Hollow Body Guitar Feedback

[PTChristopher]

The lowest tone impact with very good feedback damping is to plug or cover the f-holes with as light (weight) a material as possible.

Very light weigh packing tape works.

A really nice and removable/replaceable solution is two layers of EVA foam. "Craft Foam" as some US places like Michaels call it.

One layer is the thick (~6mm) stuff and is cut to the size and shape of the interior of the F-hole. The second, and top, layer is 1.5mm EVA foam cut to about 1/8 larger than the F-hole.

Easy to make, easy to stuff in the hole, not too dopey looking - especially in black, easy to remove, funciona de cojones (it works).

The two layers allow for considerable error in the shape of the 6mm layer since the 1.5mm layer also covers the holes. really crazy-easy to do.

In my opinion.

Chris

[PTChristopher]

Oh yeah, like the Hofner Jazzica covers in ebony - much nicer than all EVA. But then you have to shape the ebony for a good fit, so maybe tricky as a DIY project?

I suppose that the heavier ebony has some arguable tone impact, but I think this is really very minor at most.

Chris

[PTChristopher]

G-tube,

This has already been mentioned, but to focus the question:

Are you sure that you are hearing acoustic feedback primarily caused by the guitar body?

It is very possible that the primary location of the feedback is the PU. Some pickups can be remarkably microphonic, and some asian mini-HB floaters have only a token amount of wax inside. This lack of practical potting makes them sometimes very microphonic.

So while the guitar body is part of the feedback loop for certain, movement of the components within the PU can have a very large impact on capturing the body vibrations directly (microphonically) and promoting feedback.

Unfortunately, the best test/solution is an epoxy-potted PU. The Benedetto S6 comes to mind (and has a quirk all it own, but unrelated to feedback), as well as some Kent Armstrong and Bartolini PU's.

Anyway, good luck with the situation. With so many guys offering help here, please let us know what happens.

Chris

[PTChristopher]

I was thinking more about the microphonics of the OP's PU, and not so much the overall frequency response, as a feedback issue.

Do you have any data on the inductance or resonant peak of the BJB? I sort of think of the BJB as a fairly even response PU, a fatter Johnny Smith PU, but not so much a deep or darker PU.

But this is just very subjective based on playing them in a 165 and what I remember (really quite a while ago) as an L5, but it could have been a Johnny Smith with a BJB.

If you can get and data on the BJB, then compare the resonant peak to an S6, which is 5.38 KHz (just looked it up).

Now the shape and typical position of a small floater has a significant effect, so a direct comparison with a normal-size HB resonant peak is not exactly apples to apples.

But to sort of frame the dark-o-sity of resonant peak data:

- A PAF is often around 6 or more KHz.

- A really fat full-size Jazz HB can be 4.5 KHz or even lower.

In my opinion the DC resistance, as often quoted as the only "data", means almost nothing unless comparing two PU's that are exact in all other aspects (including the gauge of wire used in the coils).

Chris

[PTChristopher]

Yep.

I suppose data can sometimes be counter-productive to more prosaic performance description.

To maybe clarify a little:

Resonant peak is also not the whole story. You can have a "PAF" with a peak of 8.5KHz that can sound darker than one at 6KHz depending on the magnets, the gauge of wire used, and probably other things I can't think of.

But in any case I would think of the S6 as a fairly dark floater. Positioned well, and on a fairly lively guitar, it can have a very natural (and "acoustic" sound), but I still consider it an overall full-sounding PU. My opinion.

[Jazz_175]

Yeah, that was me with the black balloon trick.
And, yes it does work @ stage volume. You will be able to cut thru the mix
like you were playing a 335!
Just make sure the balloons are inflated enough to cover F-holes completely.

I just don't understand what you mean by a balloon and how you fit it in the f-holes.

[muziani]

Hello everyone. I just purchased an eastman ar 145 with a floating pick up. It wont be here for a couple weeks so I was wondering if anyone had some information on them as far as sound and feedback..thanks

[Jonathan0996]

I found stuffing the guitar with foam to be very effective. The foam blocks need to be deep enough to completely block each F-hole. I put in a large enough block that it would wedge between the back of the guitar and the top and fully extend from one end of the F-hole to the other. It takes a bit of patience, but it's both doable and reverseable. Of course, this substantially mutes the acoustic sound, but I found any change to the electric sound to be negligible. The guitar still sounded very sweet and full through the amp.

I never had any luck with balloons or EQ notching. Unless you have a studio quality parametric EQ, I don't think you can surgically notch out the frequency that's causing feedback without messing up your sound. Even then, I have my doubts.

[gerraguitar]

Hey guys...

So I'm having a bit of an issue with my freshly modded ibanez ak95 artcore. Just recently put a gibson '57 in the neck, and it sounds great of course, but it's starting to feedback if i turn the amp up too much. I realize that you have to be sensitive with hollowbodys and volume. I use a fender twin reverb and a roland jc120, and both of them will feedback and buzz at me when i play around in 7th position on the A string, really it's E and Eb that do it. I tried to raise the action a bit and it seemed to do something. I just need to be able to get the amp a little bit louder when playing in the ensembles at school. I refuse to believe that the combination of a 57 pickup and any hollowbody is never a bad thing, i'm assuming its just paying some attention to the channel and the master volume on the amp (the fender anyway).

Any advice or suggestions you guys would be greatly appreciated...

E

[spiral]

Feedback
See this post: Dougs Plugs
Packing tape or window cling film over the f-holes should help. Also, every hollow object (rooms, bottles, boxes, etc) has a resonant frequency, and if you are getting it around E or Eb, then that is likely the frequency at which your guitar naturally vibrates... amplifying it just creates more vibrations. Blocking the holes should help.

Buzzing
If it is only on a few frets, you likely have 1 or 2 high frets. Take it to a luthier / repair place and have it setup including a fret level & crown, and nut adjustment (i've never seen one cut right from the factory). Also make sure there is a tiny bit of bow in the neck: fret the low E at the 1st and 15th frets and make sure there is a little gap between the 7th fret and the string. What gauge strings do you have on it?

re: resonant frequencies.
When i sneeze, some of the guitars hanging on my wall ring out with sympathetic resonances.

[gerraguitar]

Spiral...

I used to use size 12 flatwounds but I loss my love for flats and switched back to rounds, right now they are size 11 but i like 12s so i'll switch back. i'm interested in trying the tape thing, maybe that'll help. I also messed around a bit more with the eq of the amp and it seemed to help, never ending battle.

Kawa...
Thanks for the suggestion, i actually have not been in the rooms that i'll be playing in, i've just been in my room pretty much sitting right next to the amp so i'm already close to the thing. i'm sure it'll be much easier if i get in the right setting to see what i have to do

[customxke]

I stand with my back to the amp, 45 degrees off axis. YMMV.

[Anandbhat]

I recently got an AG75 and have had similar issues. Reducing the base on the EQ,standing away from the amp and facing away from the amp does make a difference. I think I'll use a direct box if I ever gig with this guitar.

[kambor]

I've played some gigs with my af75. In the open air ones I used a jc-120, and in the pubs the zt lunchbox. I had no problems with feedback.

Instead of rising your action, try lowering the pickup and rise the poles on the thinner strings making kind of a stair. It's like a volume control for individual strings, so you can lower the relative volume of some strings and raise the others.

Also, the advice of stepping aside the amp is good, but you can't always rely on that (small stage, many musicians, or anything else). If you're stuck near the amp, try to angle it a little bit off the guitar, and try to put your body between the amp and the back of the guitar in case you can't find a nice angle. Also your right forearm can serve as a little dampener pressing the body a little bit.

Your ak95 is a laminate guitar, so with the pickup adjustement and some care, you shouldn't have to tape the holes or anything like that. I sure haven't, and I've played the jc120 with another guitar (nylon), drums, el. bass, keyboard and voice, without problems.

[Allenl]

Hey guys...

So I'm having a bit of an issue with my freshly modded ibanez ak95 artcore. Just recently put a gibson '57 in the neck, and it sounds great of course, but it's starting to feedback if i turn the amp up too much. I realize that you have to be sensitive with hollowbodys and volume. I use a fender twin reverb and a roland jc120, and both of them will feedback and buzz at me when i play around in 7th position on the A string, really it's E and Eb that do it. I tried to raise the action a bit and it seemed to do something. I just need to be able to get the amp a little bit louder when playing in the ensembles at school. I refuse to believe that the combination of a 57 pickup and any hollowbody is never a bad thing, i'm assuming its just paying some attention to the channel and the master volume on the amp (the fender anyway).

Any advice or suggestions you guys would be greatly appreciated...

E

If you stand to the side of the amp as opposed to being directly in front of the amp, should help. You'll have to experiment a bit to get the best vantage point, where you can still hear yourself without feedback issues.

[cjm]

The question of string size does bring to mind another issue with regard to feedback.

Lighter strings, a light pick and a light touch can exacerbate feedback problems with archtops because you do have to crank up the amp more to achieve a given volume level.

If, for example, 11s or 12s are replaced with strings at the upper range of medium gauge -- a set that runs say, .014 through .058 "E-to-E" -- and the player really digs in with a heavy pick -- then the amp can be turned down quite a bit. Instead of making the amp do all the heavy lifting and right at the ragged edge of feedback...you put some of the energy required to get the volume you need into the system with your picking hand.

Doesn't work every time with every guitar/amp, but it works in enough situations to make a believer of me.

[Little Jay]

Good advices here on the feedback, but if all fails, you can try to put a small block under the bridge; a small block of wood between top and back (like violins have), 1 by 0,5 inch should do it. My Japanese ES175-copy has one stock and it hardly ever feedbacks (with a Gibson Burstbucker #1 in it). It will change the (acoustic) sound maybe a bit, as it restricts the movement of top and bottom, but only slightly. I doubt that you would notice a change in the electrified sound. You can easily put it in place through the bridge PU gap.

[Anandbhat]

I wonder if the sensitivity of the pup makes a difference?
My findings with my SCXD:
The 98 Aria FA-70 (L5 copy-stock humbucker) has no feedback issue whatsoever.
I do get quite a bit of feedback with both the es-339 (classic 57's) and AG75 (Lollar CC)
Yet the Aria is the loudest of the three.
Used the same EQ settings for all three.

[kawa]

The cause are levels of frequecy at the playing position.

Just how to set the tone and volume and each balance.

These are common sence of players.

[pauln]

I play the Ibanez AG75 and have found my larger tube amps with 2x12 or 4x10 tend to be subject to feeding back even with the amps' volume and bass reduced. Yet, at the same stage volume level when I use the Princeton with a single 10 at near full volume - no feeding back; and the tone is really superior for jazz. It is all I use for jazz with the arch top now.

I think the difference is the total amount of speaker surface area in play;
1x10 is 78 sq inches
1x12 is 113 sq inches
2x12 is 226 sq inches
4x10 is 314 sq inches
... with the arch top the big ones just move too much air even with reduced volume and bass settings, but the single 10 drives a nice loud clean tone "under the radar" of the feedback susceptibility. Sometimes I sit right on the amp... no problems.

You could test this idea for yourself with the Twin by pulling a wire off the second speaker (second in parallel connection sequence from the output). The Twin will handle the impedance mismatch just fine, but if it worries you, pull two of the four power tubes to correct the impedance match (pull either the two outside or two inside tubes of the four). That will also knock your power output down to about 40 watts. Basically gives you a 40W 1x12 amp in a big cab with overspec'd power transformer and correct impedance match (and reversible anytime in about one minute).

[DedroCepue]

fret the low E at the 1st and 15th frets and make sure there is a little gap between the 7th fret and the string. What gauge strings do you have on it?

[kenbennett]

I said in another thread that feedback is an EQ problem. At least one player in that thread tried my suggestions and proved it right.

However, pauln has a point about speakers. Every speaker has a resonant frequency, the pitch to which it physically responds the most. This pitch is normally in the range of the two lowest strings on the guitar, and you might also get a problem playing an octave about that frequency.

The speaker resonance problem is less with closed back, ported speaker cabinets. The port is tuned such that the resonant peak is split into two peaks with lower amplitudes than the original peak. This has the effect of lowering the pitch and the loudness of the resonant frequency. The purpose of enclosed, ported speakers is to smooth out the frequency response and increase the potential bass response. That's why you see them in PA cabinets, bass amps, and full range keyboard speakers... not so much in guitar amps.

My common practice is to find the offending pitch (the one feeding back), and pull down the corresponding fader on the EQ by about 3 to 6db. That always works. But we're playing acoustic guitars with pickups through a PA. If you want to do it with your amp, you'll need an external equalizer. Somebody in that other thread posted some links to good ones.

[Anandbhat]

Totally agree about frequencies. I find that certain notes feedback the most.
Is there a guide for 'mapping out frequencies' on a guitar?
Since midrange is attentuated for most jazz settings will cutting back reduce the tonal quality?
Thanks.

[kenbennett]

You won't be able to kill the feedback with the tone controls on your amp. Those effect too wide a frequency band. What you want to do is zero in on a specific note, actually a narrow band of frequencies surrounding the offending note.

The ideal thing is a parametric eq. Set the frequency to the exact note that feeds back, and set the Q (bandwidth) to a very narrow setting.

Find that other thread on this forum, the one I mentioned, and look at the products recommended. I don't remember what they are.

My gig is two acoustic guitars, and we play through the PA. Each channel has low, mid, and high controls (similar to bass, midrange, and treble on a guitar amp) to tweak the tone of each instrument and voice. I use the 10-band graphic eq on the PA to shape the overall sound. There's one on the mains channel and one on the monitor channel. Cutting the 125Hz band on the monitor channel about 6db usually kills my feedback. Sometimes I have to do it on the mains as well. It depends on the room, how loud we play, and how we're set up.

Here a list of the frequencies of every note on the guitar from the low E string to the high E string on the 12th fret.


* 82.4 E - open 6th string
* 87.3 F
* 92.5 F#
* 98.0 G
* 103.8 G#
* 110.0 A - open 5th string
* 116.5 A#
* 123.5 B
* 130.8 C
* 138.6 C#
* 146.8 D - open 4th string
* 155.6 D#
* 164.8 E
* 174.6 F
* 185.0 F#
* 196.0 G - open 3rd string
* 207.6 G#
* 220.0 A
* 233.1 A#
* 246.9 B - open 2nd string
* 261.6 C - "middle C"
* 277.2 C#
* 293.6 D
* 311.1 D#
* 329.6 E - open 1st string
* 349.2 F
* 370.0 F#
* 392.0 G
* 415.3 G#
* 440.0 A - 5th fret on 1st string
* 466.1 A#
* 493.8 B
* 523.2 C
* 554.3 C#
* 587.3 D
* 622.2 D#
* 659.2 E - 12th fret on 1st string