With the release of the new Reference Series last year, we raised the bar on our already lofty standards of audio reproduction. That sounds like marketing jibber-jabber, but the truth is, we're all very proud of how amazing The Reference line sounds. This was accomplished a number of different ways, not the least of which was the painstaking method we used to select the crossover components and voice the drivers themselves.

 

A Brief Note About Crossovers

Since different sized speakers are better at different jobs, but a single loudspeaker cabinet is required to reproduce the entire audio spectrum, crossovers are need to make sure the correct signal goes to the correct speaker or driver. There are two types of crossovers – active and passive.

Passive crossovers do their work using only the power supplied by the audio signal and passive electrical components and as such are fixed – the crossover point is designed by the engineers at the time the speaker cabinet is developed.

Active crossovers are electrical circuits that use some level of processing to get the job done. The subwoofer setting on your AV receiver is a type of active crossover.

 

There are almost as many different opinions about crossover networks and how they should be implemented as there are music lovers. At the end of the day, how you enjoy what you hear is pretty much subjective, but there is a great deal of research and engineering that goes on long before you get a chance to listen to a pair of KEF speakers.

 

Designing The Reference Crossover Networks

Each component in the signal path adds some level of distortion (meaning the original sound is changed somehow). This is an unyielding fact of physics. Therefore, extensive objective testing of the components to be used in the crossovers was done to identify potential components with the lowest distortion. Surprisingly, what our engineers found was that there was very little correlation between the cost, spec, or physical size of a component and the amount of distortion it introduced. So rather than just picking or eliminating components based on those criteria, an enormous variety of components were tested to find the best match between the drivers (and the other components). One $0.05 resistor can do a great deal of damage to the fidelity of a crossover (and therefore the loudspeaker), so it's extremely important to be thorough and get it right. Having our own in-house and highly qualified engineering department goes a long way toward making sure we've gotten it right. 

 

In Figure A below, you can see the measured THD (Total Harmonic Distortion) from a 20V input signal for three different inductors that were all similar in cost and resistance but were from different manufacturers and were constructed differently. 

Figure A.

In Figure B below you can see the measured distortion (from the identical signal as above) for three capacitors, all with equal capacitance values but each from a different manufacturer with different construction. 

Figure B.

 

It's easy to see from these graphs that there's a lot more to choosing a component than it would first appear. While listening may be subjective, science is objective and the brilliance of the sound of The Reference lies in the meeting of the two.

 

It's not just that components singularly can make a difference, but how each selected component interacts with every other component in the circuit can have a huge impact on the performance of a crossover network. Even though testing weeded out a lot of components that weren't up to the task, even more were weeded out once our engineers started seeing how each component interacted with every other component. In Figure C (below) you can see some components that passed the distortion screening on their own failed miserably when they became part of a circuit.

Figure C.

To avoid distortion caused by vibrations within the individual components, mastic was applied to the capacitors (due to their construction, capacitors are very susceptible to disruption caused by vibration) and the crossovers were split into two separate sections, each mounted away from each other in the cabinet.

 

It's this attention to every minute detail of design that makes us so proud of our products.

 

Voicing the Loudspeakers

Just like the crossovers, the drivers were also designed from the measured responses of the individual drivers within the final enclosure. Once this was done, hard, subjective science made room for the soft, objective opinions of the listener.

 

This was done over the course of several months and was carried out by a large number of KEF personnel, all with different areas of expertise and with different musical tastes. Concerns raised by any of these listeners were then investigated in the lab using different measuring techniques to try to uncover the underlying cause of the concern. More often than not there was a direct correlation between the objective data provided by the listener and the subjective data uncovered in the lab through rigorous measurement.

 

Rather than simply re-voicing a driver based on concerns and issues raised through the listening process, our engineers were able to dig into the underlying reason for the concern and correct it there, rather than simply applying what could be considered an audio Band-Aid on a problem. This method is extremely time-consuming and expensive, but the end result has been absolutely well worth it.

Gratifyingly, as this systematic procedure progressed the preferred subjective performance merged with the balance that gave the best objective measurements, in particular the lowest distortion and the smoothest and flattest on and off axis frequency response. - The Reference White Paper