Active loudspeakers are always included in the very good systems. There advantages over conventional systems is something with no doubt. The following text numbers the major advantages of active loudspeakers and a small description of each. These are also mentioned by Vance Dickanson in his very successful books. Recommended for everybody from those who want to know more about speakers till the serious speaker builder.

    In following schematic you can see a block diagram of what an active system consists of and the difference from a passive one. It features a three way system.

    The major advantages of active systems using an active crossover are as follows:

    The IMD is low because the power amplifiers work in a smaller bandwidth. IMD is produced from different frequencies that modulate each other producing new frequency products that don't exist in the original signal. The amplifiers work easier and cant effect the other amplifiers. Also clipping from low frequency overloads of the amplifier in multiway active systems is not present because here only the loudspeaker can limit the signal.

    A 60W and 30W amplifier in an active system will clip at the same level as an 175W amplifier in a passive system. When a low and high frequency signal are amplified at the same time there is at high levels a sink of the maximum level because the low frequency signal makes the power supply voltages lower due to high current need. That's why active systems always sound dynamic and louder than passive systems.

    Great impulses in music reproduction create sudden and high current transients on the way from amplifier to speaker. These impulses from musical instruments hold almost all of the important information about the instruments sound and character and the room acoustics of the recording. So they carry eventually essential information that is needed to reconstruct the spatial sound image of simultaneously playing instruments in a room and this is very critical and sensitive. Any distortion of these characteristics changes the whole reproduction of recorded music so that's why different speakers sound different.

    Amplifier and speakers are better coupled directly and introduced resonances from passive crossovers are avoided. When you use a speaker cable with larger cross section the sound get better. This is always noticeable. The reason is that with lower output resistance the amplifier controls the load better. It has a better damping factor as known. Passive crossovers have a larger share of resistance losses then the cable and make the situation worse since the passive components produce distortions.

    In a passive crossover the voice coil of the speaker is always a part of the crossover. There is a very big variation in the speakers impedance from low dips to high resistances. This means there has to be a correction circuit that equalizes the impedance to more constant. In an active crossover that is placed before the amplifiers the speaker impedance is of no importance. The cut off frequency and the filter characteristics stay constant whatever the input of the amplifier is. This is very good for the DIYer who wants to experiment with the least mistakes and problems. Even a 24 dB/octave filter is practical without any of the known problem of the passive filters (most important coils and high cost of the passive elements).

    The sound quality of an active crossover is subjectively higher than a high level passive crossover. There is a big difference in working with millivolt and microampere level signals and with high current, high voltage signals. The second had problems like micro phony effect, a lot of solder points, high currents to handle with the least losses and the quality of the passive elements plays a significant role in the overall performance and quality.

    When designing active crossovers is easy and there is a great freedom in controlling the different sensitivities of the speakers. When the tweeter plays too loud you can't just put a resistor in the passive crossover to change the level. It will most possibly change the cutoff frequency or other characteristics of the filter. In an active crossover you can control the various levels through trimmers before the amplifiers like the volume control.

    With active crossovers it is very easy to manipulate phase, time delays, resonances, amplitude shaping, equalizing etc.

    Those were the advantages of an active system. But someone might ask, is there no disadvantage? Well of course there is. The only disadvantage is that the cost is a lot higher then a conventional system since it needs more discrete amplifiers plus an extra active device (the active crossover) . This is relative though. First of all when one is convinced to use a system like this, specially a DIYer I don't think the additional cost will matter so much. DIYers can make less compromises because it more flexible for them to design and build and spend money where it really matters.  Cost is very important though in commercial equipment where low cost is a major matter. Apart from that there is one thing that can make the cost lower. Each amplifier as stated before can be a lot smaller than the one very big one needed in a passive system. As conclusion I think it is worth it. The only thing I want to propose here is that no op-amps re used anymore. The sound bad and a discrete op-amp is easier to design. There are a lot of ready ones out there you can use like from the Nelson Pass article or from Erno Borbely. So go for it.