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…and if this has been banged out before, sorry. I missed it.

I recall reading that the designed function of the sides of a guitar should be focused on optimizing them as a conductor of sound energy between the top and back, and not as a component that produces sound. As such, the sides are best when they are more stiff (thicker?) than the back or top. It was even suggested that laminated sides “might” be preferred.

My comments were inspired by the previous discussion about “how sound travels through guitar wood”. I recognize that stiffness and density are good to a point, and progressively worse beyond that. And I realize that everyone probably agrees with this in principle, but judgements about how this gets translated into real life are very subjective. Care to tell me what you think should be important to shoot for and what to avoid?

And finally, assuming that all of this is correct, in my mind - it follows that a certain amount of attention needs to be given to the back as a component that does produce sound, and not something that is designed to only reflect sound. It should be “tuned”. Right?

Wish I could find a mortgage rate for my home like this!

0 interest.   

Tony,

I would intrepret this as a topic for which nobody has any developed information, factual or intuition-based. Plenty of experiments get done on tops and backs. But I can only recall assertions being made about the effects of different linings in discussions of sides.

Since backs and sides are almost always the same kind of wood, it might be interesting to do some mixing of back/sides species to see what happens.

SteveCourtright39037.4523032407

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"Building guitars looks hard, but it's actually much harder than it looks." Tom Buck

Yes. You are correct concerning the responses. Thanks for yours.

Mixing back/sides species would be an interesting experiment. Finishing them "black" would hide the fact if the contrast was hard on the eyes.

Just noticed - milestone one has been reached! I'm no longer a Forum Newbie. I'm now a Groupie. Look out serge. Funny, I still feel like a Newbie.

Tony, I think the problem here is that there are just too many variables in the wood, and too many philosophies in the builders to give you a definitive answer. For instance, some builders feel that the back should only reflect sound waves, and they build it to be very stiff. However, on another thread we've learned that high stiffness in any material makes it a better transmitter of sound; so maybe they're getting good results for the wrong reason! On the other end of the spectrum, Richard Schneider treated the back as a "second soundboard," with elaborate bracing on redwood (yep, he used redwood backs, Brazilian sides, redwood tops). Some builders just don't worry too much about the back, and construct it by feel and instinct. They've probably gotten good results through experience rather than philosophy.

Stiff or loose, thick or thin, the style of bracing comes into play, too. Ditto on all this for the sides.

See the problem?

Fred Dickens did some work on this years ago. Based on some computer analysis of equivalent electricla circuits, he decided that, however much energy was being transmitted by the sides, it was out of phase with that transmitted by the air between the top and back. He felt that it might help to minimise the motion of the sides, and added weights in the neck and tail blocks, and made the sides stiff, to that end. After a while he stopped doing that: he said that the difference was so small that it was not worth the effort. My own measurments seem to indicate the same: that there is very little energy trasmitted to the back through the sides.

I _think_, at least for now, that the back is, or can be, a net contributor to the output of the guitar at low frequencies, but probably is a net 'loser' at high frequencies. If you can tune the 'main back' resonant mode to work well with the 'main top' mode and avoid a 'wolf' in the process the output in the 'bass reflex' range is usually enhanced. This is roughly the range below the open G string pitch, or maybe up to the open B. At higher frequencies the back, being heavier (usually) than the top doesn't move enough to pump much air through the soundhole, so any energy it takes from the top through the air is likely to be wasted. Many of the higher back mode frequencies show up as 'dips' in the spectrum.

This is not to say the back should be 'dead' above the 'main back' pitch. Those dips seem to add to tone color: if you don't have them the sound can be dull. You want them to be sharply defined, though, so they don't cover too much of the spectrum.

Light backs, such as Honduras mahogany and cypress, may work differently. Most of my measurements are on Indian rosewood and such.

Remember: the ultimate 'reflector back' is the Ovation. Do you want your guitars to sound like that?

Yes, thank you Carlton. I do see the problem. I knew that any response would pretty much be a matter of opinion and personal preference. ("And I realize that everyone probably agrees with this in principle, but judgements about how this gets translated into real life are very subjective.")

I was hoping to trigger a discussion and hear all those with an opinion speak their mind. I know how I feel about it, but I'd like to have my ideas challenged - so I can either gain confidence or be convinced I need to change my mind.

I think this is another one of those situations where an answer isn't right or wrong - but better and best.

Thanks.

Well, here's part of my theory on it, for what it's worth. Which may be nothing. Forgive the non-technical language, please.

It would seem to me, that there is only so much energy being transmitted by the strings. And if that amount of energy is limited, you would want to get it to the place where it would do you the most good.
Now if energy moves through an object, it stands to reason that it will dissipate in it based on the ability of that material to hamper the energy transmission or to allow it. (Damping factor?)

If the energy is absorbed, then you would expect that most of it is absorbed at the two points where the strings are anchored, those being the neck and the top. So to my mind, you want to build the neck to be as stiff as possible so that it will absorb as little of the energy as possible, and the top to be designed so that as much of the energy as possible makes it in there. That's part one.
Part two is where the energy goes from there. If the sides are allowed to absorb energy, they can actually dissipate the energy within the top. Whereas, if they are made as stiff as possible so that they won't absorb as much energy, then the energy can remain in the top as vibration and therefore help the sound, especially the sustain of the note. If then the sound waves inside the box bounce off the back and cause the back to vibrate in harmony with or sympatheticly with the soundwaves, there can be a level of synergy between the top and back. My take is that the top is the primary driver of the energy, and that energy needs to be converted to soundwaves in the air, and not lost travelling through the sides.

So there's a bit of my theory, though certainly not original to me. I could be all wet.
Don Williams39038.5026388889

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

My thought is that the sides are mostly there to contain air and hold the back and the top apart from each other. I think most of the energy transmitted from top to back to top is air/sound pressure.

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Tickle your guitar daily, and it'll tickle you back.

Didn't I just say that?

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Maybe so but you used too many words and I just couldn't grasp it.

I guess it was all those big words you used Don, like "Damping factor" and "Whereas" or maybe "therefore"John How39037.6112037037

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Tickle your guitar daily, and it'll tickle you back.

[QUOTE=John How] My thought is that the sides are mostly there to contain air and hold the back and the top apart from each other. [/QUOTE]

I've said it before, I'll say it again, "John How is a very wise man!" Got that?

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

[QUOTE=John How] Maybe so but you used too many words and I just couldn't grasp it.

I guess it was all those big words you used Don, like "Damping factor" and "Whereas" or maybe "therefore"[/QUOTE]



Yeah, I was pokin' fun at myself after you said that, because I took 1000 words to say what you said in just a few.

A agree with Colin.

Hey, the rubber is being sent via UPS Ground, and should be there within a week.

_________________
"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

[QUOTE=tony]
Just noticed - milestone one has been reached! I'm no longer a Forum Newbie. I'm now a Groupie. Look out serge. Funny, I still feel like a Newbie.

[/QUOTE]

And now Tony, you are red with envy buddy!

I hope my silly comment about my new status didn't contribute to the change.

Don thanks for your reply. Your theory is worth a lot – and needs to be considered. And having offered it, the collective thought on the issue now has this as part of the sum. Thanks for speaking up.

“My take is that the top is the primary driver of the energy, and that energy needs to be converted to soundwaves in the air, and not lost travelling through the sides.”

Absolutely no doubt about the top being the “primary driver of the energy”, but how is it possible to prevent the energy from “travelling through the sides”? …how would it be possible to isolate the top from the sides without floating the top? And if you can’t prevent energy from travelling through the sides, then it seems that we need to determine the best way to control how that happen.

I don’t think anyone has attempted to design sides as a component that will produce sound. But I haven’t heard anyone really address the issue about a focused effort to design the sides for optimal use.

If I can’t stop the sides from receiving or reacting to the energy from the top by isolating it from the top, shouldn’t I be doing what I can to direct the energy from the top to another part of the guitar in an effort to release the energy where it can produce sound while it is being spent? Seems to me that the back (as an active componenet of the guitar) is at “the end of the line” as far as reacting to energy from the top - and the second best candidate as a component capable of producing sound from energy. IMO, the sides would be functioning the best when they act as a super conductor of energy in order to pass the energy from the top to the back plate without losses. IOW, if the sides can’t reflect energy back to the top (not so sure that would even be good) – then don’t let it dampen the energy, do everything you can to get it to the back efficently without losses.

Ok. I realize that some will say this is not all that important of an issue. But, is it worth discussing? Well, I think everyone agrees that all the components that make up a guitar have some affect on the total system. Some parts more than others. I’ve read through more than one discussion about the effects that different tuners have on the tone of a guitar, and just recently about the finish and the type glue we need to use to optimize our designs for tone and volume. I think Mairo said it best when he pointed out that its all the little things that contribute to the whole of making an exceptional sounding guitar – not any one thing.

My take is that thinner sides = better tone.

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Sure your "better tone" is not from the "Tornavoz" in your guitar Joshua?   

Interesting concept. Has anyone tried incorporating this idea outside of the spainish style guitars?

(Highjack my own thread.)

Enjoyed the visit to your site.

Tony,

Better tone from the tornavoz too ;)

Seriously though... thinner sides do seem to give a more complex and well rounded tone. Of course, I am from the school of building light, and I am making classicals, but I believe this could be translated into steel string guitars too.

Torres made his sides barely in excess of 1mm thick. They're made strong by the fact that they're curved, a drastic difference from the top or back.

But in the end, I'm very hesitant to say its all that important. I use solid linings, which stiffen the sides some, and I'm not concerned about it. Not as much as I'm concerned about someone looking inside my guitars and not seeing the braces neatly inlet into the linings... its easier to inlet into solid linings.

Yet on the other hand, everything makes a difference. There is a school of bulding that isolates the top with the theory that energy is not being absorbed in the neck, sides and back.

I subscribe to the opposite theory - that everything should work together as a whole. Even the guitarist

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I am pretty sure no one has used a tornavoz on a steel string guitar... my personal feelings are that it would have a negative effect. Its very important to approach a tornavoz guitar differently than a standard guitar, and I can't think of a way it would be applicable to steel string guitars. Would be interesting though.

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   I guess I can add my 2 cents.
   First off the top as we know is the driver. The actuall sound has been proved to be top driven. Bob Benedetto , Torres and I can't rememeber the 3rd builder. To prove a point they built guitars from local materials . Torres built on of paper Mache and one was made form an actuall pallet ( I think it was Taylor guitars and was called the pallet ). Benedetto built from local construction grade lumber )
   all 3 guitars when complete sounded pretty good according to the stories. I did get to see the benedetto one . The thing that you must learn is that the physics of the guitars are that Mass is the enemy.
   The lighter you can build and hold the guitar together the better your guitar will sound. I am not saying that the woods don't contribute as they do. But the lighter you can build the better.
    I build my guitars with sides as low as .075 and tops at .095. Backs can go to .100. The sides may absorb some energy but I feel it is the reflective quality of the wood acoustically that is important. Bracing of the top is the most important thing and then bracing of the back with sides a 3rd concern.
    THe tops movement creates a soundwave that travels through the air. There are some waves that will travel through the solids but it is the actuall sound waves that we are most interested in.
   This is one persons opinion. Rememeber that physics don't change and woods physical properties will influence the outcome of the acoustic refected tonal qualities.
john hall

I feel that the back vibrates in sympathy with the top, and doesn't take away energy from the top, but reinforces it.

The sides of course transfer energy from top to back, and the air chamber also energizes the back.

In re-voicing guitars, the back braces are crucial in allowing the back to give the most reinforcement possible, and in so doing, increase overall volume. I have found it helpful to think of the back as two, separate systems, upper and lower bout.

Sound is Round says that frequencies find resonance in rings inversely proportional to the frequency. (Sorry for the big words, John. ) The lower bout, being larger, can reinforce the lowest strings. The upper bout can reinforce the D and G string, and I find no noticeable effect on the B and high E--they just don't have enough energy to get it moving much.

I say "can" reinforce, because if the braces are too large, they dampen a significant part of each ring trying to vibrate, and reduce the amount of volume boost. The light, parabolic braces on backs of Martins from the golden era were an important part of their great sound.

I agree that mass is often the enemy. However, not enough can be a problem, too.   For both plates to work well, it is helpful if their thickness is what is needed to vibrate with the lowest frequencies the instrument needs to produce. Hardwood is denser than top woods, and can be thinner to allow the same diameter rings. Ideally, you should be able to feel the low E, tuned down to a D, vibrating in a ring inside the lower bout of the back. .095" seems to be right for most.

Standard factory top thickness of .125" seems about right to get the low E string on the perimeter of the bottom end of the lower bout. Thinner, and the E wants to resonate with a ring bigger than the guitar. My first three builds were about .010-.015", and I couldn't feel the bottom arc of lower bout vibrate until about the low G. The low E didn't have the tone of the G, although it was still loud. I later discovered that by rounding the ends of the X all the way to the kerfing, the tone and quality of the E came up to match that of the G. I'm convinced that the sides provided the extra good stuff, and that the usual corners on the ends of the X, which I originally had shaped, interferred with or absorbed the energy wanting to find resonance with the greatest distance from the cross point of the X. And a thinner top allows for larger rings for all frequencies, thus more surface area for the treble end.

And since small, thin topped guitars can work well, I think the sides must be where the bottom end generates. I wonder if too thin sides would be a problem from that perspective?

I once re-voiced a hand built guitar with very thick top and back. Top mic'd at .055" at the soundhole. The back thumped and pushed thick, too. As a consequence, the rings the low E generated on the top and back were about 3" in from the edges, and no matter how hard I drove the top, the lowest 2 inches of the top, and the outer 2 inches of the lower bout of the back, did not move at all!!! That's a lot of valuable real estate going to waste.

I reshape back braces parabolically both ways, and ususally remove 50-70% of the wood before vibration can be felt over the entire length of the braces. I've also observed that brace ends that do not tuck into the kerfing do not allow as much reinforcement. This may tie into the transfer of energy from the top through the sides, and ties in with my belief that the X should be tucked into the kerfing, too.

I don't doubt that stiff back guitars can sound great. And I know nothing about what I've heard described as "shaping" sound. For me, it's nice to feel I'm playing something that strums me back. Sure, you can dampen sound a little holding it, but the buzz is worth it.

I know, way too many words, but someone has to challenge Al for verbosity...

Scott







Scott van Linge39038.6086689815

Hey, I'd like to hear Brock Poling's take on all this...after all, he was a Physics major...

_________________
"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Scott
You may want to edit your size. .o25 is 25 thousandths and I don't think you actually build a top that thin. Martin specs that I like to go by are the older specs. the newer specs tend to overbuild for warrenty issues.
    I just did a repair on a gibby with a shaped laminate back , the gospel model and to tell the truth it was a punchy and loud of a guitar as I heard in a long time.
   Agree that to little mass is also not a good thing.You can overdrive things an that ins't good either. Balance is important . I look at things as a mechanical engineer as that is my influence. As a tool maker machinist I have to deal with forces so that influences me in my way of thinking.
   It never ceases to amaze me where the science of guitars and the art of building them take you.
    Thanks again for the information allways good to learn another angle . Looking to see what Mr Caruth has to offer.
john hall

Thanks for the Tip. Done. .125", it is. I've tried to edit my size before, but this time, it worked!!

Yes, those moulded laminate backs gave more reinforcement than a stock braced back, but not as much as one I can modify. I've worked on a few, including a Guild 12 string last spring. I could feel moderate vibration over the entire back.

Al, you there, dude? Get back when you can...

Scott

I wish I could edit my size....I'd take off a quick twenty