The room is the limiting factor in most speaker setups. The worse the room, the sooner you hit diminishing returns for upgrading any other part of the system.
In a fantastic room a $50 speaker will be nowhere near 95% of the performance of a mastering monitor, no matter how much EQ you put on it. In the average living room with less than ideal speaker and listening position placement there will still be a difference, but it will be much less apparent due to the limitations of the listening environment.
You might lose headroom or have to live with higher latency but if your complaint is about actual empirical data like frequency response or phase, that can be corrected digitally.
You can only EQ speakers and headphones as far as the transducer can still respond accurately to the signal you're sending it. No amount of EQ will give the Sennheiser HD-600's good sub-bass performance because the driver begins to distort the signal long before you've amplified it enough to match the Harman target at a normal listening level.
DSP is a very powerful tool that can make terrible speakers and headphones sound great, but it's not magic.
Pretty much my first point… At the same time that same DSP can make a pretty mediocre speaker that can reproduce those frequencies do so in phase at the listening position so once again the point is moot, effectively add a cheap sub.
There is no time where you cannot get results from mediocre transducers given the right processing.
I’m not arguing you should, but in 2025 if a speaker sounds bad it is entirely because processing was skimped on.
This varies wildly with what frequency range you're talking about. Bass region, yes - room geometry makes a big difference. The rest of the range, DSP is your friend. Loudspeakers and Rooms by Floyd Toole is an awesome resource here.
