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Old 26th September 2007, 12:33 PM   #1
arc2v is offline arc2v  United States
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Default Series Inductors question

I searched on this but did not find a good explanation, so I figured I'd ask explicityly:

I finally started building my open baffle center channel and wired up the crossover last night. One inductor in the midrange calls for 2mH. I have 2, 1mH inductors on hand (air core Jantzens from PE), so I wanted to wire them up, rather than shell out $20 for a new inductor. This is a prototype after all.

I know they need to be in series, but I'm afraid I'm at a loss for dealing with the mutual inductance. I've thought myself in circles and I think I put them opposite one another by accident.

For clarity sake, let's call the wires inner and outer, and the inductors A and B

Right now, I have A and B stacked atop one another. The signal comes in A-outer and A-inner and B-inner are connected. The signal goes to ground through B-outer. Again, these are stacked atop one another.

I got a weird distortion in the midrange, like the crossover wasn't working right (still breaking in, so no FR sweeps yet). so this was my first troubleshooting stop.

Now I'm thinking I need to have A-inner connect to B-outer.

Any advice here? If I get motivated, I will fire up Speaker Workshop and try some component measurements (even though it's not as accurate for inductors).

Thanks,
AC
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Old 26th September 2007, 01:48 PM   #2
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Think of it as if you were winding a single larger inductor. If the direction is clockwise on one inductor, you have to keep it that way on the second, lest they fight each other. You can also think of them as two transformer windings, like a dual voltage primary. wired out of phase, it doesn't work!
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Old 26th September 2007, 01:57 PM   #3
arc2v is offline arc2v  United States
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That's sort of what I was thinking. I actually thought myself in circles and just ended up doing it and figuring I'd debug it later.

Followup:
Someone forwarded me a webpage link a long time ago regarding inductors and location. It had a lot of experiments and the guy measured inductance for different orientations and separation distances and showed the results.

Does this sound familiar to anyone? If so, please resend the link, b/c I have searched for it and cannot find it to save my life.

Audioholics had a decent writeup too, but this one was more thorough.

Thanks,
Ac
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Old 26th September 2007, 03:53 PM   #4
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How about this:

http://www.audioholics.com/education...osstalk-basics
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Old 26th September 2007, 04:12 PM   #5
arc2v is offline arc2v  United States
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that's the one I was mentioning in the post. I found that, but the other one (the one I can't find) was more experimental. The guy was actually measuring changes in mH on the inductors. I don't think it was geared towards crossovers, just electronics in general.

Thanks though.

Ugh, next time, I will bookmark everything I find interesting

A
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Old 26th September 2007, 06:05 PM   #6
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Here is another good reference. I can't remember where it came from.
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File Type: gif coils_9.gif (31.7 KB, 223 views)
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Old 26th September 2007, 06:40 PM   #7
arc2v is offline arc2v  United States
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That's It!!!

That was the summary from the article I was looking for.

Now if we can just find the original

It's good to know my brain isn't just making things up.

Thanks,
A
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Old 26th September 2007, 06:48 PM   #8
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Here it is:
http://www.troelsgravesen.dk/coils.htm
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Old 26th September 2007, 06:53 PM   #9
arc2v is offline arc2v  United States
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Thank you so much!

He calls them coils, which is why my searches for inductor never found it.

Now to bookmark and never lose it again.

thanks again all!

AC
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Old 26th September 2007, 08:44 PM   #10
owdi is offline owdi  United States
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If you stack two 1mh inductors on top of each other, they will couple and sum or subtract, giving a final inductance either above or below 2mh. If you want 2mh, keep them far apart, and turn one 90 degrees away from the other.

When you replace the pair with a single 2mh inductor, keeping wire guage constant, RE will fall.

Dan
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