Large Coil Simulation Accuracy Issue and Adjustment

[just a guy]

it would be interesting plotting Le vs X
change of inductance versus position in the gap.

That would be interesting but way beyond my ability. I can't measure excursion especially at very small levels.

all this stuff* concerns small signal VS large signal models
also another biggie is delta Re as temperature
*departure of predicted models and real life. confirm models with testing under 1V

I'm not sure testing at under 1V would make much (if any) difference. 2V applied to these massive coils isn't much, it's not going to cause any kind of power compression. In the absence of power compression I would expect these drivers to behave like "normal" drivers in that there wouldn't be a whole lot of difference between frequency response measurements at mV vs 2V curve shape. Difference in sensitivity but not much difference in curve shape.

 

[Djim]

For some reason, we're getting less force. Impedance and voltage are the same as without modification IIRC, so current remains constant. Either the magnetic field or effective length of wire have decreased.

Hi chris661,

The force field (BL) is a constant and cannot change. Losses have to be compensated with Re. The problem here is in the inductive reactance (XL), which opposes the change in current and becomes the dominant force here. You can increase or lower this force by increasing or lowering the force field (BL). If you look for driver indications: high Le and/or high Mms (for its size) in relation to a low EBP value.

Cheers,
Djim

 

[just a guy]

The problem here is in the inductive reactance (XL), which opposes the change in current and becomes the dominant force here. You can increase or lower this force by increasing or lowering the force field (BL). If you look for driver indications: high Le and/or high Mms (for its size) in relation to a low EBP value.

Cheers,
Djim

Here's the first link I looked at wrt inductive reactance - http://www.learnabout-electronics.org/ac_theory/reactance61.php

This sounds reasonable but my eyes get a little hazy when talk turns to reactance, vectors, phasor sums and imaginary numbers. Can at least one person that knows about this stuff verify this quote? Then with Djim's permission maybe I can add this to the paper.

Also, is there a way that we can calculate XL directly and use it to directly adjust Bl? That might be a little more accurate than my method. That would mean I spent 100 hours on all this for nothing but if there's a better way...

 

[Djim]

Hi just a guy,

XL = 2 * Pi * f * L

BL = 1 / XL

Remember the paper I posted in the other thread that the model was incomplete, a parallel RL-circuit that is in series with Re and Le, is missing for VC-model.

Cheers,
Djim

 

[just a guy]

I do not recall the paper or the thread, could you link me?

I have some questions and concerns about this, maybe you can help me.

XL = 2 * Pi * f * L
inductive reactance = 2 * 3.14 * f(requency) * inductance (H)

1. This formula has frequency as a multiplier, and it's pretty significant. At subwoofer frequencies, say 1 - 200 hz, this changes the outcome of the formula significantly. For example, if we use 1 mh and 10 hz we get XL = 0.0628. If we use 1 mh at 100 hz we get 0.628. That's a big difference. Then when we do Bl = 1 / XL, for 10 hz we get 15.92 and at 100 hz we get 1.59. At 1 hz it would be 159.2 and at 1 khz it would be 0.159. I'm not sure how Bl could be .159 at 1 khz and 159.2 at 1 hz, so I'm not sure what to do with these formulas. My method isn't concerned with frequency at all and it seems to work at all frequencies.

2. A 16 ohm driver could have 48 mH of inductance and a 1 ohm driver could have 3 mH of inductance, and both these drivers would have exactly the same amount of normalized inductance (Le/Re). Normalized inductance is what matters, not inductance. These formulas do not seem to take normalized inductance into account, so a driver with high Re is going to give quite different numbers than a driver with low Re when using these formulas even if they have the same normalized inductance. What to do about this? A big part of my method is using normalized inductance and it seems to work really well.

3. Is inductive reactance what the complex inductance model by Wright and Leach are trying to solve?

4. If this is common knowledge and it's known that you can adjust Bl to account for inductive reactance, why doesn't anyone know about this and why am I the first one to make a method so simulators (that can't accept complex inductance parameters) can make accurate sims?

Thanks for helping.

 

[Djim]

Hi 'just a guy',

You are right, the formulas are frequency/inductance related so you can forget about them. Basically you treat the VC as if it behaves like a true inductor with a normalized inductance. I think you are the first because the general idea is that VC does not behave like a true inductor because it moves in a magnetic field.

So, if the magnetic field is weak enough, because (?) 'enough' VC height is sticking out the gap, the normalized inductance becomes dominant?

Cheers,
Djim

 

[infinia]

That would be interesting but way beyond my ability. I can't measure excursion especially at very small levels.



I'm not sure testing at under 1V would make much (if any) difference. 2V applied to these massive coils isn't much, it's not going to cause any kind of power compression. In the absence of power compression I would expect these drivers to behave like "normal" drivers in that there wouldn't be a whole lot of difference between frequency response measurements at mV vs 2V curve shape. Difference in sensitivity but not much difference in curve shape.

my point was 2 fold> both relates to my suggestion that testing at lower signals should get better correlation to the models.
1) Le modulation vs displacement , so small signals < 1Vrms mean lower changes to Le > it's an averaging of Le Vs displacement since you cant measure it directly. this is more pronounced at the edges of the box frequencies where small signals can give a lots of displacement.
2) and delta Re is as you pointed out is the main component to power compression which isn't necessarily related to large X displacement. this is more pronounced at the upper band width. Eg low X movements means less coil cooling.