Does the Thickness of the Back and Sides Matter to tone?

[Guitar Hack]

I was wondering if the thickness of the back and sides on a guitar makes any difference to tone so long as the top is the proper thickness.

[Darryl Young]

I'm sure everyone has a different opinion on this subject so don't think there are absolutes.

I'll make a couple of points and take it with a grain of salt.

The side probably provide better support and rigidity to the box when it is thicker.......but it bends easier when it is thinner. Probably bending limits the thickness of the sides as they have to be thin enough to bend into a guitar shape without breaking. Not sure where the limit is on how thin you can go......but thinner weakens the box. My opinion is the sides do provide some sound but likely the player is the only one who hears it......it's very quiet compared to the entire volume of the guitar. Probably fingerstyle players using guitars built for that style would notice the difference between a thin side that moves (and produces sound) and a thick, stiff side that essentially produces no sound.

To make a broad generalization, a thicker back may help the guitar project more and a thinner back moves more and creates an enveloping sound when being played (not sure if it has the same impact on a listner in front of the guitar). Per Al Carruth, when a back is tuned where the natural frequency of the back is a little above the main frequency of the top, the top and back will couple together across a broader range giving more power to a range of lower notes. Some luthiers thin the back (or thin the back bracing) to tune the back relative to the top. The back has a bigger influence on tone than the sides in my opinion........and the back doesn't have near the influence on tone as does the top.

It would sure be neat to build enough guitars to know exactly how to determine the ideal back thickness for the style guitar you wanted to build. Again, I hope this gives you a broad generalization but there are many opinions about this and many variables that affect each other so I can't say the above is absolutely correct in all situations and build styles.

[JJDonohue]

One of my early mentors used to say, "Pick tops with your ears and backs with your eyes". The meaning obviously being that the top has much more influence on the sound than the back. And while the maxim is probably overly simplistic, I eventually came to a practical resolution in my own mind based on my limited experience.

I believe that back and side woods color the tone of a guitar. I look at that effect as a function of a tonal spectrum that covers brightness on one end (Mahogany) and warmth (Indian Rosewood) on the other and other woods fit somewhere in between the two. So when I describe the sound of a back and side it refers to its position on that spectrum. As always, as I build more I reserve the right to change my mind...;)

As Darryl stated, depending one stiffness and thickness of the B&S, further modification of the fundamental sound can made. It actually takes more guitars than I have made to figure this stuff out but each build brings us more information and knowledge.

[tippie53]

My experience taught me that the to is 90% of the guitar. I have seen examples of very heavy guitars that were terrific and some that were not . I believe that the box does work together but not as much as some people may think. One fallacy I often hear is the back arch will help project the sound , this is not true .
A guitar is a sum of its parts . So each guitar is individual . The top and its bracing is most of what you can expect. The dampening effects of the wood joinery can add or detract to the the guitar. The back and side wood ,and this is my opinion , relates to the top by its mass ,density and volume. I find that a solfter wood will add complexity and warmth to a point. Hard dense wood tends to make the guitar more powerful but also a bit brighter.
I have seen gutiars as thin as .065 on the sides and back. I also seen as heavy as .100 sides and .125 on the back. I think it is more a balancing act to make it all work. Alan Caruth is a master at this and I love to read all his posts. A most remarkable builder.

[Darryl Young]

This isn't a perfect illustration, but I've heard folks describe the back as the EQ setting on PA equipment. You can sort of empasize or detract from the highs, lows. or mid-range..........within limits.

[JJDonohue]

I hope the Dog's running around our neighborhood today. I'm sure he'll have some good info based on a lot more experience than most.

I love these kind of discussions.

[kencierp]

OK -- thickness of the back may or may not make a difference and produce a sound that is more pleasing to your ear its subjective ---the reality is you would have to build two identical guitars with the exception of the back thinckness to find out if you can actually hear any change. I would suggest that you go with the common .100" dimension so the bracing is not stressed (you don't want to flatten out the contour) and shaping the back to rim will also be easier. As a side bar --- if a player makes an effort to keep the back of the guitar away from their body a drastic increase in volume will be the result. Tim McKnight makes a double back model that takes advantage of this isolation concept. $.02

[JJDonohue]

Rick...many thanks for the info and your thoughts.

My backs and sides have been between .080" to .090" depending on density and stiffness. Braces are 1/4" wide x...1/2" for #1,2....5/8" for 3,4. Haven't lost a dome in 5+ years.

I have been considering departing from the back ladder braces and experimenting with X-bracing ... your experience and observations are most helpful.

[mike789166]

I think I read somewhere that Antonio Torres once built a classical guitar with the back and sides made from papier mache to prove that they do not have much influence in the sound. The guitar is no longer in existence.

[tippie53]

Torres did build one and so did David Laplante. It is surprising what you can make a guitar out of. The thing of it is ,at this point we must look at the art and the science of a guitar. I like how Rick Davis made a reference to stiffness . Here is where experience comes in.
I am of the school of getting a deflection reading. I like to match the back and tops bracing to the plate so I know how it will react . This is stuff you need to learn. keep a building log and do not make too many changes at one time.