What tone comes from what part?

[Photojeep]

I tried using the search function but since there seems to be about a gazillion posts I found it to be more frustrating than illuminating so I'm asking you all to educate me.

Is there any consensus as to which tones come from which portions of a guitar's top?

I know that materials, build, builder, and shape all contribute to a guitar's overall tone and there is no hard and fast rule but, all things considered, are certain areas of a top "generally considered" to contribute to a certain tonal range?

In consideration of the answers I may (or may not) receive, and since it seems to me that the lower bout probably contributes more bass tones than the upper bout will, does "forward shifted" braces generally contribute more bass response than non forwarded shifted braces?

Just thought I'd ask.

Best,
PJ

[warfrat73]

To answer part of your question, yes, forward shifted braces are general considered to allow for greater bass response.

[tbeltrans]

My guess is that, since without ears we wouldn't hear the guitar being played, the tone comes from the ears.

Many discussions seem to indicate that the back and sides have little to do with the guitar's tone, but the top is the real deal.

I don't have the knowledge to dispute or support that, so all I can do is repeat it and hope people think I know more than I actually do.

Tony

[mercy]

Of course the top and braces produce most of the sound but the style of braces makes a huge difference so I would put braces at the main sound producer then the top then the back. The neck hopefully doesnt produce much sound nor do the sides. The neck and sides can reduce the sound of the guitar but do not add.

[Alan Carruth]

In the bass range the guitar acts like a 'bass reflex' speaker cabinet. There is a Helmholtz-type 'main air' resonance, where air is moving in and out of the sound hole, like blowing across the mouth of a wine bottle. The lower bout of the top acts like a loudspeaker cone, moving in and out at the 'main top' resonant pitch. Air moving in and out of the hole changes the pressure in the box, which pushes on the top, while the top moving in and out pushes air through the hole, so these two resonances work together, and each one shifts the pitch of the other from what it would be in isolation. Usually the 'main air' resonance on a guitar comes in somewhere around G on the low E string, although it can be as low as F and and as high as A# on 'normal' flat tops. The 'main top' resonance is usually about an octave higher, right around the pitch of the open G string, although, again this varies.

As you go up in pitch there are a number of other resonances of the air and the wood that can also produce sound. These tend to be more variable, and there can be a lot of them. Like the low range resonance they often work together, and this is what determines the character of each particular guitar.

I'll note here that there is not a 'bass side' or treble side' of the top in terms of where the sound comes from. Low notes come from the whole guitar, and higher sounds tend to be produced in smaller areas.

Altering the brace layout and profiling changes the distribution of mass and stiffness on the top, and thus all the resonant pitches, more or less. Although guitars that are built similarly from similar wood will share a lot of their sound in common, it's probably impossible to make 'identical' guitars and have them sound exactly the same. Small differences in the local properties of the wood can change the high frequency output in ways that are easy to hear, but impossible to control directly in advance.

I have a customer who designs satellites for a living. He has software on his work computer that can predict the way the finished satellite will vibrate, which enables him to make sure nothing will shake off during the launch. He tried using it to evaluate the way a guitar vibrates, but it was too complex for his software. This is not rocket science; it's harder....

[Earl49]

Originally Posted by Alan Carruth

.....This is not rocket science; it's harder....

I love this statement! One only has to look at Chladni patterns on a guitar top to get a sense of just how complex the topic is.

[tbeltrans]

Originally Posted by Alan Carruth

In the bass range the guitar acts like a 'bass reflex' speaker cabinet. There is a Helmholtz-type 'main air' resonance, where air is moving in and out of the sound hole, like blowing across the mouth of a wine bottle. The lower bout of the top acts like a loudspeaker cone, moving in and out at the 'main top' resonant pitch. Air moving in and out of the hole changes the pressure in the box, which pushes on the top, while the top moving in and out pushes air through the hole, so these two resonances work together, and each one shifts the pitch of the other from what it would be in isolation. Usually the 'main air' resonance on a guitar comes in somewhere around G on the low E string, although it can be as low as F and and as high as A# on 'normal' flat tops. The 'main top' resonance is usually about an octave higher, right around the pitch of the open G string, although, again this varies.

As you go up in pitch there are a number of other resonances of the air and the wood that can also produce sound. These tend to be more variable, and there can be a lot of them. Like the low range resonance they often work together, and this is what determines the character of each particular guitar.

I'll note here that there is not a 'bass side' or treble side' of the top in terms of where the sound comes from. Low notes come from the whole guitar, and higher sounds tend to be produced in smaller areas.

Altering the brace layout and profiling changes the distribution of mass and stiffness on the top, and thus all the resonant pitches, more or less. Although guitars that are built similarly from similar wood will share a lot of their sound in common, it's probably impossible to make 'identical' guitars and have them sound exactly the same. Small differences in the local properties of the wood can change the high frequency output in ways that are easy to hear, but impossible to control directly in advance.

I have a customer who designs satellites for a living. He has software on his work computer that can predict the way the finished satellite will vibrate, which enables him to make sure nothing will shake off during the launch. He tried using it to evaluate the way a guitar vibrates, but it was too complex for his software. This is not rocket science; it's harder....

It is always a pleasure to have one who really does know what he is talking about, pop in and set things straight. Since I readily admit that I don't, I just have fun with it so I can sound like those who THINK they do. Those who actually get their hands dirty and study to develop the in depth of knowledge about their craft are the ones to listen to. I enjoy the fruits of the efforts of those who actually built these instruments.

Tony

[srick]

Originally Posted by Alan Carruth

I have a customer who designs satellites for a living. He has software on his work computer that can predict the way the finished satellite will vibrate, which enables him to make sure nothing will shake off during the launch. He tried using it to evaluate the way a guitar vibrates, but it was too complex for his software. This is not rocket science; it's harder....

That's really funny Alan! I have always wondered whether Charlie Kaman (Ovation Guitars) ever passed on his work to someone, As you likely know, he also owned Kaman Aircraft and used their expertise in vibration vs. helicopter blades to design the Ovation Guitar. Or at least that's the story that was provided by the marketing department. It's very possible that he created the 'lyrachord' bowl using simple trial and error!

[srick]

I just did a quick search and found this. I think that it pretty much answers the question that I posed above . A: "Trial and Error"

ovation bracing'.jpg

[mc1]

Originally Posted by Alan Carruth

I have a customer who designs satellites for a living. He has software on his work computer that can predict the way the finished satellite will vibrate, which enables him to make sure nothing will shake off during the launch. He tried using it to evaluate the way a guitar vibrates, but it was too complex for his software. This is not rocket science; it's harder....

Perhaps because the satellite is designed to hold together while a guitar top is designed to vibrate (and not fall apart).

[Mr. Jelly]

Originally Posted by Alan Carruth

In This is not rocket science; it's harder....

I knew it! Thanks

[KevinH]

Originally Posted by mc1

Perhaps because the satellite is designed to hold together while a guitar top is designed to vibrate (and not fall apart).

The physical principles are still the same. I'd guess it's the difficulty in making a physically realistic model of mechanical response of wood and measuring all of the relevant material properties.

[justonwo]

Yes, there is a great deal of consensus. This thread is about to demonstrate that fact. Watch for all the vehement agreement.

[musicman1951]

Coincidentally, I just read this from Dana Bourgeois this AM:

It should come as no surprise, then, that while different species tend to exhibit recognizable median characteristics, variation within species often creates ambiguity. To note just one example, a slightly heavy carpathian spruce top could easily be mistaken for an Adirondack top of average weight; numerous factors—accuracy of quartering, curing history, where a set was cut from the log, and so on—could also conspire to produce remarkably similar long-grain and cross-grain stiffnesses and internal damping characteristics. To further confuse the beholder, the color and overall appearance of these two species is almost identical. Equally confounding similarities also exist between other pairs of species.

While not directly related to bracing, I think the gist of the argument stands for both: the sound of a guitar is not that predictable, and there is no substitute for playing a bunch until you find the sound you're looking for. Wood is interesting stuff.

[Alan Carruth]

A big part of the 'problem' with guitars is the complexity. It's possible to find something like a dozen different modes of vibration in a guitar top below about 1000 Hz. The back and the air inside the box each have about the same number. As you go up in frequency these get closer together in terms of pitch.

When we talk about 'the frequency' of a resonance it's not usually as tightly defined as it is for a stretched string. Once you get your A string tuned you know that it will vibrate at 110 Hz (or close multiples of that), with almost no energy outside of that frequency. That's why it sounds 'musical'. This has to do with the fact that there's very little loss in a string; the friction in the material is low, and it doesn't have to slosh it's way through a lot of air to vibrate, so it pretty much just does what the equations say it should do.

The losses in a guitar top or back, or in the air in the box, are higher. That's why a top goes 'thump' when you tap it, rather than 'bong'. The frequency response is spread out over a wider 'band width' than that of the string by the losses, so the pitch is not so well defined, and the vibration dies out faster. There are ways of defining the band width mathematically based on measurements.

When you have two things vibrating, and they're coupled together (the way the top and the air are in the 'bass reflex couple), they can exchange energy easily if the band widths of the resonant frequencies overlap. That really gets to be the case on the guitar when you get up into the range around 600-800 Hz; there are lots of resonances that can 'feed' each other. In the process, as with the 'bass reflex couple' each resonance pushes the others around a bit in terms of pitch. When there are a lot of them, as there are on the guitar, it simply becomes impossible to predict where everything is going to end up in advance. About all you can do is to put the thing together, and see what it does. If it's close to what you want sometimes you can tweak it a bit, but in the process you're almost certain to bump into something else. In other words, the system is 'chaotic' to some degree.

The result is that, as far as I can tell, it's probably impossible to make 'identical' guitars that will sound 'alike'. Even very small differences in material properties or construction become magnified by the complex response. That's probably what tripped up the computer.

I said that this as a 'problem', but you'll note it's in ellipses. If the task is to make something predictable, then the guitar is too complex. If, however, the task is to make something that's 'interesting' that complexity is what you want. It gives the player the means to control the sound and change it 'on the fly'. A student of mine, who wrote software for synthesizers at one point, said that the guitar is the hardest instrument to synthesize well, and that complexity is the reason. There simply are not enough inputs on a keyboard to give the needed level of control. Many of the 'traditional' features of the guitar, such as the shape and the location of the sound hole, seem to be calculated to make the response more complex, and thus the tone more 'colorful'. If you 'rationalize' the design too much, it's no longer a guitar.