“Black background” — What really contributes to this phenomenon?

Ever used your dB meter in a 'quiet room'?

Nothing running.  Shut off EVERYTHING.

"Black" is subjective.

Even in the 'quietest' of spaces, you're still breathing and your heartbeat is occurring with annoying regularity....

...and that blood running in your veins is 'hissing' away....*sigh*

Best you can hope for is a darkish gray....;)

Spending more of ones' time listening for flaws...mho...

..but a pair of the DS3's and a good sub would be fun for a change. *S*  Again, mho...