Foil Inductors, why the new trend?

[Guest David H]

Foil Inductors, why the new trend?

When I first started building crossovers I built a set or two using foil inductors, then I saw ALK and several others using Litz wire inductors. I inquired why Litz, I was informed that Litz has a higher Q at crossover points between 6khz and 15khz, where foil inductors have significantly higher Q beyond the audible range.

Solid core inductors even have a higher Q than the Foil inductors up to 2Khz. This is why ALK uses Solid core or Iron core for bass and Litz wire for HF.

So why the sudden trend of using Foil? I have even seen Litz removed in favor of Foil.

What am I missing?

Here is a Link to ALK's Q&A page if anyone would like to see more. http://www.alkeng.com/dload_xo.html

[Schu]

HMMM

Could it be the shape of the curve that is helping to determine the desirability and delivery?

the two are very distinctly different in profile...

Edited July 21, 2014 by Schu

[Fjd]

I think it is confusing and I do hope a few of the engineers weigh in as I've read in various forum threads that crossover designers (Klipsch included?) often choose the inductors with a specific DCR and capacitors with a certain ESR to control the Q of the filter as a whole without any external resistors.

Often times, I see reprimanding-type remarks when people just blindly substitute an inductor even when the value (i.e. mHy) is the same.

However, it would seem that foil inductors would reduce potential 'skin effect' in the same way as the litz wire inductors.

For my diy stuff I tend to use the litz wire for any mid and high frequency areas and have not tried foil (yet).

I also wonder if the curves that ALK has presented would change with different size inductors?

Edited July 21, 2014 by Fjd

[Guest David H]

HMMM

Could it be the shape of the curve that is helping to determine the desirability and delivery?

the two are very distinctly different in profile...

I would think the higher Q would be more desirable.

[Guest David H]

I think it is confusing and I do hope a few of the engineers weigh in as I've read in various forum threads that crossover designers (Klipsch included?) often choose the inductors with a specific DCR and capacitors with a certain ESR to control the Q of the filter as a whole without any external resistors.

Often times, I see reprimanding-type remarks when people just blindly substitute an inductor even when the value (i.e. mHy) is the same.

However, it would seem that foil inductors would reduce potential 'skin effect' in the same way as the litz wire inductors.

For my diy stuff I tend to use the litz wire for any mid and high frequency areas and have not tried foil (yet).

I also wonder if the curves that ALK has presented would change with different size inductors?

It would think changing the size of the inductor would effect ESR more than Q.

As best I can recall from my short stint at VVC, skin effect is negligible at audible frequencies.

I have several of each type of inductor, I guess I will have to run a few tests myself.

I agree, maybe some engineers will be able to shed some light. I don't think ALK is going to post, however his input is always appreciated.

Dave

[Schu]

HMMM

Could it be the shape of the curve that is helping to determine the desirability and delivery?

the two are very distinctly different in profile...

I would think the higher Q would be more desirable.

I know... you said that in your introduction.

Never the less, the delivery seems very different between the two plotted profiles... perhaps that difference as one delivery type is more desirable than the other?

[Guest David H]

What delivery are you referring to? I clearly don't understand your meaning. Its a basic XY plot.

BTW, I just checked a couple of the inductors I have on hand, and can confirm the Foil is better at frequencies above 10 KHz than the air core of nearly the same values.

I do not have a Litz inductor on hand to test.

Q @ Frequency 100hz 120hz 1000hz 10000hz

Air Cores:

Jantzen foil AWG14 1.34 1.36 8.7 25

Jantzen foil AWG 12 .49 .56 3.8 19

Jantzer Air core AWG 15 1.2 1.4 9.9 10.26

Iron cores:

Perfect Q Iron AWG 15 6.5 7.8 20.2 7.15

Jantzen P-Core AWG 15 8 9.5 55 35

Erse I Core AWG 18 2.4 2.9 14.45 7.1

This was a quick test, the inductors were not identical in size or gauge but reacted similarly.

Very interesting. I am anxious to add a Litz wire inductor to the list.

There is more to consider when choosing an inductor than Q, but from a Q standpoint alone, Foil inductors don't belong in the woofer filter.

I used a BK 885 for testing purposes.

Dave

Edited July 21, 2014 by GotHover

[Guest David H]

Good news, ALK is going to email me some additional information and test results as he gets time.

It will be nice to get crossover information from an expert.

Dave

[Thaddeus Smith]

I think they look pretty cool.

[mark1101]

Dean built me 3 Lascala Super AA networks years ago with copper foil inductors for the front of a home theater setup. ALK was all over us citing that it made no sense from an engineering standpoint. However, listening tests revealed a different situation. Those inductors gave my lascalas more bass definition than they ever had. Perception of more bass, cleaner, better all around. It was definitely noticable. This was about 6 years ago. I sold a pair but still have one left.

I know this to be the case because I sent the networks back to Dean twice.........rejecting his progressively more expensive builds..........until these showed up with Audio Cap Thetas and foil inductors.........and I kept them.

It's not always in the measurements.

[Guest David H]

Dean built me 3 Lascala Super AA networks years ago with copper foil inductors for the front of a home theater setup. ALK was all over us citing that it made no sense from an engineering standpoint. However, listening tests revealed a different situation. Those inductors gave my lascalas more bass definition than they ever had. Perception of more bass, cleaner, better all around. It was definitely noticable. This was about 6 years ago. I sold a pair but still have one left.

I know this to be the case because I sent the networks back to Dean twice.........rejecting his progressively more expensive builds..........until these showed up with Audio Cap Thetas and foil inductors.........and I kept them.

It's not always in the measurements.

Excellent. Thanks for the input.

Was an in room comparison done between the Foil inductor and a Quality Iron or air core done?

Foil inductors do look cool, they are also large and some quite pricey.

Dave

Edited July 21, 2014 by GotHover

[Guest David H]

I think they look pretty cool.

Yes they do.

[mikebse2a3]

Dean built me 3 Lascala Super AA networks years ago with copper foil inductors for the front of a home theater setup. ALK was all over us citing that it made no sense from an engineering standpoint. However, listening tests revealed a different situation. Those inductors gave my lascalas more bass definition than they ever had. Perception of more bass, cleaner, better all around. It was definitely noticable. This was about 6 years ago. I sold a pair but still have one left.

I know this to be the case because I sent the networks back to Dean twice.........rejecting his progressively more expensive builds..........until these showed up with Audio Cap Thetas and foil inductors.........and I kept them.

It's not always in the measurements.

Mark did you do any measurements of the frequency response of the different builds.? If the frequency response of all the builds were identical or not that would be very interesting to see.

Were al the inductors copper foil types in the network?

The reason I ask is because sometimes I wonder if it's the frequency response changes that we are hearing or is it some other aspect of the capacitors or coils that we aren't measuring that's responsible for what we hear.

miketn

[Guest David H]

The reason I ask is because sometimes I wonder if it's the frequency response changes that we are hearing or is it some other aspect of the capacitors or coils that we aren't measuring that's responsible for what we hear.

Bingo....

BTW, ALK sent me some very nice plots, I will post them as soon as I get more time.

What I also found interesting is the influence frequency has on inductance, especially those with lower Q. Looks like I have some more homework to do.

Dave

[mark1101]

I never did any measurements. This was several years ago before I got into that. The copper foil inductors were 12 ga. in the woofer filter, smaller ones in the other filters. I would have to go and look at it to be certain. The networks had some serious weight to them and honestly looked a little funny.......over done.

The first networks I sent back to Dean had the iron core inductors..........junk IMHO.

I know I have some pics of all these. I'll have to see if I can find them.

[mark1101]

I just figured out by looking at old pics it was sometime in either 2006 or 2007. After a Klipsch gathering with Roy in late 2007, in early 2008 I had 402 horns and quit playing with these toys.

The point is Dean (and I) were using copper foil inductors almost 10 years ago.

The pics of the boards themselves are at home. But I not only definitely have them.........I have the network itself.

[Deang]

Foil Inductors, why the new trend?

Where are you seeing this "trend"?

[babadono]

The reason I ask is because sometimes I wonder if it's the frequency response changes that we are hearing or is it some other aspect of the capacitors or coils that we aren't measuring that's responsible for what we hear.

miketn,

From your signature:

Einstein: "Not everything that can be counted counts, and not everything that counts can be counted"

[Deang]

... or is it some other aspect of the capacitors or coils that we aren't measuring that's responsible for what we hear.

At some point you have to become comfortable with not fully understanding why you hear what you hear. In other words, I think it's okay to enjoy improvement without measurable evidence of why you're hearing what your're hearing. That doesn't necessarily mean the evidence isn't there, it just means a method for measuring it hasn't been found yet. In some cases it has been found, but some don't want to accept the findings.

I used some Jantzen 12 gauge copper foils in my own crossovers mostly because they were practically given to me by the guys down at Parts Express. Even though they're massive, the DCR is within a couple hundredths of an ohm of the stock iron core. If based on that alone, there shoudn't be any audible difference, but there is. The bass lines are more prominent (defined/easier to follow), and the kick drum has a higher "whack factor". I've got a Jantzen waxed copper foil in the tweeter sections with the Jupiters, which is kind of extravagant for that position.

The old iron core everyone is used to seeing is in the process of getting the same facelift the autoformer got -- larger wire, bigger core, bigger frame, and wax impregnated. I have no problem with good iron cores. I've been using a lot of 14 gauge air core types (Solen and Erse) in the low pass section because they sound marginally better to me than the stock part, and they don't add that much more money to the build. I'm still using Litz in the midrange section of the SuperX.

I say if you can afford them, go for it -- they really do a good job of getting out of the way.

[mark1101]

When I had the pair of lascalas with those foil inductor networks (which I sold locally to a buddy).........I did make some measurements after all now that I think about it. I was able to clearly count more empty beer bottles on Saturday morning.

Dean made a smart statement.......that you need to get comfortable with the fact that you can't measure certain aspects of sound and/or differences that you hear. These mics and PC tools we use just aren't going to account for all things we hear. I never had an issue with that because when I started using measurements I immediately figured out you couldn't measure differences in timber and tone with the tools I had.