QSC K10 & KSub

QSC's K-Series speakers look serious enough, but can their sound wow the crowd?

The current K-Series range of portable self-powered speakers from well-known manufacturers QSC consists of three two-way full-range designs — the K8, K10 and K12, with the numbers corresponding to the low-frequency (LF) driver sizes — and a band-pass subwoofer called the KSub. All the models, including the KSub, are compact and easy to handle, and they all use the same QSC Class-D amplifier module to provide the power. I spent a couple of weeks getting better acquainted with a complete system: a pair of K10 speakers and a single KSub.

The QSC K10 is part of a range of speakers, also inlcuding eight- and 12-inch driver versions.I have to start by saying that the K10 is a good-looking piece of gear, with a very solid feel about it. The enclosure is, unlike that of many self-powered speakers on the market, made from ABS rather than the more common polypropylene moulding. The result is a hard, rigid structure with a smooth, matt black finish, reminiscent of a clarinet or recorder body. It's interesting to come across something a little out of the ordinary, and the use of this harder material is claimed to not only make the cabinet stronger than many of its competitors, but to offer acoustic benefits at low frequencies.

The smooth finish seems fairly resistant to surface scratching and is much easier to wipe clean than a textured poly moulding. The K10 unit appears to be very well made and didn't produce any clunks, creaks or internal rattles when I gave it a bit of deliberate rough handling, including dropping it from about 12 inches onto the hard, carpet-tiled floor of my workshop!

The entire front area is covered by an attractive powder-coated steel grille that fits securely, and appears to offer excellent protection to the drivers behind. One thing I do like about the K-Series top boxes is the slightly concave shape of the front surface, which prevents the cabinet from rolling around if it's laid face down. It also makes life easier when packing things up against the speaker, and it's almost impossible to make a dent unless you're really determined.

Good Handling

The K10 is equipped with two cast-aluminium handles, one on the side and the other on top. These are of excellent design and quality: a really good plus point and not to be taken for granted on portable equipment. The handles are large and are backed by good, deep recesses, which offer plenty of room and protection for your hands. There's only a handle on one side because the K10 is asymmetrically shaped for use as a floor monitor, in which orientation it is stable and secure — and it actually looks like a proper monitor, rather than a PA speaker laid on its side.

Underneath the K10 is one of my favourite features: a pole socket which offers a choice of vertical mounting — speaker firing straight out parallel to the floor — or a downward angle of 7.5 degrees. When speakers are so equipped, I often like to use them angled down toward the audience area, especially in smaller venues. The sockets on the K10 are very easy to adjust: they rotate smoothly through 180 degrees and click firmly into place, and with the speakers mounted on a standard 35mm pole or stand, the cabinet doesn't wobble or spin round under the hanging weight of the attached leads.

Do note that the information in the user manual: "K10 WARNING! Do not use a loudspeaker support pole longer than 28.5 inches (724 mm) when supported by the KSub subwoofer”, can be safely ignored for the K8 and K10, provided the pole length doesn't exceed 47 inches (the height of the supplied 31-inch pole plus the optional 16-inch extension). However, I found the supplied pole too short for many applications without the extension.

Round The Back

The K-Series speakers are all fitted with the same amp module, which is rated at a generous overall 1000W. That should ensure there's way more than enough headroom available for normal operation, especially when the on-board protection, limiting and driver capability are taken into account. The low- and high-frequency sections have independent amps rated at 500W each, and the efficient Class-D design delivers a high power-to-weight ratio.

The rear panel of the K10 is full of controls, including switches for controlling the tone and a handy socket for remote gain control.It would be pretty surprising if a product with a QSC badge didn't incorporate some clever amplifier technology, and the K10 is equipped with a comprehensive set of protection measures to guard against amplifier and driver malfunction. In terms of what's available on the panel itself, there's a lot. The input section is actually a two-channel mixer, with inputs labelled A and B. Channel A has an XLR and jack combi input that can be switched to work with either microphone or line-level signals. Channel B is line-level only but the XLR/jack input is complemented by a pair of unbalanced RCA phonos, effectively providing a third input allowing replay devices to be directly connected.

Each input channel has a direct, balanced link output and there's a balanced, line-level mix output too, for onward connection to another K10 or remote system. The two level controls are fitted with nicely recessed rubber knobs. I think this is a very good practical feature, as they are almost completely protected against accidental bumps, scrapes and adjustment. The mains input connector is a locking type (it has a locking socket, but is fully compatible with ordinary non-locking IEC power leads) which is another useful feature: I've lost count of the times I've seen mains leads escape from active floor monitors.

Take Control

The rear panel contains a number of other controls that access more of the K10's feature set. A degree of preset sound shaping is available using two slide switches: one looks after the HF range and offers the choice of 'flat' or 'vocal boost' EQ, while the other provides three options for the LF, namely 'ext sub' which introduces a high-pass filter, 'Deep TM' for additional low-end extension and the standard 'Norm'.

I experimented with these controls in my workshop and in two different venues, and was able to find settings that worked well in all three locations. When they were working as full-range cabinets, and particularly with playback material, I preferred the K10s set to 'flat' and 'Norm' as I liked the tightness of the low frequencies and the smoother mid and top. I did deploy the vocal boost setting when using the rig for a loud-ish pub-rock band, though (with the external sub too, of course), and then went back to the flat setting when using the speakers for a speech-only presentation event, as it just seemed to suit the room.

A useful option is the ability to change the behaviour of the front-mounted LED indicator. Another slide switch can be set to 'power' (the normal on or off indication), 'limit' (which also shows power on and off but the LED glows more brightly under limiting conditions), or 'off' which saves you having to tape over the indicator if it would be a distraction, for example with AV work.

Taking the flexibility theme a bit further, the K10 can be remotely controlled with a simple passive circuit, and a three-pin Euroblock connector is provided for this function. The gain can be controlled by applying a control voltage (zero to 5V DC) to the middle pin, while one pin provides a suitable 5V supply and one is at chassis earth. All that's needed to control the input level of one or more speakers from another location is a simple variable-resistor circuit. This is extremely useful if the speakers at installed at a great height.

Digital Performance

Self-powered speakers have numerous advantages over their passive counterparts, including integral signal processing, which not only provides protection but optimises performance. Overall energy efficiency is high on the agenda these days, and the K10 has an automatic standby mode that kicks in when the DSP hasn't detected the an input signal for a five-minute period: the power amp is switched off, but everything comes to life instantly when a signal is received.

In practice this isn't noticeable: the idle noise is generally low on these speakers so you don't notice when the amp shuts down unless there's absolutely no ambient noise. Protection against thermal threats is provided by a combination of monitoring and control processes, including signal limiting and an automatic internal fan. The fan runs only when necessary and is extremely quiet, while clip protection is also discreetly taken care of. You'd have to be doing something silly to overdrive or overheat this amp.

The DSP is programmed to make a number of frequency-related amplitude and timing corrections, in order to achieve the best result from the whole set of components in the system. This includes taking account of the driver and enclosure characteristics, and results in a consistent performance across the usable frequency range. The QSC monitors use a proprietary process that they call 'Intrinsic Correction', which takes a large number of performance measurements and applies the exact correction needed to achieve an even response. If you really want to know the ins and outs of this there's an interesting read to be found at www.qscaudio.com/products/dsp/SC28/intrinsic_correction_whitepaper_2007.pdf.

Normal mode produces a substantially flat overall response, but the K10 can produce additional low-frequency output: the Deep TM setting applies an EQ boost to the LF signal, and since driver over-excursion and power-amp clipping need to be avoided, the K10 DSP detects and attenuates only the very short transients that would otherwise cause problems, but doesn't affect the rest of the material. The effect sounds quite natural (just like turning up the low EQ on the mixer), and there's a marked increase in LF output when Deep TM is applied, even at relatively high volumes. For me, the LF performance of the K10 was more than fine anyway, and I liked the sound of it without the extra lows, but it's nice to have it there for use as required.

Good Coverage

The three full-range models in the K-Series are interesting in that they share the same basic styling and external proportions, and also use the same HF compression driver, but they are engineered to produce three different horizontal dispersion angles.

This is because the three different-sized woofers all have their own dispersion characteristics, and what QSC have done is to match the HF coverage to that of the LF driver at the crossover frequency. This means that the HF and LF balance doesn't suddenly change between different listening points. The K10 has a nominal 90-degree HF coverage, which is the most common figure for portable speakers in this format, and I found the coverage to be even and consistent.

The Lowdown

The KSub has some wonderfully sturdy castors on the back, making it pretty easy to move about.The KSub is an unusually shaped compact sub using two 12-inch drivers in a band-pass design, and is the only enclosure in the K-Series that's made from birch plywood. It's a slim, elegant-looking thing and is endowed with good handles and a set of superb-quality castor wheels — the best I've ever seen. It ships with a mounting pole that screws into the threaded socket built into the top surface. The KSub uses two of the same 500W power amps common to the rest of the range, but has a slightly simpler control panel.

It still has two independently controlled inputs (which are summed and sent to the amp) but no mix output, unbalanced inputs, mic input or vocal EQ settings. It does, however, have an input polarity reversal switch. The two line outputs are derived directly from the inputs, and therefore output full-range information. When fed to the K10s, the 'ext sub' setting would normally be used. The same Deep TM technology as described for the K10 is also employed in the KSub, and noticeably boosts usable low-end output.

Good Vibrations

I spent several days using this system, and I found it to be an even-tempered and adaptable rig. Despite the high amplifier power capability this obviously isn't a solution for large venues. It does produce a powerful sound, though — much more than you'd expect from something this size — and could easily handle your average, loud pub band. When I used the K-Series speakers for such a job, they were pushed hard and performed well, maintaining vocal clarity with ease, and the KSub pumped out a generous amount of kick drum and bass. In fact I had to back off the sub level twice during the evening and never needed to fire up the Deep TM circuit.

While not quite as feature packed as the K10, the KSub has enough options to suit fifferent situations, including a little extra low end in DEEPTM mode.I did feel the system sounded a little light in the mid-range compared to my usual speakers, and it took me a few numbers to get used to it. But quality always wins, and by the end of the night I was wondering if I could afford (or justify) a pair in my own inventory. One noteworthy point was the cool running of these speakers: after a somewhat sweaty but successful live session I was surprised to find that the rear panels on all three units were barely warm — almost cold to the touch — and it wasn't because the band had been holding anything back!

Although, in amplifier rating terms, you could quite properly describe this system as '3kW' I think the K10 and KSub combination is more about quality and consistency, with a virtually idiot-proof amount of headroom and automatic protection. My favourite application was using the system for a business presentation, where something visually discreet was required. This is a very compact and very clean-sounding setup, and I'd be equally happy using it in posh mode or pub mode.

Thumbs Up!

The K10 speakers are great little performers and have a sweet and even mid and top end, with very consistent coverage which, in my 'real' venues, provided good intelligibility beyond the specified 45-degrees off-axis point.

When teamed up with the KSub they grow into somewhat bigger performers altogether, and can deliver an abundance of crisp clear output suitable for a full live performance system. I like the look of the K10 and KSub a lot, and when used together, the proportions and styling look just right. The K-Series is a classy system all round, combining powerful performance values with portability, and I'll be sorry to return it.