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
