After my experience of improved sound quality with a household RF lockdown, it was apparent that the AC Mains power connection was manifesting the difference. My tests showed that powering my networking and consumer electronics with an On-line (Double Conversion) UPS or battery (AC inverter) sounded better than when plugged directly into the AC wall outlet. As per the diagram below, when I moved my Residential Gateway/DSL Modem (Bell Home Hub 3000) and Fibre Media Converter (FMC) to Goal Zero Battery or Tripp Lite Online UPS power, my sound quality (SQ) greatly improved.
What was going on? My networking equipment was on another floor and far away from my listening room, my source chain was inside RF-STOP on battery power and optically isolated; my DAC (...direct to headphones for this test) was also on battery; ..so how could changing the networking AC power source matter?
The only possible explanations are:
A : It is something inherent in my fibre network signal - RF or phase noise made it way to my NUC despite the isolation and reclocking in the FMCs. I tried ultra-shielded CAT8 cables (from FMC to NUC and DSL Modem to FMC) and Tripp-Lite MI-005 Ethernet Isolators. I confirmed no SQ difference with these changes - the issue remained, leaving the only other option...
B : It is due to electromagnetic emissions affecting the DAC. Somehow, the longer length AC mains home wiring was a better radiating antenna than the much shorter battery power cord. Despite the fact that the wavelength of 50/60Hz AC power is on the order of kilometers, the higher frequencies of the switch mode power supplies were modulating the AC power with sufficient radiated energy to affect the DAC.
Magnetic fields are radiated when electricity is flowing through a wire and as the energy (current) increases, the magnetic field increases. Magnetic fields can pass through most objects and can't be blocked as easily as higher frequency RF fields. So aluminum or steel DAC enclosures dont present much of an obstacle to magnetic and lower frequency RF radiation (<30Mz or so).
One solution to this issue is to remove all household electronics except for battery isolated components required for audio. Of course, this is impracticable! Hence, the only rational approach is to directly shield the DAC and look for ways to magnetically shield audio components and cables. The first product Audiowise has released in this regard is the DAC-WRAP Magnetic Shield. More products will follow shortly.