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[dph9254]

I have a Mackie 808M FR powered mixer. This unit has Mixer Line Out and Power Amp In jacks. Is this where I would hook up a feedback suppressor/eliminator unit (such as the Behringer Feedback Destroyer or the DBX AFS2 Suppression Processor)? Are such units beneficial?

[Wonks]

Yes (and no). The line out and power amp in will be internally patched together unless you plug leads into those sockets, and so you'd feed a feedback destroyer unit from the line-outs and feed it back into the power amp in, but you'd primarily use a feedback destroyer on monitors, rather than the FOH speakers, as monitors are the normal cause of feedback.

If you are using one output channel of the mixer for a mono FOH mix and the other for a mono monitor mix, then I'd just put a FB destroyer in the monitor loop and leave the FOH as it is. Get the FOH speakers in front of any mics and you'll rarely have a problem from them.

It is obviously best to position monitors and mics to avoid feedback in the first place, and that comes with experience (and sometimes just luck). But if one is really necessary, then it is normally recommended that they are not used in a constantly adapting mode, but each FB destroying 'slot' is allowed to operate once only and then not change. So once all your 12 'slots' are used up, that's it. However these should be the 12 worst frequencies for feedback and they should be notched out with a narrow-band cut that doesn't affect the sound too much. The constant auto-correct modes will typically work like that at first, but then each notch becomes deeper and wider and the sound can really suffer.

If you aren't having real feedback issues (the odd squeal is normally allowable), then you are best off without using one. If you've got someone mixing FOH, then it should be something they take care of with monitor levels, but if the band self-mixes, then sometimes it's better using one than nothing at all. What it will do is take a simple mistake - like someone pointing a mic at a monitor - and then notch at the main frequency of that feedback - and it may use several 'slots' to do that, giving a worse sound as a result and leaving less 'slots' free to deal with real feedback issues. So using one has pros and cons.

[dph9254]

Thanks Wonks. I should have outlined my particular application. It's a bluegrass band, and we've tried to go with one center condenser mic for vocals/instruments, 2 side instrument mics, and then a line for the bass. So we've tried the setup without the use of monitors at all - the idea being that we're closer together and can hear each other (that part has seemed to work well). But we can't push the system volume up very much at all without getting feedback.

[AlecSp]

we've tried to go with one center condenser mic for vocals/instruments, 2 side instrument mics, and then a line for the bass. So we've tried the setup without the use of monitors at all - the idea being that we're closer together and can hear each other (that part has seemed to work well). But we can't push the system volume up very much at all without getting feedback.

Things that will help you will be mic choice, mic positioning, speaker positioning, speaker patterns, EQ.
Ultimately, though, you won't be able to change the laws of physics which are causing you problems.
I suspect you'll be disappointed with what a feedback destroyer will achieve.

[resistorman]

Politics aside, the question was: is this the correct way to hook it up? Yes. Try it out.

[AlecSp]

Politics aside, the question was: is this the correct way to hook it up? Yes. Try it out.

The OP asked two questions - was it the correct way to hook it up, and were such units beneficial.

Given that he appeared to be considering the purchase of a feedback destroyer, then the caution not to, and the suggestions about zero cost ways of avoiding feedback were all spot on target.

While the single mic bluegrass thing is not my scene, you're likely to find that there's limited level you can achieve without feedback. Close micing is a thing in contemporary music for a reason! Given the right room, and an attentive/quiet audience, and an expectation of low levels, you can probably do OK. If you want rock levels, then you're likely to fail.

Interestingly, there's a long and heated thread about bluegrass reinforcement here, unfortunately dominated by a few of the usual GS "I know best, there is no other way" egos...

[dph9254]

Thanks for the comments resistorman and AlexSp. Internet information (not just on SOS) on single/condenser mics for bluegrass bands is all over the place, ranging from the best thing in the world to never even try it. I've seen 4 condensers used with a band in a 300-seat auditorium with high volume and no problems. And then one condenser with a band in a smaller environment with feedback problems from the start. Our goal with condensers is to try to (1) reduce clutter on stage and set-up time, and (2) improve our vocal harmonies by being closer together. We'll probably end up micing everything individually, but I may give the suppressor a shot.

[AlecSp]

I've seen 4 condensers used with a band in a 300-seat auditorium with high volume and no problems. And then one condenser with a band in a smaller environment with feedback problems from the start.

Again, I'm no bluegrass expert....

I suspect the more successful events you've seen will be in a venue with a well controlled acoustic, and a quality PA that keeps stage bleed low.

Take the same act into a reflective venue with a PA with poor control and you'll start to have trouble.

In the end, feedback quite simply comes down to how loudly a microphone is hearing the sound from the speaker(s). The room and the speakers have a lot to do to affect this. And, of course, the pickup pattern of the mic.

[James Perrett]

One other thing - weren't the original single mic bluegrass bands using a ribbon with a figure of 8 pickup pattern? That way you could arrange the main speakers to be in the null areas of the mic's pickup. This also relies on a venue with well controlled acoustics and a quiet audience.

A single mic will only ever give you gentle reinforcement of the sound though.

[AlecSp]

One other thing - weren't the original single mic bluegrass bands using a ribbon with a figure of 8 pickup pattern? That way you could arrange the main speakers to be in the null areas of the mic's pickup. This also relies on a venue with well controlled acoustics and a quiet audience.

All of that, but remember that the performers also have to make sure they're not in the nulls of the mic's pattern! They need to understand how to "play" the PA as another instrument.

[resistorman]

I have found the Mackie graphics to be really terrible sounding and drastic. If you have a FBS plug it in with the graphic at 0 or better yet bypassed completely if possible. Start with the best positioning of speakers and mic you can get, work with the channel eq and any switches like locut and pattern selection on the mic and tune it as much as you can, then kick in the FBS. Tune it and lock it in. As to mic pattern, don’t be afraid to try the figure 8... it has some deep nulls you can take advantage of.