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Old 18th May 2016, 05:24 AM   #1
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Question How to Tweak a Passive Crossover

I've been an audio engineer for well over a decade now, and I trust my ears much more than SMAART or PCD or REW or whatever. I've even designed well-liked and used FIR filters for a very popular live PA speaker.

That being said, when it comes to electronics, I'm an idiot. I've designed a few pairs of speakers that sound pretty good; but, I feel like I'm skating by on luck with my designs in PCD. I don't REALLY know how to tweak a crossover.

I get it, buy a slightly smaller value component than predicted and add tiny values to it to suit your ears. Ok, but physically how do I wire that? For inductors is that in series (Add a .1 to a .5 in series to get .6)? Capacitors stacked on top of eachother? Resistors? I can't seem to make sense of it!

I would gladly accept a link so somewhere else to read about this. I just can't figure out how to apply electronics 101 to crossover tweaking. Maybe I have a great pair of ears with a dull brain in between them. . . Any help appreciated here.



FYI - Attached is the design I'm working on - recently found out it's actually a popular driver config by Carmody - but I had no idea when I started, and my XO looks way different. It's a gift for my wife who is graduating medical residency and I just want it to be right. It will be paired with a Model 1060 Marantz and a record player of some sort.
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Old 18th May 2016, 06:02 AM   #2
Zero D is offline Zero D  United Kingdom
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Hi,

Caps in series decrease value

Caps in parallel increase value

Res in series increase value

Res in parallel decrease value

Ind in series increase value

Ind in parallel decrease value

Have a look/try here for eg Capacitors - Parallel and Serial Connections
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Old 18th May 2016, 06:10 AM   #3
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Try my blog posting here.

A Speaker Maker's Journey: Crossover Basics

There you will find a link to Xsim which will make a very good learning lab.

Best,

Erik
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Old 18th May 2016, 06:21 AM   #4
TMM is offline TMM  Australia
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A useful thing to do is to "bake in" some adjustment into your crossover design.

i.e. Try adding resistors in series with all the caps/inductors and changing existing resistors to see the effects. Work out if you can adjust a large range of frequencies up/down a couple dB without messing up the phase alignment by changing just by changing the resistances. Then if you find a certain range of frequencies is sounding too hot or recessed after you build it, it's easy to fix. You could even take it further by adding a switch to the cabinet so you can select different resistors.

Last edited by TMM; 18th May 2016 at 06:29 AM.
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Old 18th May 2016, 06:29 AM   #5
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by G Speakers View Post
Attached is the design I'm working on - recently found out it's actually a popular driver config by Carmody.
From looking at that crossover (system response chart), I suggest that you build the design by Paul Carmody.
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Old 18th May 2016, 06:56 AM   #6
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Quote:
Originally Posted by Jay View Post
From looking at that crossover (system response chart), I suggest that you build the design by Paul Carmody.
Just for kicks and giggles I typed in his component values and got a pretty crazy response. My driver response data seems to be very different than his, and I trust my data as it was taken in box and at several angles to verify all anomalies. I agree that ultimately his SPL graph looks better, but just typing in his values doesn't seem to do it for me.
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Old 18th May 2016, 08:13 AM   #7
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by G Speakers View Post
Just for kicks and giggles I typed in his component values and got a pretty crazy response.
Can you show that response? The frequency response itself is not too important in such simulation. You can make 10 very different networks and the responses are more or less the same, right? (but the sound quality will not be the same).

BTW, I think the data was not right.
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Old 18th May 2016, 02:10 PM   #8
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Quote:
Originally Posted by Zero D View Post
Hi,

Caps in series decrease value

Caps in parallel increase value

Res in series increase value

Res in parallel decrease value

Ind in series increase value

Ind in parallel decrease value

Have a look/try here for eg Capacitors - Parallel and Serial Connections

Zero D - Thank you. I don't know why I couldn't find it stated so simply somewhere else! Just to make sure I understand the practical application, when wiring a component in series I literally just add it in line after another, but parallel I just stack them with their leads touching on both sides, right? Not sure why it so easy for me to understand with speakers but not XOs
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Old 19th May 2016, 08:54 AM   #9
TMM is offline TMM  Australia
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Quote:
Originally Posted by G Speakers View Post
Just to make sure I understand the practical application, when wiring a component in series I literally just add it in line after another, but parallel I just stack them with their leads touching on both sides, right?
Correct.

When you wire inductors or resistors in series, the values simply sum together. Same thing with wiring capacitors in parallel.


Wiring multiple components to reduce the overall value gets trickier - this when you would wire two inductors or resistors in parallel, or two capacitors in series. The resulting value is C = 1/((1/A)+(1/B)) where A and B are the values of the two components and C is the resulting value when you wire then together. As a result of this if you only want to reduce the value of a component by a little bit then you need another component which is much much larger in value. For instance, if you wire a 8ohm resistor in parallel with 100ohms you get 1/((1/8)+(1/100)) = 1/(0.135) = 7.41ohms. Obviously if you had an 8uF capacitor or 8mH inductor and you wanted to reduce it's value to 7.4 it would be hopelessly impractical to go and get an 800uF or 800mH component hence why the rule of thumb is to start with a components which are lower than nominal then increase them as neccesary by adding smaller components. The exception to this are inductors since you can buy one that is too large and them simply unwind some turns until you reach the required value - assuming of course you have the equipment to measure inductance.


One other thing to note when using multiple inductors is that you still need to observe physical placement rules even if they are wired together!
Placement of coils in crossover networks

Last edited by TMM; 19th May 2016 at 08:59 AM.
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Old 19th May 2016, 05:10 PM   #10
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Quote:
Originally Posted by TMM View Post
Correct.

When you wire inductors or resistors in series, the values simply sum together. Same thing with wiring capacitors in parallel.


Wiring multiple components to reduce the overall value gets trickier - this when you would wire two inductors or resistors in parallel, or two capacitors in series. The resulting value is C = 1/((1/A)+(1/B)) where A and B are the values of the two components and C is the resulting value when you wire then together. As a result of this if you only want to reduce the value of a component by a little bit then you need another component which is much much larger in value. For instance, if you wire a 8ohm resistor in parallel with 100ohms you get 1/((1/8)+(1/100)) = 1/(0.135) = 7.41ohms. Obviously if you had an 8uF capacitor or 8mH inductor and you wanted to reduce it's value to 7.4 it would be hopelessly impractical to go and get an 800uF or 800mH component hence why the rule of thumb is to start with a components which are lower than nominal then increase them as neccesary by adding smaller components. The exception to this are inductors since you can buy one that is too large and them simply unwind some turns until you reach the required value - assuming of course you have the equipment to measure inductance.


One other thing to note when using multiple inductors is that you still need to observe physical placement rules even if they are wired together!
Placement of coils in crossover networks
TMM - my main man! Thank you for this. That's what I was thinking. I was just about to order the parts, I have small ones for tweaking in the cart but I think I'll drop the values a little for the main components so I can work up from there, instead of down.
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