I'm really unsure if you want a Haas effect. German sources, e.g. Wikis
seem to be more comprehensive than English Wikis, perhaps because the
German Rundfunk does educate audio engineering. I guess in other countries
nonserious schools as the SAE are more common.
The Bregenzer Festspiele does use the Haas effect in the completely other
way as you want too use it and that's what the Haas effect should be used
for. There's a German Wiki about it.
Let's say you are close to the left speaker and on stage there's an artist
on the right side, than Haas can be used to ensure that you've got the
impression the sound comes from the right side, where the artist is, even
if you here much more sound from the left side.
Theoretically you can use the Haas effect for your "panning", but I guess
what you are looking for is a good mixing, with sane panning and not an
effect that fixes bad mixing, especially because the Haas effect is for
such stereo (or multi channel) situations and not to archive what kind of
mono compatibility ever.
I might be mistaken.
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