Cross-over question about impedance

[Jimmy154]

The cross-over has to be designed at the impedance that the x-over is operating at, right?

But I want to design a second order for the tweeter at a certain frequency. And first order for the woofer plus the natural roll-off it has at the top end.

My question is, how can I or anyone design a good x-over near the tweeters fs (about 3,000 Hz I was thinking), if the impedance hits about 20 or 30 ohms. It's a small peerles tweeter with a fs at 1334 Hz, I have more specs, but I don't know if it's necessary to post them.

I also have a Peerless (india) SKO-130-PL-SH-8 5.25" Woofer / Midrange 4 ohm, which I have no specs for. I have no clue at what frequency it rolls off at. Or about what the FR the graph will look like. Any one got a clue?

I have more questions, but I don't want to go on and on. My main problem is designing an x-over for the tweeter cause I'm confused about the impedance. I use this x-over calculator http://lalena.com/audio/calculator/xover/ There's also an attenuation calculator, but I don't think I need that, my tweeter is 8 ohm and 88 db and the woofer I figure is 86 db at 4 ohm.

If you have any suggestions or questions please say something.

[Jimmy154]

Have I stumbled onto a diyaudio mystery or is everyone hoping the goofy kid goes away? Very serious professional crowd, I know I don't fit in.

[scott_jcp]

Be patient, everyone on this forum is very helpful, but sometimes it takes a while to get a response.

And make sure that you've searched for the answer yourself.

[paulhfx]

There may indeed be some serious professional audio types in this crowd, but not I ..

The tweeter impedance is generally handled with an impedance compensation circuit (part of your crossover), which will cut your impedance at resonance frequency down to the level of the rest of the impedance curve for the tweeter.

Try here for some useful reading:
http://sound.westhost.com/lr-passive.htm#filter-types

You will almost certainly need attentuation for the tweeter - use an l-pad for this. (an L-pad is basically a component containing a set of resistors adjustable by a dial - you can dial in the right volume for your tweeter after everything is built using one of these).

Paul

[Jimmy154]

Originally posted by paulhfx
You will almost certainly need attentuation for the tweeter - use an l-pad for this. (an L-pad is basically a component containing a set of resistors adjustable by a dial - you can dial in the right volume for your tweeter after everything is built using one of these).

Thank you the linked answered my question about the tweeter x-over related to resonance right away. But why do I need tweeter attenuation? If my woofer is 4 ohm and about 85-86 db and my tweeter is 8 ohm and 88 db. So add 3 db to the woofer cause it's half the nominal impedance and you get about 88 db for both, no? This is the way it's explained at lalena.com (if they both the same sensativity you need no attenuation). But I noticed it doesn't exactly work like this, so . . . what is the deal?

Also any one know the FR and impedance graphs of the Peerless (india) SKO-130-PL-SH-8 5.25" Woofer / Midrange 4 ohm or a similar peerless woofer?