Do air core inductors make a noticeable difference over solid inductors low pass

[Jesse055]

I just wanted some people opinions and experiences with solid core inductors vs air in low pass filters in the average 3 way design say below 400 hz. While we are on the topic do bipolar electrolytic caps perform acceptably compared to poly caps that can get costly and huge(low pass only)Need the info for an upcoming build and would like to cut costs but not if too punitive to sound quality. Would appreciate the input.

[Jesse055]

Correction, air compared to solid core.

[jhollander]

Assuming the same inductor DCR no difference. The lower DCR on a woofer is better for sensitivity. I use electrolytic caps when the values get big and the space gets small. I'll use Mylar/ polyester over polypropylene to save costs

[billfitzmaurice]

If anything cored may be better, as they will generally have lower DCR. DCR is the criteria by which I choose both type and wire gauge. NPE are OK for low pass, as all they do is shunt to ground, so their higher ESR is of no real consequence.

[Jesse055]

Thanks for the opinions. I have always used the iron core inductors and NPE for low pass filters. This probably wouldn’t be advisable for the high pass section on the midrange filter? I have always used air core and poly on midrange.

[jhollander]

Like Bill said it depends on the DCR value. I'll use solid core if I'm battling a sensitivity issue with the mid and I need a large inductor

[billfitzmaurice]

With midrange I use the least expensive coil that gives DCR no more the 5% of the driver Z. Sometimes that's air cored, sometimes solid. With tweeters it's always air core, as values that small are only available in air core. I use polys in all high pass applications.

[tvrgeek]

If anything cored may be better, as they will generally have lower DCR. DCR is the criteria by which I choose both type and wire gauge. NPE are OK for low pass, as all they do is shunt to ground, so their higher ESR is of no real consequence.

"Shunt to ground"

Not disputing use of an NPE in the low pass is not a reasonable cost substitution. Not disagreeing with iron core inductors for LP. But please go learn just a little bit about electronic theory before leading others who also do not have an electronics background astray about location of the component in the network. All current is in the signal path. This is AC.

[Regore]

Iron core inductors are non linear at higher current levels and will saturate. Air core inductors have no core so can't saturate.
Lower DC resistance comes at a price, no free ride.

[LOUT]

Iron core inductors are non linear at higher current levels and will saturate. Air core inductors have no core so can't saturate.
Lower DC resistance comes at a price, no free ride.

Is there a good rule-of-thumb or crosschecking with spec's way to find roughly how much current they can handle before saturation becomes an issue?

Probably dumb question, but does that mean feeding too many amps is the potential problem (aka, generally staying under a particular wattage should keep things safe)?
If so, I'm assuming the spec'ed wattage rating is just a heat-dissipation of the resistanceVSwire-gauge, not anything directly related to core saturation?

[billfitzmaurice]

Iron core inductors are non linear at higher current levels and will saturate.

That's more of an audiophile myth than engineering fact and isn't backed up by testing results. If it was true then pro-sound speakers that operate with current levels far higher than consumer grade speakers would use air core exclusively. They don't. Cored inductors in some cases can have higher THD than air core, but still below the threshold of audibility, so it's of no consequence.

[jhollander]

https://hificompass.com/en/projects/...core-inductors

Good article here where the increasing distortion is a measure of the non-linearity

[Regore]

It's not a myth, Fitz. Do some research. Vance Dickasons Loudspeaker Design Cookbook covers it in Chapter 7.8.
For very large values iron core inductors may be an attractive alternative due to cost and DC resistance.

[PWR RYD]

Is reading a chapter in the Loudspeaker Design Cookbook considered "doing research"?

[fpitas]

Is reading a chapter in the Loudspeaker Design Cookbook considered "doing research"?

These days actually reading a book is getting unusual.