MIMF

It has been a winter of heat gunning off, necks, fingerboards, bridges, tops, and backs.

Built two guitars, Guitar Six in Fall and Guitar 7 with reverse fan bracing and Kasha placed soundhole.

Guitar Seven first- It's fit for firewood or more experiments. Over braced with a stiff top. and bridge needs to be moved outward as 20 cents sharp all over (and at 12th fret)

Guitar Six- DEAD ON spot on in tune all over every fret no buzzing clear sounding guitar but not too loud or bassy. So.... I cut the back off it and sanded a lot off the fan braces and put a Alaskan Yellow Cedar back on it vs. Indian Rosewood, (wanted to try that for resonance plus a price thing as well.)

I put a board clamped to fingerboard and bridge to hold that straight while gluing on new back. Anyhow still in tune and the action is the best action on a classical I ever played. plays like an electric guitar!

Here is for the scientists out there. covered strings with hand and bang the top the note of the top is B plus 20 cents. Bang on the back the note is the same B plus 20 cents.

OK Now put my body up against the back to stop it from vibrating and banged the top- different notes you can get. Same results to the back when you hold your body against the top and bang the back.

But B when bang either with guitar free.

Other things I read Jeffrey Elliot article in GAL big Red Book 5 and he is probably right about harmonic bars and sound hole placement.

To move the sound hole upward to increase "vibrating wood near bridge" didn't do anything for me but bad. (Oh the 6th guitar has the sound hole at the 17th fret instead of the 19th) The side sound "port" seemed to be a great improvement. It is mostly for the player. But 99% of the time it is me in my chair playing for myself anyway!

The 6th guitar has been fooled with because I accidentally domed the top at the bridge 1/8" higher, So... I epoxy heightened the fingerboard to get that corrected. (In Fall)

The reason I just tore off the back and put a new back on 6 was I am doing all this to wind up with a fairly good/ great guitar not a "OK" one. I could buy an "OK" one from the store.

Well I need to lighten up on braces. Although not ultra light because I am a chord (jazz) player. I will put the sound hole back at the 19th fret on my future guitars. I will master knowing what I am doing with fingerboard/ neck angle bridge height / string action.

I am in a learning period of mixed lucks and mistakes.

OH, what do any experts think about that "B" note resonance?

So Dennis, I have a few questions for you. Without addressing your guitars at all, and trying not to be critical, I want to ask you about your learning process. First, you are to be commended for jumping in and building some instruments of your own, and you have thought about it and had the courage to try your ideas. But I question how, and why, you go about it this way instead of listening to others who have gone this road before you, and learned the things you are now finding out? And with all respect, some of us told you these things also. Jeffrey Eliott is also right, and he, just like those of us here, have built many guitars and have learned these things. Why not listen to, and take the word of those who want to tell you things and then learn from others' experience instead of just taking your own road and finding out at the end that you should have listened all along?

Assuming that picture is of #6 and #7, which is which?

Dennis Weaver wrote:
Guitar Six- DEAD ON spot on in tune all over every fret

Try as I might, I have found this impossible to achieve even with my best intonation and compensation efforts, it all seems a bit of a compromise to me, some notes are spot on, but there are as many that are sharp and as many flat, probably due to the way that an octave has been divided mathematically by 12?

Alan Carruth wrote:Assuming that picture is of #6 and #7, which is which?

Dennis Weaver wrote:Guitar 7 with reverse fan bracing and Kasha placed soundhole.

#7 on the right, I guess.

Bob Matthews wrote:

Dennis Weaver wrote:
Guitar Six- DEAD ON spot on in tune all over every fret

Try as I might, I have found this impossible to achieve even with my best intonation and compensation efforts, it all seems a bit of a compromise to me, some notes are spot on, but there are as many that are sharp and as many flat, probably due to the way that an octave has been divided mathematically by 12?

A guitar is not going to intonate well to anything but equal temperament because of the 12th root of 2 division of the fretboard. So if you're looking for Just, for example, you'll have many more problems than trying for accurate equal temperament. Decent nut and saddle compensation helps, but a responsive guitar will always suffer from some out-of-tuneness near the major body resonances due to over-coupling. What that means is that two resonators with individual natural frequencies that are close together (within a few Hz) will have slightly different frequencies when they are coupled together, like a string and a guitar top are coupled. The frequency of the higher resonance is pushed a little higher and the lower one a little lower in a sort of repulsion effect. So, if a guitar top's main resonant frequency happens to fall on say 221Hz, just a little sharp of A, an A note played on the 3rd string with the G tuned true will tend to play flat. In bad cases it can be up to 30 cents flat, even if everything else is "right". You can arrange things to reduce this effect, but on a responsive acoustic guitar it will always be there to some degree and that ultimately limits how accurately in tune it will play. These and related issues are why you seldom find really responsive guitars from "bulk" manufacturers. The easiest way to fix these issues is to make the guitar less responsive!

Thanks for pointing out the soundhole thing, Trevor: I should have figured that out. Schneider used to put the hole up in the bass side corner, and maybe that's what threw me off. The hole on #6 is placed pretty high as well. If you look at William Allen's article on air modes in American Lutherie #1, or the first 'Big Red Book' from the GAL, you'll see that that would tend to drop the air mode pitch. It won't be as much as moving it up into the corner would do, of course, but I've found it to be more effective than you might think.

As for the top and back having nearly the same tap tone when coupled, and different when one is damped: this is related to Trevor's answer about intonation. When the two plates are 'free' they couple strongly, and can shift each other's pitches. Damping one allows the other to vibrate more or less at it's own pitch, except, of course, for all the other things it's coupled with that alter it. It's a bit unusual for them to end up on nearly the same pitch when they're coupled, and that suggests to me that there's something else in that range as well. This can get tricky to track down, as nothing will 'hold still' when you change something else. And all of that assumes that what you're hearing as the top and back tap tones are really that: usually the 'main air' mode masks those pretty effectively, and you can't hear the 'wood' tones without blocking the sound hole (which, of course, alters the way they couple...).