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Fixing pick-up resonance?


This is to do with my celic bouzouki, rather than guitar, but its a stringed acoustic thing with hollow body and all that, similar but different to guitar.

In any case, acoustically its fine, well behaved and all that. But once amplified (it has its own pick-up) - the open G string will start vibrating and never stop. (it doesn't have to be that loud, I guess it is like feedback, but its such a highly strung resonance that in normal situations off it goes).

Is there any simply "cure"? Thinking that a way to dampen the G string, even some little piece of material or something like that under the string at the saddle?

Any advice appreciated.


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Re: Fixing pick-up resonance?

6/9/2012 7:01 AM

Rick Payman (10061) wrote:

Hi Clayton,

Such resonance or 'feedback' problems are very common when amplifying acoustic instruments. The resonances are largely a characteristic of the instrument itself, and each individual open or fretted string has its’ own natural resonant frequencies (fundamental and harmonics).

Feedback is a complex combination of all components involved in the amplification chain and feedback ‘loop’; the instrument, strings, tuning, pickup, pickup placement, preamp, effects/equalisation (if used), amplifier, speakers, positioning of the instrument with respect to the speakers, walls etc., and characteristics of the room.

Changing any one of these components will affect susceptibility to feedback at a given volume, together with the frequency and nature of the problem signal, as the different resonances contend to find a dominant feedback mode.

Starting with the instrument, I would personally only consider permanent string damping as a last resort, but guitarists do employ palm-muting techniques to facilitate playing at very loud volumes.

One common solution is to use frequency equalisation, which could be anything from a simple mixer/amplifier tone control, to a graphic equaliser, or even dedicated pre-amp which includes anti-feedback control, commonly in the form of a tuneable notch-filter. Experimentation is the key, but the adjustment need not necessarily be complicated; a simple reduction of lower (bass) frequencies may be sufficient to do the trick.

Perhaps the simplest (but not always practical) solution is to experiment with instrument/speaker placement, such as avoid having the instrument directly in front of a loudspeaker; even your body placement comes into play here!

Hopefully given some ideas to try – Good Luck!

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Re: Fixing pick-up resonance?

6/11/2012 10:22 AM

Ken Richardson (9051) wrote:

Based on what you describe, I would consider using a graphic EQ and seeing if you can reduce the feedback using that.

Another idea is is to move either the instrument or the speakers a little, to get them further apart.

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Re: Fixing pick-up resonance?

6/12/2012 9:05 AM

Clayton Werner (62) wrote:

Thanks gents,

Any comments on the idea that loose cables exiting the UST / saddle, anchors having come loose, might be responsible for this kind of problem?

Regards, Clayton

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Re: Fixing pick-up resonance?

6/13/2012 8:39 AM

Ken Richardson (9051) wrote:

I don't know if a loose wire like that would cause feedback.

Probably worth looking at securing that wire again so it does not rattle.

Perhaps if you anchor them again, the act of adding the anchor/hook into the inside of the instrument cound dampen some resonance... perhaps could dampen that bit of resonance/feedback for the G note.

What was the wire anchored to?

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Re: Fixing pick-up resonance?

6/15/2012 2:30 AM

Clayton Werner (62) wrote:

Evidently some pick-up systems can cause this kind of resonance / feedback if cables are not secured, but in describing mine to my guitar tech, this isn't among them.

Thus my "G" - 98Hz super resonance is likely caused by a resonance in the sound-board (the other possibility, that it is due to the air cavity is explored and discounted by the use of a suitable feedback buster).

I will try a little graphic EQ to explore the possibilities (I don't think it'll be good, but I've been wrong before)...

Should I try to change the resonance? how would I lower it, which would be the ideal situation, to below the tuning of any of the strings.

Will also play with my capo to check if capo at 1 or 2 does similarly fix the problem...(which is not a long term solution so much as an exploration)

Regards, clayton