Semi-Le_Calc: Calculator for Advanced Inductance Model Incorporating Semi-Inductance

[bolserst]

Originally Posted by Josh Ricci

It's here
Bolserst's Complex Driver Inductance Calculator - Bass Gear - Data-Bass Forums

Thanks! I will add link to your forum at the beginning of this thread.

[bolserst]

Originally Posted by mwmkravchenko

Stiffness and impedance peak is related to the elasticity of the enclosure...The relationship is perhaps found in elasticity modulus differences between the enclosure materials.

The stiffness of the enclosure is certainly important to avoid enclosure resonance at low frequencies. But I think it is the damping coefficient of the material that gives an indication of how much energy is lost during deflection of the enclosure and how much is returned to the system. Compared to wood, most metals are low loss, but there are some exceptions like certain stainless steel alloys.

[mwmkravchenko]

Originally Posted by bolserst

The stiffness of the enclosure is certainly important to avoid enclosure resonance at low frequencies. But I think it is the damping coefficient of the material that gives an indication of how much energy is lost during deflection of the enclosure and how much is returned to the system. Compared to wood, most metals are low loss, but there are some exceptions like certain stainless steel alloys.

I think that you are right. Knowing both parameters, stiffness and damping is probably the way to do. But as you know the methods to create an enclosure are many. And the stiffness of any container is linked to the methods used to keep it stiff.


Why people can spend a good part of their career on seemingly simple things.


The simple things are not really all that simple right!

[bentoronto]

I see it is an advance on the good old T/S model. First mentioned by Leach long ago?

Can somebody add a few words about how "semi-inductance" is "caused"? Just in the driver or also influenced when mounted? What steps mechanically collapse it to conventional inductance and is that a good design purpose for driver designers or just something for crossover designers to remember?

B.

[bolserst]

First investigated and physical theory proposed by Vanderkooy in 1989.
See Post #15 for references *.pdf with link to free download along with many other relevant papers.

If you look at the measured impedance of a woofer without any shorting rings, you will see the phase of the impedance above resonance tends to be roughly 45deg over a broad range, rather than quickly approaching 90deg of a pure inductance. See Attachment #1 in Post #30.

In a few words, the cause is the frequency dependent eddy-current losses in the unlaminated pole piece. It is a property of the woofer motor construction and has nothing to do with mounting or enclosure. Use of laminated pole piece would largely avoid the semi-inductance, but result in much higher inductance and rolled off high-frequency response, so not a good idea. The approach taken by most higher quality woofer designs is to incorporate shorting rings to keep the impedance flatter and more resistive(lower phase angle), extending the high frequency response as well as reducing distortion from inductance modulation.

The 2011 model proposed by Thorborg and Futtrup that is slowly finding its way into more and more software packages incorporates not only the semi-inductance behavior, but can also account for shorting devices inside and/or outside the magnetic gap.

[Brian Steele]

Nice brief explanation. If you don't mind, I'd like to include it in the next update to the my semi-inductance page at The Subwoofer DIY Page - Semi-Inductance.

[mwmkravchenko]

Originally Posted by bolserst

First investigated and physical theory proposed by Vanderkooy in 1989.
See Post #15 for references *.pdf with link to free download along with many other relevant papers.

If you look at the measured impedance of a woofer without any shorting rings, you will see the phase of the impedance above resonance tends to be roughly 45deg over a broad range, rather than quickly approaching 90deg of a pure inductance. See Attachment #1 in Post #30.

In a few words, the cause is the frequency dependent eddy-current losses in the unlaminated pole piece. It is a property of the woofer motor construction and has nothing to do with mounting or enclosure. Use of laminated pole piece would largely avoid the semi-inductance, but result in much higher inductance and rolled off high-frequency response, so not a good idea. The approach taken by most higher quality woofer designs is to incorporate shorting rings to keep the impedance flatter and more resistive(lower phase angle), extending the high frequency response as well as reducing distortion from inductance modulation.

The 2011 model proposed by Thorborg and Futtrup that is slowly finding its way into more and more software packages incorporates not only the semi-inductance behavior, but can also account for shorting devices inside and/or outside the magnetic gap.

Great explanation!


The shorting ring can also be a pole piece sleeve. This is done in most drivers that are a wider band device like a mid-woofer. Not really used in narrow bandwidth devices like a subwoofer.

[LORDSANSUI]

Congratulations for the well done job.

Can neodymium drivers, due its lower size and more dense magnetic field, improve any losses regarding eddy-current in the pole piece?

[bentoronto]

Thanks for clear explanation. Vanderkooy (a local star*), not Leach?

Wouldn't eddy current loss be a source of non-linearity due to magnetic hysteresis or is that only in non-coppered iron cores?

As Mark said, not a big factor to grind into the model except when the band is wide.

B.
*Didn't he do a remarkable study of super-low resonance AR-like woofer drivers?

[bolserst]

Originally Posted by Brian Steele

Nice brief explanation. If you don't mind, I'd like to include it in the next update to the my semi-inductance page at The Subwoofer DIY Page - Semi-Inductance.

I don’t mind at all Feel free to include any text or attachments from this thread on your web page.
You might add a link to this thread for questions, similar to what you have on your Horn Folding web page.