KEF uses rear-ports to help you get more punch for your dollar, and we spend a tremendous amount of engineering resources on making sure our ports enhance your enjoyment and don’t detract from it.
Bass ports are an asset to a loudspeaker, they lower the loudspeaker’s bottom frequency and add punch and clarity to the loudspeaker’s bass response. But bass ports can also introduce unwanted noise and resonances, and if they are not designed properly bass ports can leave a speaker sounding soft and underwhelming.
The Problems With A Poorly Designed Port
Ports can allow resonant frequencies that develop within the internal air cavity of the cabinet to escape and those resonances interfere with the pure musical output of the loudspeaker.
In the mid-range frequencies ports can develop “organ pipe resonances” which muddle and distort mid- and high-frequency output. Think of pipe organs in cathedrals – with a very low amount of power they sound massive because each pipe is tuned to a specific note so when that note is excited inside the pipe the volume of that note is greatly increased. Organ pipe resonances are fantastic in a pipe organ, not so much in a loudspeaker.
Ports also create their own turbulence at each port end and this turbulence causes the phenomenon known as “chuffing” where the port actually creates its own noise which obviously interferes with the music you want to hear.
How We Created A Better Bass Port
Placing the port is a lot more important than people realize. In our new R Series, using computational fluid dynamic computer simulation we found the spot where the resonances inside the cabinet were at their least powerful. These are called anti-nodes and that’s where we placed the ports. You’ll notice the ports on the new R Series are off-center because they are located where the anti-nodes are. This ensures the sound coming out of the port is what we want without the extra resonant noise.
Ports are also typically made of PVC or a PVC-like material – they’re hard and brittle. That hard surface and their round shape allows for the development of standing waves within the port. These standing waves can eliminate certain frequencies while artificially boosting others. Either way the result is unpleasant and unnatural.
We solved that issue by changing the shape of the port to an oval: The increased surface area reduces the ability of standing waves to form and interfere with the wanted output. We also use a closed-cell foam material and a port design that expands as the sound pressure within the port increases. This allows you to really throttle up the output without having to deal with the unwanted sonic clutter that typical ports produce.
Lastly, we tapered the ends of the port to allow for a gentle roll-off of turbulence. The energy level of the turbulence is gently and gradually reduced without harming the intended output.
Blade, Reference, LS, R Series
Through diligence of design we’ve been able to lower the bottom end response of our speaker cabinets without introducing unwanted noise and distortion – truly a monumental achievement in port design in its class.
The result? Tighter, faster, punchier bass that sounds the way it was intended to sound.
We think all of the time and resources dedicated to our ports is well worth it.