Explain this crossover

audiokid25 · 8th July 2005, 07:54 PM

Hello all, could someone explain this highpass XO for me. I know its a 3rd order, but what does R1 do. Dont you normally need 2 resisitors for a pad? And why are C1 and C2 the same value? The crossover is from an Adire kit, that I want to use a different tweeter on. The XO freq is 3500hz.

SY · 8th July 2005, 08:26 PM

R1 drops the driver level. You need two resistors for a pad only if you don't want the series resistor to change the load impedance. For a parallel crossover, it's a non-issue.

audiokid25 · 8th July 2005, 08:34 PM

Ok, so I could replace R1 with a pot and be ok then? And is it unusual that both caps have the same value?

SY · 8th July 2005, 08:41 PM

The ratio of the caps' value is an indication of the sharpness of the crossover rolloff.

If you're thinking about using this crossover for a different driver, you're heading in a bad direction, potentiometer or no potentiometer. What you need to do is, using the actual impedance and SPL data of the original tweeter, determine what the electrical and acoustic response near the crossover region look like. Then your task is to duplicate it with a different tweeter. Doing it right will not be trivial, but with real data and a good command of a speaker CAD program, it is possible.

steenoe · 8th July 2005, 09:08 PM

SY, how come you have the danish actor, Dirch Passer, as your avatar??

Steen

SY · 8th July 2005, 09:11 PM

Ding ding ding! You get the award! He attracted my attention when I was a kid with his role in that classic piece of Danish cinema "Reptilicus."

Now I have to find a new one.

steenoe · 8th July 2005, 09:18 PM

What is the reward then? A years free subscription to "my" forum?? Well, I did donate the 20 bucks, allready

Any Dane would guess that one

Steen

Well, it is much prettier than the ugly puppet you had before

Made me sick

AuroraB · 8th July 2005, 09:47 PM

Unless R1 is incorporated in a corrected Rtot for the load, it will also modify the slope of this HP section.
Without knowing the details of rest of the circuit, it is next to impossible to know the exact purpose of R1.
If the sole purpose was to reduce the level of the tweeter, there should be an R2 to ground, to complete an L-pad.

SY · 8th July 2005, 09:51 PM

You only need an R2 if you're trying to keep the impedance the same. Why bother to do that in a parallel crossover? Remember, R1 is not an aded component for a modification, it is the resistor that is part of the original design.

AuroraB · 8th July 2005, 09:58 PM

that's exactly what i mean....
The filter is undoubtably 3rd order, but R1 will also modify the stop band curve, or the "knee" if you like, so unless you know the details of the total contraption, or more exactly the designers purpose, there is several options to the function of R1

8th July 2005, 08:26 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	R1 drops the driver level. You need two resistors for a pad only if you don't want the series resistor to change the load impedance. For a parallel crossover, it's a non-issue. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

8th July 2005, 08:41 PM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	The ratio of the caps' value is an indication of the sharpness of the crossover rolloff. If you're thinking about using this crossover for a different driver, you're heading in a bad direction, potentiometer or no potentiometer. What you need to do is, using the actual impedance and SPL data of the original tweeter, determine what the electrical and acoustic response near the crossover region look like. Then your task is to duplicate it with a different tweeter. Doing it right will not be trivial, but with real data and a good command of a speaker CAD program, it is possible. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

8th July 2005, 09:11 PM	#6
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Ding ding ding! You get the award! He attracted my attention when I was a kid with his role in that classic piece of Danish cinema "Reptilicus." Now I have to find a new one. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

8th July 2005, 09:51 PM	#9
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	You only need an R2 if you're trying to keep the impedance the same. Why bother to do that in a parallel crossover? Remember, R1 is not an aded component for a modification, it is the resistor that is part of the original design. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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8th July 2005, 08:34 PM	#3
audiokid25 diyAudio Member Join Date: Oct 2004	Ok, so I could replace R1 with a pot and be ok then? And is it unusual that both caps have the same value?

8th July 2005, 09:08 PM	#5
steenoe diyAudio Member Join Date: Mar 2004	SY, how come you have the danish actor, Dirch Passer, as your avatar?? Steen

8th July 2005, 09:18 PM	#7
steenoe diyAudio Member Join Date: Mar 2004	What is the reward then? A years free subscription to "my" forum?? Well, I did donate the 20 bucks, allready Any Dane would guess that one Steen Well, it is much prettier than the ugly puppet you had before Made me sick

8th July 2005, 09:47 PM	#8
AuroraB diyAudio Member Join Date: May 2001 Location: Norway, -north of the moral circle..	Unless R1 is incorporated in a corrected Rtot for the load, it will also modify the slope of this HP section. Without knowing the details of rest of the circuit, it is next to impossible to know the exact purpose of R1. If the sole purpose was to reduce the level of the tweeter, there should be an R2 to ground, to complete an L-pad.

8th July 2005, 09:58 PM	#10
AuroraB diyAudio Member Join Date: May 2001 Location: Norway, -north of the moral circle..	that's exactly what i mean.... The filter is undoubtably 3rd order, but R1 will also modify the stop band curve, or the "knee" if you like, so unless you know the details of the total contraption, or more exactly the designers purpose, there is several options to the function of R1

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