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Old 13th December 2006, 11:49 PM   #11
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I've used Erse iron core coils; the best I've seen.
http://www.erse.cc/coils/ov/coils.asp I used the Super Q hammerheads as I needed lowest possible DC resistance in series with the woofer.

In general, air cores are preferred. I prefer to use foil inductors, but unless you're pretty picky they're not necessary. A coil in series with the woofer especially, and to a lesser extent the mid, should usually be as low in resistance as possible.

In a series trap (L-C-R) you can use a small gauge wire for the L. For example, if the trap calls for 5 ohms, just subtract the coil resistance from the R; 5-1.- 1.4 Ohms, for a 3.6 Ohm resistor, and a total of 5 ohms.

When mounting the coils on the XO board, if they are close (within 2 inches?) mount them at right angles to each other to minimize coupling. One flat, and one on edge for example.

By all means stay away from ferrite cored inductors. I remember a system a friend had with those in it, and when he played it loudly, the core would saturate and collapse, making a "crack" noise. That's a big reason why I tend to be very conservative on the size of the steel core coils.
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Old 14th December 2006, 07:52 PM   #12
Klimon is offline Klimon  Belgium
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http://www.northcreekmusic.com/COILS.html

This webpage addresses amongst others the issue of ferrite core inductors
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Old 14th December 2006, 08:24 PM   #13
Jonasa is offline Jonasa  Belgium
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Thanks for the answers there are real specialists on this forum.

For several months i'm busy with a design of a crossover.
I looks realy nice now. I use lspcad for simulation.
But before I order components I must know it for sure about the inductors.

So it would be good to use a coil for the first order filter that I'll use for woofer.
But to flatten the frequency response I've used several noth filters in my design. Because I want to keep the Q factor high I need to use large L.
The crossover design is for realy small speakers so I have not much space for big inductors.

The inductors in the notch filters are between 1 and 2 mH.
Current in noth filters is not so high. (correct me if not)

So would it give a difference in sound when I only use steal core inductors for the notch filter? With good luck they never reach the saturation level.
But will the hystersis of the inductors be audible in sound? Are there some tests that I can do with a functiongenerator and oscilloscoop???

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Old 14th December 2006, 08:40 PM   #14
Jonasa is offline Jonasa  Belgium
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Type mistake:
So it would be good to use a coil for the first order filter that I'll use for woofer.
I mean:
So it would be good to use a air coil for the first order filter that I'll use for woofer.
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Old 14th December 2006, 09:28 PM   #15
Tenson is offline Tenson  United Kingdom
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Hi,

Is there a way to calculate the DCR of an inductor from its value and wire gauge or something?

I have been getting to grips with passive Xover simulation using the FRD consortium tools and Speaker Workshop. I have what seems to be a good Xover design but when I remembered to add some DCR to each inductor (I tried 1 ohm for each inductor?) it got pretty messed up. Some things I couldn't seem to compensate by changing other values.

So, what is a common DCR for good air-core inductors? For something small like 0.5mH and something bigger like 1.5mH? Just to give me an idea...

Do foil inductors have lower DCR? What are their negatives/advantages, high capacitance, low resistance maybe?
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Old 14th December 2006, 11:58 PM   #16
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Most sites that sell air core inductors give the DCR as well. 1 ohm is typically on the high side. You can't give a generic number for the resistance, since it varies with the gauge, and many sites offer coils in 2 to 4 gauges.
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Old 30th November 2010, 08:26 AM   #17
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Under normal listening condition Iron Core inductors sound better due to its low DCR. Loudspeaker will sound bright and harsh if air core inductor is used in low pass circuit in 2-way system designed for flat response. If you use air core you need to pad down the tweeter by a db or a half and you need more powerful amplifier.

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Old 30th November 2010, 08:16 PM   #18
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Unfortunately - or fortunately - different ferromagnetic
core materials behave fairly different.

Also dimensions of the coil and the core play a
significant role.

This supplier provides some distorsion measures
for his "iron core" coils.

Unfortunately in german, maybe you can find
an english version too.

http://docs.ts-audio.de/a/ax/svqxmzq...osselspule.pdf

There are some cores which come somewhere near
to an aircoil, at least from upper bass upwards.

When weighting the pros and cons
my personal limit for an aircore might be
1 ... 2.2 mH depending on the application.

For significantly higher inductance i would look
for a good core material.

You need lots of wire in an aircore for larger values
if you want acceptable Rdc. *

Independent from the core material, the windings
of a coil should be very tight and either
backed enamel should be used or the coil should
be vacuum drenched to keep it "silent".

I want to try this grain-oriented dynamo sheet
"I" cores, in the next weeks:

Lautsprecher Shop Intertechnik - I130/3.3/132 | I Kern :: Drosselspulen :: Frequenzweichenbauteile ::

---
* On the other hand, if you have reasons to increase effective Qts
of a woofer, a higher Rdc in a series inductor might be useful,
which may call for an aircore even with higher inductances as an
exception to the rule.
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Last edited by LineArray; 30th November 2010 at 08:36 PM.
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Old 30th November 2010, 11:00 PM   #19
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Location: flyover country
Quote:
So would it give a difference in sound when I only use steal core inductors for the notch filter? With good luck they never reach the saturation level.
But will the hystersis of the inductors be audible in sound? Are there some tests that I can do with a functiongenerator and oscilloscoop???
Probably most competently made inductors, steel core or air, will sound better in a notch configuration to flatten response than not having a notch at all. But you may still prefer the sound of the air core in a notch application, even so.
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Old 1st December 2010, 02:21 AM   #20
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Steel core coils sold for audio use have what amounts to a very large air gap, which linearizes the coil, so that hysteresis is not a factor. I have never seen saturation in a steel core, and because the currents are so limited in a notch filter due to the narrow bandwidth, I am sure it would never be a problem. As mentioned several times above, DC resistance is an issue, which steel cores minimize, but in a Series notch (R-L-C) part of the R can be in the coil, just so long as the discrete R and the coil R add to the desired value. In the parallel notch |-L+Rc|
o-|-C-|-o
|-R-|
it's a little trickier, but your optimizer/simulator will get you through. Tape wound air core coils are my preference, then steel core, then wire.

Don't spend a lot of concern on the issue, as your use in notch filters will minimize the sonic impact in any event.
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