Foil Inductors, why the new trend?

[Deang]

Maybe you should try ordering 10 at a time. Al knows about the problem, he's experienced it himself. The laminations shift, and then the screws won't pass through the holes. You have to slide the laminations back in place before you can push the screws through. Did you miss the part about them not being dipped in anything?

UT knows how to make a coil. I've already been told what the DCR will be, which is all I really care about (besides construction quality).

BTW, these measurements were done about five years ago - is there some point in doing them again?

[Guest David H]

Did you miss the part about them not being dipped in anything?

Dipped coils are a good idea, I have no issues with that. I have even potted a few myself. I don't think it is 100% necessary but certainly doesn't hurt.

UT knows how to make a coil. I've already been told what the DCR will be, which is all I really care about (besides construction quality).

No question, Universal Transformer makes a fine product.

Just thought you might want to add the test results to the pool.

Dave

[Deang]

"Dipped coils are a good idea ... I don't think it is 100% necessary ..."

Why's that?

[Guest David H]

Dipped coils are a good idea, I have no issues with that. I have even potted a few myself. I don't think it is 100% necessary but certainly doesn't hurt.

"Dipped coils are a good idea ... I don't think it is 100% necessary ..." Why's that?

Not had any issues with Super Q or Sledge Hammer inductors.

Dave

[Deang]

http://en.m.wikipedia.org/wiki/Magnetostriction

The wire is elastic, and is stretched and compressed (at an almost microscopic level). This excites the windings and they "sing". Over time, the windings can actually work loose off the core. The problem is exasperated if placed near a magnet. Properly designed coils address this problem by doing something to keep the windings as stationary as possible, hence -- wax, varnish, epoxy ...

This doesn't necessarily mean it's audible for our applications, but it does speak to construction quality. However, I've handled a lot of old coils where the windings were so loose that they weren't technically attached to the core anymore, I don't see how that could be a good thing.

Edited August 7, 2014 by DeanG

[Guest David H]

Wow, look what North Creek has to say about Foils.

I don't necessarily agree with everything listed here.

Inductor FAQ's

Why does North Creek make wire wound inductors, and not copper foil inductors?

North Creek has had the ability to make copper foil inductors since 1995, but the fact of the matter is that when properly made, wire wound inductors have much better bass and a smoother midrange than any of the copper foil inductors available today - even those we make here. There are two reasons for this:

First and foremost, our wire wound inductors are made on a custom built, tension-free winding machine. This winding method minimizes the stretch and mechanical deformation of the copper, so there is no strain on the copper and its conductivity remains at a maximum. All copper foil inductors (and most copper wire inductors) are wound at very high tensions, so both the copper and the insulating film are stretched and remain under tension for the life of the product. Tension is differential stretch, which creates microfractures in both the copper and insulating material. This is about the worst thing one can do to a conductor.

The second factor is mechanical stability: North Creek inductors are varnish sealed in a vacuum chamber, which bonds each winding to the six surrounding it throughout the entire body of the coil. Most copper wire inductors are varnish dipped, which seals the outer wraps but not the coil body. Copper foil inductors are usually heat sealed, which seals the edges but not the body. Typical copper wire and copper foil inductors will have a number of mechanical resonances that are activated by current flowing through the inductor, and can be heard to "sing along" with the input signal. Because of their unique vacuum impregnation, North Creek inductors do not show any signs of mechanical resonance.

Copper foil inductors also have long term stability problems. This is because over time, air entering the coil body slowly oxidizes the copper surface and begins to penetrate the foil. This oxidation gradually degrades the conductivity of the copper, and over time the performance of the inductor.

The only application for copper foil inductors - where high DCR is acceptable and low ACR may be beneficial - is as series inductors in small dome midrange circuits.

[Guest David H]

Here is the entire Q/A + FAQ page from North Creek.

They have plenty to say about several inductors, not just foils.

http://www.northcreekmusic.com/COILS.html

[Full Range]

Good bit of reading on the subject we are discussing

The only application for copper foil inductors - where high DCR is acceptable and low ACR may be beneficial - is as series inductors in small dome midrange circuits.

Well I believe my crossover build falls within the North Creek preferred parameters for foil application

That being the foil inductors are only fitted to the mid range and tweeter sections

Furthermore the midrange also has a primary solid 3mm copper coil before the foil coil so it's a series inductor

Weather by design or a guesstimate - Glad I am doing something right ( I think ?)

[Deang]

I like their coils, but they really do their customers a disservice when they tell them to replace all existing coils with coils wound using the largest gauge copper possible -- it just doesn't work that way. I've often thought about using them, but if they'll lie about that, it makes me wonder what else they're lying about.

Edited August 8, 2014 by DeanG

[Fjd]

From Dave's link, are you referring to this Q&A?

*[Why does a larger gauge always lead to better sound?

While I can not objectively prove this, I believe it is all about DCR.

A larger gauge wire means lower DCR, and lower DCR means the amplifier has better control of the woofer cone at low frequencies, particularly near resonance. A lower DCR always translates directly to tighter bass.

For parallel inductors, low DCR keeps the crossover slope order the same. A high DCR parallel inductor will at some point cause the crossover slope to decrease by one order, limiting attenuation of the midrange or tweeter. This means that at some point, low frequency information will begin to crawl into those drivers that were not designed to handle it. This is especially important in series crossover circuits, where the DCR of the parallel inductor sets the limit of the tweeter's attenuation.]*

Not that it would necessarily correlate with what we hear and I'm sure that, rather than the absolute largest available, there could be various sizes of inductors that still achieve the goal in a crossover; however, here is an area I would have interest in what the measured or electrical impact of an inductor choice would actually be.

I like their coils, but they really do their customers a disservice when they tell them to replace all existing coils with coils wound using the largest gauge copper possible -- it just doesn't work that way. I've often thought about using them, but if they'll lie about that, it makes me wonder what else they're lying about.

From my basic understanding it seems that the high frequency part (i.e. tweeter) of the crossover circuit tends to use capacitor(s) in series and an inductor in parallel (as a shunt) to attenuate and roll-off low frequencies at some pre-determined slope (i.e. first-order, second-order, etc.) and pass high frequencies.

The low frequency part (woofer) of the crossover circuit tends to have an inductor in series and a capacitor in parallel (as a shunt) to attenuate and roll-off high frequencies and pass low frequencies.

If I’m thinking about this correctly, by having the tweeter receiving a signal in series from a capacitor and having an inductor shunting it, it would seem that as the frequency decreases the capacitor displays more resistance thus rolling off the power to the driver and the inductor has less resistance creating a steeper roll-off.

These thoughts were part of the reason for one of my initial questions in this tread;

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.

Maybe my question should not have focused on "Q" alone. It would seem that the value of the inductor’s DCR being higher than the "planned resistance" needed to achieve the transition point where an electrical second-order or third-order crossover filter could potentially transition back to a potentially “less desirable" first-order filter that, depending on the overall goals of the specific crossover design, could create problems.

I say less desirable because if the tweeter is at the lower end of the recommended crossover point or lower than the recommend crossover point, the lower frequencies would seem to be reaching back into the tweeter over what was originally planned, and, even though the acoustical output is very low, it could be introducing additional IM distortion, and a possible loss of transparency in the music, that would not necessarily be desirable.

Now layer in that we don’t have drivers with fixed impedance, as they all vary all over the place, which can also impact the crossover frequency and driver phase-angle.

Finally, to add insult to injury, a driver’s sensitivity varies over frequency as well.

It is kind of amazing that crossovers work at all and we get the music experience that we do.

[Deang]

I've compared two .20mH coils in the midrange of the SuperX I build. The midrange circuit is comprised of a capacitor, coil, and the autotransformer. I invite others to try this, and if you hear a difference, please let me know, because I just couldn't hear any. I expected at the very least to detect a small discernible difference in output levels due to the big swing in "Q" numbers, but I didn't. No copper foils on hand in that value -- I'll do those later.

 

I'll keep using the Litz at that position because people expect to see them, and just because I don't hear something better, doesn't mean someone else won't.

[halikarnas36]

Hi

Does it matters if i use 0.300mH Jantzen lits wire instead of 0.200 mH which is sitting on my crossboard ...I have come over one pair Litz with 0:300mH 15 AVG and wonder if i may have better result with those Litz Wire air coils….I have all ready changed capacitors with Mundorf and got much better sound…     Regards Yaraman

PS..Jantzen LITZ Wire Wax Coil 0,300mH 15AWG 0,17Ohm. My sitting standart air coils in speakers are 0.200mH 15AVG 0.13 Ohm

[Deang]

Which speaker? Which crossover? What is the DCR of the original part?

[MotoGP93]

Here's a really good explanation of the tradeoffs in inductor designs by Paul from PS Audio.

-Larry