CurtPalme.com Home Theater Forum

whats6x7 · Joined: 04 Oct 2006 Posts: 5924

OK, I'm lazy. Do one of you geniuses know what I need to cross an 8 ohm super tweeter over 10,000 hz? Let me clarify what I mean by lazy. Could you just post a link to the cap at Parts Express or something? Is there a chart somewhere that makes it easy?

Thanks in advance!

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

For 6 decibels per octave crossover you would need around 2uf. I'm to lazy to find it also.

whats6x7 · Joined: 04 Oct 2006 Posts: 5924

So this . . .

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=027-724

Does it have an in and an out? Positive side, right?

I found a chart but it doesn't go that high . . .

http://www.colomar.com/Shavano/crossover6db.html

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Oh, if dollars is not a real big issue you may want to consider a higher roll off. Of course you may loose a little more amp power, but again, its a tweeter.

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

I used Solen caps before, Partconnexion has them fairly cheap in your range.

http://www.partsconnexion.com/capacitor_film_solen_pb.html

Athanasios

whats6x7 · Joined: 04 Oct 2006 Posts: 5924

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Those Solens are a very good crossover cap.

The attached chart is for a 12 decibel per octave crossover. There are many crossover value programs out there if you want to google more but they all pretty much say the same. If you want to go more the 12 then the programs can help you there also. Or just ask if you get confused.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Ha. I was looking at that image I just posted and couldn't figure out what was wrong with it. The letters L and C are in the wrong place but the symbols are correct. The cap goes in series and the inductor goes across the lines.

whats6x7 · Joined: 04 Oct 2006 Posts: 5924

Forgive my ignorance on this subject but I need 2 pieces? One on the positive side of the wire and 1 between the wires?

whats6x7 · Joined: 04 Oct 2006 Posts: 5924

I also found this . . .

http://www.carstereo.com/help/Articles.cfm?id=1

but it just shows the capacitor. What is the L side that connects them?

greg_mitch · Joined: 03 May 2006 Posts: 5320

Parts express has assembled HF crossovers but nothing that goes up to 10kHz.

How did you come up with that number?

whats6x7 · Joined: 04 Oct 2006 Posts: 5924

I'm building a super tweeter. I need something to add sparkle and headroom. If I cross it over like a regular tweeter at 5k it will just add too much treble and sound nasty.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

whats6x7 · Joined: 04 Oct 2006 Posts: 5924

whats6x7 · Joined: 04 Oct 2006 Posts: 5924

I ordered the caps but what is the L thing called? Can somebody send me a link?

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

L thing is an Inductor. Solen also makes those as well. Id get the audio versions as they are best than a normal iductor. So only use air core indctors like in the link.

http://www.partsconnexion.com/inductor_solen14.html

Athanasios

whats6x7 · Joined: 04 Oct 2006 Posts: 5924

I understand the cap but what is the function of the inductor?

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

NOt 100% sure but it is just part of the frequency cut off. Not sure but I think it helps the cap or smoothes out the results. Mac or someone else would no more, it was long time ago that i rebuilt a cross over for some AR1 speakers that i put soft dome tweeters in and i forgot most of what i researched on that subject.

Athanasios

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

A capacitors job in a cross over is to block unwanted frequencies starting at a frequency based on the selected value. Your choosing 10khz so you use a cap known to start blocking at that frequency. However the unwanted frequencies cannot be totally blocked by the cap. It can only attenuate (restrict) at a rate of 6 decibels per octave. So the first octave below your selected crossover point will only be attenuated 6 db, which is not very much. So that octave of frequencies will still be very much heard. The second octave below your 10khz will be attenuated 12db which is double the original 6db. This doubling continues on every remaining octave. So 6db per octave is all a cap is capable of blocking, regardless of the value. The value only chooses the crossover point.

But what if you want to block these unwanted frequencies even more. How would you do that?

In comes the inductor. The inductors job is to try to short out the unwanted frequencies. The cap tries to block them and the inductor tries to short them out. And it will short them out at a similar rate of 6db. But when both are used together they are combined to a capability of 12db per octave. So the 1st octave below your crossover frequency will be attenuated 12db. The second octave, 24db. And so on, doubling on each lower octave.

So as you can see, your are attenuating much more of the unwanted frequencies with a 12db crossover.

Same goes for 18db or 24db. The rating number is the attenuating factor of the 1st octave below the crossover frequency, and doubles for each octave following.