Yet Another Polarity Question....

[Chas]

I am in the process of a first listen to my newly revised DIY 4333's that for all intents and purposes have morphed into an S-22 system, 2231A(reconed with 2235), 2441/2311/2308 and 2405H.

According to the JBL notes, all drivers are what they term as "negative polarity", no problem, so far.......
Here's the question: the 4333 xover (actually Giskard's brilliant adaptation of an equivalent) originally had all drivers connected with identical polarity with the exception of the 2405, which was reversed. Now, I am thinking...the 2311 (HL93) horn is a heck of a lot shorter than the 2312 (HL92). Maybe that's no longer the case....?

Luckily all drivers connect to terminals on the rear, the xover is external, so I've been experimenting with different polarities and there doesn't seem to be a clear winner. Does anyone know what JBL recomended?

It would help to, at least, have a point of reference to start from.




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[Tom Loizeaux]

I used to think that all drivers should play in the same polarity. To check for this I would use a signal gererator set at the crossover frequency and switch or rotate polarity until I had maximum output (both drivers putting out around equal SPLs at that frequency.
However, I later learned that sometimes you don't want uniform phase! JBL figured this out pretty well in their larger studio monitors.
I suppose running a signal sweep and adjusting polarity at each crossover point, going for the smoothest transitions and most "even" sound could show you the best polarity set-up for your speakers.
There is, undoubtedly, a mathamatical formula which would include your special horn length and crossover design, etc., but I don't know how to figure that. Maybe some one else on this forum can.

Tom

[Chas]

Tom, thanks for your thoughts, when I have some time maybe I'll give your suggestion a whirl.

After posting last night, I pulled out my collection of JBL xover schematics and found the 3107, that I believe, was used in the 4350. It shows the 2440/1 in reverse polarity to the 12" woofer/lower midrange and the 2405 UHF. For now, I have convinced myself that this is the way to go. The system sounds pretty good, although I have some positioning and level adjustments to make.