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

How to enjoy the tiniest of musical details and lowest noise floor against the blackest of backgrounds?  
Power? Sources? DAC? Amps? Cables? Tweaks?  Vibration control? Any of these in particular?

Power first,get that part right from the in the wall and from the wall and work your way up from amp ,source ,preamp and good cables . The room and speakers will let you know if you've succeeded . 
Power? Sources? Turntable? Amps? Cables? Tweaks?  Vibration control? Any of these in particular?

No. Not really. It's all of them, and more.

Oh and, fixed it for you.
room, noise, appliances, AC, windows, etc....think BIGGER than just the stereo and AC power...few do..

double core door, weatherseal, etc...

and a good spl meter will help you establish a baseline noise floor, so few audiophiles own or use them...
Noise floor down. Power, components, cables, vibration control, room,.......mood, and no lights.

@tomic601 what spl meter do you use? I like that suggestion.

Overall, I think it has been the dedicated line that helped the most so far. Unfortunately, there is a refrigerator 25 ft from the listening position that ain't going anywhere... 
"ebmEverything helps."

It is the result of a low noise floor. Everything matters, from low noise power supplied to your system, to draining internal noise from components, to how components work with the rack where they are placed, and isolating components from outside noise and vibration.
I agree that eliminating noise from the system will achieve that 'black background' that many are looking for. I also think it's helpful to put noise into two different categories, one being interference and the other being random noise.
Interference is what most people think of and is under your control to a degree - so mains hum, radio frequencies etc. There are established strategies to deal with these and you can move equipment around or switch off sources of interference.
Random noise (think white noise) however is a product of the electronics within your equipment - so the designer has decided how much noise is acceptable and that is what you may or may not hear. This is mostly dictated by the resistances in the signal path e.g. if you have a pre-amplifier with a 10kΩ pot for a volume control then the absolute minimum amount of noise will be -114.9dBv if that is followed by a power amplifier with 30dB of gain then the noise floor can be no lower than -84.9dBv (as the noise is amplified along with the signal). So to get the lowest possible noise you need Hi-Fi equipment designed to operate with low internal resistances. For example if you replace the pot in the above example with a 500Ω attenuator then the noise values are -127.9dBv and -97.9dBv respectively. So if you want truly low noise you need to have equipment that is designed with exactly that in mind.
pragmasi gets closer than most. There's at least four main types or categories of noise.

First and most obvious is room noise. Fans, heaters, airplanes, all that stuff. This is the one out of all the noises you might actually be able to quantify with a meter. It is also the least relevant to obtaining a black background.

Then there's the room noise that is created when playing your music causes the room and everything within it to vibrate and resonate, and all that chaos of vibration gets fed back into the air as noise. Which if the room is treated just right we like it and call it ambiance. Otherwise we call it slap echo or whatever. Either way, again, very little to do with black background.

Then there's system noise or what most call S/N ratio. People sucked into the digital con game tend to love measuring stuff and digital does measure really low S/N. But then we have no way of hearing it without hooking it up to all the other stuff in the system, which is in a room, and the much worse S/N of all of that drowns out the digital number, which was only there to look good on paper in the first place. In any case, and as usual, go f, oops sorry that was Tom Cruise in Tropic Thunder. As usual, this one is not all that either. Although it probably is a lot less unimportant than the others, which are almost completely unimportant. 

In terms of obtaining a black background the one that rules above them all is the one no one has figured out how to measure but everyone easily hears no problem, and that is the purity of the signal and the ability of the system to stop as fast as it starts.  

Most audiophiles shoot themselves in the foot here. They think, fast is good! Gotta have fast! It is real easy to hear when something is fast, it takes off instantly. This catches your attention and you buy it, only later to tire of it because this kind of fast tends to be more etch, hype, grain, not true speed, and you catch onto this, get fatigue, upgrade. Round and round. 

True fast is the sound stops just as fast as it starts. 

The black background we want to hear, it is the acoustic of the recording venue. Being typically either a well treated recording studio or a large concert hall, either way the room itself makes no sound of its own. The sound we are looking for is extremely low level. But here is the key: low level relative to the music signal. 

This is why the room noise matters, but not that much. And the system noise matters, but not that much. Because when you are listening, whether to a recording or a live event, you are not some meter measuring out absolutes. You are a human being making comparisons. It is the sound of the room relative to the sound of the performance that tells you where you are. When you get that balance right in your system, there is your black background.

This is why springs work so well. Without them you play music, it excites the whole room. Your speakers, amp, source, are all part of the room. They all vibrate, and this noise feeds right back into the signal and smears those subtle acoustic cues and you lose that black background. Then you add springs, now the room still vibrates but no longer feeds back into the system. Signal purity improves and you get a black background. Speakers, free to move on their own, are no longer anchored to the chaotically vibrating room, and you get your black background.

Or you add a good power cord, interconnect, or speaker cable. Signal purity is the hardest one of all. When the signal is as unmolested as possible then you get your black background. 

Proof positive of all this is in my room. The room noise is very low and so everyone easily hears the system noise. When turned up to satisfying volume level the system noise is easy to hear from the sweet spot. But that doesn't matter because when the needle drops the groove noise is all you hear. But that doesn't matter either because when the music starts then suddenly, amazingly, there it is, floating in the room, in a background big and black as a cave. 

Oh and this thing stops so fast with signal so pure you can hear that black background acoustic even when the music gets good and loud and complex. Freaking amazing! Because even though I said those other things don't matter all that much, they do matter some, and you want it all you just have to do it all. 

Just use your ears. Not a meter.
Proof positive of all this is in my room. The room noise is very low and so everyone easily hears the system noise.

That was my point... the system noise doesn't need audible either, it's the components that are creating it.
there are 3 sources of noise:

Mechanical noise coming from unwanted vibrations and resonance...

Electrical noise floor level of the HOUSE not only from the room and gear...

Acoustical treatment and controls to help listening what has been gained by controls of the mechanical and electrical dimensions.. But the room non isolated will be also a source of noise...

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redwooodaudio B and K calibrated mic into Studio Six on an ipad. The trusty and hyper durable Radio Shack analog meter is quite good for low frequency work. Yes dedicated line is wonderful 

true fast is all the drivers start in the right direction , see the impulse response test for loudspeakers. The flat earth random discovery society is anti meter and anti laser. They are no substitute for listening but they are valuable tools. We don’t attain black backgrounds in the recording studio by letting environmental noise in. 
@tvad what kinds of mods did you undertake?
The first notable improvement in blackening background in my system came from components with robust power supplies. These changes initially came from having early source components modified with significant improvements made to power supplies. The background became blacker. No question. Improvements were easily heard. 
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I like the question. I purchased components already known for their quiet background. I really like a black background and low noise floor, silent computer, etc. And after getting a black background you just found out that your new noise floor is your tinnitus...

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...

i never understood the "black background" bit- any well-reproduced audio lets you hear to "the bottom" as it were, a black background gives a language parser the impression that the instruments [as described by the listener] are heard as coming from an abyss with no audible studio acoustic or studio electronic noise along for the ride. it reminds me of people telling me that "phonograph recordings properly produced and reproduced, have a black background," when with my own ears i ALWAYS heard some noise in the background. 
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practikl wrote:  “And after getting a black background you just found out that your new noise floor is your tinnitus...”

I literally laughed out loud as this has been my experience!  I frequently work in an environment that has multiple (40ish) video recorders in a huge racks that all have fans going within them.  Then there’s the noise generated by the robust heating and (mostly) cooling systems.  Toss in a TV and you’ve got the perfect recipe for tinnitus, which I have!
When I listen, I do from 11 pm til 3-4 am. Power is cleaner, and sounds better.

 Myself as also mentioned, lights off or lights on dim and jam out.
I’ve found you have to filter EMI/RFI from as  many physical connections into your system as you can to achieve the true experience of the recording. Mains supply is obvious and for those who stream from subscription services or locally stored FLAC, the Ethernet cable is another delivery system for it. Filter out RFI from your Ethernet for happy days.
Miller's whining on about springs again.   Boing boing.
Just the wrong way to go.  Equipment shouldn't be allowed to oscillate.
Particularly speakers, springs lead to fuzzy unfocussed sound. Blowing in the wind.
Even TT designers have mostly moved from spring suspension to mass loading in the last 10-15 years.
And the more mass the better.
Interesting points but you could save time & effort by purchasing a Puritan PSM156. I did. Incredible. 
Don't listen to pricks who haven't tried one commenting on filters. It works perfectly. 

In my experience, a black acoustic background is elusive for all the reasons cited by previous commenters. I have a few years of experience with sound reinforcement as well as an audiophile. From that perspective, I may be able to offer a few practical solutions that can isolate your audio from electrical noise that can creep into any system, no matter how well designed each component.

1. Start with audio components and signal cables that are well shielded against RFI and EMI. I've found that XLR cables resist RFI and EMI as well as premium RCA cables. If you use components that accept XLR plugs, you may find that their greater cost is offset by the relatively lower cost of good quality XLR cables, i.e. Canare. In fact their solder connections are easy enough to use that most persons can customize their cables with a minimum of fuss.

2. Star ground your components to a single and EFFECTIVE grounding point. Any component whose mains plug doesn't include a grounding pin or uses a grounding pin lifter defeats the purpose. I prefer removable IEC plugs because I too often find that the component's cable receptical has no grounding pin. Unless you take this step, your system is susceptible to ground loops which introduce hum into your audio signal.

3.  If you can, use a single 110 V. outlet for every component in your system. Homes that have 220 V. electrical service use two of the three "legs" furnished by your electrical utility service. If you can't plug everything into a single outlet, ensure that every outlet you use is on the same "leg". If you skip this step, your system will be susceptible to hum.

4. Plug all your components into an effective power conditioner that can handle the total power your system requires. IIRC, Monster offers three levels of power conditioning to consumers. I use their most comprehensive conditioner in my system. This not only protects your equipment from power spikes, it also isolates the system from electrical noise induced from outside your system.

5. Above all, trust your ears.

My most recent experience in this arena was eight years ago; and the suggestions I've offered could be obviated by ongoing advances in technology. Also, please understand that the list of solutions I've offered may not be exhaustive.

Happy listening!
A thought on Noise (the nemesis of silence between notes) starts at the front of the gain stage chain (assuming that all the stages are working right).  It has a simple equation from information theory,

 Noise = f + 1/f  + 1/f^2 + 1/f^3 . . . .

So look to the beginning of the chain.

Resolution in audio focuses on the distortion of the timbre of the sounds to which you are listening.  Noise between the notes is the biggest problem, as I have written elsewhere, it is a cascading effect, most pernicious in its nature, one hard to combat, and completely disruptive of the illusion of reproduced music. 

It all matters, but what is the priority? Power, Power, and Power! It starts from the fuse box. Besides removing things off of the line to your system you have to control the ground. I know MC has done this years ago. OCD Hifi on YouTube has done this. If it didn’t matter in a huge way they would not have done it. It’s not cheep done right if you have to go a large distance or through a lot of complicated walls and floors. The last is if you cannot control the power coming to the room the you need devices. Puritan is the best I have tried. Also it lets you install a separate ground to handle those issues. Puritan PSM156 will filter out the DC garbage on your line and also filter the over the air garbage from cell phones, WIFI, and Bluetooth getting into the power. Most will “condition” and protect the power to the components. Where they lack is what and how they filter. Despite running four 8’ silver coated copper ground rods into the ground for a dedicated ground system the Puritan still helped bring the noise to ZERO. This is how you get the biggest start to a black noise floor. I bought my Puritan PSM156 at 
If you are in the Chicagoland area you can try before you buy. No risk plus it will be broken in so you will know how good it is immediately. 
Filtering the AC noise is what will provide a black background.  You can do this with adding an AC filter choke to most components.

Happy Listening
I have to admit I’m a bit bemused with focus on noise from the mains... I’m not saying it’s not a problem, it’s just never been a problem for me... can someone explain what mains noise sounds like in a way I might understand, like bangs, pops, thuds, hissing, hum, buzzing?
Mains noise you can hear sounds like a hum at 50 or 60 hz but there is more to it than that , cheap switch mode power supplies, powerline ethernet adapters LEDs especially ones you can dim in your home all introduce additional noise (most of which is at frequencies you can’t hear) and DC offset. This and groundloops destroy your soundstage, tibre and microdynamics.

some excellent advice already in this thread.

Higher end components can deal with noisy mains better , but you can still improve by paying  attention to details. Once you have this sorted then you can look for even quieter (blacker) backgrounds by moving on to vibration control.

well designed cabling (which doesn’t have to cost your left nut) and well dressed can also really help but this is about protection of the system from rfi/emi mostly

I’m assuming you have already given thought to speaker and room interactions.

take care off all of that you will get great sound.
@yermajesty, Shielded XLR like the Mogami Gold 2534 can help IF you really have RFI/EMI problem, otherwise the 6db gain (or so) of XLR versus RCA will just raise your noise floor by 6db... I experienced the thing and got back to a good shielded RCA.
Low noise.

And the most significant factor in getting this is using specially manufactured low noise transistors at the VAS stage of the amplifier.

Of secondary importance is to have very well shielded cables, maybe a ground lifter and no ground loops.

The resolution of the components and cables matters a lot too. Not only to reduce noise, but to being transparent enough to discern the micro detail and air in the recording. Getting the black background and not wasting it with lossy signal path is a real investment! 
Setting up your entire system with low noise components and power conditioning and dedicated line feeding your system will guarantee that blackness you want.
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....;)
When we have obtained a blacker background in our gear it always comes down to two things- noise and intermodulations.

Noise can be hiss but buzz is a noise too. So components and layout have to be carefully considered. Intermodulation is a bit trickier. It can occur if a buzz is latent in your system, but the linearity of the circuitry is paramount- the more linear, the less ability for intermodulations to occur.

So I can see that reducing noise on the AC line can help. But for the most part, most 'high end audio' devices do that are so much junk, excluding DC blockers and actually good power conditioners of which in high end audio the only good one I know of is made by PS Audio. Elgar is a company that was never in high end audio, but they made some of the best power conditioners ever made a long time ago. So Elgar and PS Audio have pretty much set the bar for power conditioning; unfortunately I don't see other high end audio companies stepping up to bat. I'd love to be proven wrong. Anyway, the effects of clean power on audio equipment is easily measured and heard.

Power cords, fuses, special outlets and 20Amp AC wiring won't get you a blacker background but they can help in other ways (of these the fuses are the least bang for the buck) which are also measurable. They contribute to a more stable power supply. This is particularly helpful for circuits that don't employ power supply regulation, such as in power amplifiers. But these things have the biggest effect (most measurable and audible) when the amplifier is making power, when the power supply is most likely to sag.

Vibration control IMO/IME affects tonality, but can also affect distortion. So keeping that down in a turntable or preamplifier can really help, but is more likely to be an effect at higher volume levels so is more likely to affect harshness rather than the background.

In phono preamps, having good high frequency overload margins helps to reduce ticks and pops as well as improving the phono section's stability. So that can affect the background quite a lot if you are playing LPs.
After getting a black background you just found out that your new noise floor is your tinnitus

This is the hard truth. After playing drums in bands, endless touring, and playing in clubs for 30 years where your headphones have to cut through the already blaring soundsystem, I'm sad to report that my backgrounds hover at a dark grey, rather than black. Sigh.
In the digital domain it’s all about inherent noise contaminating the signal. The best designs today take great pains in power supply design to address this, and it not only makes the contrast between quiet and music more distinct, it allows one to hear deeper into the mix so to speak.
Audioquest Niagara system with appropriately matched power cords did it here. Another step you can take is use sheet copper to maintain a barrier between analogue and digital components. In my case I use copper sheeting under my pre-amp and FM tuner. Streamer is directly below the tuner and my Benchmark DAC is right below the pre-amp. I also use Pearl tube coolers and solder a wire I can take to ground to them to drain off any RFI or EMI that may effect tube performance + the cooler has the tube’s head running 20 - 25 degrees cooler for longer life.