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  #46  
Old 06-07-2018, 06:26 PM
printer2 printer2 is offline
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Originally Posted by Herb Hunter View Post
I don’t think the term, transducers, applies to acoustic guitars, they are passive radiators. Of course, if they are equipped with pickups, then they are radiators equipped with a transducer or two.
I have enough trouble searching this age old brain of mind for 'a' word never mind the right word. But you are right, a transducer takes one form of energy and converts it into another. I do not think of them as passive radiators either as passive radiators are usually thought of in the speaker context. Acoustic coupler perhaps.
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  #47  
Old 06-07-2018, 06:42 PM
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Originally Posted by dneal View Post
Sorry, but I disagree. I think the commonalities are important, to recall why we finish wood in the first place (and that's the context of the thread). The way you go about finishing a guitar and a piece of furniture might differ in material and method, but the reason is the same.



I said fundamentals for a reason. Yes, that is a "broad stroke" and was intended to be. The only point being missed is by you. A mortise is a mortise is a mortise. It doesn't matter if you're timber framing, assembling a cabinet door or attaching a neck to a guitar. Of course they're different applications, using different types and dimensions of lumber; but it's still a fundamental and common to all. Controlling for humidity is a fundamental of woodworking.
People sometime are surprised at some of the things I pull out of my hat but I tell them, really there are only two options available when making something. Either you take away something or you add to it. Whether you cut with a saw drill with a bit, use an EDM machine to blast particles away, bolt a joint together, glue a joint, weld it, it is all the same. In that context then your table is a guitar.

But when you talk about using solid woods and you do not want them to crack, a table where the edges are not captured resulting in limited stresses building up due to moisture loss as compared to a guitar that binds the soundboard and back. My monitor and keyboard are on an oak desk that I built many years ago. It went through the same low humidity season as the guitar bodies I have built but have not been able to build necks for them. A number of the bodies have cracked over the winter, the desk has not. They may be both built out of wood and some of the same joints used in both are the same but the peculiarities of the guitar limit the mitigation that you can use in a piece of furniture. But then again, we do build plywood guitars.
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  #48  
Old 06-07-2018, 08:08 PM
dneal dneal is offline
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Originally Posted by printer2 View Post
People sometime are surprised at some of the things I pull out of my hat but I tell them, really there are only two options available when making something. Either you take away something or you add to it. Whether you cut with a saw drill with a bit, use an EDM machine to blast particles away, bolt a joint together, glue a joint, weld it, it is all the same. In that context then your table is a guitar.

But when you talk about using solid woods and you do not want them to crack, a table where the edges are not captured resulting in limited stresses building up due to moisture loss as compared to a guitar that binds the soundboard and back. My monitor and keyboard are on an oak desk that I built many years ago. It went through the same low humidity season as the guitar bodies I have built but have not been able to build necks for them. A number of the bodies have cracked over the winter, the desk has not. They may be both built out of wood and some of the same joints used in both are the same but the peculiarities of the guitar limit the mitigation that you can use in a piece of furniture. But then again, we do build plywood guitars.
The thing is, we were originally talking about finishes. Furniture (and finishes) were introduced. Then, the argument was made that a guitar and table have nothing to do with each other.

If we're talking musical instruments, that's a good point. When we're talking about woodworking (particularly finishing wood), it's ludicrous. The reason you apply a finish to a guitar or a table is the same in each case. The type of finish and manner of application can of course differ - but that doesn't change the reason why you're applying it.

The point of the breadboard end was also in the context of woodworking, not in the context of specific wood products or projects. The point was simply that you have to consider the effects humidity may cause when working with wood. How you deal with this varies, and is why I listed a range of situations. I have a hard time understanding why some folks can't comprehend this simple point.
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  #49  
Old 06-08-2018, 08:52 AM
gr81dorn gr81dorn is offline
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Quote:
Originally Posted by dneal View Post
I have a hard time understanding why some folks can't comprehend this simple point.
It's because you keep changing the conversation to try and win the conversation instead of reading the comments and understanding the points being made - very competent and clear ones.

Proof is in your statement:

Quote:
Originally Posted by dneal View Post
the argument was made that a guitar and table have nothing to do with each other.
That isn't even close to an accurate statement. That statement said that they only share inconsequential similarities and within the context of the conversation, weren't really comparable. You're omitting the context, the substance supporting the statements and the entire point altogether.

This doesn't need to be any kind of argument like you keep wanting it to be. It's really quite simple - You make a soda can very differently than you make an airplane, despite them both being made of aluminum. Same thing here.

The OP asked why the underside of soundboards aren't finished and the answer is because the type of product, material and end use doesn't render it necessary. Other products that are made of wood may render it necessary. Plain and simple.
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  #50  
Old 06-08-2018, 10:37 AM
charles Tauber charles Tauber is offline
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Quote:
Originally Posted by gr81dorn View Post
You make a soda can very differently than you make an airplane, despite them both being made of aluminum.
You might be on to something here: deep-drawing of aircraft bodies.
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  #51  
Old 06-08-2018, 11:35 AM
dneal dneal is offline
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Originally Posted by gr81dorn View Post
It's because you keep changing the conversation to try and win the conversation instead of reading the comments and understanding the points being made - very competent and clear ones.
Et tu gr81dorn?
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  #52  
Old 06-08-2018, 11:36 AM
arie arie is offline
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Quote:
Originally Posted by Earl49 View Post
I see this supposition all the time. I've spent a lot of time looking at absorption data for a wide variety of materials (34 years full time in the acoustics business) and near as I can tell, the only difference that might occur in absorption / reflectivity of sealed versus raw wood occurs at 30 kHz and above - a far higher frequency than a normal human ear has ever heard. Our range of hearing is typically 20 Hz - 20 kHz. Even a dog or cat might not hear frequencies that high, except in their youth. It is quite the technical challenge to even measure absorption coefficients at those frequencies.
very interesting. >30khz? finally somebody with potential data -thx!

-so we've got an idea of reflectance/absorption.

-plate hardening data anyone?

-tangible moisture barrier data seems like a wash...

-opinions of "proper" crafsmanship seems like another wash...

Last edited by arie; 06-08-2018 at 11:44 AM.
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  #53  
Old 06-08-2018, 11:53 AM
Alan Carruth Alan Carruth is offline
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arie asked:
"-plate hardening data anyone?"
See "On the acoustical properties of violin varnish" by Martin Schleske, 'Journal' of the Catgut Acoustical Society, Vol. 3, #6, pp.27-43, November of '98. Along with the 'usual suspects' of violin varnish he covers nitrocellulose, and drying oils. I've already mentioned some of his results.
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  #54  
Old 06-08-2018, 11:59 AM
cobalt60 cobalt60 is offline
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Perhaps a more productive approach might be to list builders who do apply finish to the inside of their soundboards, and those who do not. Individuals can then determine if they prefer one cohort or the other, or have no discernable preference.


Trying to deconstruct the complex network effects and suggest how a finished top might influence the sound of YOUR build is quite a stretch.
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  #55  
Old 06-08-2018, 12:21 PM
printer2 printer2 is offline
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Quote:
Originally Posted by dneal View Post
The thing is, we were originally talking about finishes. Furniture (and finishes) were introduced. Then, the argument was made that a guitar and table have nothing to do with each other.
The funny thing about posting in forums, sometimes the topics branch off in other directions. I was answering points being made, made my own points. I do not find this at all too unusual.
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  #56  
Old 06-08-2018, 12:22 PM
arie arie is offline
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Quote:
Originally Posted by Alan Carruth View Post
arie asked:
"-plate hardening data anyone?"
See "On the acoustical properties of violin varnish" by Martin Schleske, 'Journal' of the Catgut Acoustical Society, Vol. 3, #6, pp.27-43, November of '98. Along with the 'usual suspects' of violin varnish he covers nitrocellulose, and drying oils. I've already mentioned some of his results.
indeed. thx. though violins are a different beast, a fair amount of the core principles apply.

although, i wouldn't want to use potassium silicate on my guitars
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  #57  
Old 06-08-2018, 12:24 PM
arie arie is offline
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Quote:
Originally Posted by cobalt60 View Post
Perhaps a more productive approach might be to list builders who do apply finish to the inside of their soundboards, and those who do not. Individuals can then determine if they prefer one cohort or the other, or have no discernable preference.


Trying to deconstruct the complex network effects and suggest how a finished top might influence the sound of YOUR build is quite a stretch.
what good would a list do? divide and categorize people even more than they already are?

how about a list of ambidextrous luthiers? my left hand might chisel in more tone than my right...
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  #58  
Old 06-08-2018, 12:40 PM
Edgar Poe Edgar Poe is offline
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"Wood is dead: it does not need to breath.

Wood is hydroscopic, meaning it absorbs and desorbs moisture in response to its environment. As it does so, it changes size - and geometry. There is almost nothing that can be done to prevent it from doing so. At best, one can slow down the absorption and desorption by applying a finish to its surfaces."

Charles,
That sounds very much like a description of the action of breathing.
I do not think jschmitz5 was suggesting the wood is living, and actually breathing air. Rather that it takes in something, expands, and later releases that something, and shrinks. Like your lungs.

Ed
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  #59  
Old 06-08-2018, 01:17 PM
Herb Hunter Herb Hunter is offline
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Quote:
Originally Posted by Alan Carruth View Post
Herb Hunter wrote:
"I don’t think the term, transducers, applies to acoustic guitars, they are passive radiators."

Actually, IMO, guitars are precisely transducers: devices for changing one sort of energy into another. In this case they change the somewhat regular application of force by your right hand into sound. With a bit of an assist from your left hand it can even be musical! Note that guitars are not 'amplifiers': they don't use an external power source to reinforce a small signal and turn it into a louder one. All of the power comes in from your hands, and most of it is 'lost' in the process of being turned into sound.
That is an interesting way to look at it. To my way of thinking the kinetic energy of the right hand is transferred to the guitar. Once transferred it is still kinetic energy. I don’t see a change from one form of energy to another as when electric energy is converted to sound waves or when torque applied to a piezoelectric crystal, motion, is converted into electric current.
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  #60  
Old 06-08-2018, 02:33 PM
cobalt60 cobalt60 is offline
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Quote:
Originally Posted by arie View Post
what good would a list do? divide and categorize people even more than they already are?

how about a list of ambidextrous luthiers? my left hand might chisel in more tone than my right...
Since you asked, though I thought it was clear: If guitars you like generally have finished tops, maybe you prefer something about that. If not, then perhaps not. There is a huge sample set of real-world results.

But no, you're right to enjoy the currently focused state of this discussion, your hilarious argument included.
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