Originally Posted by Kevin Haskins
From a speaker design standpoint it is sure much nicer to design an active loudspeaker than it is a passive. You gain several degrees of freedom in what you can do with the response and you can make low frequency changes that are not possible with a passive network.
It can cost progressively more but not much considering the inexpensive high-quality amplifier choices available these days. Passive networks are not cheap with large inductors & caps so when I look at the BOM in a comparable design the parts cost isn't much different based upon just the PCB. If you use a chassis for the amp/crossover that can get expensive.
Most HT equipment is designed around passive set-ups. I wish more of them were preamp only set-ups that would output a balanced line-out only. Active loudspeaker designs have so many advantages that in a high-dollar theater there is no good reason not to design that way. Cost is the only reason not to design active loudspeakers.
The cost factor becomes bigger when you have a finished crossover design that someone else designed for you... assuming you don't have any desire to tweak it much. If you are just constructing and assembling vs. designing, passive can be much cheaper if you want it to be.
Perceived cost and real costs can converge quickly if you start going toward premium parts and amplifiers for passive solutions, or if you have to factor in the parts and time purchased in the design phase if you really want to polish out the result. If you are designing your own, I can't see a reason not to go with something like a MiniDSP, DCX-2496 or similar over the passive route other than cost of the amplifiers. With cheap multi-channel amplifiers it can be much more feasible than in the past. Also remember you often can get much greater efficiency in sections of the design than with a passive design, requiring lower power amplifiers than a passive design.
What I've often recommended to those who want to experiment with customized, more ambitious options is to find a capable mid-tweeter solution you can EQ as you like and go active for the midbass section. Crossover below 500Hz can be progressively tricky to execute passively while maintaining a desirable load impedance and smooth response. It's accomplished and adjusted to any frequency in a few clicks of the mouse in an active system.
Paraphrasing how Tom Danley likes to boil it down: "Each bump you fix in a passive crossover requires three parts. Actively it's a few clicks of the mouse." Finally, any narrow notches in a passive crossover vary with component tolerances, while an active crossover is the same every time you punch in the same numbers.
Both approaches have merit, both have benefits.