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  #1  
Old 06-15-2019, 12:22 PM
tippy5 tippy5 is offline
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Default Dana Bourgeois and back response.

https://acousticguitar.com/guitar-gu...eid=4ec58168ce

Real nice explanation of different algorithms and tonewood.
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Old 06-15-2019, 01:44 PM
Jaden Jaden is offline
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Thanks for passing this along; it was interesting reading especially concerning the issue of forward projection vs more enveloping sound.
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Old 06-15-2019, 01:57 PM
Mr.Sunburst Mr.Sunburst is offline
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Thanks for sharing.
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Old 06-15-2019, 02:25 PM
The Kid! The Kid! is offline
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Thank you for this.
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Old 06-15-2019, 04:22 PM
Alan Carruth Alan Carruth is offline
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A nice short explanation as far as it goes. I'd just add that an 'active' back can increase the output of the guitar in the lowest range of frequencies; the 'bass reflex' range. This runs (roughly) up to about the pitch of the open G fundamental, although the greatest effect is around an octave lower than that, give or take. Above that range, and especially from the open high E fundamental up, a back that is too loose will cost power.

Here a lot depends on the mass of the back (IMO) and, to a lesser extent (again IMO), the damping. A heavy back with low damping is probably the 'best', which explains the popularity of rosewoods. In any event, most of the sound is still in the top: a well made back of, say, maple, can be 'better' than a poorly made one of Brazilian rosewood. It is distressingly easy to make a bad guitar from good wood.
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Old 06-15-2019, 04:35 PM
Tnfiddler Tnfiddler is offline
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Thanks for sharing! A great article from one of the most knowledgeable luthiers In the business concerning make wood into premier instruments!
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Old 06-16-2019, 12:03 AM
Mycroft Mycroft is offline
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All that I can say is that when I take care to not let my fat belly muffle the back, the sound of my McAlister becomes absolutely three-dimensional.
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Old 06-16-2019, 12:19 AM
jrb715 jrb715 is offline
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Alan,

Thank you for adding to the information. A question: so is a lightly damped cocobolo (a relatively heavy wood) theoretically an ideal back wood?
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Old 06-16-2019, 08:38 AM
Mycroft Mycroft is offline
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Quote:
Originally Posted by Alan Carruth View Post
A nice short explanation as far as it goes. I'd just add that an 'active' back can increase the output of the guitar in the lowest range of frequencies; the 'bass reflex' range. This runs (roughly) up to about the pitch of the open G fundamental, although the greatest effect is around an octave lower than that, give or take. Above that range, and especially from the open high E fundamental up, a back that is too loose will cost power.

Here a lot depends on the mass of the back (IMO) and, to a lesser extent (again IMO), the damping. A heavy back with low damping is probably the 'best', which explains the popularity of rosewoods. In any event, most of the sound is still in the top: a well made back of, say, maple, can be 'better' than a poorly made one of Brazilian rosewood. It is distressingly easy to make a bad guitar from good wood.
Increase the output of the guitar where, Alan? Out front, or from the perspective of the player. A I had understood it, a more active back will take some of the out front perceived volume but add to the effect on the tone that the back has. After all, the energy input is always going to stay the same: what is imparted into the guitar by the strings.
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Old 06-16-2019, 08:57 AM
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rick-slo rick-slo is offline
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Quote:
Originally Posted by Mycroft View Post
After all, the energy input is always going to stay the same: what is imparted into the guitar by the strings.
You can have a guitar string stretched out between two nails in a board and picked - same energy.
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Old 06-16-2019, 09:04 AM
Mycroft Mycroft is offline
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Quote:
Originally Posted by rick-slo View Post
You can have a guitar string stretched out between two nails in a board and picked - same energy.
Exactly. It is what the guitar does with that energy...
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Old 06-17-2019, 09:50 AM
freaktone freaktone is offline
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Thanks for posting this. Good read! My question is: how did the Gibson luthiers from the 30s and 40s get such huge projection with backs that were less stiff?
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Old 06-17-2019, 10:01 AM
zmf zmf is offline
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In general, do the various guitar builders adopt an "active" or "stiff" back approach? Or will a given builder vary the approach depending on the model (e.g. dread vs parlor)?

I'm guessing that Santa Cruz, for example, tends to use the "active" back approach.
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Old 06-17-2019, 10:47 PM
tippy5 tippy5 is offline
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Quote:
Originally Posted by freaktone View Post
Thanks for posting this. Good read! My question is: how did the Gibson luthiers from the 30s and 40s get such huge projection with backs that were less stiff?
This subject does open up a lot of questions.

I have a 5lb Macassar ebony back guitar that apparently relies on the top for the tone. I have a late 50's Gibson that I can feel in my ribs.

I know that too thin of sides can cause the neck joint to move and need a reset. I had a Martin that had two CS warrantied resets and on the third go round they declined another reset. They said the sides were no longer up for the job. BTW: They were wonderful through both 7 month repair cycles.

So a question is how light or active can a back be designed to and matched for what grade stiffness of braced spruce top?

Are there some folks who commission active lightly built sides and backs for a type of top? Hmm...
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Old 06-17-2019, 11:09 PM
Dustinfurlow Dustinfurlow is offline
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Really cool read, thank you for sharing!
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