Crossover and speaker resistance impact

Hello everybody,

This is my first post in this forum, and its a question.

I am thinking a custom 3 way component set dor frequencies 100hz and beyond.

I also plan on using only one 2 ch amp for this, and design a custom 3 way passive xovers.

If I were to wire 3 speakers in parallel (asssuming each one is 4ohm) I would get 1.33 total resistance, right?

Well, one friend told me that if there is no overlap in frequency ranges, the impedance will essentially be the same

as the speaker that's operating in any given range of frequencies.

That got me confused... does that mean the resistance won´t change? Is that right?

Thanks,

-Erasmo

That's the purpose of a properly designed crossover.  In very gross terms, it essentially only allows one speaker to be connected to the amplifier at a time so the amp is only loaded by the impedance of that one speaker.

In reality it's not quite so simple as that, but that's the general idea.  Your friend was correct.  :)

So if I wire 3 speaker and use a passive crossover so the frequency doesn´t overlap in any of them, what impendance should I expect to see? 1.33 ohm?  In that case there is no real benefit of setting the xover like that...

excuse me if I sound dumb, but this escenario is very confusing to me. I don´t have exoerience setting up configuratios like this.

I had a component set but it came with a xover unit. I remember it was 4ohm, but I dont remember if the speakers were 8ohm each... or 4ohm and the frequencies were not overlaping.

Thanks for your help. I read all the articles about xover in this and another article, but I still don´t get it.

Maybe I will have to setup the system and the meausure the impedance...

Thanks,

-Erasmo

In a 3-way (or 2-way or 25-way) set of speakers using a properly designed passive crossover, the amplifier "sees" the impedance of only one speaker.  If they are all 4-ohm, the amplifier "sees" 4-ohms.

Here's a link that may help you understand this: http://www.diycable.com/main/pdf/2641.pdf

Look at the impedance curve of this 3-way speaker on page 7.  If you notice it provides the impedance of all the individual speakers (blue, red, and green) and their combined impedance.  As you can see the impedance doesn't act like a series or parallel circuit as you describe.  The only time when they interact is when the frequency response of the two drivers overlap.