cross over stuff

sean Bourg

I have a question for some one thats nore wise than I... looking at the specs on my NEW and first polks... what is the difference or significance of first and second order cross overs..

I believe my 800i has two second order cross overs...

anyones opinion or facts would be great!!!

jcaut

It has to do with the crossover slope---How steep the roll-off is above or below the crossover point.

A first order crossover has a slope of -6db per octave.
A second order crossover has a slope of -12 db per octave.
Third order would be -18 db per octave, etc..

The best crossover slope for a given application depends on many factors. One is not necessarily better than the others-- It just depends on the application.

Hope that helps!
Jason

sean Bourg

ok i do understand tha a little.. is there more reading I can do on this matter ... If i recall my 800i's have two secon order cross overs and the 400i has the same I think....

my un-mounted or used surrounds (35i) have two first order cross overs....

can you explain this to me ...

Cheers

jcaut

I'll give it a shot:

Basically, a crossover in a multi-driver speaker system has the job of directing the different frequencies to the drivers that are best able to reproduce them. This is done mainly with capacitors and inductors. Without going into the electrical reasons, capacitors tend to pass high frequencies and resist lower frequencies, and inductors pass low frequencies and resist higher frequencies.

A crossover network in a speaker system generally contains both high- and low-pass filters. They don't necessarily have to have the same slope (or share a crossover frequency, for that matter).

As I said before, a second order filter gives a slope of -12 db/octave above or below the crossover frequency. In the case of a "second order high pass filter at 2.5 Khz", that means that the output of the tweeter (electrically speaking) will be down 12 decibels from the reference level at 1.25 Khz (1 octave below 2.5 Khz), and would continue to drop at - 12 db/octave. If this were a first order fliter, the response would be down 6 decibels at 1.25 Khz, etc..

Low pass filters do the same thing, but in reverse: They roll the response of a driver (woofer) off above a certain frequency.

The design of a crossover also has an effect on phase relationships among the drivers, and also the acoustical radiation pattern of the drivers. It can be a rather complicated subject, but that's the basic idea.

Jason