KEF’s vented tweeter technology offers the purest, fastest and most articulate high-frequency response you'll likely ever treat your ears to. Here's an in-depth discussion of what exactly a vented tweeter is and why your ears deserve them.


The Problem the Vented-Tweeter Solves

Air build-up behind a tweeter dome results in excessive force pushing back on the tweeter dome which in turn develops unwanted harmonics.


The Details

In order to be fast enough to properly replicate high-frequency vibrations, tweeter domes are small and thin, which also means the KEF Vented Tweetervolume of space behind the tweeter dome is small. Since soundwaves vibrate off the front and back of a driver, this makes tweeters especially vulnerable to the non-linear vagaries caused by pressure build-up behind the tweeter dome itself.


In typical tweeter designs, the energy that radiates out from the rear of the tweeter dome has nowhere to go, so since it exists and has to do something (every action has an equal and opposite reaction) it pushes back on the tweeter dome. When the dome moves backward the cavity size behind the dome is decreased causing the pressure behind the dome to increase. This causes the return pressure on the dome to become non-linear. That non-linearity produces unwanted harmonics in the signal.


The Solution

By increasing the cavity volume (without changing the essential shape and size of the tweeter itself) we have reduced to the point of elimination this pressure build-up and subsequent pushback, resulting in better high-frequency response, clarity and articulation.


In the R Series and the 12th Generation Uni-Q we’ve gone a step farther and dampened the vent and accounted for air turbulence in the gap between the mid-range and tweeter.


The Science

  • When the tweeter is resting (not creating sound) the air pressure behind the dome is equal to the air pressure in front of the dome, so there is no force on the dome from air pressure
  • When the dome moves backward as it vibrates, the volume of the space behind the dome shrinks (the cavity volume decreases)
  • This reduced cavity volume increases the pressure on the dome (from the rear cavity)
  • The change in pressure causes a restoring force that pushes the dome back to its original, resting, position
  • This force becomes a non-linear "spring" that causes harmonic distortion


KEF R Series Shadow FlareIn theory, the solution is to make the cavity behind the dome bigger but that's not as easy as it sounds: We still have to create a tweeter that is responsive and actually sounds good in its intended frequency range.


With all of this in mind, and with a lot of notes on scraps of paper and calculations that would make the heads of mere mortals explode, our engineers have placed a sealed duct (vent) behind the tweeter dome assembly which serves to increase the volume of the cavity. Acoustic damping material that neutrally absorbs the rear-firing sound energy was added to the vent, eliminating a build-up of pressure and standing waves in the expanded cavity space.


There's more to it of course, but we'll let all those speaker companies that don't have vented tweeters figure out how to do it on their own.