Sound System problems in a live room

Subject: Sound System problems in a live room
From: GUEST,annamora
Date: 19 Jun 02 - 10:06 AM

We just had a nightmare gig where we couldn't turn our system up loud enough to compensate for the crowded bar noise. Yeah, we were background music but we didn't want to be so much in the background that people didn't even know we were there. Problem was, everytime we tried to crank up the volume, we'd get low frequency feedback. We even have Behringer Feedback Destroyers, one for the monitors and one for the mains. Each was set on Setting 3, to automatically find and destroy frequencies leading to feedback. We have good equipment that should have been plenty powerful enough. Our volume was so low that some of the crowd was standing directly (almost leaning against) in front of our mains. The problem did not seem to be affected by the crowd size or proximity of people to our speakers. Does anyone know if we were doing something terribly wrong or forgetting something? We set up the monitor sound first and had no feedback problems and plenty of volume. This leads us to think we were getting a bunch of reflective sound from the mains. The room is very live, wooden ceilings and floors with funny walls here and there for noise to bounce off of. We tried raising and lowering the speakers to compensate for possible ceiling backwash, to no avail. It wasn't that we just weren't loud enough, we couldn't crank the volume even up to the board's unity setting. There are so many factors involved and so many places to turn up volume that I am now confusing myself. Does turning the speaker volume knobs up affect sound differently than turning the board's main faders up? How about individual channel trim vs. overall sound with the main fader? As I am typing, I realize that I just have more and more questions. Bottom line is, I don't want to have to go through such a horrible night again. If you can offer advise, it will be most welcome. If you want more sound system details, I will gladly include them.

Subject: RE: Sound System problems in a live room
From: GUEST,annamora
Date: 19 Jun 02 - 10:07 AM

Sorry about the one paragraph thing. I copied and pasted from Word. Guess that doesn't get all the paragraph breaks. At least the info is the same. Again, much appreciation for any feedback on our feedback problems. Cheers. annamora

Subject: RE: Sound System problems in a live room
From: NicoleC
Date: 19 Jun 02 - 11:19 AM

Annamora,

Without being in the room and with the equipment, it's say anything specific. I'm not familiar with a Behringer Feedback Destroyer, but I've very, very skeptical about it's effectiveness in a complex environment. I would guess that it's a gate of some sort, eliminating frequencies that peak too high...

Highly reflective rooms are tough, but if you are experiencing low frequency feedback, the issue may be more than you have hollow walls. 300 Hz is a likely culprit.

Does your equipment, or the house equipment, include a good graphic EQ for the house mains? Frequencies that are feeding back through the entire system should be kicked down there first. If individual mics or instruments are feeding back, their EQ's should be adjusted on their console channel.

In terms of increasing volume, you need to think about gain first. If you have the gain (aka trim) on the instruments and mics turned way up, but the volume (i.e. the fader or the speaker volume knob) low, you will be more likely to feedback than if you have the gain low and the volume maxxed out. Depending on where you are "turning up," you could be doing more harm than good. The gain should be set as low that still gets the signal you need, and _volume_ adjustments made through the console.

It sounds like you are pretty unfamiliar with how to use the equipment and the basics of sound reinforcement. I would definately consider a little light reading of the subject -- it won't make you an expert overnight, but at least you won't be frustrated and confused about what to do when you want to be thinking about your performance.

If all else fails, hire a sound engineer. Despite all the sound guy bashing that goes on in here, they have been known to have their uses :)

Good luck, Nicole

Subject: RE: Sound System problems in a live room
From: M.Ted
Date: 19 Jun 02 - 03:38 PM

You have obviously invested a lot in a sound system, you should invest in a sound technician who can give the same attention to that that you give to playing--another thought is that you should always do a rehearsal in the space with soundcheck before the performance--that way you've worked everything out ahead of time--

Subject: RE: Sound System problems in a live room
From: JedMarum
Date: 19 Jun 02 - 03:53 PM

You can first try to eliminate the monitors ... easiest thing to do to reduce noise/feedback. You can look at each channel to see if one of them is more offensice then others; cut or greatly reduce each channel, one at a time with the others at their normal settings. You might find that one mic or instrument input was way too hot and was causing the entire problem. You were possibly alos picking up the crowd noise in your mics and amplifying it.

In noisey rooms microphones are the enemy! Reduce their use. Make every player use a pick-up (or stop playing noisey rooms). Elimnate the use of condenser (powered) mics.

The work with the freqs. If you don't have overall EQ - work with each channel to see where it rings (low end ring you spoke of earlier coud be a guitar pik-up) find the most offensive ringing instruments/mic channels and cut the offending freqs; low, mid, hi etc ...

When I play a room that tends to be noisey, and the crowd noise increases when the music starts; I turn the system DOWN. It means the talkers want to talk and you've increased the moise level so they need to talk louder. If they want to hear you, they'll quiet down. Play for a set and se if it doesn't work. When you take a break and start up again - they'll be glad, and not expect to have to shout over you.

A sound tech is good - but you need a damn good one. Many can make you sound worse!

Subject: RE: Sound System problems in a live room
From: treewind
Date: 19 Jun 02 - 04:32 PM

If you are getting low frequency feedback, make sure you have turned down the low frequencies on any instruments or voices that don't need it. I know it sounds obvious, but I once made a deep ringing boom vanish totally by applying full bass cut on three fiddle channels that *really* didn't need any bass at all. The fiddle sound was still perfectly OK, of course.

Having said that, the Feedback destroyer should have done the same thing, but maybe it was getting confused by the ambient noise in the room.

For the person who asked what the Behringer Feedback Destroyer is, it's like a multi band graphic equaliser that adjusts itself to cut the frequencies where it thinks there is feedback. Used carelessly, it can equalize hurdy gurdy and bagpipe drones into oblivion!

As for condenser mics, why ever should they make feedback worse? Since they usually have a flatter frequency response than dynamics, they should be better. More important is mic directional response - sometimes hypercardioids can help. Re-positioning mics can also help.

Anahata

Subject: RE: Sound System problems in a live room
From: GUEST,Slickerbill
Date: 19 Jun 02 - 06:01 PM

Great thread. I'm learning this kind of thing myself so it's interesting reading.

Our local fest was running a stage recently where, outdoors, mind you, the feedback problems were huge. I think what it finally came down to was tons of instruments on stage, with monitors all way up, and a low tent roof that was (I think :?) bouncing sound down and all over the place. The worst was the flute; we had to cut her monitors right off. I think it was the condenser she was using was just picking up everything.

One question, if I may. Is it possible there was a phase problem in annamora's case? Or is that ruled out by the feedback problem? sb

Subject: RE: Sound System problems in a live room
From: GUEST,greg stephens
Date: 19 Jun 02 - 06:24 PM

Sounds to me that on that particular occasion you probably had a specific technical fgitch, rather than some room generated feedback problem. In general, though, I've found that it's often the guitar in the frequency range of the A and D string that can be a real nuisance. A bit of EQ adjustment, and the guitars position in relationship to monitors and vocal mikes, often works wonders. Agree about sound technicians in general, but the practicalities of the economics of folk music and noisy pub gigs tends to rule it out most of the time! Alas.

Subject: RE: Sound System problems in a live room
From: GUEST,annamora
Date: 19 Jun 02 - 06:31 PM

Thanks everyone for the answers.

There is good advice here. Unfortunately, either we had tried it (cut out the monitors, adjust mics, adjust certain frequencies) or it was impossible to do (practise in the space before hand). I fully agree about the soundman. They are necessary but only helpful if they are good and understand the sound the band is going after.

We do a lot of vocals so we must use mics. All other instruments have pick-ups. I know that I sound quite inexperienced and that I don't know my equipment very well but I have worked quite successfully with it all before. It was a combination of crowd noise, room config and panic on our part. We turned down the monitors comletely for much of the time until we couldn't live with not hearing ourselves. The room was so noisy the ambient crowd noise was registering on the board. Turning the monitors back on didn't seem to do more harm and helped us hear.

What is more acceptable during a gig, living with an OK but softer sound or spending a bunch of time trying to locate offending frequencies?

I guess a few things we should have thought of was to turn down the low frequencies where we could. And turn off what we weren't needing at the time. Trouble is we switch instruments a bunch.

We will have to find a very live room to practise in and try to work out some of the bugs. It sounds like from all this advice that we covered much of it. Like I said, though, we were starting to panic and when panic sets in, I start questioning everything I thought I understood or knew. Another lesson is perhaps that we don't want to play somewhere that is so crowded and noisy. On the other hand, if we get it all figured out, St. Patrick's Day should be snap.

Thanks all. Cheers. annamora

Subject: RE: Sound System problems in a live room
From: GUEST,annamora
Date: 19 Jun 02 - 06:36 PM

Greg, funny that you should mention the guitar and the A and D. The D really seemed to be a problem but intermittently. There were certain songs that I would cringe everytime the D chord came around. Especially if the bass was playing too. Other times, we heard the same noise but no D chords. Maybe it was the A. Interesting concept and something we will test when we find that ultra-live room to practise in.

annamora

Subject: RE: Sound System problems in a live room
From: NicoleC
Date: 19 Jun 02 - 10:24 PM

Annamora --

If you were picking up ambient room sound in the mics onstage, then:

a) your gain is WAAAY to hot b) your singers are way too quiet (doesn't sound like the most likely scenario) c) you are using mics with inappropriate pickup patterns. For a live gig, hypercardiod mics are usually the way to go.

I absolutely love condenser mics, but I they wouldn't be my first choice for an all-round take-anywhere kinda mic. They sound better, but they're fussier. If you already have a nice mic setup, add a couple of cheapie hammers- er, dynamic mics, to your bag of tricks. When you end up in a lousy room with a noisy crowd, no one is going to hear how lovely your mic sounds anyway, so opt for the less fussy one.

To answer your question about being quiet vs. spending gobs of time on the sound system -- IMHO, I'd go with quiet. Maybe some folks can't hear you, but nobody is going to stop and listen if you aren't playing. Besides, it throws off your concentration, you get frustrated, and suddenly it's not fun anymore.

For the audiophiles: Something that occured to be today: what would happen if you had room with a standing wave problem, and that frequency started to feedback?

FLUTE in the monitors? Those suckers cut through anything -- if the flute player couldn't hear herself it was *mighty* loud onstage.

Subject: RE: Sound System problems in a live room
From: Peter Berryman
Date: 20 Jun 02 - 12:02 AM

It's great to hear people talk about feedback, because I think it is a problem more of the time than is realized, sometimes lurking just below the howl-stage, distorting everything subtly.

We are a duo, with accordion, 12-string, and 2 vocals. We have used both the Behringer Feedback Destroyer and the newer Behringer Shark ($65) and are gradually learning how to use them properly (I hope). Documentation is horrible with these things.

One thing to be avoided is sending too much of a signal to these units, because they work first by digitizing, and digital distortion is a nightmare.

The second catastrophe (so far) is setting them so that they are too sensitive, which allows them to take out whole instruments and turn the overall sound weird and quiet. (At which point I panic and turn up the gains so that everything distorts, and all hope is lost.)

The best way for us with the Feedback Destroyer was to ring out the room with it before the sound check, with all mics and instruments plugged in and ready to go. We used the factory preset which has 9 channels lock in on offensive frequencies and stay there for the night, while 3 are left to roam. Problem: the memory is "volatile," so if unplugged accidentally, all settings are lost (not true of the "Shark"). And you can't ring out the room mid-gig. This also doesn't work if there is no opportunity for a sound check.

By screwing up and talking with sound people and reading, and screwing up some more, we have come up with the following for setting gains properly (I do believe), assuming a mixer is available with level indicators of some sort. And setting gains properly helps everything, including the anti-feedback devices.

To set individual channel levels, you needn't even have an amp or speakers. Set the master fader (volume control) all the way UP. Test mics or instruments one at a time. Plug in, say, a mic. Turn that channel fader all the way UP. Sing as loud as you can into it, while turning up the GAIN control unitl it VERY rarely, almost never, "peaks."

Unplug that mic and turn that channel's fader all the way down (but leave the gain control as is).

Do the same for each channel. When finished, turn all individual channel faders all the way up again, but then back them off about 10dB to leave room for controlling relative volumes.

Ideally, from what I understand, the overall volume is best controlled with the amp's gain control, leaving the main mixer fader all the way up, and the individual channel faders as high as possible while still leaving room for adjustments relative to each other. We have found our best quality sound in this way. NEVER turn up the individual channel gains beyond where they are set as described above, or distortion will result.

This is what I've gleaned, and it seems to be working so far. I'd love to hear of others' experiences with the Behringer Shark.

Subject: RE: Sound System problems in a live room
From: pavane
Date: 20 Jun 02 - 02:55 AM

As you know, feedback is usually high frequency and usually via the mike.

BUT low frequency feedback MAY be caused by physical feedback of vibrations throught the stage floor to the instrument pickups.

Is the feedback destroyer just hooked up to the mikes? If so, it won't catch this at all.

Also, condenser mikes tend to be more sensitive than moving-coil mikes at long distance, and therefore more susceptible to feedback. You really need a mike which will pick up only what is very close to it.

What sort of pickups are on the instruments? Some kinds are just internal microphones and will be sensitive to external noise, probably more so at low frequencies.

Subject: RE: Sound System problems in a live room
From: Chris/Darwin
Date: 20 Jun 02 - 06:51 AM

I played in an Australian Bush band for many years, in halls that ranged from nicely lined barns to tin sheds. We used a range of acoustic instruments from fiddles to mandolins, banjo, guitar, whistles, etc. I remember the first time I played in one of the tin sheds, and the noise was unbelievable. When you played, say, a guitar chord, you didn't hear it out of the monitor, but off the back wall half a second later! I remember trying to stay in beat by watching everyone else's hands. Trying to turn up the foldback lead to feedback.

Eventually we got ourselves good 31 band graphics on both front of house and foldback, and went through a set procedure.

1. Set FOH and FB master faders about two thirds up. Set all graphics flat. All other faders off.

2. Starting with vocal mics one at a time, set fader about 60% up and adjust trim so that FOH is about right. Set tone controls to suit vocalist. Adjust FB send so that vocalist is happy. Turn fader off.

3. Set instruments one at a time using similar procedure. If you know particular instrument has a particular feedback problem (e.g., boom), then make some compensation with tone controls.

4. Wind back master faders 20dB, and all individual faders back up to preset value.

5. With each vocal mic place a hand flat about 2 inches away, to duplicate sound bouncing off your face into the mic. Leave all acoustic instruments on.

6. Slowly wind up FOH master until something starts to take off, and then wind back a notch.

7. One channel at a time, bring up the FOH graphic until feedback occurs, and then wind back a set amount ( e.g., 12dB).

8. Repeat procedure for foldback.

9. By this time you should have notched out the booms and most of the other room resonances. However, you can still get high frequency reflections off flat instruments, so get every acoustic musician to hold their instrument about the right distance from their mic, and run through the same procedure for the 2k - 10k range.

The advantage of this procedure is that you have tuned the PA to the room, and the overall sound will be pretty smooth, because the overall gain is fairly flat over the whole frequency band.

Once the whole band is used to doing it, it takes about 5 minutes, and everyone ends up happy.

You also have a fair bit of head room if you need to crank up a bit.

I have only limited experience with active filters, but I formed the opinion years ago that they are not as good as properly tuning the graphics, because you start off with an unequal frequency response, and the filters act randomly. The sound is not so good.

I have played in loud clubs with concrete walls and ceilings, and was not happy with the result. In these cases the 12dB range on my graphics was not enough to notch out the resonances. In one extreme case I remember putting two graphics in series and notching up to 20dB - but that was unusual.

My band has played in large carnivals, etc., with professional sound guys, who seem almost universally to be deaf ex rock musicians. I have experienced boom problems with them, because they did not understand acoustic instruments.

I hope this is of some help.

Regards
Chris

Subject: RE: Sound System problems in a live room
From: JedMarum
Date: 20 Jun 02 - 08:52 AM

Condenser mics are NOT good performance mics, for many live sound situations. They increase feedback and stage noise considerably - because they pick up sound so well and at such a distance. They should be used sparingly, and with great care - if they are used at al on stage.

Subject: RE: Sound System problems in a live room
From: GUEST,annamora
Date: 20 Jun 02 - 07:07 PM

Thanks for so much more info. I will have to take some time to digest it all. I see right now that we can be smarter about initial sound check. Although, when a bar's house pa is blaring CD's I would think it would be hard to "tune to the room." To answer a few questions... The feedback destroyers were hooked one the the mains, the other to the monitors so all mics/pickups were going through them. I don't know what kind of pickups are being used. Various types I'm sure. We discussed much of your ideas last night so now we have a few more tricks in our arsenal. Thinking back, it is possible that we never reduced the trim from the initial set up and we should have in order to turn up the main faders. It is possible too that the Feedback Destroyers were cutting out too much because we did get some "weird and quiet" results. As for the house noise, it was *mighty* loud up there. I got to the point where I was pointing at the setlist to indicate what song to do next or we would pass the word individually from one to another. We got tired of shouting. Ah, what how we suffer for our art.

Cheers, annamora

Subject: RE: Sound System problems in a live room
From: M.Ted
Date: 21 Jun 02 - 12:24 PM

You probably won't know for sure what caused your problem(unless you are "lucky" enough to have the exact same thing happen again)--most of the time, the problem comes from something overlooked, a mike you didn't realize was on, or a level somewhere that you neglected to set--One of the early lessons that I was taught bears repeating here, though, and that is to keep the gain low and control the volume with your voices and instruments--

Subject: RE: Sound System problems in a live room
From: Chris/Darwin
Date: 22 Jun 02 - 04:26 AM

With faders positions, the thing to remember is that every amplifying stage brings a certain amount of fixed noise - say -80dB. If you run an output signal level of -20dB out of that amplifying stage, you get a signal to noise ratio of 60dB (the difference between the output signal level and the noise floor). 60dB is good.

However, if you run a stage at a signal level of only -40dB, then you get a signal to noise ratio of only 40dB, which produces noticeable noise.

The trick then is to ensure that each stage is running at reasonable gain.

In a desk you have a preamplifier which brings up the level into the various channel tone and send circuits. The output of this goes through the main channel fader onto the main busses. From each main bus another amplifier brings the level up to the line output, through the main faders.

If you run any fader flat out, it follows that other stages will need less amplification. For example, if you run the main and channel faders near the top, the preamp stage on each channel will be set very low. This will have the effect of the later amplifying stages amplifying the noise produced by the preamp.

Of course, every desk is different, and some of the more modern desks have stage signal to noise ratios better then 100dB. With such desks the old rules about amplifying stage gain are less important. Consequently, trial and error with your own equipment is the best guide. However, it pays to know what is happening when you get particular effects. Also I have not seen a desk yet that doesn't produce noise if you turn everything up.

In a perfect desk it would not matter where the gain came from - that is, from the outside you would not be able to tell whether most of the gain came from the preamp or the main amp.

Regards
Chris