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Old 20th November 2012, 02:13 PM   #29601
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Originally Posted by Esperado View Post
Does mosfets models follow exactly gate capacitors behaviors ? (real question)
My experience is limited to power mosfets of the IR and IXYS type, gen 3, die size 3 and up. There is a built in transmission line effect because the gate polysilicon is sandwiched by SiO2 between the silicon below and the source metalization cover above. If you turn it on very fast into a really low inductance load, you can destroy the device near the gate wirebond (because a small portion of the device has turned on). If you turn it off very fast, you will destroy the device on the other side of the source bond (because it is the last part of the device to turn off).

It's easy to perform failure analysis of this with a TO-3 can. Not so easy with an encapsulated device. (Note, this understanding helped in determining a snubber topology for a hf switcher.)

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Originally Posted by gpapag View Post
Thank you again jn.

George
You are always welcome.

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Unfortunately, that is not correct.
Frank
You do not understand the problem as I meant..probably poor explaining on my part... That is of course not an issue which will stand between us. If you wish to discuss it further, PM me. Or, we can do here for the benefit of others.

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Originally Posted by abraxalito View Post
Because that would make the voice coil run much hotter than using copper. Also probably poorer eddy current damping but that might not be an issue in some cases.
I do not understand how eddy current damping will be affected by the conductivity of the conductor. VC's by nature do not have large cross section wires, so eddy losses should be very low into the hundreds of Khz.

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Originally Posted by Esperado View Post
I was referring to efficiency losses with power, due to thermal coefficient. (What do you think ?)
But i have the answer:
Constantan conductivity = 49 E-8
Coper= 1,7 E-8
I am confused. Copper should have a higher conductivity.
edit: oops, missed the minus signs...my bad..
cheers,
jn

Last edited by jneutron; 20th November 2012 at 02:22 PM.
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Old 20th November 2012, 02:31 PM   #29602
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Quote:
Originally Posted by jneutron View Post
I do not understand how eddy current damping will be affected by the conductivity of the conductor. VC's by nature do not have large cross section wires, so eddy losses should be very low into the hundreds of Khz.
I wasn't thinking quite straight when I wrote this. In fact I intermingled two issues - plain damping, provided by the amp which is a function of the voice coil resistance and eddy current damping which is indeed a small effect. But so far this latter the only hypothesis I have for why the acoustics guys always said that lower resistance voice coils on bass units sounded 'tighter' (and they definitely preferred them) than high.
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Old 20th November 2012, 02:40 PM   #29603
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Originally Posted by abraxalito View Post
I wasn't thinking quite straight when I wrote this. In fact I intermingled two issues - plain damping, provided by the amp which is a function of the voice coil resistance and eddy current damping which is indeed a small effect. But so far this latter the only hypothesis I have for why the acoustics guys always said that lower resistance voice coils on bass units sounded 'tighter' (and they definitely preferred them) than high.
It sounds reasonable that low resistance vc's would be tighter. I believe the essence of "damping factor" is one of control of the conversion device by the amplifier. When I model an inductor using Ls/Rs, the Ls is the only part of the model which represents the conversion from current to magnetic field. (note that inductance is by definition the relationship between the current in the system and the total magnetic energy stored in the system as a result of that current. E = 1/2 L I^2.

I believe using Rs as part of the numerator in damping factor calculations is not accurate. It is a parasitic which dissipates energy, not part of the conversion process.

jn

Last edited by jneutron; 20th November 2012 at 02:52 PM.
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Old 20th November 2012, 02:55 PM   #29604
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Yes on reflection perhaps its the consequent lower inductance of lower resistance vcs which conveys their sonic advantage?

Damping factor (as traditionally defined, in relation to a nominal 8R) for an amplifier's output impedance I see as rather a misleading number in that much larger magnitudes convey smaller and smaller increases in damping. The difference between DF=50 and DF=500 isn't worth very much at all in practice.
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Old 20th November 2012, 03:41 PM   #29605
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Originally Posted by Wavebourn View Post
Why do you think so? I even downloaded the PDF and read it.
In your first response
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Originally Posted by Wavebourn View Post
you assumed current PFB only.
In your second response
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Originally Posted by Wavebourn View Post
you commend on a filter at the input which causes some boost below Fs. This is not what goes on in that patent.
If you have the desire to go past your initial assumptions I am sure you will notice the methodology.
Whatever you do is OK for me. Just please yourself. Remember, this is a hobby

That patent did not address the variations of coil electrical Z.
It is due to the nature of the proposed compensation (not a boost filter), that this omission causes - as an unintended consequence - the formation of a 18db/oct LP filter around 100Hz. (not bad in the case of a subwoofer ). For a good explanation of the above, read Bass amplifier with high frequency response

One invention that attempts to address a lot more issues (of the driver, driver coil, speaker box and cable) than Stahl, is here:
Impedance compensation circuit in a speaker driving system

By design, it is not restricted to a particular freq. range or for an enclosure type.
As a conception, I find it robust.
It turns to be complicated in the implementation.
Apart from this, results I guess will depend on the “fit” of the equivalent impedance model (item 4) and on the time constant of the integrator (item 52).

Of course, as every “load current sensing” method I have seen, it makes use of current PFB to a degree.

George
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Old 20th November 2012, 04:03 PM   #29606
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Originally Posted by 1audio View Post
You then must eq the system to get the desired response....The loop delay on any servo really limits what you can do.
Yes, unless complicated eq around vent and cone resonance, bad time for vented boxes. That what we experimented too.
Same for bandwidth. Reserved for subs. Then appears an other problem, homogeneity with the upper driver... short waterfalls in servoed sub, long in basses.
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We actually had an acceleration servo derived from back emf as well.
Did-you mean a coil on the LS back plate is able to sense changes in the magnetic field due to moving coil's movements? If so: brilliant idea !!!!
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It used a variation on a metal detector to sense the position of the diaphragm
If it is not a problem for you to be more talkative about-it, you have teased my curiosity.
For having experienced the work involved in servos for Loud Speakers, may-i congratulate-you for your courage and perseverance (and innovative ideas) ? As you said, it is pretty complex...
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Old 20th November 2012, 04:10 PM   #29607
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The passive filters of my enclosure (misses the compensation for the crossover itself):
Attached Images
File Type: gif aeria.gif (21.2 KB, 152 views)
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Old 20th November 2012, 04:13 PM   #29608
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Originally Posted by jneutron View Post
There is a built in transmission line effect because the gate polysilicon is sandwiched by SiO2 between the silicon below and the source metalization cover above. If you turn it on very fast into a really low inductance load, you can destroy the device near the gate wirebond (because a small portion of the device has turned on). If you turn it off very fast, you will destroy the device on the other side of the source bond (because it is the last part of the device to turn off).

jn
I read it as a tribune to Ivor Catt.

George
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Old 20th November 2012, 04:27 PM   #29609
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Originally Posted by kgrlee View Post
I must send my lawyers to see you
Was-i so disagreeable with you ?
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I tried optical methods and double coils too but the ACE stuff works so well that I abandoned the other stuf
Recorded.
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Last edited by Esperado; 20th November 2012 at 04:54 PM.
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Old 20th November 2012, 04:39 PM   #29610
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Originally Posted by PMA View Post
John, what would you think about the added capacitors (parallel to dividers), pl see image.
Hi Pavel,
How did you determine the values of those capacitors (which are non-standard values)?
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