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Problem with "resonance" using electro-acoustic
by courteous on 2011-09-30 13:36:23

Hello to LINE6 community!

First the parameters:

  • Ibanez AEL20 electro-acoustic (with the hole-cover on it)
  • Planet Waves 4.5m cable
  • 2.x firmware
  • "MIC IN" knob turned off (100% left)
  • guitar plugged in "GUITAR IN" input (#1 in the manual; not the "AUX" one)
  • guitar's pre-amp settings all in the lower 3rds (the "bass" is off; see picture)

Now, the problem is that there is some kind of "resonance" that could (by the sound of it; listen to 2 recordings below in red) easily destroy the amplifier. The problem is aggravated further on non-CLEAN presets (particularly the METAL or INSANE) where I had to be really careful plucking even one (1) string!

On CLEAN I dare to let it resonate ... but on METAL/INSANE I have to mute the string that is "resonating", otherwise I'm afraid it will tear the speaker (or fry some transistor). Listen to it for yourself in these 2 recordings (CLEAN at 40% master volume, METAL at 20%). [; didn't know any better ]

From my un-systematic diagnosis I can tell that there is particular "resonance" with the open D string (namely, its frequency) ... though I can't tell whether this is the "resonant" frequency for all settings. In bullets, the problems are with:

  • open D string
  • 5th fret A string
  • 10th fret E string

I didn't check the D frequency on upper strings (G, B, E) ... but the problem is more pronounced at the low frequency (at the bass strings).

BTW, can you help me understand

  1. the NOTCH FREQ. knob on the guitar's pre-amp (and its role in "cutting" the feedback)
  2. whether the hole-cover really helps with the un-wanted feedback ... or does it worsen it (by trapping and bouncing sound waves inside the guitar's cavity)?

Also, I'm not a complete novice at circuits (but no expert either, by any means), so you can give more details than usual (though I don't know what the "usual" is).

Thank you for the help.

EDIT: I've already tried different outlets/electric plugs, but it didn't help. I'll also try different guitar cables (and guitars) to eliminate other possible sources of trouble ... and also update to 2.09 FW. Hoping to hear from you, too!

RE: Problem with "resonance" using electro-acoustic
by Line6Don on 2011-10-05 15:57:40

Hey courteous,

This problem is pretty common when trying to plug a acoustic electric guitar into a standard amplifier. These type of guitars usually have some sort of internal mic/piezo pickup that captures the acoustic string sound. The problem with these pick ups is that it is very easy for them to feed back, hence the reason why they make things like the planet waves sound hole plug you got. Those only help to reduce the possible feedback but not cure it.

The first suggestion would be to not face the amp when you play, this will reduce the amount of amp bleed that enters the sound hole.

The second is to use the built in notch filter on the guitar to find the frequency that is causing the feedback and remove only that frequency. For more info on this refer to Ibanez's instructions on how to use it.

Make sure not to use alot of gain on the amp setting, or alot of treble either. Cutting bass and treble from the onboard preamp on the guitar will help to.

Lastly, try and keep as much distance between the amp and the guitar as possible.

Re: RE: Problem with "resonance" using electro-acoustic
by courteous on 2011-10-07 07:43:40

Don, these are useful suggestions ... except for the last one. I wouldn't dare let the amp be out of my-hands-reach (in case of this "resonance" problem), for it might "blow up". For instance, what would (likely) happen in the METAL at 20% recording (in the OP), if I didn't mute the string?

Regarding the pre-amp settings: I've already had "bass" completely off. Will play around with the NOTCH FREQ. setting though.

Also, I've noticed that the amp (the instrument cable in fact, I think?) acts as an antenna! If it is the cable, then does this necessarily mean that the cable (its shielding) its faulty? I will try/buy another cable as soon as possible either way.

Thank you for now.

EDIT: Oh, and there is the "hum" when the MASTER VOLUME is relatively high (at ~50%). I mean, it is there already before, but it's audible at about that MASTER VOL.

Also, why is there such a discrepancy between overall volume between, say CLEAN at METAL pre-sets? I know, that the DRIVE, BASS, etc. settings naturally have to be different (from, say, CLEAN preset), but the METAL is about "twice" as loud! The difference is so pronounced, that I have to (1) first lower the MASTER VOL. and (2) only then dare to change to another the pre-set ... although now I dare use only CLEAN pre-set, till this problem is solved (somehow).

RE: Problem with "resonance" using electro-acoustic
by Line6Don on 2011-10-10 11:12:43

Hey courteous,

I don't the problem being related to your instrument cable, although if you have a suspicion that it may be faulty, you might want to try and replace it.

Different amp models on the amp have different volumes by default, metal is louder because it has more gain treble, so it comes across a lot louder. You can edit and save your own presets if you'd like though. Instructions on how to do so may be found on page 2.2 of the Spider Jam Pilots Guide available at the link below:

The information above may not be current, and you should direct questions to the current forum or review the manual.