Feedback problems with acoustic guitar

[david.elsbury]

Well, Be*ringer do one... so there must be someone else. Sorry, I don't really know that much about the beasts.

 

Oh, also for what it's worth, there's a program called Simple Feedback Trainer. http://sft.sourceforge.net/

SFT (Simple Feedback Trainer) is an application designed to simulate the process of 'ringing out' a sound system and train the user to recognise frequencies by ear.

[Simon Lewis]

Would be very interested in hearing more about these.... Anyone?

 

MM made these in the 70s.... but they were 4U and not that good. Peavey resurrected the idea - but their marketing department made it look like they invented it ;-)

 

It's useful to a point, and can be good for training your ear. Personally, I'd prefer to buy Smaart and set it to Spectrograph mode.

 

 

As long as the delay is only a few mS no-one will notice.

 

Any advice on how to delay the signal by changing the conductance? Or did you mean milliseconds instead of millisiemens? ;-)

 

Runs for cover....!

[simplay13]

On the subject of those light-up graphics, I have used the version by behringer quite abit. Its ok as a standard graphic but when you switch the FBQ on, it becomes pretty useless.The feedback has to be howling and very loud before it picks up on where its coming from. Also its not very specific and will most of the time light a section of frequencies rather than just one fader. just my experience of the product.

[WillW]

(And yeah, I'm one of those boring nerds who prefer to do my own EQ to stop feedback rather than trust an FBE!)

 

A properly set up feedback eliminator can provide e.q. when its needed and give you your clean sounding flat room response when you aren't over your feedback threshhold. I admit I used to think they were a bit nasty until I had been loaned a couple of decent ones to play with (I had only used the feature on the Ultracurve and couple of others). Its true with FBE's even more so than some other things that you get for what you pay for.

[paulears]

While there is a place for auto feedback eliminators - the process is flawed. Even with clever processing, they can't detect the subtle ringing and remove it without the damn thing needed to properly feedback in the first place. In a situation where the talent is static and the overall mix doesn't change, you can do it at rehearsal. In a live scenario they are just not predicable enough. And, they treat any single frequency that is static as feedback, even when it isn't. Some are of use as manual sweep and suck devices, but that's about their limit, in my experience.

[david.elsbury]

Yup. I don't use them myself... I'm okay with a graphic EQ, but I don't do sound a lot, so I have a long way to go.

Agreed with Paulears about that suble ringing that only one's ears can pick up on.

 

 

Is it possible to use a light-up graphic just to show the pretty lights, and then use a regular graphic to make the changes? Or disable the auto-FBE part but keep the lights going?

[dbuckley]

Well, I hope dbuckley doesn't count this as a flame

Not at all....

 

As a general opening observation, FBEs do seem to attract an inordinate amount of hatred from people who are otherwise well balanced. Its like Behringer kit. Sane people start frothing at the mouth on hearing the B word.

 

While all the techniques he mentions are good "last resorts" to cure feedback problems, I WOULD view them as just that...last resorts.

Absolutely. Using the most appropriate microphone, paying attention to positioning are all first resorts, and if you dont get this right (or at least make an attempt that is as good as your ability and circumstances allows) you deserve all you get.

 

Having said that, electronic manipulation will give you an additional often big improvement over the pure accustic approach so if level remains a problem then get the electronics in. I've been using these techniques for decades; my first feedback eliminator (which still exists, though its no longer boxed!) was the Wireless World analogue pitch shift design from the seventies. We now have magic digital boxes. These techniques do work, you can get a significant increase in level, and its often enough to make a big overall difference.

 

The one major item of electronics I WOULD try first (if you don't have one already) would be a 31 band graphic EQ to "ring out" your system.

Yep, solid advice, but one has to be careful. A 31 band EQ is a blunt tool in the wrong hands, and using it to suppress instrument resonant frequencies (which is almost certainly what we're talking about here) will probably result in some deep cuts, and the problem with GEQs is those deep cuts are also broad. As GEQs are almost invariably patched into the mix out, you're applying horrible EQ to the whole mix, and thus compromising the overall tonality (or maybe having to do the opposite EQ on channel strips) to get a louder accustic guitar. Not omptimum. That GEQ on the outs should be used to "correct" the tonality of the overall system to some standard, by ear, by RTA or by Smaart.

 

A very workable approach is to shove a GEQ into a group (or in this case channel) insert, so you can mercilessly rip the offending instrument's tonality to bits to get level, whilst not destroying the rest of the mix's tonality.

 

I should alsmo mention here as I've forgotten to mention it elsewhere that you dont put a FBE across a whole mix, you use it on a group or channel, ie, where its needed.

 

I think feedback eliminators switched to auto are the devils spawn. In my experiences, auto mode is totally useless, very unpredictable and when it does hone in and zap a real sproggie, it leave the sound thin and lacking andy definition.

Err - yep. When the music is playing they do get more than a tad confused, and will screw you up. But in manual or locked mode they are no more than a parametric eq with very useful characteristics, namely deep cut with narrow bandwidth. It is, at the end of the day, "just EQ". Use as appropriate

 

 

Auto feedback elim's are sh!te IMO.

You're welcome to your opinion, as I said, your mileage may vary. They're a tool, in the right hands they contribute, but they are no more, "buy, fit, forget" than any other audio tool with a DSP in it.

[Bobbsy]

Yep, solid advice, but one has to be careful. A 31 band EQ is a blunt tool in the wrong hands, and using it to suppress instrument resonant frequencies (which is almost certainly what we're talking about here) will probably result in some deep cuts, and the problem with GEQs is those deep cuts are also broad. As GEQs are almost invariably patched into the mix out, you're applying horrible EQ to the whole mix, and thus compromising the overall tonality (or maybe having to do the opposite EQ on channel strips) to get a louder accustic guitar. Not omptimum. That GEQ on the outs should be used to "correct" the tonality of the overall system to some standard, by ear, by RTA or by Smaart.

 

Moving slightly off topic, this is one of the reason I'm now addicted to good digital boards. Having a four band fully parametric EQ on every input and output has very much changed my ways of doing things. However, I don't think an OP who just asked for advice on a £100 mic wants to hear he needs to spend £5K on a DM1000!

 

Having said that, I still like to have a 31 band GEQ on the main output. Parametrics are great...but if something starts ringing during a live show I want to be able to pull down a single frequency fast!

 

I think my objection to FBEs is that in auto mode they are likely to go made and quench a guitar solo; used in preset mode they don't do anthing I can't do manually. I also agree that my ears are quicker to pick up the subtle "edge of ringing" sound than an automatic system.

 

I was going jump in at this stage and post the link to the feedback trainer but I see David got there before me.

 

Bob

[Rich]

Wow! This is the first topic I've started when the little file has gone red. I feel imprtant now!

 

Back on topic, the nights have been going really well recently, so the management have decided to start paying me. Now I'm getting money through for them I feel more inclined to bring a better setup (hense the Allen&Heath), so I've got a DBX 2231 which I'll patch in, and hopefully notch out some of the feedback.

 

Somebody mentioned rig size/positioning of speakers. It's a small rig, only two 15" boxes on stands. Theyr'e quite high up, and tilted down by 7.5 degrees. Due to the odd shape of the bar, and for maximum coverage, the right hand speaker is pointing 90 degrees from the stage, and the one on the left is at about 45 degrees. Both speakers are a good foot in front of the microphone line.

 

There seems to be some well justified dislike towards the C1000s, so I think I'll give the SE Electronics a go, besides you can nearly buy two of the SE's for the price of a single C1000s.

 

So as a summary, I'll try the mic techniques suggested, give a small daiphram condesner a go (I'll try the one I've got first), and see if I can notch out the offending frequencies without upsetting the mix. If anybody can offer any advice about speaker positioning aswell, I'd love to hear it.

 

I'm being called away urgently to Ireland this weekend, so I'm having to leave this week's in somebody else's hands, so it'll be just over a week until I can report back with the results to you.

 

Thanks for all your help.

 

Rich

[Hambone]

Not being 'pro,' I'm not adverse to using Behringer kit. If you rely on it, I'd carry a spare, though!

 

I've used a Feedback Destroyer for years. It works very well. It will identify the offending frequency and notch it out with parametric EQ with the smallest band/Q necessary, much faster and more accurately than a 'pro' and his 31-band or parametric EQ. The resulting effect on the overall EQ is minimal, unless the microphone is stuck right up against the PA!

 

All the EQ in the world during soundcheck won't always help, as the dynamics of evolving sound and the crowd change during the performance. But by turning the PA up during the soundcheck, the most offensive frequencies can be identified and controlled. The Feedback Destroyer is constantly hunting for feedback, so it's never a problem, although it can sometimes 'latch on' to a long sustained tone.

[paulears]

yes, but my arguement is that a competent op can hear the start of feedback as ringing, and drop the fader a bit before it starts. nomatter how fast a processor latches on and notches, it has to honk first, and this, in my book, is the cardinal sin, if I let it happen, I curse myself. I'd rather eq properly in tec, and then rely on fader control than suck out notches all over the place, which I think are definately audible. If they work for you, great = theyjust don't for me.

[Carey D]

I'm running an acoustic night in a bar at the moment, and I've got problems getting the level of acoustic guitars up without feedback.

 

Hi Rich.

As Bob says, try some EQ on the house PA to tune the system and notch out the most prominant resonant frequencies that may cause feedback. Avoid using too much EQ, particularly the 'smiley face' so popular with graphics. Cut frequency bands rather than boosting where possible, and then by no more than 4 to 6dB or so. A miked acoustic guitar can be challenging, especially in a small room such as a bar with reflective surfaces and speakers close to the performer.

 

Use the guitar channel EQ to help tune out the feedback from that mic. The GL2400 has two swept frequency mid bands. Start with all the EQ set flat. If you hear a resonant frequency or a ring about to start, it can help to actually boost a band of EQ a few dB sweeping the frequency to the point that makes the effect worse (have a quick finger on the master fader to avoid a ring taking off into a howl!). Once you have found the offending frequency you cut it a few dB below the centre 0dB position. This should give you some more gain before feedback. If the problem is with very low frequency feedback you could switch in the HPF and cut some LF EQ.

Hope that helps,

Carey

[Rich]

I was going jump in at this stage and post the link to the feedback trainer but I see David got there before me.

 

That program is fantastic. I'm a little concerned I can only hear 16K in one ear though!

[Panzerman]

Why not get a couple of cheap sprung acoustic pickups, can't remember who makes them, but they just slot straight into the sound hole, a 30 second job, no real installation as such. I used them a few years back and they were great when the guitarists couldn't decide which instrument they were going to use, or there were loads of changes. The lead isn't very pretty hanging across the front of the guitar (I wouldn't want it making the front of my Takemine look ugly, but then it has decent electronics anyway) , but it does the job admirably.

[Clive Alexander]

I have never used, but like the look of, those graphic EQ's with the LED's that light up when they think they are identifying feedback

 

Would be very interested in hearing more about these.... Anyone?

 

You need some BSS 31 band EQ's and a nice Drawmer compressor/limiter. Mic wise I use AKG D 109's for acoustics. 30 years old and still doing their job!!

Clive @ empiresound-light