The first time I started dabbling with active setups was when I ventured into car audio.
With speakers placed all over, in doors, in A panels, sub in the boot, acres of glass, plastic all over the dashboard, dirty power, road noise and proximity of the listener to the speakers, makes it a nightmare to get good audio in cars.
Audiophiles shudder at the thought of the term 'audiophile' when one talks about music in cars.
But if done properly it is much more pleasurable and intimate than listening at home, unless one has the luxury of dedicated rooms.
There are some excellent active head units, and nowadays with lots of integration with OE head units, Digital Sound Processors (DSP) have taken the place of active head units.
Some of the audiophile grade active head units include Clarion HX-D2, HX-D3, Pioneer P99RS, Pioneer 80PRS and its iterations and the Eclipse CD7200 mkii. All these are single din HUs.
Some great features offered by some of these head units include excellent DACs, full copper chassis, isolated power supplies, 6/8 channel outputs, powerful processing features like setting varieties of crossovers, slope, time alignment of individual drivers, delay, attenuation, phase change and so on.
In addition these HUs came with Parametric or upto 32 band graphic equalizer which could be applied to each of its 6/8 outputs.
All the processing ofcourse happen in the digital domain.
However these head units have almost hit the dust after car companies started to offer lots of integration features in the OE head units leading to development of outboard Digital Signal Processors with both analogue and digital inputs.
The only caveat of active setup is that you need amplification for each channel....8 channel or 4-way active setup (tweeter, midrange, woofer, subwoofer) means 3 stereo amps and one monoblock....6 channel or 3-way active setup (tweeter, woofer, subwoofer( meants 2 stereo amps and a monoblock.
It gives immense flexibility at the users hand and is an excellent learning curve to understand what each octave does to the overall music.
Though initially I dabbled a lot with measurements etc., I soon decided the best way to tune is with ones ears, after all music is heard and not seen.
At one point, I was running Class A amp into tweeters, Class AB into the midrange and Class D into the midbass and subwoofer in my car.
But now I have a much more simple 4-way active setup with all Class D plam size TDA3118 amps.
I also wonder why this fixation even among high end companies which keep stating 'Out reference solid state amp sounds like tube'....why the hell then make it SS, better stick to tubes.
@Ravindra Desai Sorry for this long post sir, just highlighting that DSPs are truly the way to go, especially with power amps getting so cheap.