Why The 12th Generation KEF Uni-Q And Single Apparent Source Are Significant

Over the last 30 years, KEF has developed over 50 examples of the Uni-Q driver array, designed specifically for the range or models in mind. In addition, these 50+ iterations have been grouped into various generations. Within each generation, different Uni-Qs present various levels of performance, with a common technological thread.

Uni-Q is now in its 12th generation. For the new Blade and The Reference series, KEF engineers took the opportunity to redefine the state of the art and provide a flagship technological example of the latest and greatest 12th generation Uni-Q. This iteration of Uni-Q presents an advancement in every single aspect of the driver array and every single component has been revised without compromise. Both midrange and tweeter have been designed from the ground-up for this application, ensuring seamless integration of both drivers into one, both acoustically and as a physical package.

To understand the significance of the 12^th generation Uni-Q mid-range/tweeter it helps to understand a bit about psycho-acoustics. Basically, Uni-Q is a heroic effort to address what has been known for decades about how the ear and brain process sound. The problem, and hence the heroism, is that it isn’t so easy to deal with what we know about the ear/brain.

How We Perceive Sound

To understand this, imagine a piano in a room. A pianist plays a note. How do we know where the piano is in the room?How do we know it is a piano?

We know from much scientific study that the ear/brain uses the very first sound to arrive from the piano to identify its location. Simple enough. This makes some sense if you put it in evolutionary biology terms: hundreds of thousands of years ago as humans were evolving, those who could accurately identify where the predator lion was survived more often than those who couldn’t. Simply put, having an ear/brain system that can localize sounds is important. Humans are good at this.

But, if you think about it, we also want to know the difference between the lion and a sparrow. To do that, the ear/brain relies on something called the precedence effect. In effect, the brain adds up what the ear hears in the first 25-50 milliseconds in a way that integrates all the available sounds into “one sound”. This seems to maximize the available information so that humans can identify what is making the sound. In the case of our piano, the addition of the direct and early reflected sounds is what allows us to perceive the note being played as coming from a piano, not a violin or a guitar. Humans are good at this too, and you don’t even have to think consciously to do it.

How Loudspeakers Affect Perception

This becomes important when we consider loudspeakers. The loudspeaker radiates sounds at various angles into the room. Ideally, we want the output of the speaker to mirror the input signal. We don’t want cellos to be massively louder and flutes to be massively softer than they were in the original orchestra when it was recorded. So, we say we want the speaker to have flat amplitude response across musical frequencies. Again, simple enough. But now that we know the ear/brain integrates all the sounds in about the first 50 ms to perceive what the orchestra is doing, we can also understand that we want the speaker to have the same flat amplitude response off the main axis so that reflected sounds are naturally balanced. The level doesn’t have to be the same as the direct sound, but if the off-axis response exaggerates or diminishes certain frequencies, the ear/brain will add this into the sonic picture and it will make the piano or guitar or bass or violin sound different than what the musicians intended.

Why Uni-Q Is Important

 The smooth off-axis response goal so that direct and early reflections sound as similar as possible isn’t an easy engineering task. Uni-Q combines the midrange and woofer to avoid driver to driver interference. This integrated mid-range and tweeter also simplifies aligning the timing of their sounds. It also provides an acoustic waveguide to help make the off-axis response of the mid-range and tweeter as similar as possible across frequencies. The crossover networks play a role in this as well. You can see in this chart how the early reflection measurement has a very similar character to the listening window measurement:

The idea of Single Apparent Source, used in the Blade One Meta and Blade Two Meta, is to extend the engineering for time alignment and smooth off-axis response into the lower frequencies. Bass with most speakers is omni-directional, but we have to remember that the bass drivers will typically have meaningful output well into the midrange. For a state-of-the-art speaker, this extra effort is another step toward ideal music reproduction.

Minimizing Distortions

And, now that we understand the precedence effect, it is a bit easier to understand that we want to minimize distortion. It helps to add that musical instruments sound different in large measure because they make sound over time. Middle C on a piano and guitar have the same frequency, but the resonances and vibrations of the hammered piano string and frame are totally different from the resonances and vibrations of a plucked guitar string. These resonances and vibrations decay to very low levels, but levels which we still can hear and use to characterize the sound. So, if the signal has even small distortion components added to it, then those distortion components will be added and the guitar won’t sound as much like a guitar. Or a Stratocaster and a Les Paul may sound more similar than they should.

With the 12^th generation Uni-Q, KEF has addressed a range of distortions. As an example, the KEF team found that the elastomeric damping typically used to isolate the driver from the cabinet still allowed the cabinet or the driver to radiate out of phase sounds into the room. So, the engineers developed a way to move the damping inside the cabinet toward the back of the Uni-Q driver. The result (green curve below) is to smooth out resonant spikes that more traditional damping systems still had:

You can appreciate that packaging the tweeter and mid-range together provides a range of challenges. Every part of the Uni-Q array has been designed to bring further improvements, including a new tweeter gap damper and new waveguide design. The Uni-Q driver has a completely new set of motor systems as well with and new spider and advanced magnetic properties.

This provides greater electro-magnetic linearity and is especially effective at higher output levels. The moving mass has also been improved. Note the improved linearity of the blue curve with displacement for example:

Metamaterial Absorption Technology

There are many more improvements on offer. The biggest of these, the use of Metamaterial Absorption Technology, merits a separate discussion which you will find here.