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12th October 2006, 03:50 PM  #1 
diyAudio Member
Join Date: Jul 2006

How to calculate the BL of driver
Hi,
I am a rudimental guy of driver.I want to know the BL of driver by calculate,who can tell me How to calculate the BL of driver,thanks! BL=B*L(TM) But how to confirm the L,thanks!: 
12th October 2006, 08:03 PM  #2 
diyAudio Member
Join Date: Feb 2004
Location: Stockholm

L is the length of thread that is exposed to the magnetic flux density B. The unit is tesla*meter or newton/ampere (which is the same thing). Calculating Bl from B and L is typically only possible for the loudspeaker manufacturer, we other deadly people measure it as the force factor, ie we run a current through the coil an detects the force generated in one way or another.

12th October 2006, 08:10 PM  #3 
diyAudio Member
Join Date: May 2006

I don't know how to do it but WINISD does. Assuming all other driver parameters are correct, enter what you have into WINISD and it will fill in the blanks.

13th October 2006, 02:05 PM  #4 
diyAudio Member
Join Date: Feb 2002
Location: Italy

Hi,
knowing the T/S parameters BL=2,51*√(Fs*Re*Mms/Qes). 
13th October 2006, 03:42 PM  #5 
diyAudio Member
Join Date: Jul 2006

Thanks all,
I know that the BL may pass some softwares to obtain(eg finemotor or spead), but if know that the magnet of the driver and a specification of voice coil only, how to beg the BL, have the in general use formula? Thanks! I am a primers of dirver designs, so want to know whether there is such formula can beg the BL. Execuse me, my English is not good, hope your apprehensibility the meaning that I say, also hope to get the help of everyone, thanks! 
13th October 2006, 06:12 PM  #6 
diyAudio Member
Join Date: Jun 2002
Location: USA, MN

Diy dynamic driver
Bl is just the magnetic field in the gap times the length of wire in the gap. The fringing field may be approximated, but because of it there is no simple formula. At the link above you may find a driver design spreadsheet that I made.
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13th October 2006, 11:00 PM  #7 
diyAudio Member
Join Date: Jun 2003
Location: Chamblee, Ga.

Greets!
Cool! Thanks for sharing! GM
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14th October 2006, 03:57 PM  #8 
diyAudio Member
Join Date: Jul 2006

Dear Ron E ,
Thank you for your help,Your document of Excel is very good, very practical, thanks!ˇˇHowever I want to know that how "Rms" is obtain, the "BL" calculates through this formula of( Res=( BL)^2/( Rms+2 Rmrses) that arrive the "Res" and is how to beg? Hope your help, thanks! Eric 
15th October 2006, 12:33 AM  #9 
diyAudio Member
Join Date: Jun 2002
Location: USA, MN

Rms is a characteristic of the spider and surround and the voice coil former material. It is a lumped measure of the mechanical losses in the moving system. It is a material characteristic which must be measured, although there are general trends...
Conductive formers have a higher Rms, as generally do heavier surrounds. Each of these has an individual contribution, and when lumped together they constiitute Rms. As Rms increases, it causes a lower Qms and a lower impedance peak. I'm not sure what you are asking in the last bit with the formula? Are you working on an electrical impedance model/simulation?
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Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. Carl Sagan Armaments, universal debt, and planned obsolescencethose are the three pillars of Western prosperity. —Aldous Huxley 
15th October 2006, 04:45 AM  #10 
diyAudio Member
Join Date: Jul 2006

Dear Ron,
Thank you for your help, the material of the vibration system affects to the Rms very greatly, especially the voice coil former affects to the Rms biggest. The demand writes in the Rms concrete value in your document of Excel, I want to know that how you are makes sure what this be worth Thanks, Eric 
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