I've played 4-brace Favinos that had no bass to speak of, and played 5-brace Duponts that had a ton of bass. I honestly don't know of any way to predict how much bass a given guitar is going to have, especially a petite bouche. Even within a given production run of guitars made from the same wood, they'll all sound different - so I'm told.
I never considered it or heard this discussed before, but I think guit box is onto something when he talks about the bridge and braces being closer to the center of the lower bout on the short scale guitar. I guess the two designs have more differences that the obvious ones. Maybe the entire petite-bouche long scale guitar is a result of the law of unintended consequences...
Something Martin has done over the years is move the position of the x-brace N and S - anybody know anything about the reasons for this? Is this something similar to what guit box describes?
My own observations - I've never played any 14-fret Selmer type guitar that has the bass "boom" of a well made d-hole 12-fret, even though the body of the d-hole is typically slightly smaller. The shorter scale can't seem to generate the "growl" that a good Favino has on the low notes, though.
All things being equal, increasing mass lowers the resonance frequency of a vibrating substrate.
The strange part is that this doesn't necessarily increase bass response. It increases the "Q" of the the part of the system that is acting as a transducer (in this case, the soundboard) but the effect of this on the system is not perfectly correlated.
I don't really know what the resonance fundamental of a soundboard is, but the lowest note on a guitar is about 81hz and the highest is... what.. a bit more than three octaves higher? Just call it 80hz - 800hz to make the numbers easy to work with. You have a soundboard that probably weighs in the 9 gram range... maybe 15 grams when you figure in a bridge, a moustache, a pickguard & some finish. The suspension is rigid and loaded with dozens of pounds of downforce... Given all this - I would have to believe that the resonance frequency of the soundboard is "hecka-high" (technical term But seriously... removing a 1 gram chunk of wood from a 15 gram system whose suspension is so stiff that it is completely dominant and whose fundamental resonance is probably octaves above anything resembling a bass frequency... this loss of mass just isn't going to have that big of an effect on the bass. What's more likley is that the braces comprise a portion of the suspension and that the removal of one of the four load bearing braces makes the suspension more compliant.... (the 5th brace is primarily to support the fingerboard & neck over the body)
There is an interesting book called something like: "Luthiery for the left side of your brain" that I've been meaning to get & read. There are so many concepts that translate well between transducer design and speaker system design and guitars. Some of them have obvious and clear analogies... others are less clear because though the equations are probably similar - the variables are weighted much differently and so the nature of the system is not quite as intuitive... for example... in this discussion it's hard for me to predict how much changing one variable will affect the system because I'm used to dealing with systems where the compliance of the suspension is a relatively small (but sensitive) variable and in guitars it seems as though it could be the dominant (or one of the dominant) variables. So... is it still as sensitive to change? What is the relationship between soundboard resonance and system resonance? etc.. it's like trying to solve a math problem with multiple variables when you don't know any of the variables... to solve it you must have some constants or at least have a good gut feel for the the interrelationship between the variables so you can give some of them "common sense" values and approach the problem that way. So, to make a very long story as short as I can: "I don't know... but I'm on the path to finding out... and in the interim the only thing I can tell you is that the interrelationships of the pieces of the system you're discussing are probably not as linearly correlated as you might imagine."
I've never played a Fox ergo - I may get to in March...I hear there is a show in the college down the street from me. (in West Linn, Oregon)
You get one chance to enjoy this day, but if you're doing it right, that's enough.
Comments
I never considered it or heard this discussed before, but I think guit box is onto something when he talks about the bridge and braces being closer to the center of the lower bout on the short scale guitar. I guess the two designs have more differences that the obvious ones. Maybe the entire petite-bouche long scale guitar is a result of the law of unintended consequences...
Something Martin has done over the years is move the position of the x-brace N and S - anybody know anything about the reasons for this? Is this something similar to what guit box describes?
My own observations - I've never played any 14-fret Selmer type guitar that has the bass "boom" of a well made d-hole 12-fret, even though the body of the d-hole is typically slightly smaller. The shorter scale can't seem to generate the "growl" that a good Favino has on the low notes, though.
The strange part is that this doesn't necessarily increase bass response. It increases the "Q" of the the part of the system that is acting as a transducer (in this case, the soundboard) but the effect of this on the system is not perfectly correlated.
I don't really know what the resonance fundamental of a soundboard is, but the lowest note on a guitar is about 81hz and the highest is... what.. a bit more than three octaves higher? Just call it 80hz - 800hz to make the numbers easy to work with. You have a soundboard that probably weighs in the 9 gram range... maybe 15 grams when you figure in a bridge, a moustache, a pickguard & some finish. The suspension is rigid and loaded with dozens of pounds of downforce... Given all this - I would have to believe that the resonance frequency of the soundboard is "hecka-high" (technical term But seriously... removing a 1 gram chunk of wood from a 15 gram system whose suspension is so stiff that it is completely dominant and whose fundamental resonance is probably octaves above anything resembling a bass frequency... this loss of mass just isn't going to have that big of an effect on the bass. What's more likley is that the braces comprise a portion of the suspension and that the removal of one of the four load bearing braces makes the suspension more compliant.... (the 5th brace is primarily to support the fingerboard & neck over the body)
There is an interesting book called something like: "Luthiery for the left side of your brain" that I've been meaning to get & read. There are so many concepts that translate well between transducer design and speaker system design and guitars. Some of them have obvious and clear analogies... others are less clear because though the equations are probably similar - the variables are weighted much differently and so the nature of the system is not quite as intuitive... for example... in this discussion it's hard for me to predict how much changing one variable will affect the system because I'm used to dealing with systems where the compliance of the suspension is a relatively small (but sensitive) variable and in guitars it seems as though it could be the dominant (or one of the dominant) variables. So... is it still as sensitive to change? What is the relationship between soundboard resonance and system resonance? etc.. it's like trying to solve a math problem with multiple variables when you don't know any of the variables... to solve it you must have some constants or at least have a good gut feel for the the interrelationship between the variables so you can give some of them "common sense" values and approach the problem that way. So, to make a very long story as short as I can: "I don't know... but I'm on the path to finding out... and in the interim the only thing I can tell you is that the interrelationships of the pieces of the system you're discussing are probably not as linearly correlated as you might imagine."
I've never played a Fox ergo - I may get to in March...I hear there is a show in the college down the street from me. (in West Linn, Oregon)