Tech Tips: Battling Magnetic Hysteresis Distortion to Achieve Pure Sound 

The pursuit of achieving pure sound is an exceedingly tricky undertaking. It can take a lot of mathematics and testing to combat one of the greatest impediments — magnetic hysteresis distortion. One of the best teams at this endeavor are the audio engineers at Danish design house, Purifi. They share a passion for music and a common goal to remove technical limitations in the enjoyment of reproduced music. Presently, they focus their research and development on loudspeaker drivers as the by far biggest overall quality limiter and the audio power amplifier which until now has been the weakest link in the electronics chain. 

Hysteresis happens in any coil that has a magnetic core, for instance, the iron yoke in a speaker driver which sits inside the voice coil. Or cored inductors in crossover filters. Or the ferrite inductor in a class D amplifier. The cause is the ferromagnetic material that’s added to inductors to bring inductance up to usable levels. 

Left to its own, hysteresis produces a recognizable grainy texture in the sound, a blanket of fuzz that always stays just this side of audible, taunting and infuriating like an itch you can’t scratch. This is why the engineers at Purifi put so much effort into removing it from their amplifiers and speaker drivers. 

It could be tempting to simply grasp for a non-hysteretic material, but that is an elusive search. All materials with a permeability above that of air have hysteresis and the objective is to get rid of the distortion, not the magnetic core. “Magnetic cores are just too bloody practical to throw out on the first strike: they keep the stray field locked up and vastly reduce size and power losses,” explains Purifi in two fascinating blogs on the subject. “Changing ferrite grades will not get us very far – the best aren’t more than twice as good as garden variety types.” To see the detailed explanations, begin with, “This Thing We Have About Hysteresis Distortion”. 

5.25-in extended-stroke woofer for ultra-low distortion 

Purifi applies its technical prowess to developing an extensive line of amplifiers and transducers designed to bring new levels of precision and performance for audiophiles. A couple of its newest transducer products are shown here. 

8-in extended stroke driver with ultra-low distortion 

Located in the city of Roskilde west of Copenhagen, Purifi also operates a subsidiary, Purifi Transducer Technology. For more info, see