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Cross Dipole
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Author:  Jim Kirby [ Sat Jan 06, 2007 12:13 am ]
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On video 4 the question came up of how to maximize cross-dipole on a steel string. The general answer of how to maximize it in general was to use fan bracing, but the steel string question went by with a few suggestions but no conclusion. My reaction was, scallop the middle of the lower bout parts of the X braces heavily. My reasoning is that, in order to let the cross dipole move, you need to allow a motion that has maximum curvature at a distance 1/2 way between the rim and the centerline. To allow the surface to flex in this position, you want to reduce the bending stiffness of the main braces crossing this line. This means we need to reduce the bending stiffness of the lower bout ends of the X braces in the region about 1/2 way between the X and the ends of the braces - pretty much a standard scalloping pattern.

Parabolic bracing would seem to be fighting this motion, or perhaps keeping it less accentuated in relation to the long dipole, which would seem to be helped most by shortening the brace ends.

Comments?

Jim
Author:  TonyKarol [ Sat Jan 06, 2007 1:32 am ]
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Is the goal to max the cross dipole, or make the cross and long even between each other ??? Early on Ervin mentions that good sounding guitars exhibit all three modes in balance does he not ???

Cross dipole gives long range volume/projection, long dipole close range volume correct ... thats why classical guitarists wnat cross dipole, to fill a small concert hall. Whats the goal for long range projection in a steel string ??? Bluegrassers want the guitar to cut in front of a single mic .. thats more a long dipole thing .. personnally I wnat more eveness of tone, and would rather have a more complex sounding guitar than a loud one - PUs and mics can get you volume, and most guys laying use that anyway - in the studio it wont make a difference IMO, and most bigger, louder bass heavy guitars are tougher to record. I lent a friend who went into a studio a coupel months back an all maple jumbo, 16 5/8 lower, sitka top - right off the bat , the engineer noticed it didnt sound like a typical jumbo does - didnt have the overbearing or boomy bottom .. its very even, but has what I call enhanced bottom end, the timbre is different - the engineer had a sound in no time, and couldnt believe how easy is was to get set up. The guitar has my typical tapered bracing, as shown in the bracing thread.
Author:  DoctorX2k2 [ Sat Jan 06, 2007 1:50 am ]
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Tony,
I was under the impression that long dipole was projection and cross dipole was short range volume. When he compared Flamencos to Classicals, he said flamencos had more cross dipole and less long dipole thus can't travel the sound as far as a classical... but maybe I got confused.
Author:  TonyKarol [ Sat Jan 06, 2007 3:12 am ]
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Just went back and had another look at the end of tape 2 - you are indeed right Alexandre - cross dipole is close prox volume, long dipole is long range projection - kind of makes sense as the cross dipole is shorter, and wouldnt have the carrying range. But lets go back to the top post, maximixing the cross dipole - why ??? As Ervin points out, you want to max it, use fan bracing and you get an Ovation. Why not balance it with the long dipole ?? Most heavily scalloped guitars are only scalloped in the lower bout, the upper X is left straight, or somewhat tapered - think again bluegrass dread, lots of immediate punch to cut thru to the mic over the other instruments - works if thats what you need a guitar to do - do they have long range power - they probably dont care, they want to cut thru at close range. Scalloping will likely also enhance the bass at the expense of something else, because you are greatly loosening up the lower bout - Alan C has mentioned somewhere that scallops usually scoop mids, tapers create a more even response - it all comes down to what you want/need the guitar to do, and how you like a guitar to sound.
Author:  Jim Kirby [ Sat Jan 06, 2007 5:02 am ]
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The original question wasn't why maximize the cross-dipole, it was how.

But I think Tony's comments just above do provide the analysis or conclusion. The bluegrass dread is scalloped heavily to give a lot of short range projection. More balance in the long vs cross probably makes a much more pleasant solo guitar to listen to.
Author:  letseatpaste [ Sat Jan 06, 2007 5:20 am ]
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It seems to me that as far as scalloping the X brace, you're affecting both the the cross dipole and long dipole response at the same time since the braces are generally running at 45 degrees.

So my uneducated guess would be that the following would be useful for shifting the balance between the cross dipole and long dipole response:
1.) Spreading or closing in the angle of the X brace
2.) Placement and angle of tone bars to vary stiffness in different directions

I'm still wrapping my brain around how this would work, as this is all still pretty non-intuitive to me...letseatpaste39088.5565625
Author:  TonyKarol [ Sat Jan 06, 2007 5:46 am ]
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I still tend to think that scalloping doesnt enhance the long dipole as much as you think - you have a very loose lower bout due to scalloping, but the area above the soundhole isnt as loose because the X is genereally not scalloped up there (It becomes very assymetric in stiffness) - if it was scalloped, it could enhance the dipole, but most certainly also increase the likelihood of collapse about the soundhole. . Again one of those get something at the expense of something else scenarios. It might also start to increase the effect of the monopole such that its now overbearing - boomy .. .. the top becomes too loose and floppy everywhere. In general, lows comes from looseness and highs from stiffness - so balance is key - the question is what is the correct (whoa is that loaded - everyones ears hear something different so what is 'correct' to begin with) balance and how to achieve it.

I always go back to an analogy from the 100W shootout in GP years back - there was talk about what is good tone, and someone put forth this example - guy tries out a strat, and to him its muddy .. guitar next to it cuts like a knife, and he likes that for his situation. Another guys tries same two guitars, and the cutting strat is too thin for his taste, he like the fatness of the other guitar.
Author:  Brock Poling [ Sat Jan 06, 2007 8:08 am ]
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I really would rather let Ervin speak for himself about this, but I can answer the question to some degree with his philosophy (since I spent a week listening to it).

Ervin thinks that guitars whose strength is maximized at the x joint and tapers evenly to the edges produce the best sounding guitars. Think of a bell curve rotated horizontally around an axis that transects the x joint.

That (to me) implies no scalloping. AND.... the other thing it implies is that you want a tight coupling between all your braces... so you would not scallop them as the meet one another (think tone bars and finger braces.)

In my post class work controlling this coupling and the overall height of the braces has given me the most dramatic levels of control over the overall voice of the guitar.

Author:  Colin S [ Sat Jan 06, 2007 9:24 am ]
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[QUOTE=Brock Poling]
I really would rather let Ervin speak for himself about this, but I can answer the question to some degree with his philosophy (since I spent a week listening to it).

Ervin thinks that guitars whose strength is maximized at the x joint and tapers evenly to the edges produce the best sounding guitars. Think of a bell curve rotated horizontally around an axis that transects the x joint.

That (to me) implies no scalloping. AND.... the other thing it implies is that you want a tight coupling between all your braces... so you would not scallop them as the meet one another (think tone bars and finger braces.)

In my post class work controlling this coupling and the overall height of the braces has given me the most dramatic levels of control over the overall voice of the guitar.

[/QUOTE]

My feelings exactly Brock.

Colin
Author:  Brock Poling [ Sat Jan 06, 2007 11:05 am ]
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[QUOTE=Hesh1956] This picture was posted prior and facinated me to no end...... and it seems appropriate now to show it again.

I don't recall what the thread was about or if this is even one of Ervin's guitars - Brock do you recall when this was posted and what the story is/was?



[/QUOTE]

Yeah, this is one of Ervin's guitars. IIRC Dave Bland posted this from his course, but I have a bunch just like it.      That is a good example of where the box is in construction when he braces it.

Also... notice how all of the braces are coupled (or nearly coupled) to the bridge plate.

I don't know if Ervin would agree with this thinking or not, but one of the things I came away from the class thinking was that braces are more like "irrigation ditches" that channel the energy through the top vs. structural supports that keep the guitar from imploding.

I realize they do both, but shifting my thinking to PRIMARILY the ditches model has made a significant difference in my post class guitars.

Brock Poling39088.7976967593
Author:  Brock Poling [ Sat Jan 06, 2007 11:18 am ]
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You know. Something occured to me that I think is worth mentioning. Please realize that as enlightening as this conversation is, and as inspiring as those videos are.... this is really just standing on the sidewalk outside the pizzaria smelling the pies.

When you walk out of that class you really have a good handle on how to control the sound of your guitars and a methodology to tackle just about any type of project.

I just can't say enough good things about it.

Author:  TonyKarol [ Sat Jan 06, 2007 11:28 am ]
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thanks for the insights Brock .. they certainly have put some ideas in my head ...
Author:  dgalas [ Sat Jan 06, 2007 11:31 am ]
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[QUOTE=Brock Poling]
You know. Something occured to me that I think is worth mentioning.
Please realize that as enlightening as this conversation is, and as
inspiring as those videos are.... this is really just standing on the sidewalk
outside the pizzaria smelling the pies.

When you walk out of that class you really have a good handle on how to
control the sound of your guitars and a methodology to tackle just about
any type of project.

I just can't say enough good things about it.

[/QUOTE]

I coudn't agree more. It's not just about top material, stiffness, bracing
layout, body depth, size, shape, scale length, neck weight, etc. it's about
all those and more and they all contribute. After an intense week, I
realized just how much I didn't know, but I also felt like I was given a
good plan for how to proceed on a life long learning path.
Author:  TonyKarol [ Sat Jan 06, 2007 11:37 am ]
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Few things I notice when looking at this top bracing - the upper transverse is not scalloped at the sides, or at least not much anyway - seems to run in full height, then the kerfing is buttressed on top of it - very stiff (same idea as in the top tapping mold Ervin has in the videos). The soundhole braces are fully coupled at the X, but have a taper down to uncouple them at the upper transverse. NONE of the other braces are tucked. The back braces will be tucked - see the notches in the linings. Oh, the lattice on the bridge plate is NOT coupled to the X directly, and no side supports of any kind.
Author:  Brock Poling [ Sat Jan 06, 2007 2:37 pm ]
Post subject: 
[QUOTE=TonyKarol] Few things I notice when looking at this top bracing - the upper transverse is not scalloped at the sides, or at least not much anyway - seems to run in full height, then the kerfing is buttressed on top of it - very stiff (same idea as in the top tapping mold Ervin has in the videos). The soundhole braces are fully coupled at the X, but have a taper down to uncouple them at the upper transverse. NONE of the other braces are tucked. The back braces will be tucked - see the notches in the linings. Oh, the lattice on the bridge plate is NOT coupled to the X directly, and no side supports of any kind.[/QUOTE]

Again, I can't speak for Ervin and why he does what he does. But.. his rims ARE very stiff. They are laminated from two thin sides with exoxy and when the linings are in they are MEGA stiff. The thinking was that they become like the rim of a drum and don't absorb energy from the top.

And the lattice that connects to the bridge plate doesn't NEED to connect to the X brace because it is picking up the energy directly from the plate.

Author:  Jim Kirby [ Sun Jan 07, 2007 1:01 am ]
Post subject: 
[QUOTE=dgalas] [QUOTE=Brock Poling]
You know. Something occured to me that I think is worth mentioning.
Please realize that as enlightening as this conversation is, and as
inspiring as those videos are.... this is really just standing on the sidewalk
outside the pizzaria smelling the pies.

When you walk out of that class you really have a good handle on how to
control the sound of your guitars and a methodology to tackle just about
any type of project.

I just can't say enough good things about it.

[/QUOTE]

I coudn't agree more. It's not just about top material, stiffness, bracing
layout, body depth, size, shape, scale length, neck weight, etc. it's about
all those and more and they all contribute. After an intense week, I
realized just how much I didn't know, but I also felt like I was given a
good plan for how to proceed on a life long learning path.
[/QUOTE]

No doubt! But for me it isn't going to happen anytime soon, as the course conflicts with my teaching schedule. So osmosis is important here.
Author:  Jim Kirby [ Sun Jan 07, 2007 1:14 am ]
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How does this beast fit in this scheme?



This is David Schramm's take on the Smallman guitar. Referring back to Ervin's picture of the classical vs steel string active soundboard area, this takes the notion that the classical soundboard is dead above the lower transverse brace to the extreme - I think this thing is structural plywood above that region. In contrast, the active area soundboard is drumhead thin - about as monocoque as one could imagine. The top doesn't have to provide any structural integrity for the body, just resist the local string pull.
Author:  Ervin Somogyi [ Sun Jan 07, 2007 5:22 am ]
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[QUOTE=TonyKarol] .. .. the top becomes too loose and floppy everywhere. In general, lows comes from looseness and highs from stiffness - so balance is key - the question is what is the correct .[/QUOTE]

Hi, Tony & everyone reading this: You're right. I'm impressed with the high level of critical thinking and discourse around this topic, on everyone's part. The interesting thing is that as soon as one gets hold of an idea or concept and tries to apply it to real wood, a whole new world of "hmmm, JUST EXACTLY HOW thick/thin/long/scooped/tapered/profiled . . . should I make this?" opens up. Every sentence can take six months of work to explore. It certainly is an antidote to the boredom of doing the same mindless thing over and over again forever, hoping to "hit it right" every now and then. cheers, Ervin Somogyi
Author:  Shawn [ Sun Jan 07, 2007 7:15 am ]
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Jim,

It really surprised me when David Schramm who has studied Hauser's contruction so extensively ventured into Smallman construction and then even more surprised when he liked the sound of it!

The foundation of the Modern Classical Guitar comes from the Spanish guitars that Torres built. Hauser modified his German construction to build a version of that Spanish style of construction but Smallman is going in a completely different direction.

Everyone that has heard a Smallman remarks on its volume but very few when discussing a Smallman will mention tonal color or quality. When you look at the inside of one of Erwin's guitars or any other quality built instrument you will be able to see the craftsmanship, even before you have heard it.

When I look at the inside of a Smallman school guitar it looks much more like the interior of a speaker cabinet than a musical instrument. To each his own but to me plywood never looks good in a guitar.

I think the stiff rim is the one element that almost everyone agrees makes complete sense, bracing patterns can work in various configurations, but it is all of the elements together that define the sound.

One last thing...when I was playing in garage bands back in high school many years ago we would have really junky amps with cheap speakers...we could crank them up to the max but while the sound would get louder, it never got any better because the speakers were the weak element. The same music if played on quality equipment with good speakers would have projected much better at much less amps because the speakers would be projecting the sound in a more balanced way.

That is how I think of the sound of my tops when I am building and voicing them...the quality of wood for the top determines how thin I can take it, the balance of the braces and voicing controls the shape of the sound that it puts out.

I got alot of great info out of the ASIA session that Erwin did and would love to attend his class some day. I also have gotten a ton out of the voicing class that Alan Carruth did...two very different approachs to the same goal, both complimentary and in many ways flip sides of the same coin...the pursuit of a well voiced instrument.
Author:  TonyKarol [ Sun Jan 07, 2007 8:41 am ]
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Hi Ervin .. hope to meet you in person someday !!

Just watching the videos made me think a lot more from a structural engineering standpoint - not that I am one (electrical actually), but I did take ome of their courses, and understand beams and such fairly well from a high level standpoint - dont ask me to do much math anymore, those days are long gone. Lke Larrivee said one time, I'm not a numbers guy, I'm a sawdust guy !!!
Author:  tony [ Mon Jan 08, 2007 2:55 am ]
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Curious. I haven't heard anyone comment on the kerfing in the picture posted by Hesh.

It would appear that there is 2 rows of kerfing on the bass side.

Can some one explain what I'm seeing and why?tony39090.4566203704
Author:  tony [ Mon Jan 08, 2007 3:04 am ]
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Optical illusion. I think my eyes were tricked because of what appears to be the top wood showing between the two lines of kerfing (at the waist).

With bracing so radically different from what I would have expected to see, my mind was prepared to see anything...
Author:  Steve Saville [ Tue Jan 09, 2007 3:36 am ]
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Edit....SteveS39094.8185532407
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