Using FEMM and how much flux density for mid driver - Page 2 - 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 11th February 2013, 08:45 PM   #11
diyAudio Member
 
speaker dave's Avatar
 
Join Date: Nov 2009
Location: The Mountain, Framingham
Increase 50% (to a length of 150%).

Your short coil long gap design will give great linearity but unfortunatly wastes a lot of "B".

Note that Bl alone isn't usually enough information for a full comparison. If you add turns to the coil Bl goes up but DCR does too. In the end, the best comparison between drivers is via: B squared * l squared / Re. That is the measure of motor strength.

Efficiency is then related to the product of B squared * volume of copper (impedance normalized out). This generally leads to a conclusion that efficiency grows with more copper in the coil until the coil mass and diaphragm mass are roughly equal.

Regards,
David S.
  Reply With Quote
Old 11th February 2013, 08:46 PM   #12
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

You can't drive a dome like that, from near the centre.

rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
  Reply With Quote
Old 11th February 2013, 08:52 PM   #13
diyAudio Member
 
Join Date: Jan 2013
Quote:
Originally Posted by sreten View Post
Hi,

You can't drive a dome like that, from near the centre.

rgds, sreten.

Why you can't? I don't see the difference? It is a cone with the motor on the other side. Are do I miss something?
It is a 7" driver out of carbon fibre, that will maybe change something ;-)

Last edited by Jef Nuyts; 11th February 2013 at 09:08 PM.
  Reply With Quote
Old 11th February 2013, 09:03 PM   #14
diyAudio Member
 
Join Date: Jan 2013
Quote:
Originally Posted by speaker dave View Post
Increase 50% (to a length of 150%).

Your short coil long gap design will give great linearity but unfortunatly wastes a lot of "B".

Note that Bl alone isn't usually enough information for a full comparison. If you add turns to the coil Bl goes up but DCR does too. In the end, the best comparison between drivers is via: B squared * l squared / Re. That is the measure of motor strength.

Efficiency is then related to the product of B squared * volume of copper (impedance normalized out). This generally leads to a conclusion that efficiency grows with more copper in the coil until the coil mass and diaphragm mass are roughly equal.

Regards,
David S.

Offcourse I mean the total lengt 150% :-) dutch englisch, englisch dutch brrr confusing..
Oké but L has more weight in the formula than Re.
DCR on this moment for (6mm height) => 6ohm so i can raise a bit to 7.2 for +/- a 8ohm speaker. But that isn't enough damn. I have ordered alu wire to lower the mass. So maybe 9-10Tm is enough for a decent Q (I have to calculate that) So much variables to deal with...

Everyday is a good day to learn

Last edited by Jef Nuyts; 11th February 2013 at 09:17 PM.
  Reply With Quote
Old 12th February 2013, 06:48 AM   #15
diyAudio Member
 
Join Date: Jan 2013
I was thinking this night for a solution to lower the resistance of the coil.
If you put 2 wires together for winding the voicecoil (winding with 2 wires at the same time) so you will have the two wires in parallel. DCR wil drop by half. I think the efficienty will raise. Not? I mean with the same resistance as therefore the lenght wil double so Bl wil raise..
B will drop a bit because the gap has to be higher. Thx,

Last edited by Jef Nuyts; 12th February 2013 at 06:52 AM.
  Reply With Quote
Old 12th February 2013, 07:40 AM   #16
diyAudio Member
 
Join Date: Nov 2010
Default New idea!

To improve efficiency don't waste the flux in the front gap.
You could have an extended voice-coil there and a short coil in the back!
I think over AND under voice coils would be unique.
You could still put ferro-fluid there to help centre the cone or dome.

Serious now, have you looked at the JBL Dual Coil Drive (DCD)?
A clever way to totally eliminate flux modulation and they have other benefits too.
The JBL tech. note writer does not seem to understand clearly how they work but the note is still worth a read.

Best wishes
David

Last edited by Dave Zan; 12th February 2013 at 08:05 AM.
  Reply With Quote
Old 12th February 2013, 10:06 AM   #17
diyAudio Member
 
Join Date: Jan 2013
Oke good thought Dave! Over and under coil would be a good solution.
The extra force would compensate the extra mass easely, especially with alu windings.

I looked at the dcd system. almost the same but I need underhung for the electromagnetic suspension (2 layer system).
The reason why the extended voicecoil is in the middle is for the higher flux density because of the two magnets are polarized in opposite direction. The gap is bigger but the density is the same as the small gap.
I'm gonna calculate and see if the parameters are good with these modification.
Keep u posted
  Reply With Quote
Old 12th February 2013, 11:56 AM   #18
diyAudio Member
 
speaker dave's Avatar
 
Join Date: Nov 2009
Location: The Mountain, Framingham
Quote:
Originally Posted by Jef Nuyts View Post
I was thinking this night for a solution to lower the resistance of the coil.
If you put 2 wires together for winding the voicecoil (winding with 2 wires at the same time) so you will have the two wires in parallel. DCR wil drop by half. I think the efficienty will raise. Not? I mean with the same resistance as therefore the lenght wil double so Bl wil raise..
B will drop a bit because the gap has to be higher. Thx,
Read what I said about B square l squared over Re. (also B squared over V gap or V copper) If you go from 100 turns of a gauge to 2 x 50 turns of the same gauge you can parallel connect or series connect. If you parallel connect you have half the length and 1/4 the resistance. Same (Bl)2/Re. If you series connect you have the same coil again. If you shrink the gauge to allow two windings of the same number of turns your packing factor will reduce and efficiency will drop.

More copper in the gap gives higher efficiency (not voltage sensitivity, but true efficiency). Impedance, or how you slice the copper, is irrelevant.

Regards,
David S.
  Reply With Quote
Old 12th February 2013, 03:29 PM   #19
diyAudio Member
 
Join Date: Apr 2007
Quote:
Originally Posted by Jef Nuyts View Post
i use planar in FEMM but i don't know if this is correct)
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.
  Reply With Quote
Old 12th February 2013, 05:23 PM   #20
diyAudio Member
 
Join Date: Jan 2013
Quote:
Originally Posted by speaker dave View Post
Read what I said about B square l squared over Re. (also B squared over V gap or V copper) If you go from 100 turns of a gauge to 2 x 50 turns of the same gauge you can parallel connect or series connect. If you parallel connect you have half the length and 1/4 the resistance. Same (Bl)2/Re. If you series connect you have the same coil again. If you shrink the gauge to allow two windings of the same number of turns your packing factor will reduce and efficiency will drop.

More copper in the gap gives higher efficiency (not voltage sensitivity, but true efficiency). Impedance, or how you slice the copper, is irrelevant.

Regards,
David S.
Yes i understand what you mean. The thrue efficiency is not affected. But most amplifiers are 4ohm stable so higher current gives more lorenz force and the length of the wire is the same (in the gap). Like you said voltage sensitivity wil raise and that is also oke for me. In other words the amplifier wil give more power on the same output level (so I use the amplifier to compensate). Not a problem for normal amplifiers but for tubes is another story... But the solution of Dave is better :-)

Last edited by Jef Nuyts; 12th February 2013 at 05:25 PM.
  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 06:34 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