Film-Tech Forum ARCHIVE: Surround Speakers Polarity

This is topic Surround Speakers Polarity in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by German Marin (Member # 918) on 08-30-2003, 11:00 AM:

Few months ago I was checking the polarity of all the speakers in several auditoriums. I use a "phase checker" and "toc toc" test CD but I've noticed when I reach the surround speakers (JBL 8330) the bass is in correct phase but the medium and tweeter has the polarity inverted. Why is the conection setting in this way? Is there a reason?

Posted by Darryl Spicer (Member # 711) on 08-30-2003, 11:17 AM:

I think there may be an actual switch on top of the speaker that changes this. You may have to take a look and see.

Posted by German Marin (Member # 918) on 08-30-2003, 11:22 AM:

The switch is present in old model but there's not in the new one.

I don't think it's wrong wired...

Posted by Paul Mayer (Member # 355) on 08-30-2003, 01:41 PM:

Some speakers are designed with one driver connected for reverse polarity in order to get a smoother overall frequency response, especially near the crossover frequency.

Take a look at the very last section of this JBL Tech Note to see an example of this.

Posted by German Marin (Member # 918) on 08-30-2003, 04:57 PM:

Thanks Paul!

They has a unknow reasons to build speakers on that way whatever I didn't understand but now I know they has a reason.

Posted by Jean-Michel Grin (Member # 1360) on 08-30-2003, 05:19 PM:

Hi,

By the past I've used an polarity tester and a "toc-toc" CD to check the polarity, but this method din't gave me an accurate result.
It was better to climb up a stair and check the connection of each speakers.
At this occasion, I noticied that 2/3 of the surround speakers was wired with the wrong polarity [Mad]

I had to correct this problem quickly, but never a customer notified a surround problem in this auditorium [Big Grin]

Bye,

Posted by Richard Fowler (Member # 893) on 08-30-2003, 05:26 PM:

The switch on the JBL 8330 is for roll off ( if required ) for analog surround or full range when this speaker is used for foreground music applications. To check phasing more properly would be to use pink noise and an analyzer on the speaker. When doing a phasing test with "pop" type sound signal on a surround, the bass speaker should be favored and the pick up mike as close as possible to the speaker as not to pick up reflections in the room that may cause false readings. The CD set up is not as accurate as dedicated "popper" and receiver test tools. Stage speakers are usually easier to isolate the High ( Mid ) Low due to the more spread out location of the components.