Air Core inductor vs. Steel laminate (sound quality)

[djkest]

Very Simple Question. Is it worth replacing a $9.00 Steel Laminate Inductor with a $23-32 Air Core Induction that is in-line with midwoofers?

Steel Laminate is 0.22 ohms DCR. System impedance is probably close to 4 ohms minimum.
14 gauge Air-core is $23-32 and has a DCR of 0.32 ohms. Now this isn't a huge difference, but when you add in the other inductor the DCR of 0.26 ohms it becomes a fairly large portion of the DCR and I've heard some people say no more than 5% is allowable. I know that the inductors used were the ones modeled, and changing either of these inductors would change the response in some way - not as the designer intended. So I guess I have 2 questions.
1) Is going from 0.22 ohms to 0.32 ohms (or 0.43 ohms for 16-gauge) for a 4-ohm nominal design going to have a significant effect on the crossover / overall sound?
2) Is upgrading from a steel-laminate to air-core inductor going to cause a real and noticeable improvement in sound quality?

I saw this paper that said for lower frequencies, steel laminate was actually better suited-
http://www.die.ing.unibo.it/pers/gra...ers/ciep00.pdf

I've read the biggest issue with steel laminate, iron core, ferrite core type inductors is that if the core saturates, they experience hysteresis which greatly increases distortion. But I'm not sure if that's an incremental issue or more of a binary one. I am also not sure at what power level an inductor would reach hysteresis.

I've noticed that most high-end designs use 100% air core inductors, but the DCR of those air-cores has been properly factored into the crossover during the initial design, so that's not necessarily comparable.

ETA: I would ask the designer but Jeff Bagby has PMs turned off and I think he is trying to reduce the number of messages he gets.

[carlspeak]

If it's a Bagby design, I'd presume he mulled over his inductor choices (as you are now doing) and ended up with what you have in your speakers. Are you questioning his choices? If so, why?

[djkest]

If it's a Bagby design, I'd presume he mulled over his inductor choices (as you are now doing) and ended up with what you have in your speakers. Are you questioning his choices? If so, why?

That's a good point. I'm sure he knows more about inductors than I do. I'm just uncertain if the decision to use steel laminate was based on affordability or best quality. That's my only reason for wanting to make the change.

[carlspeak]

If you are hearing saturation distortion, invest the ~$50 for the air cores. Just be sure to match the original core DCR so you don'e mess up JB's original XO design.

If you are not hearing any distortion with the original coils, then you are delving into the 'twilight zone' of hi-fi where many re-cappers now reside; wondering if their polypropylene capacitors should be replace with a boutique polypropylene cap at 10X the cost. :-)
Good luck.

[billfitzmaurice]

Very Simple Question. Is it worth replacing a $9.00 Steel Laminate Inductor with a $23-32 Air Core Induction that is in-line with midwoofers?

No. Myths abound in audio. The notion that cored inductors will saturate at much lower levels than air core and as a result sound better is one of them. For equal inductance and DCR air core cost a lot more, and that feeds into another audio myth, that higher price equals better performance. Since 'high end', as in 'high price', designs tend to embrace myths that explains why air core are popular with them. Jeff doesn't fit into that mold.

[thekorvers]

I've read the biggest issue with steel laminate, iron core, ferrite core type inductors is that if the core saturates, they experience hysteresis which greatly increases distortion. But I'm not sure if that's an incremental issue or more of a binary one. I am also not sure at what power level an inductor would reach hysteresis.

Actually hysteresis and Eddy currents are always present in the core of an iron-core inductor, whether saturated or not. Hysteresis losses increase with frequency, but are not much of a factor in the lower audio frequencies where iron-core inductors are used.

Saturation of the core does indeed drive up non-linear distortion to a high level in the form of harmonics and intermodulation distortion, but it takes considerable power to do so. Unless you listen to your music at ear splitting levels, it will not be much of a factor. Issues like over excursion and such are more likely to occur first.

Of course the application is relevant as well. You will probably want to use a beefier inductor for an 18" subwoofer than one used in the “Quarks” for example.

[Geoff Millar]

Hello

I also have a query about iron-core inductors, but it's not about sound quality: where a design calls for iron-core, can you use air cores or plastic cores instead? For example, Paul Carmody's Classix 2.5 use a 2.0mH iron core, which I can't easily source in Australia. It's used between the two woofers to give the 0.5 feature.

Any ideas appreciated!

Thank you

Geoff

[fpitas]

Geoff, as long as the DCR of the replacement is similar you should have no problem. That may take a pretty hefty air core inductor.

Francis

[Geoff Millar]

Thanks for the quick reply, Francis,

So is the DCR rather than the actual mH value the the key specification?

I'll need to find the DCR of the iron-core; I assume it will be included in the product specs so will have a look.

I may have to order the iron core as it seems to be a critical part of the crossover and I wouldn't want to do anything to muck up Paul's good work.

Geoff

[billfitzmaurice]

So is the DCR rather than the actual mH value the the key specification?

They're both key. Plans should specify the acceptable range of both Le and DCR.

[Geoff Millar]

Thanks Bill

I checked the specs: the 2.0, 18AWG iron core is 0.29 DCR and the air core 2.0, 18AWG, is 0.8: quite a difference.

I'll ask Mr Carmody to be on the safe side

Cheers

Geoff

[scottvalentin]

Geoff that is a fair bit off and to get an air coil with that DCR you will probably have to go to a larger 14AWG which can be quite a bit more expensive. Good luck!

[djkest]

Thanks Bill

I checked the specs: the 2.0, 18AWG iron core is 0.29 DCR and the air core 2.0, 18AWG, is 0.8: quite a difference.

I'll ask Mr Carmody to be on the safe side

Cheers

Geoff

It's definitely too big of a difference. I am sure there is an iron-core or steel-laminate core inductor for sale in Aus somewhere, just need to do a little digging!

It looks like Erse Audio will ship inductors to AUS for about $14, however they are out of stock. Have you checked the shipping price for Parts Express?

[mattsk8]

Where's Wolf ? He did a fantastic inductor comparison at a DIY get together and this is what my ears told me when I heard it (inductors all shared the same inductance and DCR)...

1. It was a short time I spent with it, so given more listening time my opinion might change, and might even change using different drivers than the ones Ben used (I'm not sure).
2. I actually think I preferred iron core on the woofers; but I can't remember if this is because I couldn't hear a difference and I know the iron cores are cheaper??
3. The only place I heard a difference that might motivate me to actually spend a little more on inductors was in the tweeter's xover- I preferred a litz inductor on the tweeter over foil and air core... and I was actually surprised that I preferred the sound of a standard air cor over a foil inductor.

So in conclusion, IMO I would stick with the iron core on your woofer. My 0.02 FWIW... hopefully Ben will chime in and offer his opinions as well.

[mattsk8]

If it's a Bagby design, I'd presume he mulled over his inductor choices (as you are now doing) and ended up with what you have in your speakers. Are you questioning his choices? If so, why?

I'm going to go out on a limb and take a guess at answering for him... but maybe (just maybe) it's because he wants to know if he prefers the sound of one inductor over another?? Just a wild guess on my part. Is it the Cardinal sin to attempt to swap some xover parts around in someone's kit? What if Jeff Bagby used a Dayton capacitor and djkest was sent an Audyn? Would that also be changing the design?