Using FEMM and how much flux density for mid driver - Page 3 - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th February 2013, 07:52 PM   #21
diyAudio Member
 
Join Date: Jan 2013
Quote:
Originally Posted by Baseballbat View Post
I guess your magnetics circuit is axisymmetric (like most drivers), so the correct setting would be exactly that: "Axisymmetric". "Planar" is more for planar drivers, like ribbons or magnetostatics.

I don't know if this gives a difference here.

@Dave Zan: a far more clever method to reduce modulation distortion is to saturate the magnetic circuit. For best results you need a magnetic material with a nearly rectangular B-H curve and with the "knee" that low that you can never drive the material out of saturation. It is not very easy, but is done today already.
Thanks I redraw the magnetic circuit in FEMM axisymmetric and now i got a more realistic B value. 0.9T for the long gap 1T for the smal gap. But this looks oke for a good motor.

regards
  Reply With Quote
Old 12th February 2013, 10:16 PM   #22
diyAudio Member
 
Join Date: Nov 2010
Quote:
Originally Posted by Baseballbat View Post
a far more clever method to reduce modulation distortion is to saturate the magnetic circuit...
This is an older method to reduce flux mod. but is a somewhat wasteful of (expensive) BH.
The JBL technique eliminates flux mod. completely, not just reduce, and wastes no BH at all.
An improvement in every aspect is what I call clever. Have I missed some point?

Quote:
Originally Posted by Jef Nuyts View Post
I looked at the dcd system. almost the same but I need under...
There is no reason that a DCD could not be implemented as short coil/extended field
It would be more expensive but looks like the best possible structure for performance.
I have wanted to try it for years but too many other projects in line. So I really hope you do this!

Best wishes
David
  Reply With Quote
Old 13th February 2013, 12:41 AM   #23
gedlee is offline gedlee  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Novi, Michigan
You should show the axi-symmetric plots since the planar ones that you have shown will be completely wrong.

Saturating the motor structure does reduce the flux modulation, but cannot eliminate it. that's why a flux ring will still work.
  Reply With Quote
Old 13th February 2013, 01:49 AM   #24
diyAudio Member
 
Join Date: Nov 2010
Quote:
Originally Posted by gedlee View Post
Saturating the motor structure does reduce the flux modulation, but cannot eliminate it. that's why a flux ring will still work.
The flux turn can still only reduce the modulation. The DCD still seems better.
Have you analysed the idea?
The Tech Note looks incorrect and I would love to have some expert confirm that or correct me.

Best wishes
David

Last edited by Dave Zan; 13th February 2013 at 01:53 AM.
  Reply With Quote
Old 13th February 2013, 01:57 AM   #25
diyAudio Member
 
Kindhornman's Avatar
 
Join Date: Aug 2012
Location: Los Angeles, California
Dave,
I wouldn't argue whether the JBL magnetic circuit is an improvement over a standard magnetic circuit but the math doesn't appear to add up. If you have the same magnetic mass in the circuit and now two instead of one gap the total energy in the gap should actually be lower, this is equivalent to increasing the gap width which would lower the flux density. Something is wrong with the written explanation and I will have to read a better paper on the subject to comment further.
  Reply With Quote
Old 13th February 2013, 02:30 AM   #26
gedlee is offline gedlee  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Novi, Michigan
As far as I am concerned DCD is purely a marketing gimmick. Structure saturation and flux demodulation work.
  Reply With Quote
Old 13th February 2013, 02:52 AM   #27
diyAudio Member
 
Kindhornman's Avatar
 
Join Date: Aug 2012
Location: Los Angeles, California
Gedlee,
I have been looking into electrical steel from Carpenter , Advanced specialty, titanium and powder metallurgy materials from Carpenter Technology, which has a better saturation than typical 1008 or 1010 steels. As far as the shorting ring there is much to be desired in many implementations of that to reduce eddy currents. I agree it doesn't make sense many of the claims for the JBL magnetic circuit. The same amount of wire distributed over two gaps instead of one would add nothing to the BL factor and two gaps of equivalent clearance of a single gap is going to reduce the flux density total. Isn't marketing great!
  Reply With Quote
Old 13th February 2013, 04:57 AM   #28
diyAudio Member
 
Join Date: Nov 2010
Quote:
Originally Posted by Kindhornman View Post
... the math doesn't appear to add up. If you have the same magnetic mass in the circuit and now two instead of one gap the total energy in the gap should actually be lower, this is equivalent to increasing the gap width which would lower the flux density. .
Quote:
Originally Posted by Kindhornman View Post
... As far as the shorting ring there is much to be desired in many implementations of that to reduce eddy currents...the same amount of wire distributed over two gaps instead of one would add nothing to the BL factor and two gaps of equivalent clearance of a single gap is going to reduce the flux density total.
The improved symmetry means that a shorted turn is totally unneeded. Even the writer doesn't mention that so I assume s/he is not the inventor.
JBL do not claim any improvement to the BL/Re factor, in fact they emphasise that it is identical.
JBL also emphasise that the coil widths is halved. So ideally two in series will have the same reluctance as one wider one.
What JBL brush over is that a narrower voice coil still needs some clearance and this does not halve. Need some data on typical wire ribbon width and clearance to evaluate impact of this.
The fact that the new drivers used in their own systems use DCD imply that is more than spin. My analysis bears this out to some extent, despite a few omissions.

Best wishes
David
  Reply With Quote
Old 13th February 2013, 05:09 AM   #29
diyAudio Member
 
Kindhornman's Avatar
 
Join Date: Aug 2012
Location: Los Angeles, California
Dave,
Even though the magnetic circuit may be balanced this does not remove eddy currents. That is a completely different issue. I don't think that they had an effective place to add a shorting ring except to plate the pole piece. I am very surprised that this was left out of the design.
  Reply With Quote
Old 13th February 2013, 05:39 AM   #30
diyAudio Member
 
Join Date: Nov 2010
Quote:
Originally Posted by Kindhornman View Post
Dave,
Even though the magnetic circuit may be balanced this does not remove eddy currents. That is a completely different issue. I don't think that they had an effective place to add a shorting ring except to plate the pole piece. I am very surprised that this was left out of the design.
Eddy currents are different issue, as you say, so I don't quite understand your point. Flux mod. manifests as 2nd harmonic and is usually solved with a shorted turn. Eddy currents in the pole piece manifest as 3rd. The DCD solves flux mod. but they make no claims about eddy currents in the pole piece and I never mentioned them.

Best wishes
David
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to use FEMM? Spasticteapot Planars & Exotics 23 11th February 2011 04:44 PM
Flux Density in Car SMPS Toroid Preamp Power Supplies 10 24th November 2010 01:32 AM
TS parameters when changing Flux Density f4bok Multi-Way 4 24th December 2008 11:33 AM
TS parameters when changing Flux Density f4bok Pass Labs 2 23rd December 2008 02:46 PM
Core saturation and flux density calculations machinehead Power Supplies 8 17th January 2006 07:45 PM


New To Site? Need Help?

All times are GMT. The time now is 08:19 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2