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Everything a crossover has to do ...

Gang,


In my continuing efforts to encourage informed dialogue, I want to talk about how much a speaker crossover has to achieve, sometimes simultaneously. A crossover is a component which makes sure that the right frequencies go to the right drivers. That is, tweets should tweet and woofers should boom. Otherwise no sound comes out the woofer, and the tweeter becomes ballistic.


So, with those basics out of the way, here is a not-exhaustive list:


  • Filter. The simplest crossovers are just collections of low and high pass filters. Sometimes just one. Filtering is described above: Getting the right signal to the right component.
  • Level match. Drivers all have different voltage sensitivities, so making sure the drivers are playing uniformly is important. Imagine only seeing red on your TV for instance.
  • Equalize. Most crossovers have some sort of basic tilt built into them. Sometimes through dedicated components, sometimes just by picking the poles judiciously.
  • Impedance correct. Either to make speakers more tube friendly, or to make the filters more effective designers may put in components to solve the impedance problem alone. This alone is not something you find in an active crossover.
  • Temper driver resonances. As an example, lots of mid-woofer designs, even very good ones, have a resonant peak above their useful range. A notch filter can take it out and make the low pass better behaved.
  • Phase match. Below, at and above the crossover point drivers need to work seamlessly. Poor phase matching can cause lobeing, notches and peaks you don’t want. This is also very important in active crossovers, but you can often use digital delays to enhance the ease of the design.
  • Baffle Step compensation. A type of EQ that is the result of the driver/baffle size and arrangement. Yes, active crossovers should do this as well.


The point is, designing a crossover, whether active or passive, is not as simple as often assumed. To design any crossover, active with analog devices, DSP based or passive takes tools and effort to do well.


I hope some of you find this informative, and encourages you to learn more, if not experiment on your own.

Best,

E

erik_squires
koestner
637 posts
 
This could be a very interesting thread. For example: do high order crossovers (24 db/oct.) rob the drivers of speed and dynamics?
timlub
2,039 posts
 
Very well said Erik.  The only thing that I might add is parts selection in crossovers. 
The type and quality of caps and resistors change the character of how a speaker sounds.  The coils combined with the resistance and inductance of the drivers also change phasing.  As well as how a steel core, an iron ferrite core vs and air core sound. 
Nice write up brother. 
erik_squires OP
16,004 posts
 
Hi @timlub!
Thanks for the kind words.


Those discussions are happening on Audiogon from time to time. When I wrote my post I wanted to stick to those things which are not arguable.


I am confident that D'Apppolito and Toole would agree with everything I wrote up there.


The target curves, quality of a type of filter, and component parts are all areas we can discuss but which fall far short of universally agreed to electro-acoustic physics.


Best,

E
erik_squires OP
16,004 posts
 
I don't know if anyone noticed but I did not ascribe any sort of desirability to my list.


That is, I point out types of things crossovers may be designed for.


And so the trolls go hungry.
avanti1960
1,426 posts
 
very well said- and not understood by many.  Some of those functions are not necessarily available in active systems and as such people assume active is always better which is not the case.  
Amateur application of bi-amping with DSP for example misses several critical functions that a good passive crossover performs.  
However there is lots of art and black magic "taste testing" etc that goes into the equalization "voicing" phase of the design.  More black magic happens when the crossover frequency and slopes between drivers is selected- they can sound completely different for better or worse depending on the frequency- and change radically going up or down half an octave or so.  Voicing and frequency selection can make or break the sound of a speaker- even with the best drivers and enclosures-  and it is very subjective, you really need golden ears to make some magic.  
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