How to wire passive crossover?

[SAC]

Sorry for the basic question but out of dozens of web pages this single element is missing or contradictory in my experience.

Electricity flows from - to + as I understand it. Do I put the inductor/capacitor between negative and the driver OR between positive and the driver?

Also, please see attached image. On "input" where is the positive? Top or bottom?



Thanks for any help
Any webpages/links that deal with this specifically are also welcome.

[tinitus]

Originally posted by SAC


Do I put the inductor/capacitor between negative and the driver OR between positive and the driver?

Also, please see attached image. On "input" where is the positive? Top or bottom?

Positive is defined by amp

Series components on positive line
If a paralel curcuit like a zobel(resistor/cap) connect cap to positive and resistor to ground

If you need reversed polarity on a drive, do it after filter
I always do it on filter out, and not on driver terminals

I solid core wire for all connections
I use seperate wire to all drivers, only connected at speaker terminals

http://www.troelsgravesen.dk/coils.htm
Study his site

[Inductor]

Originally posted by SAC
Electricity flows from - to + as I understand it. Do I put the inductor/capacitor between negative and the driver OR between positive and the driver?

You are not working w/DC here but AC.

[SAC]

Thanks for the link Tinitus. It answered my second question on the crossover page.

Thanks also "Inductor" for the info.

[BlueWizard]

You are confusing Electron Current flow with Conventional Current flow.

Electron Current flow is based on the movement of electrons which are negatively charge particles. Consequently, in reality, electricity flows from Negative to Positive. This is the model used by electronic techs.

Conventional Current flow says that, from a design perspective, it doesn't matter which way the current is flowing, as long as we adopt and stick to a standard. The conventional standard adopted by electrical engineers is that the Positive (+) terminal is the source of current.

In practice, you simply stick with the convention. The (+) on the amp goes to the (+) on the crossover capacitors and on to the (+) on the speaker.

The flow of actual current doesn't matter. Parts that are polar, have a polar marking, and you uses those (+) and (-) markings consistently through out all your projects.

Just one exception, sometimes for design reasons, a midrange or a tweeter will intensionally be wired backwards. In this case, you somewhat ignore the polarity markings and treat the (-) as if it were the plus. Remember, in a speaker the (+) marking simply determines which way the speaker will move when a positive voltage is applied. As long as, in the final design, the speaker is moving the way it needs to move, you disregard the polarity marking.

So, in designing crossovers, we assume the RED (+) on the amp is the source, and orient all components accordingly.

However, since our signal voltage is swinging through both Plus and Minus, half the time the components are on the wrong side anyway. So, theoretically it shouldn't matter whether the components are in the high side or the low side.

BUT, conventions were established for a reason, and it is best to stick with common conventions so that other people can understand your work.

Steve/bluewizard

[Stu]

Don't think of the + or - in terms of electrons flowing from one to the other, we're talking AC here so it's constantly oscillating back and forth anyway.

What you posted isn't really a circuit diagram - more of a simple figure to illustrate the concept.

The figure below IS a circuit diagram (taken from http://www.diyaudio.com/forums/showt...10#post1005310), and a proper circuit diagram should be like this - with all the polarities marked.

The +'s and -'s are just there to make sure everything is in the right phase, you can reverse everything and it should still work, but follow the circuit diagram exactly and you can't go wrong.

[Andersonix]

Originally posted by BlueWizard
BUT, conventions were established for a reason, and it is best to stick with common conventions so that other people can understand your work.

Steve/bluewizard

Well said.

It will come more naturally with experience, SAC. If you concentrate on physically replicating the schematic diagram's layout with your real components and wire, you'll be well on your way.

[ChrisA]

Originally posted by SAC
[
Electricity flows from - to + as I understand it. Do I put the inductor/capacitor between negative and the driver OR between positive and the driver?

In an AC signal the polarity changes hundreds or thousands of times per second. So it hardly matters.

With speakers the "+" means that positive voltage on that speaker terminal drives the cone forward and when the signal reverses the cone is driven backward into the basket. It does not matter much how they are connected but EVERY driver on both left and right need to be connected the same. So a speaker really has no "positve" side. The "+" is just a marker to help you keep the phase corect.

Actually the net flow of current is zero

Yes the physical electrons move the way you describe but engineering convention is to assume the current is positive. Just because we hate to see so many negative numbers

[PeteMcK]

'sometimes for design reasons, a midrange or a tweeter will intensionally be wired backwards' - usually when a 2nd order xover is involved...

[SAC]

Wow, very informative answers. Thanks.

I was confident enough to wire a first order crossover between my 6ohm visaton b200 and 4ohm BG Neo 3 PDR (back cup removed), just a .4 inductor and a 20mH capacitor. A frequency sweep to my ear showed it to be reasonably flat from mid to highs. An improvement from the shouty highs of the b200 previously.

However, I expected to get 10ohms at least from the circuit but measured closer to six. Is this to be expected???

Must sleep now.