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Old 21st November 2006, 01:40 AM   #1
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Default Serious newbie has a crossover question

Ok, I get the capacitors used in series on the tweeters to pass the lower frequencies.
And I get the inductors used in series on the woofers to pass the high frequencies.
But what is with the capicitors wired in parallel on woofers and then inductors wired parallel on tweeters?
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Old 21st November 2006, 02:13 AM   #2
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Same thing. The parallel cap on the woofer provides a path of lower resistance at high frequencies than does the woofer itself, so (to simplify a bit), that's the path they take. Same situation for an inductor paralleled with a tweeter, the inductor looks like a piece of wire at low frequencies, so lows are shunted through the coil.

The reason you use a series cap first on the tweeter is so that you don't present the amp with too low an impedance at low frequencies.
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Old 21st November 2006, 01:00 PM   #3
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So, for example, on the tweeter you use the capicitor in series and then the inductor in parallel to more accurately isolate the frequency you want than you could with the capicitor alone?

Would a resistor in series also increase impedance to protect amplifier and I could measure that with ohm meter?
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Old 21st November 2006, 01:44 PM   #4
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A resistor is no good. The capacitor and the inductor impedance varies with frequency, which is why you get a cutoff curve then slope the way you do. Because there are two elements that change impedance, you get two 'poles' to the response, i.e. second-order.
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Old 21st November 2006, 09:30 PM   #5
lndm is offline lndm  Australia
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Quote:
Originally posted by Binkstir
Would a resistor in series also increase impedance to protect amplifier
That is not the right way to do it. It will cause problems. You don't normally have to worry about this.

A resistor has a use in a crossover, very often with a tweeter to make it more quiet.
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Old 26th March 2009, 08:48 PM   #6
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Default Low crossover point - why?

Many designs use 2000Hz or lower crossovers.
Is it for better off axis response or for lower distortion? Does the lower crossover point have any disadvantage in general? Is there a thread or website dealing with my questions about the lower crossover point issue?

Thanks for the answers.
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Old 26th March 2009, 09:05 PM   #7
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The ear is most sensitive in the 3kHz region so it's desired to try and keep the crossover out of that region.
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Old 26th March 2009, 09:13 PM   #8
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Quote:
Originally posted by richie00boy
The ear is most sensitive in the 3kHz region so it's desired to try and keep the crossover out of that region.
Is it that simple?
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Old 26th March 2009, 09:29 PM   #9
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No you could spend the next 5 years reading about XO's and still not be an expert. Also in your first post you talked about frequencies being passed. To pass means to allow so you have the two backwards. ie: A capacitor is a high pass filter meaning it allows highs to pass through but blocks the lows.

Also a single cap will give you a shallow slope, 6dB per octave. When you add the coil in parallel it now becomes a 12dB per octave filter so will better protect your tweeter from the lows.

Resistors usually get used in a combination of series and parallel to leave the overall impedance the same. As mentioned above, if you change the impedance you have to change the value of your caps and coils.

It's a long and winding road my friend.
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Old 26th March 2009, 09:46 PM   #10
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Getting started in Crossover Design

The basics (You've got to understand the rules before you can break them :-)
http://sound.westhost.com/lr-passive.htm
choosing xover point:
http://www.speakerbuilder.net/web_fi...xpointmain.htm
Baffle Step Compensation: http://sound.westhost.com/bafflestep.htm

Getting it done:
Jay has a page on designing xovers using manufacturers specs without measuring:
http://www.geocities.com/woove99/Spk...esigningXO.htm

Calculators:
http://ccs.exl.info/calc_cr.html#second
http://www.sengpielaudio.com/calculator-Lpad.htm
box calculator:
http://www.linearteam.dk/default.aspx?pageid=winisdpro

Measurement freeware:
Synrta - http://libinst.com/SynRTA.htm
ARTA http://www.fesb.hr/~mateljan/arta/download.htm
ARTA Jig - http://zobsky.blogspot.com/2008/01/s...t-jig-for.html

Examples from the designs of others can be quite instructive:
http://www.zaphaudio.com/
http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm
http://www.rjbaudio.com/projects.html
http://www.humblehomemadehifi.com/
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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