Mics for stage

[Jon Fairhurst]

Paul,

It's not clear how much boundary you recommend behind the mics on the audience side. Also, what is PFL?

And yeah, even though we're just using one Stage Mic (essentially a PCC-type design), we also get additional feedback by raising the levels of the handheld mics and even source music. A mic can add more feedback of course, but the source music will add more energy to the reverberant room, it builds up nasty notes, hits the mics, and away we go. Hopefully, the kid(s) who will do the mixing are sharp enough to learn how to twiddle the knobs smartly. (Many kids do great with computers and phones, so I might just get one who rocks it.)

Rick,

The speakers are on stands, placed wide in the auditorium. We were a bit cable limited with our first test, but moving them around and angling them differently didn't have much effect. From the stage, I didn't hear much direct radiation at all. I mainly heard the energy buildup in the room. I think the key will be to place the speakers as close to the audience as possible so they will be able to hear the direct sound at a low level. No matter where we place them, they act like "exciters" in the reflective room.

We won't do a recording this year, but if we were, I'd absolutely set it up pre-fader. I wouldn't want the recording volume to change while the mixer chases the levels just before feedback. I don't know that the little Behringer has a pre-fader send, but they'll need to upgrade that before long anyway. My Mackie VLZ-1402 does pre-fader, and that's roughly their next step for more inputs.

[Greg Miller]

Originally Posted by Paul R Johnson

forget external feedback killers - to latch their filters onto a problem frequency you need to let the thing feedback. If you can do it in rehearsal, fine, but live, with no prep - they're hopeless.

With all due respect, IIRC that's not entirely accurate, at least with the Sabines we used. They have some filters that latched onto a fixed frequency. But they also have some filters that do not latch. As the talent was moving around with the mics, the mic-to-speaker distance changed, the ringing frequencies changed, and the Sabines kept up with everything just fine. With my experienced ears, I could hear a little ringing begin, then disappear. I doubt that many people in the audience even noticed that; it was certainly a lot less objectionable than uncontrolled feedback.

Originally Posted by Paul R Johnson

They also cut huge notches into the spectrum and they sound horrible.

I certainly wouldn't use them on a pipe organ or orchestra (not that either of these would require amplification anyway). I did not get the impression there were any "huge notches." The filters are much narrower than a 1/3 octave graphic. AFAIK, they were only notching out frequencies when they started to detect ringing.

Originally Posted by Paul R Johnson

I have a pile in a rack somewhere that have not been used for maybe six years!

Perhaps you could donate one to Mr. Fairhurst, and let him evaluate it in his venue! Or lend him one, and if it works for him, he can buy it with next year's budget.

Originally Posted by Paul R Johnson

When you push the fader, and start to hear the ringing - if it's one frequency, then a tweak with sweepable eq is as far as you can go

I agree with that. The room resonance is not going to change. If the mic is in a fixed location, the mic-to-speaker distance is not going to change. So you likely have a small number of fairly obvious peaks. Pull them down with a sweepable eq if you have one; if not, you can try to make do with a 1/3-octave EQ, but of course the results won't be as good.

And this is exactly what the Sabines do ... they have multiple automatic sweepable filters. Configure for a few fixed filters if you want, do the "gain raising" procedure to kill your fixed room resonances. They are much narrower and more accurate than a 1/3-octave graphic. Then the remaining non-fixed filters will chase any ringing that moves around in frequency.

Admittedly I think the OP is trying to make a silk purse out of a sow's ear, but while he may not end up with Gucci, with a little forethought and patience he may end up with something better than boot leather.

[Paul R Johnson]

How odd, I had no luck with Sabines or Behringers because the problem is they have two basic modes, one where you can push the system a bit and then they'll find the problem quickly and notch it but the auto mode needs feedback to happen, and they don't detect ringing properly. They do, however, detect some instruments as feedback. Sustained guitar or perhaps a high sax note that doesn't move. They're too random. I treat one mic that is allowed to feedback as a mistake, and these gadgets are crude and unpredictable.

Jon - the Bartletts and the pcc160s that were popular before work quite well on the edge of the stage, with space behind them. The only distance issue is how far between them and the talent.

The feedback issue when you raise other faders is normal. As I said, increasing the number of open mics just makes things unstable. The floor mics are simply an unobtrusive useful mic, that's a bit more efficient on the floor than others.

PFL is pre fade listen,you can hear each microphone or other source before you fade it up. Indispensable for live sound, as hearing a toilet sound before you fade up a radio mic can prevent much embarrassment. I think most of us have made this mistake at some point!

It's very common for small fills to be used to give small areas of the audience coverage so the main, more distant speakers don't have to be aimed into areas that would leak back on stage.

Now we are using digital desks, multitrack recordings are now so easy. Simply plug in a USB cable to your laptop and hit record. All that messing around with cables has gone, thank god!

I doubt that kids will be able to do this. In many cases, in school stuff, the technical team are selected because they are not performers. This doesn't mean they have any abilities in technical operation. Some will simply be terrified to touch a fader! In my experience of education, dancers are often very good technical people as they know how to listen. I would give kids perhaps sound effects to trigger, and maybe a fader or two to add music. As for listening for feedback about to happen and reacting? I would consider that far too dangerous. Too hard for adults to do too sometimes. If the lights don't go out, nobody notices, a mic feeding back, and not being able to stop it kills the show. Doing it without at least one skilled person is crazy.

[Greg Miller]

Mr. Johnson,

Indeed, it's very interesting that our experience differs. You mention the FBE latching onto sustained guitar notes, and maybe that's a clue. When I used them, I was using them only on vocal channels, and was not feeding any instruments (with their sustained notes) through them.

IIRC the depth of the automatic filters depends on the loudness of the ringing that's detected. So perhaps we weren't pushing our system very hard, the feedback was minimal, and the filter depth was minimal. I suppose if one cranks the gain up far enough, the filters will become very aggressive and then one might start to hear a lot of the problems that you describe.

Also, I note that Sabine now makes single-mic units, so that each mic gets its own processing. I never had the opportunity to try these, but it makes sense. So Mr. Fairhurst could use one of these on the floor mic, and one on the stand mic. That might work a bit better than one overall FBE on the mixer output.

And I certainly agree with your final comments about inexperienced operators. Playing video games does not necessarily prepare one for running PA. I remember running the PA system when I was in high school, and I certainly didn't have much of a clue about what I was doing back then. So good luck with kiddie techs!

[Jay Massengill]

As I also stated, I had good success with the Shure FeedBack Reduction units I used.

They could operate as stand-alone units, but I usually connected a laptop (via the serial port) to them so I could see on the large screen what they were doing with the notch frequencies and depths and make manual adjustments as well. Saving and pulling up scene memories was also helpful. All this was done during setup and rehearsal, but the filters were free to adjust themselves slightly if needed during the show.

I normally assigned the vocal mic inputs (especially the problematic lavs) to a submaster which fed into the FBR.

The output of the FBR came back to a mixer input. None of the other "regular" audio sources ran through the FBR.

For recording I would use a post-fader aux send (that wasn't notched) on one recording channel of the program audio and a good ambient mic and preamp on the other recording channel that was isolated from the feed to the PA so it could never cause feedback no matter how loud I needed it set.

So I could set up independent levels for the individual inputs, and had independent control for the two or three main destinations on separate masters (PA, Recording, Telephone Send). Everything followed the normal live mixing of the individual faders, once all inputs were routed and main levels were set.

[Jim Andrada]

Indispensable for live sound, as hearing a toilet sound before you fade up a radio mic can prevent much embarrassment. I think most of us have made this mistake at some point!

Or made the mistake of being the guy who used the toilet with an open mic. In Sydney. Got a huge hand when I walked out on stage. Mixed with all kinds of creative comments. Oh well, at least I had their attention.

[Paul R Johnson]

The real snag (for me) is that when running at show levels with hand helds, then having a distinct single feedback frequency burst out when you were not prepared can be grabbed by the feedback processors reasonably quickly, but the burst was needed to kick start the process. The kinds of ringing and hollowness with distant miking doesn't sound like feedback - just a wider band extra component to the sound sources and the processors don't detect it as 'feedback'.

On the Behring X32, in one of the recent updates, the EQ screen now has a waterfall style overlay that shows were in the spectrum energy is, and it does make searching for and notching out spikes quite easy - I thought it a bit of a gimmick, but it's surprisingly useful. However, it also shows ringing is so low in level, it can't be seen, just heard, and I guess this disparity between full level and the ringing level is what stops the auto devices doing a good job, because there's always something in there that is louder and stopping the ring being detected.

The other thing with the auto devices is that zapping one loud feedback frequency usually starts another off, and then worst case, yet another. This sounds really bad. A much better solution is simply a quick finger, to drop the fader a little.
Greg (and please feel free to call me Paul) The guitar thing often happens when the backline leaks into the vocal mic, and it's a pain. In most cases, the lead vocal also has a bit of compression, which tends to make it worse. I do come across a few people who try to use them on the LR outputs, and this is even in some of the instruction books, but this is a dreadful way to work.

I'm actually on both sides of the mic, and in our tribute band (Beach Boys), my vocals often consist of one long sustained 'aaah' or 'ooooh', and that is also very bad news for the auto devices. We don;t use them, but I'd expect anyone who uses autotuned vocals would also trigger the filter.

If anyone is local to Great Yarmouth in Norfolk (the UK Norfolk) over the summer and wants to borrow one - I'll happily pull one out of the rack.

[Jon Fairhurst]

I emailed Bruce Bartlett about my application and got a response over the weekend.

His top recommendation was treating the stage area with 703 or acoustic foam. The reflection from the stage is on-axis to the mic, so there is no in-mic rejection.

His second recommendation is to use a cardboard file folder in front of the mic to create a LF baffle. Add foam/insulation between the audience and file folder (but not touching the folder) to reduce mids and highs. This won't affect the polar pattern and might or might not increase gain before feedback. He recommended testing it as the "look" is cleaner if I don't need it.

He also noted that automatic feedback suppressors don't work well in his experience. He also recommends EQ.

The limitations make sense,
- Their notches are often too wide.
- They need stimulus before they kick in. (This is okay in rehearsal and for casual performances, but would not be acceptable in a pro setting.)
- False positives can cause them to suppress non-feedback tones.
- False negatives can cause them to miss lower level broadband feedback.

Yep. I get all of that. Then again, it still helps a bit. The main hall sounds so ugly that the uglification due to the feedback unit is secondary.

This past weekend, they had a Blueberry Pancake Breakfast there. An older guy with a hearing aid performed some gospel/country songs with a close vocal mic and gently strummed electric guitar using his own sound system. He ran some bizarre effects on his vocals that made him sound really thin. You could barely hear him sing. At some point he turned up the gain a bit and got some high-pitched feedback. I told him between songs, but the poor guy couldn't hear it. What was worse is that he walked off the stage to stand in front of the speakers. As soon as he got there, his body damped the sound and the feedback went away. Now he *really* can't hear it. Oh well, he turned it down a bit and the feedback went away. Yet another reason why the musician shouldn't be his own sound guy!

[Paul R Johnson]

Interesting advice from Bruce. A foam baffle to reduce the mids and HF coming back into the rear of the mic from the audience side. Worth a try, but in most cases, that's not the path the PA speakers are taking to the mic when they feedback, they're being picked up from the sides, aren't they?

[Jay Massengill]

Unless they are randomly facing the wrong direction, as I would often find the PCC-160's taped to the front edge of the stage in the local theater when I would visit during rehearsal week.

The sound mixer would usually say, "Ohhhh!, No wonder..." As in, "no wonder I wasn't getting anything worthwhile from that mic!"

[Jon Fairhurst]

Yeah, when I first hooked up the Bartlett, I "pointed" it longitudinally at the actor's space. Then I looked at the arrow on the mic's bottom...

Regarding the direction of the feedback, the speakers were on the left and right sides and were pushed reasonably forward of the mic. (I'll push them even further forward with longer extension cords in hand.) But I found that I didn't hear much from them while standing on the stage. The venue is so live that you hear the room, not the speakers. The experience is not one of hearing yourself from the speakers. The experience is hearing the tones in the room that were excited by your voice from the speakers. Without a PA, the experience is similar, though a bit quieter. (I can't sing, but I can make the room sing!)

[Greg Miller]

Jon, thanks for passing along the comments from Bruce Bartlett. I've never used a Bartlett mic, and I'm sure Mr. Bartlett knows what he's talking about so that should be useful information.

I can't quite visualize the file folder gag, but it sounds interesting. You said "in front of the mic" but do you mean "on the live side" or perhaps "on the dead [audience] side"?

Be that as it may, I am curious about his comment that the filters in feedback suppressors are too wide. I checked the specs for a few Sabine units and they claim 1/10 octave wide. Traditionally, bandwidth is specified at the -3dB point, and that would make the Sabines a lot narrower than a conventional 1/3-octave graphic. As I say, I'm not disagreeing ... just curious.

[Paul R Johnson]

I suspect it's when they are trying to recognise ringing. This is not an individual tone but a cluster of individual notes spanning a quite wide range. My old symmetrix had variable width filters that closed u in width as the attenuation increased. I don't think the more modern units have this mode any longer. I mention feedback killers to a visiting engineer and he said they are as much use as a plastic hammer!

[Jon Fairhurst]

I found the reference on Page 312 here under "Baffles Improve PCC Rear Rejection":
http://www.crownaudio.com/media/pdf/mics/memo22yr.pdf

(Lots of interesting reading at that link!)

This shows the mic on the folder. in the email, Bruce noted that having the file folder placed under the mic slightly degrades the mic's frequency response, so it might be preferable to turn it around. The key is having the vertical part between the mic and audience and allowing it to move freely.

[Rick Reineke]

FWIW,
Bruce used to work for Crown.