THX certification may cost extra, but the benefits are well worth it. Stephen Dawson investigates the new TXH in-wall speakers from Klipsch.

Klipsch, distributed in Australia by Powermove, is a brand of loudspeakers that established its image in 1946 with its first product, the truly iconic Klipschorn. Incredibly, this loudspeaker has remained in production ever since. In large part because it does something that’s very rare: it turns a reasonable amount of an amplifier’s power into acoustic power.

But, why talk about that when reviewing new in-wall speakers? Because the Klipschorn heritage has influenced the design of most of Klipsch’s subsequent products, including the KL-7800-THX in-wall speakers.

Sound vs Power
Loudspeaker design is hard. There are many competing requirements – improve one aspect of performance and you detract from another – and the physics do little to make the task easier. So here’s an unfortunate fact to do with loudspeakers: the average high quality loudspeaker runs at 0.4% efficiency.

Let me be clear about that: if your amplifier sends 100W to your loudspeaker, 99.6 of those watts get turned into heat in the loudspeaker’s coils and workings, while the remaining 0.4W becomes acoustic energy, filling your room with sweet, sweet music.

That’s an average loudspeaker with a sensitivity of 88dB. (Sensitivity measurements are made with a 2.83V input at a distance of 1m. I’m assuming 8Ω impedance. Mathematically, a loudspeaker of 4Ω is only half as efficient as an 8Ω one if both have the same rated sensitivity.) A compact loudspeaker in a sealed enclosure – this is the design of these Klipsch in-wall units – may well have a sensitivity of 85dB, which makes them just 0.2% efficient. The Klipschorn, by contrast has a sensitivity of 105dB, which works out to around 20% efficiency.

These speakers – the Klipsch KL-7800-THX in-wall speakers – manage a remarkable 91dB sensitivity, or 0.8% efficiency, which is twice as high as a typical loudspeaker, and three to four times as high as that delivered by a compact sealed loudspeaker.

Looked at another way, those efficiency numbers mean that rather than buying a 200W amplifier you can buy a 100W one for the same output levels as less efficient loudspeakers.

Doing it
The trick here is the use of horn loaded compression drivers for the tweeters. There needn’t be much difference between a regular tweeter and a compression driver tweeter, except that the latter may need to have a more robust dome because it is designed to actually compress the air into a small space behind the throat of the horn. For reasons way too mathematical to get into here, that and the gradual opening of the horn results in a closer match between the acoustic impedance of the air and the electrical impedance of the loudspeaker, increasing power transfer and therefore efficiency.

In this case a 25mm titanium dome is used. The throat isn’t smaller, or at most is barely smaller, than the silver dome visible within it. But some rings and struts within the throat achieve the same purpose, as well as directing the sound. Naively designed horns end up being both highly directional and favour particular frequencies, resulting in a honking effect. Klipsch has designed its ‘Tractrix’ horn to avoid all that.

This is a real horn, not merely the hint of one you see on many loudspeakers. As closely as I could measure, the surface of the dome is recessed a good 65mm behind the baffle, while the 80º horn walls open up to around 150mm at their edges.

Below the tweeter is a 200mm aluminium cone woofer. The crossover between the two is at 2,300Hz.

Klipsch specifies the system frequency response as 80 to 20,000Hz +/-3dB. Aside from a relatively limited bottom end, they are true high fidelity specifications.

These are mounted into the aforementioned sealed enclosure which appears to be very solidly made of a high impact ABS compound. Each speaker has six integrated clamps on the sides behind the bezel which can be put in place and tightened using the Philips head screws on the front. They can be likewise loosened, with the clamps swinging back into place clear of the cut-out, by screwing in reverse. A cardboard template is provided to give dimensions for the cut-out.

The bezel is white, as was the finish on the perforated aluminium grille.

The speaker terminals are gold plated, spring loaded, and drilled with a sufficiently large hole to accommodate 12 gauge wire or banana plugs. Having them on the top does expose them to a slightly increased possibility of shorting from contact with in-wall debris, but that can be dealt with by covering them with insulation tape after making the connections. Against that, having them at the top makes the wiring easier since you can rest the units against the bottom of the cut out while wiring.

The enclosures only reach back 94mm from the front of the wall. The front panel measures 298mm wide by 527mm tall.

Loud
As soon as the first music appeared from these speakers it was obvious that they were noticeably louder than my regular high quality standalone bass reflex loudspeakers for a given volume level.

So of course I turned up the power. The Pioneer SC LX-87 receiver is good for at least 140W in stereo mode, but I was reluctant to approach that kind of power. The volume levels were extremely high well before that, thoroughly filling my large test room with clean, musical and dynamic sound. Primus gave a good sense of that because for all the complexity of the music, it also has plenty of ‘space’ within it and depends a great deal on well controlled loudspeakers. These were, with the drumming punching through as it ought to. Claypool’s voice exhibited just a touch of sibilance once or twice, but otherwise the tonal balance was quite qood, with a slight bias towards brightness.

That brightness translated into a particular sweetness with classical piano, with a slight emphasis on the upper harmonics of the middle notes of the keyboard. Likewise some of the early Beyoncé (e.g. Sweet Dreams) hit a sibilant peak at several points, although this wasn’t evident with tracks recorded in a more restrained manner.

I had the speakers mounted against my wall rather than in them so I’d expect the bass level to rise slightly when properly installed thanks to boundary effects and the almost inevitable sympathetic vibrations within modern walls. You will generally not be listening to these speakers on axis, since they must conform to the angles of the walls, and the tweeters cannot be adjusted for direction. So the slight brightness was useful in leading to a smoother off axis balance.

The 80Hz bottom end meant not very much in the way of a solid bass underpinning for the system, and this in part was also responsible for the slight brightness, for you really need that deeper bass as balance. The upper bass delivered by the speakers was strong and clean. But ideally you’d use these speakers with a subwoofer.

They are THX Ultra2-certified, and THX has a clear preference for smaller speakers combined with one or more subwoofers and a crossover frequency of 80Hz, so that in mind I coupled them with my own subwoofer and that completed their sound. With that running they sounded almost completely in balance, and somehow even more powerful than before, without losing any of the clean, detailed performance they’d previously exhibited.

The THX certification assures you of performance quality, and the Ultra2 level means that it is capable of delivering movie reference levels in a 3,000 cubic foot room (that’s 85m3 in Australian), which is a good sized room indeed.

Conclusion
The Klipsch KL-7800-THX in wall speakers are far from cheap, but THX certified gear, especially that certified to one of the Ultra levels, never is.

Nor are any speakers capable of delivering cinema levels of performance for your movies along with high levels of quality music reproduction. Just budget for the subwoofer as well to really get what you’re paying for.