Feedback from acoustic guitar

J

Jared Koopman

Junior
Jun 13, 2012
303
0
16
Colorado
So I was running sound for a gig yesterday and had an odd (to me) issue with feedback from an acoustic guitar. The guitar was hooked up direct into a di box into the system. Sound check had no issues. two songs into her set she hits a note and it suddenly starts howling (in the 5-700 hz range). I turned down the gain a bit and it went away. She started the song over and 4 notes in hits the same note and it sets off howling again. I backed off the gain a bit more and it never had feedback like that again, but every time she hit that same note you could hear a funky resonance in the tone, but it didnt cause feedback.


So what the heck. Is it the pickup having problems? Di box? Purely a gain issue?
 
Re: Feedback from acoustic guitar

Did her guitar have the built-in f***itup digital EQ/processing thingie?

I had a guy with a Martin that had a "sophisticated" digital LCD read-out thing in place of the usual lo/mid/hi sliders. Absolutely the worst to deal with I've ever encountered.
 
Re: Feedback from acoustic guitar

Jared Koopman said:
So I was running sound for a gig yesterday and had an odd (to me) issue with feedback from an acoustic guitar. The guitar was hooked up direct into a di box into the system. Sound check had no issues. two songs into her set she hits a note and it suddenly starts howling (in the 5-700 hz range). I turned down the gain a bit and it went away. She started the song over and 4 notes in hits the same note and it sets off howling again. I backed off the gain a bit more and it never had feedback like that again, but every time she hit that same note you could hear a funky resonance in the tone, but it didnt cause feedback.


So what the heck. Is it the pickup having problems? Di box? Purely a gain issue?
Click to expand...

If it's ringing in the 500-700Hz range, wouldn't you just cut that a bit rather than reduce the gain? Or by "reduce the gain" do you mean you cut that frequency?

Some pickups are just really crappy, and by chance wherever they're located in the guitar they pick up certain resonances.

Another thing - if she had a passive pickup and you weren't using an active direct box, it's going to sound very weird or worse.
 
Re: Feedback from acoustic guitar

Did they have a "feedback buster" rubber disc in the sound hole. Or did she say something like "I don't like those because my guitar does not sound natural using one" Then you ask them if feedback sound natural to them.
If people want want their acoustic guitar at face melt levels in the monitor your going to have to dig a little with the EQ.

- The rubber disc plugging the sound hole helps some.
- Good pickup in the guitar is always a plus
- Generally not the frequency range you mentioned but use a high pass on acoustic guitars.
- As mentioned a good DI matched to the type of pickup will help smooth things out ( I got a Radial PZ-DI just for that!)
- Any gimmicky toys between you and the guitar can spell trouble.

I had a guy who took what would have been a great sounding Gibson acoustic electric guitar but he ran it through not one but three various Fishman pre amp/effect pedals and what was left coming to me sounded like high frequency driver with shattered diaphragm. In that case no feedback issues but just horrendous tone.
 
Re: Feedback from acoustic guitar

We recently had an issue on tour where the acoustic guitar starting feeding back around 200hz. I cut 200 in the monitors, muted it in the house, but nothing fixed it. It wasn't like it took off, but it would just sustain forever. Eventually we muted everything and realized that it was the guitar itself. Some bracing had come loose. It had to go in to get fixed, and then it was fine. If this had been a one off we may never have figured it out.
 
Re: Feedback from acoustic guitar

Had it happen a few times over the years. Channel strip EQ will usually fix it or at worst case you might have to notch the monitor or even the house EQ as well. It really depends on what is causing the peak. I have had the same guitar on the same system never have a problem but all of the sudden howl like crazy one night in a particular room when I was a touring BE. In that case the stage had a room mode in about the same frequency you are describing. It actually fed back through the mains as well as the monitors and this was after we had already notched the frequencies at set up. It just happened that the room mode excited a strong resonance in the acoustic guitar body.
 
Re: Feedback from acoustic guitar

Silas Pradetto said:
If it's ringing in the 500-700Hz range, wouldn't you just cut that a bit rather than reduce the gain? Or by "reduce the gain" do you mean you cut that frequency?

Some pickups are just really crappy, and by chance wherever they're located in the guitar they pick up certain resonances.

Another thing - if she had a passive pickup and you weren't using an active direct box, it's going to sound very weird or worse.
Click to expand...

In hindsight I should have done that. (next time!) I was just shocked and unsure of where it was coming from. It was a passive EWI DI.
 
Re: Feedback from acoustic guitar

A lot of them "acoustic amp" things for solo performers that have an instrument and separate mic input have a notch filter in them - acoustic guitars tend to have a body resonance that you need to "fix".
 
Re: Feedback from acoustic guitar

Ron Kimball said:
A lot of them "acoustic amp" things for solo performers that have an instrument and separate mic input have a notch filter in them - acoustic guitars tend to have a body resonance that you need to "fix".
Click to expand...

I just had a parade of "acoustic" guitar rigs last week, but I was on the FOH end of the snake. I know that several performers gave me amplifier outputs but I have no idea what was done to the signal I received. For the most part they were good, but a couple were boomy and a couple more rather "sizzly". I don't find string winding/fret noise peaking @ 6.3kHz to be an acoustic attribute... A fair number of artists that had pickups used our provided AT4041 for PA and the DI signal for monitors, others desired a blend, "if it sounds good, use it." Lots of microphone-only instrumentalists.

Presenting "front porch music" to 4,000 people in a grandstand is kind of ironic, but it can be done. From the same event, last year, live vid with camera microphone audio... Winfield Winners 2012 - YouTube

And when did the accordion become a bluegrass instrument, Dick?
 
Re: Feedback from acoustic guitar

I have never come up with a reason but it seems by far the "A" series seem to resonant on its own in dreadnaught style acoustics. While this example sounds a bit higher, I would look carefully at 110, 220, 440 hz series.
 
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