^This. Any system w/ monitors and open mics will have a max. stage volume before feedback.
You can squeeze more useable-volume-before-feedback out of a rehearsal system in a few ways:
1. With the gear you have...
- Keep using the speakers as monitors. (Turning them away from the band in a rehearsal room will just make it harder to hear the vocals.) With all three of your mics, it looks like the best feedback rejection occurs at 180º from the capsule, so keep the monitors behind the mic. Angle the mics so the null point points down into the monitor speaker.
- Find out if one of the mics is more prone to feedback (my guess: the PG48). Give that to the singer with the loudest voice, so that you can run the channel w/ lower gain.
- You can't eq much with the PA you have, but as much as possible, try cutting the low a little (given high room volume, the low end may be adding rumble from the drums into the monitoring system, making it harder to hear vocals). Otherwise, flatten out the eq as much as possible. (Given your mics and PA, this might be different from setting each channel's treble knob at noon. You'll have to listen a bit hear to trim peaky treble.)
- Cut the reverb entirely. It's easier to hear pitch and articulation on dry vocals.
2. If you can add gear, I'd start in this order. . .
- Mics. I'd look for hypercardoid mics (all else equal, these will give you better feedback rejection, although they will also require your singers to stay more directly on-mic). Tight budget? Replace your weakest mic first, as this will be feeding back first. BTW, some folks prefer running one type of vocal mic for all the singers (that way, the frequency peaks for all mics are the same, so it's easier to clamp down on feedback at the system level). That might work for you, but in other cases intelligibility-before-feedback improves when you match the mic choices to the qualities of each singer's voice. (BTW, not all mics have the best rejection at 180º, so if you replace mics pay attention to the response chart when deciding where to place the mic relative to the monitors.)
- EQ. Glancing at the Stagpas 300, I don't see that it offers master insert points for outboard eq. If I'm just overlooking this feature, patch in a parametric to tame the frequencies most prone to feeding back. Ringing out the room this way will let you bring up the overall volume of the monitoring system. You can also use the parametric the set a hi-pass (low-cut) filter to better keep the low-frequency mud out of your vocal monitoring system. (Obviously, you could use a graphic eq in place of the parametric, although the parametric would be my first choice.)
- Headphone monitoring. You don't need wireless in-ears for rehearsal room monitoring. Closed-ear headphones run from a flexible headphone amp can save everybody's ears. However, a good mixer and decent (multi-source) headphone amp are really the ticket here. Otherwise, everyone in the band gets the same headphone mix. Unfortunately, it doesn't look like the Stagepas mixer will let you set up different aux mixes
- Flatter board/speakers. Now you're looking at spending some money. The better your preamps, though, the clearer (and often flatter) the sound. It makes a difference. Similarly, if your speakers are uneven and peaky, they can be less intelligible and/or more prone to invite feedback.
3. Or, as other have suggested, make the commitment to the overall band sound and lower the instrument volume. With some players, that's the obvious and assumed default. With other players, it's somewhere between unthinkable and merely heretical. I know what I prefer, but YMMV.
