Vintage JBLs, negative polarity, and distributed bass

[aschup]

I'm currently running a pair of JBL L112s, and I'm going to add a few subwoofers to give distributed bass a try. My understanding is that the JBLs were designed with negative polarity such that a positive input voltage to the woofer causes it to move in rather than out, which is the norm today.

Which makes me wonder, will I have to switch the inputs from my amp to my JBLs to avoid opposing woofer motions between the JBLs and the subs, to avoid cancelling out of low end frequencies?

If yes, will this have any negative effects on sound from the other drivers?

Thanks!

 

[JoeESP9]

There is no way of telling ahead of the actual installation exactly what sub woofer phase (polarity) will best integrate with your main speakers. This is why most powered subs have a phase (polarity) reverse switch. Some even have a potentiometer that allows variable adjustment of phase.

The reason phase is the more appropriate word is because a switch is either in phase (polarity) or 180 degrees the opposite. With a variable control you can adjust for the best phase. The best phase may be something other than the same as the mains or 180 degrees different.

You can use test tones and a microphone to adjust this or your ears. Usually the phase (polarity) that sounds best is the best.

 

[Chris Brown]

Yes, on all 3 pairs of my JBLs the cone moves inward when the positive end of an AA battery is connected to the positive terminal of the speaker.

You shouldn't change any wiring to your JBLs. Most powered subs have a 180 degree phase toggle switch just for situations like this.

 

[aschup]

Thank you both for the replies. That helps a lot. The subs I'm getting have a variable phase feature.

 

[toxcrusadr]

If you had a sub that did not have the switch, it would be easy to test the sub with the battery test too.