Toroidal or foil, which is best?

[diamondsouled]

Am building some Xovers for my Altec/JBLs and am wondering if it is better to go with toroidal or foil inductors.

Any feedback would be appreciated.

Thanks

Lar

[mini]

Am building some Xovers for my Altec/JBLs and am wondering if it is better to go with toroidal or foil inductors.

Any feedback would be appreciated.

Thanks

Lar

Hi,

Nice avatar, really. Regarding the coils I would suggest if somebody asked me, none of both would suit. Both come with some precipitous promises. Both fail in keeping them. This You can take for granted.
The special winding technique of both, even as they are different to each other alter the inductance of the coil with higher frequencies. So, there are audible differences. But only because both types are inferior in according with specs.
I assume You selected them especially for its exotic poultice, but exactly that should keep You away. Do You buy a car for its square wheels? Not even in spite of. What a strange craze in audio ...

Sincerely

[Baron030]

Hi Lar

While, I can't say for sure which is better, toroidal or foil coils.
An argument could be said in favor of the air core coils as being superior by not have any magnetic hysteresis. And yet, the large high-end toroidal iron cores have such low magnetic hysteresis that it might not really be an issue.

But, there is one thing that I am very certain about. Upgrading the coils will make a very noticeable sound improvement over the small iron cores that are often used in most stock crossover networks. The small iron core coils can saturate and cause distortion at high volume levels. So, upgrading to an air core or a much larger iron core coil will give you a much cleaner sound.

Since, you are most likely going to build your new networks based on an existing Altec or JBL design. Then I would suggest going with coils that have similar DCR values to the original stock coils. And if the stock DCR values are not known, then follow a general design rule of keeping the DCR value to less then 1/20th of the driver's impedance. So, for example, if your woofer has 8 ohm impedance then you would want to keep the coil's DCR value to under 0.4 ohms. This general "less than 1/20th" rule particularly applies to all coils that are wired in series with a driver.

Baron030 :)

[diamondsouled]

Thanks guys.

Sounds like a good quality air core is the way to go.

Lar

[badman]

There are a couple major factors in the comparison we're looking at.

Core v. no core

The toroidal ones have a magnetic core, which introduces some distortion, can be saturated, and have other more esoteric issues. But it also comes with more inductance per inch of wire. So you can use a less resistive coil, with the associated advantages in improved damping and less power loss.

Foil vs. wire

Foil can be packed for more inductance in the same space, and accordingly, lower resistance. As mini says, there are some high frequency effects to this approach, but he's wrong in that it's 'worse' than other "standard" inductors. All inductors act funny at high frequencies. Inductors and other magnetics are very flawed and will remain so for quite some time.

If you want to spend, I'd go with either the foil or a very large gauge aircore. But here's the caveat: depending upon the crossover, some speaker coils WANT high DC resistance. Either the crossover is tuned with that resistance, or the driver wants a little less electrical damping.

You should see what my 5.5mH 10 awg aircores cost, too. That'll teach ya to want to upgrade them all! :D

[Mr. Widget]

You should see what my 5.5mH 10 awg aircores cost, too. That'll teach ya to want to upgrade them all! :D...and I bet that was before the current run on copper and the really high prices associated with it. :(


Widget

[mini]

As mini says, there are some high frequency effects to this approach, but he's wrong in that it's 'worse' than other "standard" inductors. All inductors act funny at high frequencies. Inductors and other magnetics are very flawed and will remain so for quite some time.


So myself would have given incomplete but not wrong advice. But yes, they are worse. We have had an investigation by a well known German hobbyists magazine. The claim of lower mechanical (!) imperfection has not been prooven. But the impedance vs. frequency plots showed strange behavior. The hobbyists investigation has been independently accomapied by some parallel measurements @ VISATON - a distributor - as far as I remember. Foils and toroids are at least funnier than standart devices. What makes me really sad is, that I couldn't give You any link to the graphs. I'm sorry. I'm afraid it would make no sense to encourage anybody to check for that issues themselfs objectively by measurement.



... some speaker coils WANT high DC resistance. Either the crossover is tuned with that resistance, or the driver wants a little less electrical damping.


The effect of Rdc is overestimated regularly. The speakers impedance is given being +/- 10% or so. And even JBL drivers will use that range and still are held as being o/k. To be sure just take what the OEM has taken with reason before. There is nothing left for improvement. The less if one considers the extra cost.

Sorry again for not showing the graphs!

ps: along with the investigation on exotic coils it had been shown that air core coils shouldn't be mounted close to a conducting plane. 'Cause eddy currents etc pp, strange things to.

so long

[badman]

So myself would have given incomplete but not wrong advice. But yes, they are worse. We have had an investigation by a well known German hobbyists magazine. The claim of lower mechanical (!) imperfection has not been prooven. But the impedance vs. frequency plots showed strange behavior. The hobbyists investigation has been independently accomapied by some parallel measurements @ VISATON - a distributor - as far as I remember. Foils and toroids are at least funnier than standart devices. What makes me really sad is, that I couldn't give You any link to the graphs. I'm sorry. I'm afraid it would make no sense to encourage anybody to check for that issues themselfs objectively by measurement.

Wrong may be a strong term, but I think it's presumptuous to claim something to be worse in a field of (badly) flawed devices. Each has advantages and disadvantages.... not sure where the mechanical component comes into the discussion, I said nothing about it, though in my opinion any field device is affected by mechanical resonance as well as electrical. This includes every single device in electronics, more or less. Checking the issues out with our own independent measurements might be difficult for some soooo:

I'll likely play with some inductor impedance measurements in the near future as I have some bass tuning to do, so if I remember, I'll post some results. I have small and large awg aircores, some



The effect of Rdc is overestimated regularly. The speakers impedance is given being +/- 10% or so. And even JBL drivers will use that range and still are held as being o/k. To be sure just take what the OEM has taken with reason before. There is nothing left for improvement. The less if one considers the extra cost.

Sorry again for not showing the graphs!

ps: along with the investigation on exotic coils it had been shown that air core coils shouldn't be mounted close to a conducting plane. 'Cause eddy currents etc pp, strange things to.

so long

Tolerances of a voicecoil which resides within a magnetic gap are somewhat different than a series resistance prior to that coil. But my point was that many of the little tiny inductors you see in some crossovers, with high DCR, cannot simply be upscaled. The DCR may be necessary to tune a notch filter, or keep the load from having an excessive dip, or even, in some cases, to alter the effective Qtc.

[mini]

... mechanical resonance ...


This term is used to hype the foil inductors. With the toroids the claim is skin effect, isn't it? I can't remember every audio hype to exactly, and I guess I won't. There is no use in both of it. A standard air core will work pretty well if not better as the precious exotics.



Tolerances of a voicecoil which resides within a magnetic gap are somewhat different than a series resistance prior to that coil.

I'm not sure about it. My experience is that a different Re within a pair of drivers leads to different sound pressure levels.

We agree completely in that the Rdc of coils in an x/o may be very specific. From that I suggested not to alter this value to much with example given above mentioned exotics. Some people think that a lower or even rather zero resistance would bettern the "control" of bass and the like. A common misconception when it comes to DIY and people are keen on "doing the best". Burning money worsens zound here as I guess.

so long

[badman]

...and I bet that was before the current run on copper and the really high prices associated with it. :(


Widget

Yer darn tootin', these are 2003 dollars or thereabouts. Turns out, I may have made an excellent long term investment :applaud: