if you have a pair of floor-standing loudspeakers that are around the same physical size as the Krix Epicentrix Mk2 and you want better centre-channel sound than you’re currently achieving, swapping out your current centre for an Epicentrix Mk2 could be the answer to your prayers.#

For more information, contact Krix Loudspeakers

Readers interested in a full technical appraisal of the performance of the Epicentrix Mk2 Loudspeakers should continue on and read the LABORATORY REPORT published on page 00. Readers should note that the results mentioned in the report, tabulated in performance charts and/or displayed using graphs and/or photographs should be construed as applying only to the specific sample tested.

Laboratory Test Results

The room response of the Epicentrix Mk2 is very flat, extending from 70Hz to 10kHz (this last the upper graphing limit for this test—measured performance at higher frequencies is shown in Graph 2) within ±3dB. As you can see from the response measured by Newport Test Labs (shown in Graph 1) the speaker’s response is very linear, rising to the 90dBSPL point at around 170Hz after which there’s a very small (–3dB) suck-out centred at 500Hz, which rises to the 90dBSPL line at around 1.5kHz, after which it tracks out to nearly 6kHz before rolling off slightly.

The high-frequency response of the Epicentrix Mk2 is shown in Graph 2, the traces for which were obtained via an extremely accurate, high-resolution gating technique that shows the response that would be obtained if the speaker had been measured in an anechoic chamber. You can see the response without the speaker grille fitted (black trace) is very smooth and exceptionally extended, with output maintained at almost reference level right out to 40kHz (in this case the upper graphing limit). The trace with the grille fitted (red trace) shows the grille is remarkably acoustically transparent for the most part, but it does introduce a small suck-out in the response centred at 4.6kHz, a smaller one centred at 14kHz and another up around 28kHz. All are so narrow in bandwidth and so small in level (as well as so high in frequency) that they would not be audible, so if you prefer the look of the speakers with the grille in place, this is how I would recommend using them.

Graph 3 shows the near-field low-frequency response of the Epicentrix Mk2. The output of the port (red trace) is fairly narrowband, peaking at 52Hz and 6dB down at 40Hz and 80Hz. The bass drivers (black trace) roll off below 100Hz and above it are flat out to 200Hz where they are rolled-off to 300Hz so the midrange driver (green trace) can take over.

The impedance of the Epicentrix Mk2 shows that Krix is using the crossover network to do so some serious frequency compensation in order to get the flattest frequency response possible. Although the speaker will mostly present an 8Ω load to your AV receiver, the fact that it drops close to 4Ω from around 3kHz to 40kHz puts the nominal impedance at 6Ω, according to IEC 268-5.

Newport Test Labs evaluated the frequency response at 55Hz to 40kHz ±4dB, which is an excellent result. Sensitivity was measured at 87.5dBSPL at one metre for an input of 2.83Veq. # Steve Holding