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Old 11th November 2002, 08:12 PM   #1
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Default i don't understand

ok, there is a schematic, http://sound.westhost.com/project09.htm , that has me a little confused. i'll start off with a few major premises not entirely related to the circut:
1.) I am an engineering student, and don't know everything already. i would appreciate it if you dumb it down a little.
2.) I am a student and have little money. Please do not suggest i buy something.
3.) I am confused with this circut, not another one you might suggest. while i do value you're opinions on this crossover, that is not my question.

The 3 way circut has me confuse. there is a lowpass followed by a highpass, which i assume is used for a bandpass filter. but the confusing issue is with the second lowpass which occures after the first. Why? Why does that lowpass filter follow the first lowpass filter and not simple follow the input buffer?
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Old 11th November 2002, 08:35 PM   #2
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"Why does that lowpass filter follow the first lowpass filter and not simple follow the input buffer?"

Possibly to increase the slope of the low-pass section, but in my opinion the final result is very close. Fantasy ? Abstraction ?

Regards, Pierre Lacombe.
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Old 11th November 2002, 08:50 PM   #3
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I think the basic idea here was to keep the phase shifts caused by the filters at the crossover points related to each other by using a common inputs.

XO: hi to mid: same input signal
XO: mid to low: same input signal

Hope that helps.

Later
Bruce
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Old 11th November 2002, 08:57 PM   #4
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Default Re: i don't understand

Quote:
Originally posted by theChris
The 3 way circut has me confuse. there is a lowpass followed by a highpass, which i assume is used for a bandpass filter. but the confusing issue is with the second lowpass which occures after the first. Why? Why does that lowpass filter follow the first lowpass filter and not simple follow the input buffer?
In his 1st iteration he wires the inputs of all three sections together. In this the one that he calls correct, the woofer low pass is preceeded by the mid-range low-pass. I suspect it has to do with getting the phase correct as each 4th order filter rotates the signal thru 360 degrees. Don't quote me on it...

Why don't you send Rod an email?

dave
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Old 11th November 2002, 09:39 PM   #5
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The first lowpass filter is at 3100Hz. The second lowpass filter is at 310Hz, a full decade away. You could just as well connect the woofer low pass section to the output of the buffer - the difference between the two connections is insignificant.
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Old 11th November 2002, 09:55 PM   #6
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Quote:
Originally posted by Bill Fitzpatrick
You could just as well connect the woofer low pass section to the output of the buffer - the difference between the two connections is insignificant.
That is what i would have thot, and is how Rod connected it in the 1st version, but he seems to think that was an error


dave
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Old 12th November 2002, 03:08 AM   #7
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you see, i had planned to make a technically 4 way setup in my car. while i know there are certian stereotypes about car audio and the people who enjoy it. it is necessary for me, as my room leaks sound (good enough analogy). i also have no home amps. also, i enjoy the option of using a sealed box. (i may have to put 2 woofers in just to fufill the stereotype though...)

I had planned a 4 way setup becuase i kinda wanted to. i had figured the L-R alignment would be nice due to the overlapping of the drivers. I had intended to use a 50-60hz for low, and then 250 as the high. there would be a passive crossover on the front mid and tweeter.

i've been thinking of crossovers for about a week and what would be good and not as good and why. I may just get some help from the school, they have a spectrum analyser they're dying to get excuses to use. the info gained from this would likely help me with choosing crossover points that are actually related to the system and not just best guesses.

as for the circut, i had figured either phase, or something to do with acoustic coulpling.
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