Network expander and AC quality

i have been curious about this as well

be great if someone who is truly qualified to answer would chime in on this question

Totally qualified. Before answering, we understand the question to be: 

We know RFI is bad, but what if we paid to put it there? Is it still bad even then?? 

That's the question? ;)

@millercarbon

i won’t speak for the op, but yes i think your restatement of the question is correct - to expand a bit....

my situation is like many -- no lan/ethernet connection in a particular hi fi/media room -- so lots of music streamers with ethernet-only connections (no wifi) can’t be used unless we employ a gadget that brings the ethernet jack into the subject room from another room -- these gadgets use the ac powerlines in the house as the transmission medium - something like this:

https://www.amazon.com/TP-Link-AV600-Powerline-Ethernet-Adapter/dp/B00AWRUICG/ref=sr_1_3?crid=2SEJ31NIOKHAI&dchild=1&keywords=ethernet+extender+powerline&qid=1598397375&sprefix=ethernet+exten%2Caps%2C249&sr=8-3

so the question becomes - geez we obsess already over having a clean ac feed to our precious hifi gear, use expensive cleaners/filters etc etc for best possible SQ - so what is this thingy gonna do to that pursuit? all said and done are we worse off if we use it?

bearing in mind, without the ethernet connection, we are streaming via wifi so there is already airborne radio frequency pollution - but i guess in this case it is not in the powerline...

As an addendums to my question,
1. If not filtered out, what is the sonic consequence of this added rf to the AC power? I.e, how does it affect the sound?
2. Which components would filter out this rf? Power conditioner? or power supply inside streamer, cd player, preamp, amp, etc?

This is not radiated rfi. It is directly on the AC power line.

Yes the RFI is on the line and yes it will sound better without, but its not like you think. It can be reduced with a transformer. The way a transformer works, the field in the primary induces a current in the secondary and because of the physics of the way this works only a certain frequency range makes it through. Which is fine because with AC its all 60 Hz. RFI is radio frequency, much higher, orders of magnitude higher, and so it doesn't make it through. 

This however is only a small part of the story. Rather than focus on RFI or other noise on the line its much better to think only of things that improve sound quality. Forget why, focus on what. Because bottom line it really doesn't matter if its RFI or what it is, if it sounds worse it sound worse and if it sounds better it sounds better. So cut out the middleman and focus on the sound. 

Then what you can do is actually listen, and learn. Listen to your system with the darn thing connected and on, and listen with it disconnected and off. If there's no difference either you're a lousy listener or it really makes no difference. Either way, if you can't hear a difference then who cares what anyone here says? Which also means if you can't hear a difference why spend money on some story about making a difference? That's how easy it is. 

Then to find out what RFI really sounds like, for free, listen to your system some nice evening. Stop for a minute, flip off a bunch of circuit breakers, go back and listen again. That nice reduction in grain and glare you just heard? That is what less RFI sounds like. 

Every wire everywhere is like an antenna. That's all an antenna is, is a wire. (A tuner tunes into one particular frequency out of this whole mess of frequencies. That's why we call it a, uh, tuner.) Radio waves everywhere induce tiny amounts of current in every wire. If you look inside your panel you will see they are all connected together. Flipping breakers breaks this connection. Each one disconnected is that much less RFI. You can even prove its RFI and not other noise by switching off circuits with things running and circuits things are not running on. 

Okay so that's RFI. But you can also compare things like power cords and conditioners. Forget the stories, the marketing stories, they are just that, stories. Just try some and listen. What you want is that same sort of improvement you heard with the breaker test.  

Or, if you heard no improvement, that's fine too. You get off easy. Long as you can live with the gnawing feeling there really was something there you should have heard. Because there was. And so now you know about RFI.

MC,

Thanks for your take on RFI, and your suggestions on personal comparisons.

I have done a decent amount of experimenting and tweaking with power cables, interconnects, power conditioners, room effects - even fuses, but to a lesser degree. So I know that everything matters. I belong to an audio society that meets monthly at different local high end dealers. So (before Covid) I got to hear many components and tweaks there, (including SR equipment). I try things out at home as well, always trying to balance expenditures and SQ. 
I have two good quality systems in separate rooms. Both systems are better than they have ever been, and it’s taken years to get to this level. The less expensive one sounds slightly better, but I believe that it’s due to the room acoustics, and listening position, not the equipment so much.

I actually enjoy listening to music more than ever, but the upgrade urge never quits. Strange hobby.

One more little tidbit: recently enrolled in three virtual Zoom music courses - Russian Classical Composers, Rock & Roll of the 60s, and The Blues.

Regards