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Gore and Gillet propose that mass in the sides of the body, based on their research, introduces a larger vibrating plate on the top and more clarity in the higher register.

I've seen this to be true in my own guitars where I've stiffened the top and had to bolt weights onto the side braces just below the waist (planned ahead for this of course) to get the tone I and the customer wanted.

Have any of you fellow guitar makers pushed to add mass in other ways with success? I want to do this to whatever extent possible, but would like to avoid bolting multiple pieces of steel bar stock to the inside of my guitars.

I understand there must be a balance between the top strength and the side mass, but I feel like I'm nearing the long-term limits of the top's abilities to do it's job and weaken it any further.

Thanks in advance!

Not side mass on guitars, per se, but I think the concept is the same as you see on banjos. On banjos, the "tone ring," a, usually metal, part that sits on top of the rim and forms the perimeter of the banjo head, has quite a bit to do with the tone, sustain, and volume of a banjo. Inertia pretty much dictates that if you have a really heavy and dense perimeter of the head (soundboard), more vibrations will stay on the head/soundboard and reflect back from the much denser rim. The heavy mass at the edges of the soundboard are hard to move, so the vibrations tend to stay on the soundboard.

But, again in banjos (and undoubtedly the same in guitars), there is a sweet spot. Too much mass on the edge can add a lot of volume and sustain, but not necessarily lead to the best tone. Like everything else, it's a compromise.

A banjo is a pretty nice model for experimenting with side mass since the head is homogenous, and really adds very little of its own in terms of tone, unlike the soundboard of a guitar. In general, a heavier tonering on a banjo produces more bass, more volume and more sustain. But there are subtlties in the tonering (solid vs hollow, solid contact with the rim vs truss like suspension above the rim, overall weight, material, etc.) that make huge differences in tone, for better or worse. Looking back at nineteenth and early twentieth century banjo patents document this pretty well.

Anyway, sorry to get off on a banjo tangent, but there are definitely similarities to the guitar, and no really good formulas to follow. Mass of the sides definitely does make a difference, but figuring out how to tame this difference is key. I think the bottom line though is inertia. Heavy sides tend to make vibrations stay on the top, since it's a lot harder to energize a heavier mass. Whatever tonal advantage/disadvantage this creates is pretty much up to personal taste. I tend to like the sound of guitars with thinner sides, like on earlier Martins and Gibsons, but that's personal taste.

Dave

I have not experimented with that yet but I also would like to some day. I do tend to make my sides thicker then most it seams and I have tried reverse kerfed and even solid linings but I doubt I would ever be able to know that makes any difference.

If you haven’t listened already, the episode of Michael Bashkin’s podcast with Trevor has a good explanation of the origin of his side mass experimentation.

https://podcasts.apple.com/us/podcast/l ... 0446440500

Brad


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Brad took the words right out of my mouth. I thought this was the most interesting part of the episode!


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There is no doubt that Trevor Gore is correct. I have seen him demonstrate it. I built a couple with the bracing in the sides incorporating nuts to screw on weights for added side mass - following the G&G method. It definitely does change the top resonant frequencies and the tone. But I needed to add quite a lot of mass and I don’t like the heavy feel. Maybe I would get used to it. But I ended up removing the weights. I am now playing around with laminated sides and solid linings to try to get the same sort of rigidity in the rims that Dave was referring to - but without the weight.

Thanks guys. I currently put these mounting blocks in my sides just within reach of the sound hole (few inches below the waist) so that I can add weight if I miss my top resonant frequency. I had a guitar last month where the client wanted extra volume (my guitars are already really loud) but I obliged and made his top a little stiffer than usual. Ended up almost 20hz higher on the top frequency when it was done. Adding the weight to those mounting blocks took it down to my target frequency and solved the overall tone problem, and did seem to add some clarity on the top end... and loud as all heck.

I don't want to go for this overall sound on every guitar, but if I could add a little mass and get a little of that high end clarity going forward, I'd take it.

Dave Ball wrote:
"Anyway, sorry to get off on a banjo tangent, but there are definitely similarities to the guitar, and no really good formulas to follow. Mass of the sides definitely does make a difference, but figuring out how to tame this difference is key. I think the bottom line though is inertia. Heavy sides tend to make vibrations stay on the top, since it's a lot harder to energize a heavier mass. Whatever tonal advantage/disadvantage this creates is pretty much up to personal taste. I tend to like the sound of guitars with thinner sides, like on earlier Martins and Gibsons, but that's personal taste."

Dave makes an interesting point. The more you keep the vibrations in the top the less effect the back and side materials have on the sound of the instrument. The instrument may be louder but lose the interaction of the sides and back with the top. Romanillos, commenting on the "Modern" classical guitar designs said he felt they failed to capture the true Spanish sound. Torres used some very thin sides And his guitars were known for the "quality" of their sound more than the loudness of the instrument. I have measured the thickness of the backs and sides of some of the old parlor guitars I am putting back together and some are in the range of 40 -50 thousandths for the sides and 70 thousandths for the backs. Admittedly, they are smaller guitars and strung at lower tension. Still, I have to think the back and sides come into play more than on instruments that use thicker scantlings and are heavier braced.
So I see more massive sides as a win some/lose some proposition.

Check out ‘structured’ sides ala Serge de Young, James Dion, Indian Hill etc.

The top can feed energy to the back in two ways; through air pressure changes in the box, and also through the sides. These two mechanisms are generally out of phase with each other, so they can tend to cancel each other out. The couple through the sides is strongest at the 'main top' pitch, since the phase of the force is the same all the way around the lower bout. The 'air' coupling would be stronger at the 'main air' pitch an octave lower. The mass of the back, and the 'main back' tap tone pitch are likely to enter into all of this as well. All of this probably introduces some complexity to the sound; 'tone color'. Moving to heavier sides would possibly trade some 'color' for 'power', moving the guitar away from it's normal type of sound more in the direction of a resophonic or banjo type of instrument. It is certainly useful to have that ability, but I think the trade-off is inevitable, and you have to decide what you're after.

In the earlier days of banjo making, there were a number of methods attempted in order to get beyond the fairly simple tone of the banjo and to move towards more traditional luthiery of the day. This patent kind of covers it all in my opinion:

https://patents.google.com/patent/US591288A/en?q=benjamin+mclaughlin+banjo&oq=benjamin+mclaughlin+banjo

When I first saw this patent, I figured it was yet another of those late nineteenth century patents that never actually resulted in more than a patent model. But it turns out, this guy made at least one (which I own). Does it sound great? Can't say that it does, but it's not bad. Is it extreme? Pretty much is...

This kind of experimentation has been going on a long time. As Alan said, you have to decide what you're after.

Dave

I had the most extreme example of side mass come in my shop about eight years ago. A 70's classical by east coast luthier John Toliver. Double sides with a lead mesh laminated between them and a lead fill of the upper lining supporting the top as well as lead filling in a diagonal upper brace and the neck. Banjo hefty.

It was LOUD but no tonal complexity and really a pretty unappealing sound other than volume.

Toilver Guitar I by Terence Kennedy, on Flickr

I am a big fan of double sides but for me the right combination of volume and tone seems to occur with double all Mahogany or Maple outer with a Rosewood inner side. I have been less impressed with the all-Rosewood doubles. Loud but maybe a little tubby tone-wise out of the gate.

I recently did a double side IRW outer/Maple inner/Lutz OM with carbon fiber tube headblock supports. The support stanchions for the tubes on the sides added mass as well. It was really loud but seemed a bit harsh. Happily as it has been played it has settled down but like Alan said, my limited experience seems to also indicate that at some point and perhaps with certain woods increasing your side mass while it always seems to increase volume will do so at the expense of tonal complexity.

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That's wild.