We have a LRL setup in our auditorium for the PA. On my stereo input channel for the IPad that we use for playback music, I get some strange panning and canceling behavior.
if I leave it in LR configuration the top end sounds great and is panned properly, but the subwoofer no longer receives any signal.
If I change the configuration to where the left sides polarity is switched, all of the bass comes back but the top end is panned very weirdly…. Almost as if it’s only coming out of one side of the PA. Any suggestions?
Obviously your subs are out of phase somewhere. That’s why, when you flip one side, the subs come up and the mains cancel out.
Could be flipped on an output socket, controller, amp rack, even a reverse wired cable going to one of the subs or a setting on one of the subs as well.
As mentioned somewhere in the signal path the phase / polarity has the as been flipped, check everything all the way through, the subs and mains. Don’t forget the cables both XLR and speaker.
The main speakers are fed from the main LR bus going into a stereo matrix. The sub is fed from the main LR going to a mono matrix.
what’s odd is I just tuned the system and everything seemed to be in phase. The left main speaker was out of phase with the other mains so I did end up flipping the polarity on that speaker only.
My impulse response measurements showed every speaker and sub as being in phase.
What about the input cable? Is it a mini-jack to XLR? Try to use a USB interface instead.
Is the problem still there if you replace the iPad inputs with your audio (measurement) interface?
Where is the signal to the third main speaker generated? Or did I misunderstand the config?
Just for future reference- the problem was happening at my DI box. When I ran the stereo channel as a standard LR config, all my metering would disappear at the sub matrix due to the phase cancellation. Flipping the polarity of the left side on the console would bring back the sub but cause weird panning behavior. In summary, if you know your PA is in phase and tuned properly, check the cabling and DI box!
FWIW, I’d recommend LCR/LCR+ (or LR+M) over LRL. You can probably get the highs balanced, but for everything else the room is hearing two speakers worth of left and only one of right.