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« The Reference: Designing the Crossovers and Voicing the Loudspeakers | Main | KEF's Z-Flex Surround: Smoother HF Through Science »
Oct 21 2014

Tangerine Waveguide: It Does Way More Than You Think

The picture of the swamp at left was taken with a fish-eye lens. I was looking for one of those funny fish-eye pictures with a dog's face. You know, where his nose looks ginormous and his eyes are pleading at you not to make fun of him, but I couldn't find any that were licensed for re-use, so you'll have to deal with the swamp picture.

In photography, a fish-eye lens uses a principle known as . Snell's Window is the circular area of light above the water that a person (or presumably a fish) underwater views through a "cone" of light which is caused by light refracting through the water. The area outside the cone of light is either dark or a murky reflection of objects on the bottom of the body of water.

For our purposes, the fish-eye lens distorts the otherwise linear light waves passing through the lens making them appear convex, or non-linear. To use this analogy for a tweeter, we can basically view the distortion of the light waves as similar to the non-linearities of frequency responses across the face of the tweeter.

The parallel between a fish-eye lens in photography and our Tangerine Waveguide basically stops there, but the comparison is a good way to get your head around the audio science we're going to explore next.

Let's Talk About Surface Normal Velocity

As usual, when it comes to all things audio, in order to understand one thing, we have to know about other things first. Without getting involved in things like tensor calculus and covariant derivatives, let's just say that the surface normal velocity toward the dome perimeter is smaller than the surface normal velocity at the center of the dome.

Translation: The center of the dome moves faster than the outside of the dome.

This is because the curved nature of the shape of the dome causes the perimeter to move slower (and at an angle) as compared to the center. A perfect surface normal velocity for a tweeter would be the same over the entire dome surface, but this is not possible because the dome surface would have to stretch. Tweeter domes that stretch don't sound very good at all.

Because the Tangerine Waveguide corrects for the non-ideal dome motion, sensitivity at the top end of the audio band is increased. Dispersion is also improved because KEF's engineers have been able to shape the fins and channels of the waveguide to control the expansion of the soundwave into the horn (waveguide).

And Another Thing: Compression Drivers

The next time you go to a show in a large hall, or your neighbors call for the kids on their bullhorn, you are listening to a compression driver. Spraying your wife by using your thumb over a garden hose is an example of a) bad decision-making; b) a compression driver.

Basically, a compression driver is a small diaphragm loudspeaker that attaches to a horn (the part you see) which is a duct that radiates the sound into the surrounding air. Because the area of the diaphragm of the actual driver is larger than the throat of the horn, high sound pressure levels are created very efficiently (about 9-10 times more efficient than standard cone loudspeakers; the more efficient a speaker the less power you need to create sufficient sound levels).

This is a Celestion compression driver. The diaphragm is facing up; the threaded part connects to the radial horn (shown below).

Definition: A phase plug is a body having an input side of multiple channels for receiving acoustic waves and an output side of multiple channels for transmitting acoustic waves.

KEF's Tangerine Waveguide is basically a radial channel phase plug that creates a slight compression loading effect which results in slightly higher output gain. This extra gain from the waveguide is seen from around 7kHz to around 15kHz. Above 15kHz the effects are minimal (but so is the audio information). The extra gain also helps to mitigate the affects of the peak of the tweeter caused by mechanical break-up. This all results in more efficient high-end with greater dispersion and better fidelity.

Seen below is the Tangerine Waveguide on the tweeter of a brand-new Reference Uni-Q.

All of this and it will protect the fragile tweeter dome from Junior's curious fingers when you're not around!

For more information on KEF's Tangerine Waveguide, see .

Jack Sharkey for KEF

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