I often record speeches (sometimes music also) at wedding receptions by placing a mic in front of sound system speakers. Normally wireless.
any recommendations on fine-tuning the placement of the mic and the best types of mic to use. I have used a variety of lavs, an ME66, a shure sm58, EV RE50, and EV635. Results are acceptable even with the cheap lavs that come with the senn G2 wireless units - but they certainly could be better.
Those are fine mics for this... but you won't ever get much better results when using this technique.
Acoustical ambient pick-up of a sound system is a very poor choice if you want better sounding audio.
I understand why you do it... (we've all HAD to do it many times)
but since you're asking how to IMPROVE it...
its not really a different MIC that will "fix" it.
the way to make it sound as good as possible, is by a direct connection to the audio mixer/amp that's feeding the speakers.
There are many ways to do this, and a few words here can't cover them all.
But that's the direction you need to go if you want to get rid of that hollow room "PA speaker" sound in your audio track.