What is a passive crossover?

Indeed, a crossover between pre and power amps potentially could be ‘passive’, with components similar to those used in the crossover in a speaker - but quite different in practical terms because the values of capacitors and inductors relate to the quite low impedances of the speaker drive units (typically 4 or 8Ω), whereas before the power amp they would relate to the much higher impedances of the power amps (typically 18-50kΩ), so the component values would be much smaller (also physically smaller and cheaper). More commonly (maybe universally?) they are designed either with resistor-capacitor networks altering the frequency response of an amplification stage (analog active crossover), or, increasingly common and much more flexible, using digital signal processing (digital active crossover), either taking a digital music stream as its input, or taking an analog input from a conventional preamp and digitising it first.

And as already identified, ignoring the design of the crossover itself, the term ‘active’ has two implementations, an ‘active speaker’ putting the crossover and amplification (separate for each driver) in or attached to the speaker box, and ‘active system’ where they are separate from the speaker, allowing ‘mix and match’ of components by the user (but latter more complex and requiring greater understanding).

alan33 posted:

Never having operated or even heard, an active hifi system, I’m also slightly confused by the “dual” use of the word “active”...

In an electronics sense, as has been said, “passive” vs “active” is an easy separation between circuits (eg high and low pass filters, as used in the audio crossover application under discussion here) using only passive components - resistors, capacitors, and inductors - and those that also use active, or separately powered, components - typically operational amplifiers, transistors, or (with a nod) tubes / valves. If a crossover, essentially a combined high pass filter in front of (ie whose output feeds)  the tweeter and a low pass filter in front of the woofer, has only passive components (LRC...), then it’s a passive crossover. On the other hand, if any of the components are active (eg it uses an op amp as well), then it’s an active crossover. That’s the easy bit...

Many of the recent posts seem to use the “active system” term to describe one where the filtering happens after the pre-amp but before the power amp, such that the power amp is then connected directly to the speaker (tweeter or woofer, depending on if it’s after the high pass or the low pass filter). This could, of course, be effected using either an active crossover or a passive crossover.... hence the potential for confusion and talking at cross purposes (haha). 

In spite of my opening disclaimer, I do indeed have an active system at home: the DynAudio studio monitors attached either to our electric piano or our recording/mixing daw are powered and include an active (digital) crossover network to feed the (DAC that connects to) amps and audio drivers. 

No big ideas here, and no judgements on performance, just an attempt to join the conversation and point out that we are using one word in two related-but-distinct contexts. Happy to be corrected if I’ve missed the boat on the evolving inquiry...

Regards alan

It's still the same usage...

Active system
Preamp -> Active Crossover -> Poweramp
The crossover is built using active filters,  i.e. the passive components doing the frequency response modifications (capacitors and inductors) are built into the gain control circuitry of amplifiers - the amplifiers are built from active components, so the filter is an active filter.

Active Speakers
The speakers have their own built in amplifier - the amplifiers are built from active components.

This is a Passive crossover

One of a pair destined for the attic having been replaced by this

Which, as one might expect, is an Active crossover.

Willy.

AFAIK - in Naim active crossovers there no inductors or chokes - inside my IXO crossover there are mainly transistors, tantalum capacitors, resistors with a large transformer - two pots.

The components look completely different to the ones in my PAXOs.

Stephen Tate posted:

AFAIK - in Naim active crossovers there no inductors or chokes - inside my IXO crossover there are mainly transistors, tantalum capacitors, resistors with a large transformer - two pots.

The components look completely different to the ones in my PAXOs.

In an active crossover, an inductance can be created using an amplifier and a capacitor.  Think of an inductor as the oposite of a capacitor.  Put a capacitor in the negative feedback loop of an amplifier and it has the opposite effect to it being in the signal path.  The overall effect of this is just like having an inductor in the signal path.

Huge posted:

Stephen Tate posted:

AFAIK - in Naim active crossovers there no inductors or chokes - inside my IXO crossover there are mainly transistors, tantalum capacitors, resistors with a large transformer - two pots.

The components look completely different to the ones in my PAXOs.

In an active crossover, an inductance can be created using an amplifier and a capacitor.  Think of an inductor as the oposite of a capacitor.  Put a capacitor in the negative feedback loop of an amplifier and it has the opposite effect to it being in the signal path.  The overall effect of this is just like having an inductor in the signal path.

Ok, thanks Huge. One thing I could do when I went active was turn the volume up much higher than is usual in passive mode without any distortion or mushing up, oh those were the days!

That is because active avoids trying to put large currents through crossover components, while maximising control of the speaker drivers.

Stephen Tate posted:

Huge posted:

Stephen Tate posted:

AFAIK - in Naim active crossovers there no inductors or chokes - inside my IXO crossover there are mainly transistors, tantalum capacitors, resistors with a large transformer - two pots.

The components look completely different to the ones in my PAXOs.

In an active crossover, an inductance can be created using an amplifier and a capacitor.  Think of an inductor as the oposite of a capacitor.  Put a capacitor in the negative feedback loop of an amplifier and it has the opposite effect to it being in the signal path.  The overall effect of this is just like having an inductor in the signal path.

Ok, thanks Huge. One thing I could do when I went active was turn the volume up much higher than is usual in passive mode without any distortion or mushing up, oh those were the days!

Also worth considering small signal inductors can also look like capacitors... they are very small and so you might not be recognising them...