Active Vs. Passive Monitors
Back in the mid 70s when I fist started going into recording studios it cost hundreds of thousands of $$$ for what now cost under $10k. I remember when the akai 12trk analog recorders were ground breaking at $7k (Over 30 years ago). Monitoring has followed the same path. I agree with another author here who stated impedance matching as well as some other very important technical info. Two of the best sounding systems I've ever heard were passive systems. No.#1 was an ultra high end concentric 2-way in custom built cabinets built into the control room wall. No. #2 was a pair of Massive Multi-speaker 4-way JBL speakers Bi-Amped with Crown High Current Power amps. No passive system that I have heard ever to this day comes close to those systems; especially at high level play back.
But here's the trade off: these systems were put together by top notch sound Engineers with many years of design experience. Degrees in psycho-acoustics, electrical engineering, etc. When these engineers came into your studio to do a design, Blam $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ Plus you have to purchase the system they designed! Now put all that experience into a compact powered monitor, get a relatively low cost computer modeling program, hook a mike up to your computer and you have 30 years engineering experience and sound molding behind you. So when you say active speakers sound better than passive speakers you have to put that into some kind of perspective, perspective being your budget, experience, type of control room, and it's intended purpose. There are many great sounding systems both active and passive, but for near field I do see active becoming the standard as they do cut out a very expensive middle man/woman and simplifying a lot of perplexing technical issues bringing what was once a very costly preposition to the working musician/engineer. Finally: A monitoring system is only as good as the person sitting in front of it.