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View Full Version : Reversed Polarity on JBL Speakers,When Did It Start and Why?



Oldmics
07-14-2003, 11:21 PM
Howdy All,Now I think I know this site pretty well (I guess I"ll find out)and have seen a few remarks reguarding the red terminal causing an inward motion of the reciprocating mass when positive voltage is applied.My question is when did this start and what was the reason for doing it.I turn it over to you Oh wise forum members.Best regards,Oldmics

Guido
07-15-2003, 04:21 AM
See

http://www.jblpro.com/pub/technote/tn_v1n12b.pdf

hope this helps

boputnam
07-15-2003, 07:44 AM
... as self-accursed Watcher of Polarity ;), here's a Link from the Technical Posts where much of the results of JBL's design decision are compiled and reside: http://www.audioheritage.org/vbulletin/showthread.php?s=&threadid=9
Apologies, Oldmics, if you're already gone through it all.

However, none of this I fear will answer your question of "why?"

Might I propose, if I may, that you are looking at this all wrong, and that JBL had it right, but others went a different direction, and were merely more successful marketers, ultimately leaving JBL as the sole proponent of this "negative" polarity? Credits for this perspective go, of course, to the inimitable Giskard... :D

Oldmics
07-15-2003, 09:05 AM
Thanks to Guido and boputnam for the replys.I was aware of the JBL Professional outline on the topic.What I was trying to discover is did Mr. Lansing start with this design philosophy from the onset of his speaker building days?I know that a few of the people lurking here have some very early field coil equipment.I was wondering if this early Lansing gear was polarity reversed.When did the reversed polarity method begin?And why?I was thinking that perhaps since the technology was in its infancy that it took a technician with special knowledge(as in a JBL employee) to correctly setup a Lansing system.Kind of a guarantee that his systems would have to be maintained by his own employees for the highest quality of sound.Perhaps a direct fly against the wind mentality as opposed to the other major players of the time.Needless to say the ingenuous outlook presented by Giskard is no doubt one of the correct directions to view.I will have to remove my head from the sand and take a peek around.Any other viewpoints?? Thanks to all who respond,Oldmics

Don McRitchie
07-15-2003, 11:55 AM
I don't know how this relates to JBL's conventions, since to be honest, I haven't been following this issue that closely. However, the following is my understanding of the historical development of loudspeakers polarity standards.

The inital standard was set by Western Electric, which is understandable since they invented the loudspeaker. The original standard stated that a positive current would result in a displacement away from the magnetic field. This was simple and straightforward for single speakers. However, with the advent of multiway speakers, and the development of the compression driver, it led to a problem. Dynamic speakers, such as woofers, have their magnet assembly behind the diaphragm. Therefore, a positive current would result in a compression wave. However, starting with W.E.'s 594, compression drivers were designed with the magnet in front of the diaphragm. This means that a positive signal results in a rarefaction. In other words, a woofer and compressrion driver in a standard two-way configuration would be out of phase. However, a dynamic woofer with a dynamic tweeter would be in phase for the same standard.

Initially this was just accepted. Even though it resulted in confusion, the standard had been set. Given Altec's roots with WE, it is not surprising that they used the WE standard. This would also have been the convention that Jim Lansing used while head of engineering for Altec. It was not until the 1970's that an industry wide change to a new set of standards occured. Current industry standards state that a positive current will result in a compression wave and a negative current a rarefaction, no matter what magnet topology is used. My understanding is that is is now universally used in the loudspeaker industry.

Again, where JBL fits in here with their historic polarity conventions is beyond my knowledge of the subject.