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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
snapsc
670 posts
 
Erik

+1 for this topic. 

this topic is why Dennis Murphy... and a few others... are geniuses in this area... when they do their best work... you don’t even know there is a crossover at work!
rimo
14 posts
 
Hello!

Mr. Squires is correct when I said no crossover can sometimes be best choice for a loudspeaker system, even if is denial of my work on infinite slope patents, including new patent this year, discussed in previous postings.

My design approach has always been to maximize towards uniform spectral energy in listening room, which with infinite slope means no sweet-spot and flat frequency response in entire listening space, limited only by polar response of drivers in box. Recent patent also achieves good time response, as observed in FFT measurements in home lab and in Tech Center at University's anechoic chamber.
Expensive speakers with elaborate crossovers often fail.  Recently I heard  example of  non-uniform spectral energy distribution from a $30,000+ box.  As I sat, I moved head slightly back and forth, no more than 6". The sound changed. Rising and moving about in listening room, I heard many sounds.  Some months ago I was demonstrating my 2-wy prototype in same room with myself and 3 others, everyone observed  SAME sound balance everywhere in room!  That's uniform spectral energy at work! No sweet spot!  Here's the catch - the box with no crossover and small driver has also no sweet spot!  Uniform spectral energy! 

Therefore you can approach uniform spectral energy with one good small driver in a box, no crossover, and some bass enhancement by bass-reflex loading. System gets  midrange OK, with loss at frequency extremes, and distortion from cone breakup at high frequencies (generally 4KHz and above).  Generally sounding well at low power and on material not too challenging, for easy listening for non-critical audiophiles who listen for the music and not the sound.
RIMO

RIMO
erik_squires OP
16,013 posts
 
RIMO :

What university did you use for the anechoic chamber?

And what you are describing hearing is more akin to comb filtering. What speakers were you listening to?

Erik
audiocaseevan
24 posts
 
@erik_squires 
looks like he cites ‘Binghamton University’ as the University with the anechoic chamber that corroborated his measurements in his first post to this thread. 
Thanks for sharing your knowledge of crossovers with us! Great post.

-Evan
erik_squires OP
16,013 posts
 
Thanks @audiocaseevan

His posts were such a ramble I found it hard to find anything specific, but "hooray me."
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