I think the better question is "at what frequency can the human ear perceive directional sound", because that's the lynchpin of the issue. Mono subs tend to work because the human ear cannot perceive any direction at all (never mind stereo/mono) in low frequency output.

Below 80 Hz, it is impossible for the human ear to discern direction, because it is impossible to discern timing. See [[url=http://[/URL]="http://en.wikipedia…"]Sound localization - Wikipedia, the free encyclopedia[/]="http://en.wikipedia…"]Sound localization - Wikipedia, the free encyclopedia[/]

Above 80 Hz, sound localization perception is largely a function of room dimensions - the larger the room, the more easily a waveform can be discerned by localization, due to size of waveform versus size of room.

Now, how does this fit into your specific situation?

If you're working in a live performance situation, you should be running everything mono anyway, unless you are using multipole speakers. Why? With monopoles, even with horns, you are robbing half your audience of half the source information when operating in stereo.

So the whole question become moot - stereo perception in live sound is limited severely by the speaker systems being employed. There's really no reason to do it, unless you're in a massive auditorium, and can employ full radius speaker systems on both left and right program material, so everyone still gets to hear everything.

Scott Griffin, post: 346709 wrote: If you're working in a live performance situation, you should be running everything mono anyway, unless you are using multipole speakers. Why? With monopoles, even with horns, you are robbing half your audience of half the source information when operating in stereo.

That's the conventional wisdom and I don't buy it. I think it comes from a disproportionate fear of interference between the two speakers, and the attempt to avoid it by not overlapping the coverage of the left and right stacks. But at higher frequencies we have enough directional perception to hear them as the separate sources that they are, and at lower frequencies speakers become omnidirectional anyway. Besides, the coverage patterns will overlap at some distance out no matter what, and trying to avoid overlap could mean throwing more sound at the walls and leaving a coverage gap front and center. In bigger venues you could use front fills, but in many smaller places they're neither practical or needed.

Assuming a small gig with a room longer than wide I angle the speakers in and mix in stereo as the situation allows. Of course it's necessary to walk the room, which is true in any case. In a wider room I'd add a second pair for two arrays, but the "outfills" would be fed a mono downmix, so as you move to the sides you don't lose anything.

jbuckles, post: 346703 wrote: To ask the question a different way, what would be the highest frequency you could send to a mono sub-woofer before the listener begins to lose the perception of stereo separation in the sound?

The more critical question is: What's the highest frequency you can put through the subs that wouldn't sound better coming through the mains?

A: Typically around 80-120Hz.

bouldersound, post: 346779 wrote: Assuming a small gig with a room longer than wide I angle the speakers in and mix in stereo as the situation allows. Of course it's necessary to walk the room, which is true in any case. In a wider room I'd add a second pair for two arrays, but the "outfills" would be fed a mono downmix, so as you move to the sides you don't lose anything.

Yes, but then you get into a situation where the amount of gear you're toting exceeds the value of the gig. Pay for a small gig like that isn't going to be phenomenal, and toting an extra pair of speaks plus extra amps, doing the extra setup, and then the extra work involved in panning everything out - is it all worthwhile? I've never, ever, ever heard a member of the audience complain about a lack of stereo separation in the mains - but I have heard people complain that they "can't hear the other guitarist" because one is fed to the left and the other to the right.

Horses for courses, of course. ;)

This caution rings sadly true (that no one will appreciate, or possibly even hear / notice, and that it's a huge fuss to haul the gear and cable up the mess). A real pity for an e-Act.

Scott Griffin, post: 346786 wrote: Yes, but then you get into a situation where the amount of gear you're toting exceeds the value of the gig. Pay for a small gig like that isn't going to be phenomenal, and toting an extra pair of speaks plus extra amps, doing the extra setup, and then the extra work involved in panning everything out - is it all worthwhile?

It's not much different in terms of setup, and my amps are already configured for stereo so reconfiguring would actually be more work. Usually at small gigs I leave the subs and their amp behind and run a smaller monitor setup with one less amp.

Scott Griffin, post: 346786 wrote: I've never, ever, ever heard a member of the audience complain about a lack of stereo separation in the mains - but I have heard people complain that they "can't hear the other guitarist" because one is fed to the left and the other to the right.

Horses for courses, of course. ;)

Angling the speakers in a little makes the far one audible to listeners off to the side. Being thoughtful about your panning is required, as is walking the room. I agree mono is fine for live sound, but I've heard lots of compliments on my stereo mixes even when the audience is spread out wide. And I've seen the looks on peoples' faces when the toms roll across. You certainly don't want to take a system without some overlap between left and right and hard pan things, but I'm talking about the widest pan setting being around 10 and 2 (as on a clock), and things like guitar just nudged off of center. It helped the instruments stand out from each other and let the vocals come through a little better.

And if a guitar amp or something on stage is blasting one part of an audience and missing the rest I can pan to compensate. Some sources (e.g. certain keyboard patches) are missing important information if you use only one output, and have phase problems if you use both outputs mixed to mono. If there are equipment issues having two signal paths to the stage can help troubleshoot the issue or provide a workaround. You can always leave pans at center with a stereo system, but you can never pan something in a mono system should there be a need.

FWIW...

I saw Rodrigo Y Gabriella perform live a few months ago. They made very clever use of a FOH stereo mix: Gabriella's guitar has (at least) 2 different mics, and each one was panned differently. Depending on where she strummed and/or struck her guitar, the sound would be biased left or right. The effect was that it sounded like there were more than 2 instrumentalists on the stage.