Compared to a quality audio signal arriving at any loudspeaker’s terminals the measured output from the speaker will be between ten-to-one-hundred times worse in all relevant measurable categories depending on the loudness and complexity of the music being played.
Hopefully good passive speakers fall into the “only” 10-times worse category but even that’s based on static measurements that can’t measure dynamic degradation due to intermodulation distortion at higher volumes especially with complex orchestral music explaining the size and cost of the most expensive speaker systems.
The ear is sensitive to less than 1dB of volume at different frequencies yet a 6dB window is considered acceptable for a passive crossover speaker. We also detect timing inaccuracies on the order of microseconds that sound unconsciously unreal to us. An exciting you-are-there audio experience requires minimizing subconscious cues that tell us what we’re hearing isn’t real. All speakers benefit from active compensation such as DEQX provides as it minimizes the need for subconscious psychoacoustic reality checks.