Issues with C-Coil inductors from Jantzen

[ligonk]

I am using some C-Coil inductors from Jantzen for my Modula TMM build. Them, along with every other inductor and part get measured prior to using them in my crossover. Every other inductor i have measured in the past ends up being ever so slightly above the stated inductance, which is great because then i can just unwind a wrap or so and home in on the value i need, but in the end measure up precisely. However, when i measured these C-Coil inductors, they can in well (like ~70% of) below the stated inductance. For example, below show my measurements on the 1.5 mH and 3.3 mH c-coil inductors:





This seems too large to be typical tolerances; 1.5 mH with a 10% tolerance would yield no less than 1.35 mH. Shows is 29% of nominal value too low!! Whats is odd is that 1.07 is 71.3% of the nominal value, and 2.35 is 71.2% of nominal, it's almost like its something I'm not accounting for. There isn't some weird principle of steel core, or toroidal steel core inductors that I am not aware of is there?

I originally got a 3.3 mH to unwind down to the required 3.0 mH, but with this, i don't even know what to do. I have just installed them as is into my XO, but I am debating returning them and getting a different 14 AWG steel core, one that mey measure more accurately. I know Jon Marsh has used these in his designs, and many others have built the Modulas, so anyone else measure their c-cores and get something really off?


Thanks!

[Paul K.]

Well, there's always the possibility that the inductors were mislabeled during manufacturing (I assume there are or were labels on them listing the values you expected/wanted). Or, since your measurements for both are right at 29% low, that might indicate your inductance meter is acting up for some reason (since this occurred, I assume you've re-measured some other known-value inductors of about the same value to double-check your meter's performance). Specified accuracies considered, there should be no reason for C-core inductors to be more or less accurate than an air-core inductor.
Paul

[JonMarsh]

I have observed discrepancies with the C-Coil inductors, too, but they have been reading high in most cases- and the readings are dependent on the specific meter. There is some nonlinearity in the magnetic material they use at the very low excitation levels a typical LCR or inductance meter works at. Doing frequency sweeps at power in a crossover, however, things look the way you'd expect for the nominal values. This is something of a puzzler, and it did lead me to look at other parts, such as the 500W Erse inductors, which behave more consistently in measurement at low excitation levels.

BTW, many models of Scanspeak drivers have similar issues- to get accurate T/S parameters close to factory specs, you've got to drive them with more than milli-watts!

[ColoradoTom]

From the Jantzen site:

We are very satisfied with the result.
The C-Coil is designed for Bass, Sub-Woofer and Amplifiers, in different core and wire sizes.

Please note!

The C-Coil cannot be measured using a universal LC meter. Due to the characteristics of the core and winding method, it is important to use a professional RLC meter. We measure all C-Coils before shipping them using a professional RCL meter at AC 1 V 1 kHz.

[JonMarsh]

From the Jantzen site:

We are very satisfied with the result.
The C-Coil is designed for Bass, Sub-Woofer and Amplifiers, in different core and wire sizes.

Please note!

The C-Coil cannot be measured using a universal LC meter. Due to the characteristics of the core and winding method, it is important to use a professional RLC meter. We measure all C-Coils before shipping them using a professional RCL meter at AC 1 V 1 kHz.

There you go....

[ligonk]

Brilliant! That's what I was hoping/ expecting. My next question would then be: if I cannot measure then very accurately, how do I determine if I have unwound the 3.3 mH to 3.0mH? Would using the 3.3 add is be that bad a move for the use in the modula mkii tmm? I suppose it would lower the rolloff frequency of the bass driver in the 2.5 and create a dip there. Hmmm

[fatmarley]

BTW, many models of Scanspeak drivers have similar issues- to get accurate T/S parameters close to factory specs, you've got to drive them with more than milli-watts!

I've got some Scanspeak 21W/85555-00 woofers coming today. I only have a WT2 and WT3 to measure them with. Does that mean I'd be better off going by the datasheet T/S specs for modelling the enclosure size?

[fish fingers]

BTW, many models of Scanspeak drivers have similar issues- to get accurate T/S parameters close to factory specs, you've got to drive them with more than milli-watts!

Ah does that explain why the 7" paper illuminator is so off the specs when people take their own measurements ?

[5th element]

Does that mean I'd be better off going by the datasheet T/S specs for modelling the enclosure size?

That depends, do you trust the manufacturer? I tend to and simply use their provided T/S specs. That said if you do want to make your own measurements it is always better to do it with a bit of oomph in the signal. Like Jon says, just don't use milliwatts and you'll be okay.

Ah does that explain why the 7" paper illuminator is so off the specs when people take their own measurements ?

That depends. T/S parameters are one of those things that sometimes end up misunderstood. Firstly, regardless of the driver, T/S parameters shift depending on the drive level used for the measurements. Then things as simple as relative humidity, temperature and air pressure will also affect them, some less so than others, but nevertheless changes will occur. The most important thing to remember with T/S parameters though is that they tend to balance each other out, meaning that you may measure a scanspeak woofer as having a higher Qts and smaller Vas than Scan do, but when simulated with they give roughly the same net result. Basically you could have ended up measuring a slightly different point on a very similar curve.

Sometimes this isn't the case, sometimes a manufacturers way of measuring T/S parameters will be terrible or sometimes a manufacturers quality control will be horrendous, requiring that you measure for good results. Sometimes though the motor used within the driver may have some kind of non-typical gap geometry or arrangement that erroneously affects the softwares ability to accurately determine what a drivers T/S parameters should be.

[fatmarley]

The Scan 21W8555-00 datasheet T/S parameters are fs=20 qms=4.5 qes=0.33 qts=0.31 vas=134.

If I put these figures into a quick and dirty online calculator, for a Qtc of 0.707 I get a box size of 31.89ltr and an F3 of 45.62Hz and an Fb of 45.61Hz

On my fresh out of the box pair I get with my WT3 fs=24 qms=6.36 qes=0.49 qts=0.455 vas=75.

And with the online calculator I get - Qtc of 0.707 box size 51.08ltr with an F3 of 37.71Hz and an Fb of 37.71

So according to my readings the 21W8555 needs a much bigger box. Yes I know the calculator doesn't take stuffing, power handling, xmax etc into account but it still leaves me a little confused as to what specs to go by.

I know someone who designed some speakers with Scanspeak drivers and found that the box they made was too small, so my guess is they went with the manufacturers datasheet for modelling, but that's just a guess.

[Audiophile100%]

I have observed discrepancies with the C-Coil inductors, too, but they have been reading high in most cases- and the readings are dependent on the specific meter. There is some nonlinearity in the magnetic material they use at the very low excitation levels a typical LCR or inductance meter works at. Doing frequency sweeps at power in a crossover, however, things look the way you'd expect for the nominal values. This is something of a puzzler, and it did lead me to look at other parts, such as the 500W Erse inductors, which behave more consistently in measurement at low excitation levels.

excuse me if i aswer to a discussion of 7 yearas later, i'm sorry.
i noted the same discrepancies for my 4.7mH C-Coil one is 4 and the other is 4.3, realy worst mesurements.
redarding what says jon i measured them with clio at 3.6Vrms i think enough voltage value.
you say that at high power level the nominal value is right ? i.e. 4.7mH in my situation ?
in house i have also jantzen 4.7mH wax-coil but it has +0.40 Ohm against the c-coil, so in bass i lose -1db, what do you think about ?
is better the wax coil?

thank you;x(

[JonMarsh]

The C-Coil are intended for subwoofer and LF applications- and another issue not mentioned is core hysteresis. Inexpensive meters don't do well with that.

Which version of CLIO are you using? And one might also ask, what is the test frequency being used? These parameters can interact.

Air core crossovers have very ideal reactance characteristics, but the resistive losses are high, and large gauge wire must be used even then. What have you modeled in your crossover for the coil complex coil impedance? You can evaluate that quickly by changing the R-series in the component model.

One suggestion is to build your crossover with the actual load, and do a sweep test to see how the drive to the speaker looks; how close does it track to whatever your design tool indicates should be coming out of the filter?

[Audiophile100%]

thank you very much for your kind and quick reply.

The C-Coil are intended for subwoofer and LF applications- and another issue not mentioned is core hysteresis. Inexpensive meters don't do well with that.

yes i know
the two woofers i'm filtering have cutoff frequency of 200, 250 Hz

Which version of CLIO are you using? And one might also ask, what is the test frequency being used? These parameters can interact.

Clio Pocket latest version V.2.11
I don't know frequency test, clio do it automatically.
However i have tested with max output Clio voltage

Air core crossovers have very ideal reactance characteristics, but the resistive losses are high, and large gauge wire must be used even then. What have you modeled in your crossover for the coil complex coil impedance? You can evaluate that quickly by changing the R-series in the component model.

woofers in parallel RE is 3.3 Ohm so the c-coil (worse mH value!) is 0.05 Ohm, the wax is 0.47 ohm, so i add 0.42 Ohm to woofers: -1 db on woofers output

[ergo]

Audiophile100% - Check this link and try... this method should be equally possible with CLIO pocket

http://www.troelsgravesen.dk/Low-DCR-coils.htm

[Audiophile100%]

ok i measured my c-coil 4.7mH: before one was 4.3 and the other was 4.0; now new type of measurement linked (with cap), one is 5.0 mH and the other il 5.1 mH.

then i measured also 4.7mH wax with the same method (with cap) and both measured perfect: 4.689 and 4.678
with "normal" measurement they were 4.769 and 4.778, also perfect.

now my question is which measurement is better and affordable ?

[Audiophile100%]

is anybody there ?

[1Michael]

Patience...some people do work for a living.

[ergo]

Michael is very much right - now that Jon has retired then someone has to take over keeping the corporate world going

***

Anyhow, as the answer did interest me I tried some experiments.

I compared two coils
2mH Jantzen Air Core
2.5mH Jantzen C-Coil

Measured with
CLIO12 - in built impedance method
CLIO12 + CLIO QCbox V iSense method

First - the CLIO12 in built method with 1V and 3V (that is a max with CLIO12)
You see that while air core inductor result is not sensitive to drive level - the C-Coil one is


Next the suggested method via CLIO QCbox V amplifier



The result for Air Core at 1V, 3V and 9V - again, no influence of drive level


The result with C-Coil with 1V, 3V, 9V, 18V - you see that the resonant frequency keeps lowering


What is to be learned from this - for me the learning are
- Coils with toroidal core need higher voltage/current to measure close to the 'right' value
- There is no definite 'right value' when it comes to coils with ferrite cores - it will always depend on measurement levels/currents
- One can trust Jantzen number on the coil
- I would buy a new coil with right value instead of trying to wind down the ferrite cored coil. For air core it is safe as measurement is easy and accurate and I've done that a lot.

PS. Sorry about image quality - forum degrades it a bit too much but it is safer for future to keep images here and not link to them

[Audiophile100%]

ergo, thank you indeed for your work
i want ask about your point of view which method you tested is more releable to measure acurately inductance ?
with cap ot without ?

thank you

[ergo]

In general I'm using the CLIO12 in built method (or Dayton DATS or WooferTester) as that is the easiest to set up and use. This is good for all resistors, capacitors and air core inductors.

The only exemption are these ferrite cored inductors and especially very low DCR ones like the above C-Coil. The DC resistance of the above example I used is 0.07ohm, so no wonder it needs special tools to measure correct.
The above Tenma handheld meter would probably equally struggle to measure a Resistor with value of 0.07 ohm correctly.

If you have an impedance measurement jig - either DATS like or a resistor based method with REW or ARTA then putting the coil in circuit and measuring the resulting full speaker impedance (or just the woofer path) and comparing it to VituixCAD simulation might also be a good method instead of spending much time with measuring coil alone.

In your case - if you decrease the coil by same ratio then it will probably be close to what is needed and you can use the tools you have

Original value mH 3.30
Desired value mH 3.00
Remains 90.91%

"Tenma readings"
Original value mH 2.35
Desired value mH 2.14
Remains 90.91%

[Audiophile100%]

what's Tenma ?

i noted that the best and realiable method for c-coil is CLIO12 in built impedance method in which you can rise volts to max, i'm right ?
i have clio pocket 2.11 but it seems doesn't have CLIO12 in built impedance method, i can't raise the Volts values it is fixed to 1 !!!

[ergo]

The brand name on your LCR meter in the first post

[Audiophile100%]

ah ok

please answer to my other question, please

[ergo]

Without additional investment I do not see a way to solve the puzzle with the Tenma tester you have or CLIO Pocket. CLIO Pocket is the low cost version and as it has only one input, it will unfortunately limit what you can do in this specific case.

The ARTA-LIMP user manual shows the Impedance measurement config with Power amp in path. A setup like that would be needed to do this C-Coil measurement right. But you would need a 2-channel input for it. So Pocket is not suitable

So I would suggest just ordering an exact 3mH coil that you need and trust the manufacturer spec on it.

[Audiophile100%]

thank you for the answer ergo

Without additional investment I do not see a way to solve the puzzle with the Tenma tester you have or CLIO Pocket. CLIO Pocket is the low cost version and as it has only one input, it will unfortunately limit what you can do in this specific case.

ok i jet understand this , please could you suggest me a professional LCR meter to do exact measurements on inductance like c-coil ?, i need it.

The ARTA-LIMP user manual shows the Impedance measurement config with Power amp in path. A setup like that would be needed to do this C-Coil measurement right. But you would need a 2-channel input for it. So Pocket is not suitable

so you say that with pocket i can do that (at least with cap measurement can give a good measurement), but with arta + 2 channel audio card i will be able to do exact measurements on c-coil?

So I would suggest just ordering an exact 3mH coil that you need and trust the manufacturer spec on it.

ok but i want and i need to measure to perfect maching

[ergo]

For commercial solutions you would be looking for "Benchtop LCR meter"
But a quick look of the specs reveals that even for close to 3000EUR you don't really get higher source voltage than 2V.

You would be looking for specs like this for example
AC test signal voltage adjustable up to 2 Vrms
3 AC current ranges, selectable via 30Ω, 50Ω, or 100Ω internal AC impedance. The 30Ω setting provides up to 66.7mArms of drive

But I'm not 100% sure if that is still enough. Jantzen themselves writes "We recommend using a professional grade LCR / milliohm meter (bridge), both for coils with
an RDC of 0.1 ohm or lower, but also in general"

So in summary - I do not think it is feasible to invest in Desktop meter like this for hobby use.

And yes the 2 channel soundcard with LIMP (ARTA package) + a measurement amplifier will allow you to reach same result as I did above with CLIO12 + QCbox (amplifier). Just make sure it is "old school" solid state amplifier and not class-D. You need the amplifier "ground/ - speaker connector" to really sit at 0V.

***
3mH is not too much inductance - so if you really wanna match and be sure, get air core inductors instead. With C-Coil type you will never see one single answer. It will always depend on test instrument, drive level etc.

[Audiophile100%]

so, resonant point with capacitor method (troels gravesen) is a good method to reach good results also with 1 channel card ?

p.s.
jantzen when specify their LCR is very very ambiguous

[ergo]

so, resonant point with capacitor method (troels gravesen) is a good method to reach good results also with 1 channel card ?

You can try to put cap and coil parallel and resistor in series and see what you get. You can for sure measure impedance vs frequency with Pocket and 1 channel (thus a resonance), but I do not know what the result will be. Clio Pocket is something I do not have.