In 2011, KEF introduced the world to the Blade – the world’s first single-apparent source loudspeaker. In 2014, we introduced Blade Two – a slightly smaller version of the original. Blade is truly a magnificent re-producer of sound and music and this article will attempt to shed some light on the technology behind the Blade (and Blade Two).

Things That May Or May Not Be On the Quiz

  • • Bigger speakers are better at reproducing lower frequencies and don’t do a good job of reproducing higher frequencies
  • • Smaller speakers are better at reproducing higher frequencies and don’t do a good job of reproducing lower frequencies
  • • Crossovers are used to make sure the right frequencies go to the right speaker
  • • Nature doesn’t make sounds through speakers. Nature makes sounds naturally. Natural sounds come from a single point source (your mouth, the soundboard on a violin, a drum, etc.)
  • • By default, loudspeakers cannot easily reproduce sound from a single point source

 

To illustrate a fundamental problem in sound reproduction, let’s listen to Rush's 1980’s master-class in anthemic rock and roll: Limelight, with particular attention to Geddy Lee's vocals. 

Below is a screen-shot of an RTA graph where Lee sings “lighted stage.”

We can see by the screen capture from the Real Time Analyzer (RTA) that Lee’s voice has components that peak around 250Hz, 500Hz, 2.1kHz and 4.1kHz. These frequencies are a combination of the fundamental and harmonic frequencies in Lee’s voice, sibilance, the reverb being used and room acoustics. All of those items factor into the singular voice you hear coming from Lee’s mouth to the microphone.

The crossover points on the Blade are 350Hz and 2.3kHz (320Hz and 2.4kHz on Blade Two). This means frequencies below 350Hz are directed to the low-frequency (LF) drivers, frequencies between 350Hz and 2.3kHz are directed to the mid-range driver (MF) and frequencies above 2.3kHz are directed to the tweeter (HF driver). For the sake of this discussion let’s ignore what actually happens at the crossover point and just work with the frequencies as they are listed.

This means that to reproduce the line “lighted stage” all three speakers in a 3-way speakers system (like Blade) are being asked to work at the same time. It also means that in order to replicate a single point source, all three speakers must then deliver all of the frequency components of Lee’s voice to the listener’s ear at exactly the same time. Now add the other instruments and ambiance and you can see that to actually reproduce music as it is meant to sound, you can’t simply throw some speakers in a box and expect anything resembling a good result.

Imagine the picture to the left represents sound waves generated by different speakers producing a musical component at the same time in slightly different physical locations, and you’ll get an idea of what happens to your music with a standard 2- or 3-way speaker design. Everywhere a frequency (or ripple on the surface of the water) intersects with another ripple, disruption occurs. That disruption takes on the form of incoherence muddying the sound, sympathetic vibrations artificially making some frequencies louder and unsympathetic vibrations diminishing or outright canceling other frequencies. This is called lobing and it’s not good.

If the goal is to reproduce music as naturally as possible, such that the listener feels like he or she is sitting in front of an actual live performance, then these issues have to be overcome or all we are doing is approximating the original musical performance.

 

First the Uni-Q

At the end of the 1980s KEF engineers began work on the first Uni-Q drivers, and through continuous innovation and research, we find ourselves now with a speaker that can faithfully reproduce sounds over the frequencies covered by both drivers in unison, that is to say, the Uni-Q reproduces sound from a single apparent point source. This is not an easy task to accomplish, and it certainly requires design work that far surpasses what is found in other conventional “co-axial” drivers. There is a ton of technology and scientific reasoning that goes into the design and manufacture of our Uni-Q drivers, so we’ll skip over the nuts and bolts in this discussion, but you can get an in-depth technological description of the Uni-Q by reading “Why So Called Co-Axial Speakers Aren’t Uni-Q” (KEF Blog August 15, 2014).

The Uni-Q was a great start in accomplishing the nearly impossible: a single apparent source loudspeaker, but we have to consider frequencies below the handling capability of the Uni-Q driver, especially in a large loudspeaker designed to fill even the largest audio listening space.

This brings us to the next logical step in the evolution – a complete loudspeaker cabinet designed from the ground up to produce a single apparent source.

 

Then the Blade

Blade is absolutely gorgeous, but that’s a happy unintended result of the science that brought about the shape. Blade is a 3-way loudspeaker (LF, MF, HF) that has been uniquely designed so that all three frequency bands (and therefore all the music you are listening to) appear to come from a single point in space. To clarify a bit, this also means if an instrument is panned in the mix to 40% right and 60% left for example, the single point in space that that instrument will occupy in the soundstage created by a pair of the Blade loudspeakers will be 40% right and 60% left. No matter where you are listening from.

The four LF drivers in the Blade are in symmetric pairs and are physically very close to the Uni-Q driver. By design the cabinet is extremely narrow and curved, reducing the affect the cabinet itself has on sound dispersion while allowing all six drivers in the 3-way design (4xLF + 1xMF + 1xHF) to be situated very close to each other. Bass frequencies are non-directional, so the LF drivers are affixed firing perpendicular to the Uni-Q. All of this leaves the listener with all of the reproduced sounds seeming to come from the same point in space and time – a single apparent source.

The LF drivers on one side of the cabinet are also fastened to their mate on the other side of the cabinet through a force-cancelling tensioner which removes vibrations that would otherwise find their way to the cabinet. Since the cabinet doesn’t vibrate in sympathy with the LF drivers, you are then spared the misery of listening to the box the speakers are in instead of exactly what the speakers are recreating.

Finally, when two Blade are setup up in a stereo pair, the soundstage jumps to life and becomes three-dimensional with a clarity and coherence that simply cannot be achieved in a conventional design.

This has all been achieved not through magic or some sort of acoustic dark art that tricks the listener into thinking they are hearing something they are actually not hearing, but through good solid science and design that exactly delivers to the listener the majesty and magic of music how it was intended to be heard.

 

Jack Sharkey for KEF