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Sound Hole Plugs for Amplified Reso Playing?

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May 31, 2022 - 4:40:55 PM
503 posts since 11/28/2012

It’s not uncommon to see sound hole plugs (rubber or foam) used by regular acoustic guitar players when amplified. Various companies market and sell these, touting their feedback busting capabilities when playing at loud volumes with a piezo pickup, typically with a full band.

Which got me to experimenting with rigged up foam plugs for the 1 7/8” sound holes on my square neck…cut from studio sound proofing foam.

I only tried it with an amp, using the Fishman/JD Aura rig. As expected, it cuts down overall volume, and tames the boominess more so than the treble. Basically it saves me from having to do EQ cuts to avoid low end howl at high amplified volume. It also makes my National Scheerhorn play with more of an old-time “honk”, ie, less full and modern sounding, more like my OMI Dobro sound. So it definitely alters tone when amplified.

What I cannot yet simulate is the effect it might have on blocking the loud stage monitor sound from my internal sound chamber…especially the amplified bass guitar, which causes all kinds of vibrations and wreaks havoc with my instrument on stage.

Obviously this is for amplified (loud) situations only. This would be a very silly exercise for acoustic jams.

Funny, but since the foam cutouts are a dark charcoal color, they are barely visible…just look like open sound holes.

Let me know if anyone has been down this path, or has any thoughts.

Edit:  I should add, I play Open D tuning, so low end feedback is a bigger challenge for me than most players.

Edited by - JC Dobro on 05/31/2022 16:44:24

Jun 1, 2022 - 8:03:49 AM



1373 posts since 9/28/2010

This is an interesting experiment to read about, and possibly use. Thanks, and keep us posted.

Jun 1, 2022 - 9:39:14 AM

503 posts since 11/28/2012

Yeah I’ll post up results. Just did another loud amp experiment, cranking it up until feedback hits. The foam plugs definitely help tame low end howl.

I am going to use this solution at our next loud, indoor bar gig. The kind of joint where you need to shout to be heard, even before the band starts…lol.

BTW here’s what my mock-up looks like.  Note sound hole plugs in graphite/charcoal color.

Edited by - JC Dobro on 06/01/2022 09:43:43

Jun 1, 2022 - 10:20:41 AM

4240 posts since 7/27/2008

Jamie, maybe  it's just me, or it might be the venues you play - but you seem to be in an ongoing war with getting good clean sound. wink

I can see where the foam plugs might help a little - but I've always thought the major culprit is the fact that a dobro has a huge hole which takes up most of the top of the guitar, and it's only "defense" against a variety of issues is a very thin aluminum alloy speaker cone - which actually might add insult to injury. 

Last week my wife and one of my kids were sitting in our living room, and I let out a big sneeze. I have a guitar rack in the corner which holds multiple instruments and my Clinesmith was on there at the time. They got a kick out of the resonator "accompanying" my sneeze with some musical "fills." 

Edited by - MarkinSonoma on 06/01/2022 10:21:19

Jun 1, 2022 - 11:05:26 AM
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1373 posts since 9/28/2010

My dog's bark is just the right frequency to make the tricone sing.

Jun 1, 2022 - 11:11:52 AM

503 posts since 11/28/2012

Originally posted by MarkinSonoma

Jamie, maybe  it's just me, or it might be the venues you play - but you seem to be in an ongoing war with getting good clean sound. wink

I can see where the foam plugs might help a little - but I've always thought the major culprit is the fact that a dobro has a huge hole which takes up most of the top of the guitar, and it's only "defense" against a variety of issues is a very thin aluminum alloy speaker cone - which actually might add insult to injury. 

Last week my wife and one of my kids were sitting in our living room, and I let out a big sneeze. I have a guitar rack in the corner which holds multiple instruments and my Clinesmith was on there at the time. They got a kick out of the resonator "accompanying" my sneeze with some musical "fills." 

Lol...I'm definitely at war with feedback.  Never had this issue (ever...) until I joined a 6-man band that plays bar venues at Van Halen type volumes.  We have no professional sound guy, and our sound checks are minimal at best.  Since I play Open D, I have more bass in the mix than 95% of you guys.

The cone is certainly the main culprit.  But taming down boominess from the sound holes is a simple solution that seems to help.

I will spare you guys my Krivo pickup experiments and A/B comparisons, which are on

Jun 1, 2022 - 12:59:05 PM

4240 posts since 7/27/2008

Hey - don't spare us the Krivo experiments! I'm really curious about the pickup, and I see a lot of comments online that it sounds just like their guitar acoustically, except plugged in.

I don't really buy it - there aren't many out there, but when I've checked out demos with spider bridge resos  (in good quality Shure studio monitor headphones) it always sounds a little lap steelish to me, which isn't a huge surprise since it's a magnetic pickup. 

I do recommend it to players who need to plug in now and then but don't want to go all whole hog with  the Fishman Nashville & Aura combo, or some other expensive device to go along with the Nashville  like the ToneDexter by Audio Sprockets. Especially for someone who has a guitar  like a $400 Regal, and to get the complete Fishman program along with an adjustable spider they'll be out ballpark 700 bucks. 

Jun 1, 2022 - 1:23:25 PM

503 posts since 11/28/2012

Jason @ Krivo told me the pickup would ship this week, so that experiment is likely a couple weeks off. I’ll share those results.

Funny, I was virtually neighbors with the guy while living in Portland; I had never heard of his pickup until just recently.

Jun 2, 2022 - 8:44:20 AM
Players Union Member



757 posts since 9/2/2008

Jamie: Your experiments make sense. It's not the cone or the cone opening per se that's causing feedback issues, it's the complete resonance of the whole system (cone, soundwell or not, baffles or not, box volume and rigidity, etc.). With the acoustic foam (it's not, and can't be, "soundproofing"; different discussion for a different thread) partially restricting the soundholes, you are making a partial transition from a bass reflex enclosure to a sealed box enclosure. Yes those are speaker terms, and they fit. Bass reflex enclosures make for louder speakers because they are generally more efficient and have extended bass frequencies. However, this often comes with a resonant peak (underdamped) at the low end cutoff frequency. The sealed box enclosure is less efficient and has less extended bass, but the low cut rolloff comes without a resonant peak. So with reduced volume, less bass, and less resonance, the reso with plugged sound holes (or ports, if you will) tames three feedback factors at once.  That's why it works so well with acoustic guitar soundhole plugs, and why you are having success also.

Is there a market for this? Perhaps. Be aware your potential market numbers in the hundreds...wink

Personal experience:  I have a maple Beard Odyssey with Doubleshot that's a certified "banjo killer".  It has been accused of being "bass heavy".  I did notice a resonance around a low A (~110 Hz) that seemed to hang on after muting the strings.  The Odyssey has a semicircular baffle from top to bottom, following the front cone edge, with openings at either side,  In effect the reso is two Helmholtz resonators in series (though an engineer, I avoid advanced math, so I don't have the calculations).  Once, when I had the cone out for semi-irregular cleaning, and also had some open cell foam scraps left over from a reupholstering project, I placed foam blocks at the end of the baffle.  This partial baffle restriction tamed out the 110 Hz peak.  Volume wasn't reduced significantly.  I haven't yanked the foam out to see if the resonance comes back, partly because I'm happy with the results, and partly because it's not time for the next semi-irregular cleaning...

Edited by - daver on 06/02/2022 08:45:28

Jun 2, 2022 - 2:38 PM

503 posts since 11/28/2012

Thanks, Dave, for the insightful and data driven post! It helps me understand the science behind the real world experiment.

I’ve tried isolating the culprit frequencies in the open (non-plugged) reso, but haven’t been able to pinpoint with my notch filter. Regardless, the howling is minimized with the foam inserts installed, as your data supports.

I’m doing this stuff strictly to solve my own personal amplification challenge. I’m simply using Auralex (or similar) studio foam panels, with a 1 7/8” dia. circular cut out. The springiness of the foam tensions it in place inside the sound holes (ports). Honestly, it’s a 5-minute DIY fix.

I’m gigging tomorrow on an outdoor patio with full band. It will likely NOT be necessary to use these in that setting, but I’m going to try it anyhow to see how it sounds.

One other finding. JD Aura settings #1 and #2 work best for me at loud amplified volume. Brighter tone and less low end feedback, vs other settings.

Jun 3, 2022 - 3:07:46 PM

275 posts since 4/5/2012

Hmmm....I've found that the Aura adds increased treble as the numbers get higher...JD himself says in a video interview that he uses low numbers for recording and high numbers when he needs to cut through in a live situation...YMMV, I suppose, and it does vary overall from one instrument to another...
Re the Krivo, I've got one on my tricone, it is the only thing still available (there was another option but it isn't on the market any more). It does sound like playing acoustically...but then it adds a little of that magnetic/electric warm thing on top... Not the same as a Fishman/Aura, which is a much cleaner acoustic-type sound (I use the aura on my single cones). Played through a PA in a live gig, the Krivo does the job just fine...and there is zero feedback.

Jun 3, 2022 - 4:29:14 PM

4240 posts since 7/27/2008

Steve, I remember that you have the Krivo on your boutique build  tricone - you have posted about it multiple times here and elsewhere.

Different breed of cat than a spider bridge guitar, and I can understand why for example, National has been working with Krivo in offering it as a good pickup for their tricones. 

Now in regards to the Scheerhorn aka Nati-horn line, National offers the Nashville pickup as an option. I would imagine they can send a Krivo with a Nati-horn to one of their dealers if requested, but they don't actually show it on the website in the specs as an option, which they do show with the Nashville. 

There are a fair number of demos out there re the Krivo as used with tricones and some biscuit bridge guitars, more toward roundneck models than squarenecks. 

The majority of the members of this forum still tend toward spider bridge squareneck guitars, and my own curiosity regarding the Krivo is how it "behaves" with this style of guitar. 

Edited by - MarkinSonoma on 06/03/2022 16:38:00

Jun 3, 2022 - 5:44:04 PM

275 posts since 4/5/2012

Aha.,..right....yeah, I use the Krivo because there is nothing else for the tricone, I wouldn't use it elsewhere unless I wanted an easy, slap-it-on pickup with no install needed...

Jun 4, 2022 - 5:22:57 AM
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503 posts since 11/28/2012

Yeah Steve, I definitely perceive the Neumann U67 settings (#1 and #2) are brighter, with less low end thru my amp. Those settings will reduce any low end howl on my axe. Like you said, YMMV. Here’s the JD interview where he makes a very brief comment at 2:36.

Re Krivo...I've only found one spider bridge demo here.  That's me asking him in comments if he now uses the Krivo in place of the Nashville...and he indicated he does not, on account of string balance issues.

I'll do my own tests here when my Krivo pickup arrives.

On a related note, I played the outdoor gig last night with the foam sound hole plugs.  Worked flawlessly.  I didn't expect any issues based on the outdoor venue layout, so my main goal was to test the sound quality.  Sounded good to my ears and anyone who cared to weigh in, and it didn't vibrate like a chainsaw on my right hip.  Next checkpoint will be a noisy indoor bar gig.

Coupled with judicious monitor placement and being smart about amped bass guitar orientation, I hope to have found the solution...


Jun 4, 2022 - 10:51:23 AM
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275 posts since 4/5/2012

Hmmm....Krivo has individual string adjustments, so I don't get the string balance issue....but if you use phosphor bronze strings, the wound strings are much less magnetically resonant, so I had to completely remove the slugs on the plain strings, and then I am able to adjust for perfect balance. He probably didn't consider doing that....

On my Bonham custom CooderNator I have both a piezo Fishman and a magnetic Lollar String-through, and use D'Addario Nickel Bronze strings to get a better response on both piezo and magnetic...

Your sound hole plugs seem to do the job for you...I also notice a big difference in open sound holes vs. sound hole screens - the screens reduce the bass quite a bit, and the volume somewhat, for that more classic dobro tone...those might be another option for you to kill feedback without losing all of the tone...

JD's signature Beard model comes with open holes, but a couple of years ago he started using screens on it again, not sure Maybe he just liked (or remembered fondly) the tone he was getting on his Earls of Leicester classic 1930s dobro that has screens...

Jun 4, 2022 - 12:17:28 PM
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503 posts since 11/28/2012

^^ Good info Steve, thanks for the info on your setup! I’ll report back when my Krivo has been put through the trials.

Jul 16, 2022 - 11:25:42 PM



4 posts since 7/15/2022

Great info! Thanks!

Jul 17, 2022 - 3:49:07 PM
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1373 posts since 9/28/2010

"JD's signature Beard model comes with open holes, but a couple of years ago he started using screens on it again, not sure"

Maybe he lost a fingerpick one too many times?

Jul 18, 2022 - 10:14:21 AM

4240 posts since 7/27/2008

I see Wayne quoted Steve from several weeks ago.

Actually, the original JD signature models come with screen rings whereas the the various "Beard" models, BlackBeard, BrownBeard, etc. have the screenless rings for the more contemporary look.

Some will recall around four years ago that Jerry's "A" game BlackBeard fell out of the back of a vehicle (golf cart?) at a festival and sustained some serious damage. It was sent back to Paul for "surgery." 

Jerry did a show with his band in nearby Sebastopol when the BlackBeard was on the repair bench and he was playing one of his older JD models with screens. 

Are these guitars designed by Paul to be at their optimum with screens vs. screenless depending on the model? Or is it just for aesthetics?  I have no idea. 

The most recent time I saw Jerry was last fall with John Hiatt in Santa Rosa. He was playing the screenless, repaired BlackBeard. You'd think that being Paul's primary endorser he could have replaced the damaged BlackBeard with a brand soankin' new one, but there is apparently something he really likes about that guitar. 

Edited by - MarkinSonoma on 07/18/2022 10:25:13

Jul 18, 2022 - 10:29:55 AM

275 posts since 4/5/2012

The story of the Blackbeard has Jerry controlling every aspect...with Paul. Jerry specified the red fingerboard, to look like his very first dobro. Paul designed the cover plate for maximum sound/frequency transfer. the interview didn't say who picked the screenless soundholes ...but he left them that way until after he started the Earls with a more traditional dobro, I guess that more classic sound now appeals to him...I had a Blackbeard and really noticed the difference (tried it with and without) and started pulling the screens from every other dobro I've had since. Definitely a fuller sound, which is more "modern"...I think it now is whatever you like for yourself..not "better" or "worse" current custom dobros have big openings, like on a standard tricone...

Jul 18, 2022 - 11:45:02 AM

4240 posts since 7/27/2008

Yeah - Paul  was trying to talk Jerry out of the BlackBeard idea a number of years ago. He didn't think a no frills blackish guitar with a "red bean" fretboard would sell, but apparently it's done extremely well. And it's considerably less expensive than the earlier JD models. 

Jerry has indeed indeed put screen rings on the BlackBeard as I have seen in a variety of photos. I was looking at my iPhone photos from the Hiatt concert, but I was 2nd row balcony and I couldn't tell from that distance.

Maybe  it will start a movement of people going back to screens when they order a guitar from the various luthiers. wink

Edited by - MarkinSonoma on 07/18/2022 11:53:12

Jul 18, 2022 - 1:26:29 PM



1373 posts since 9/28/2010

"I see Wayne quoted Steve from several weeks ago." Oops.

Anyway, would the screen versus hole be similar to Telecaster versus Stratocaster? Both just fine overall, it depends on the player & desired sound.

PS- If anyone's taking a poll I'm screen & Tele.

Jul 18, 2022 - 1:55:49 PM

4240 posts since 7/27/2008

I think there is a much more audible difference between a Strat and Tele plugged straight into the same amp than there is for the same dobro with screens vs. screenless. 

I prefer the Tele myself (I have a very nice 2006 American Deluxe in Cherryburst), but  I would love to have a nice Strat as well - the only one I own is a Jay Turser knockoff. 

We have seen Vince Gill several times in concert over the years, and he gets distinctly different sounds out of the Tele and Strat when he switches guitars. But I have no idea what's going on with his pedal board when he does that. 

On the other hand, when you're playing a dobro plugged in to the Fishman Aura system which Jerry does most of the time - I have to wonder if one can hear any difference between screen vs. screenless 

Jul 18, 2022 - 5:00:48 PM

5 posts since 11/17/2013

Regarding the Krivo pickup, I recently tried the LR Baggs Voiceprint with my Krivo, and liked it much better than the Tonedexter. Setting up the model is easier as well, I used the “advanced” setting to set up the model, and played into the unit for several minutes, with much better results than the Tonedexter. I’ve also used it with my Weissenborn, and a seven string Krivo equipped reso I just finished. The Voiceprint sounds much better than the Aura to me as well, and allows you to have a guitar that sounds as good acoustically as it does amplified, I’ve never cared for the acoustic sound of the Aura saddle inserts. The Voiceprint also has much better equalization controls, and you can access most of the Voiceprint controls with your phone and/or Apple Watch, pretty cool.

The last ingredient, though, is a Grace Design Felix 2 preamp. Wow, what a piece of equipment! Not inexpensive, and if you only need one channel, the Alix might be a better choice. The Felix allows you to have a mic on one channel, and the pickup on the other, with an astounding amount of control, and the ability to mix the inputs for your perfect blend. In very loud situations though, the pickup channel alone would probably be your only choice.

The EQ and hi pass filters easily take care of any low end rumble, and the Voiceprint + Krivo has a wonderful acoustic sound. I’m told by a working Nashville musician that a lot of the acoustic playing pros are using the Voiceprint with the Grace preamps now, which is why I decided to try them. True, the pickups in most cases are usually piezo types, on guitars and mandolins and such, but in the last week of trying this combination with the Krivo has been very rewarding, and I still haven’t discovered all the Grace is capable of, and since I’m not a pro player I doubt I ever will.

Edited by - Lindamon on 07/18/2022 17:05:56

Sep 10, 2022 - 11:18:59 AM

503 posts since 11/28/2012

It’s been over 3 months since I started playing amplified using the DIY foam plugs in my square neck (see posts #1 and #3 in this thread). Over that time we’ve had about 10 gigs, both indoors and outdoors, with various types of room acoustics, volume levels, and stage configurations.

I’m pleased to report that my prior stage feedback issues have been completely resolved. So the foam plugs in screen holes will remain part of my live setup while playing with JD Aura/Fishman rig.

It takes 30 seconds to install them flush, and about 10 seconds to pop them out when playing un-amplified/acoustically.

I believe my personal search for a reliable live reso sound is over. smiley

Edited by - JC Dobro on 09/10/2022 11:19:41

Sep 10, 2022 - 1:43:50 PM
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4240 posts since 7/27/2008

Good to hear Jamie that you're pleased with the results. I have a nice acoustic/electric Yamaha flattop  (FSX5) from their Japanese facility in Hamamatsu, it was purchased in early 2020.  A  bonus that was included in the case storage compartment is a perfectly fit thick black rubber "feedback buster" for plugged in playing in  troublesome situations. 

If the idea of covering  the screen ring holes on a reso while plugged in were to catch on, I can see an enterprising fellow like Paul Beard having them produced and offering them through Resophonic Oufitters. Or on a model which comes equipped with the Nashville pickup like the BlackBeard, a pair could be included in the case. 

The thing is when I was playing out plugged in prior to the pandemic it seemed to me that some of the issues weren't just from the screen holes, it had a lot to do with the large piece of the guitar's real estate - the wafer thin resonator cone. 

Edited by - MarkinSonoma on 09/10/2022 13:47:03

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