Thick top and thin bracing, or Thin top and Thick bracing?

[silverspear]

I have recently played and examined a lowden guitar, and was astounded how thick they made their tops.. nearly 40% thicker than the norm! But I also noticed that the bracings were light and thinner than the norm, which probably compensates for the thick bracing.

I've not examined a Goodall yet, but I know that they don't scallop their braces, and yet their guitars are made loud. Makes me wonder if they thinned the tops to make it so.

So my question is: do you prefer to build with thick tops/thin braces, or with thin tops and thick braces, and why?

[dlowry]

Originally Posted by silverspear

I have recently played and examined a lowden guitar, and was astounded how thick they made their tops.. nearly 40% thicker than the norm! ...

Where did you measure the thickness of the Lowden top?

They use a soundhole reinforcement patch which adds considerable thickness around the soundhole, between the X-braces and the A-frame braces into the neckblock. This makes it look like the top is much thicker than the norm.

You need to measure at a point outside this patch to get the true top thickness.

Regards,
Drew

[silverspear]

Originally Posted by dlowry

Where did you measure the thickness of the Lowden top?

They use a soundhole reinforcement patch which adds considerable thickness around the soundhole, between the X-braces and the A-frame braces into the neckblock. This makes it look like the top is much thicker than the norm.

You need to measure at a point outside this patch to get the true top thickness.

Regards,
Drew

oh i didn't know that.. thanks for the info..

anyway, my question still stands in general.. which approach of building is preferred and why..

[Ned Milburn]

Plus, Lowden often (usually?) uses cedar which must be left thicker than spruc.

[HHP]

I prefer guitars that sound good, how they achieve that is mostly irrelevant to me. I did have a Mossman with very heavy bracing that sounded great, have a Martin with scalloped bracing that sounds great.

There is simply no formula that can't be screwed up by somebody, somewhere.

[Tom West]

Originally Posted by silverspear

So my question is: do you prefer to build with thick tops/thin braces, or with thin tops and thick braces, and why?

There is only so much power in the strings to move the weight of the braced system. If you want a responsive guitar you have to limit the weight. Most of the weight is in the bare top and a lot less in the bracing. So to get rid of weight one should thin the top. When one does this you need stiffer braces. If you make the braces twice as wide they are twice as stiff, but if you make them twice as high they are eight times stiffer. So to save more weight and make braces stiffer one makes them higher. Of course there is a limit to this and that is part of the luthiers job to come up with the combination that works.
Tom

[Rodger Knox]

It can be taken to extremes, as Smallman does, with almost no top thickness and a lattice of CF reinforced balsa bracing. On the other hand, there's the old ladder braced guitars that have essentially no bracing to carry the string load.

I believe the tone is in the top, so there needs to be enough top thickness to retain that tone. If I knew exactly how to determine that thickness, I could quit my day job. It's not that hard to calculate the proportional loading, but determining the correct proportions is another story.

That doesn't answer your question, because I don't have an answer. Yet.

[Alan Carruth]

HHP wrote:
"There is simply no formula that can't be screwed up by somebody, somewhere."

YESSSS!

[Rodger Knox]

Originally Posted by Alan Carruth

HHP wrote:
"There is simply no formula that can't be screwed up by somebody, somewhere."

YESSSS!

On the other hand, almost any formula can be made to work by somebody, somewhere.

[Silly Moustache]

It depends on what you want to create when you build a guitar.

If it is intended for light finger-style then it would be light, but if it is for robust rhythm or flat-picking then either or both the top or the bracing should be thicker.

I had a (insert well known US made (Jumbo) style guitar with two names in the brand) which was impossible to play with a flat pick unless it was given an unacceptably high action.

My luthier declared that the top was too thin and the bracing too light for the purpose for which it was designed. An expensive failure.

[Viking]

Originally Posted by Silly Moustache

It depends on what you want to create when you build a guitar.

If it is intended for light finger-style then it would be light, but if it is for robust rhythm or flat-picking then either or both the top or the bracing should be thicker.

I had a (insert well known US made (Jumbo) style guitar with two names in the brand) which was impossible to play with a flat pick unless it was given an unacceptably high action.

My luthier declared that the top was too thin and the bracing too light for the purpose for which it was designed. An expensive failure.

That's a fascinating perspective. The emphasis now adays seems to exclusively be lighter and thinner. To quote Cumpiano... "minimally adequate structure" is what the modern luthier strives for. What did the guitar sound like when played with a pick? How did you define failure? Did it sound good when played finger style?

[dekutree64]

One of my favorite topics

My current theory is that it depends on the wood and the size of guitar. A small cedar top could be so thick as to need almost no bracing below the soundhole, and a large mahogany or koa top should be super thin with stiff bracing.

With small guitars, the challenge is getting low frequency response. With large guitars, the challenge is keeping the mass down so it will respond quickly and with plenty of volume.

A small soundboard is lightweight by virtue of its size, and could use some extra mass to lower its resonant frequencies. Likewise, the total stiffness (plate and bracing together) should be as low as possible. Using a lower string-height-at-bridge, like 3/8" instead of the usual 1/2", can allow lower stiffness than usual.

A large soundboard is almost impossible to make too light with only wood. Its frequency will naturally be low by virtue of size and mass, so making it stiffer can be good to get it back up. And higher stiffness allows for a higher string-height-at-bridge, to give the strings more leverage to get it moving.

And then an interesting observation is that thin top builders tend to use constant thickness all over, and thick top builders usually thin the perimeter after the box is closed... down to about the same thickness as the thin top is all over. So the thick top is really only thick in the middle, and everyone agrees on how thick the perimeter should be. It may be possible to regain some useful perimeter stiffness on an ultra-thin top by using a large number of braces and notching them into the linings at 1/16" or so tall, but I haven't actually tested it yet.

Thin tops should have some bracing along the grain around the bridge. A large bridge plate, fan braces in the south quadrant, lattice, or whatever else you can think of. Otherwise the area just behind the bridge will flex sharply, allowing the bridge to rotate, messing up intonation and probably peeling off eventually.

Also, notching braces into eachother gives another level of stiffness control. Otherwise the stiffness at brace meeting points is equal to the plate stiffness. Fine for thick tops, but on thin tops, you might want it stiffer than that.

And one more thing, a thin plate with sparsely distributed braces feels squishy in the areas far from any brace. I'm not entirely sure what the tonal implications are, but FWIW I use more braces on thin tops and fewer braces on thick tops. A small number of really tall braces will get you more stiffness for the weight, however.

[Silly Moustache]

Originally Posted by Viking

That's a fascinating perspective. The emphasis now adays seems to exclusively be lighter and thinner. To quote Cumpiano... "minimally adequate structure" is what the modern luthier strives for. What did the guitar sound like when played with a pick? How did you define failure? Did it sound good when played finger style?

Hi, the guitar was a 12 fret Gibson Jumbo short scale style intrument made by a small US factory company.

Whilst a guitar like that isn't exactly a bluegrass "cannon" it should be playable with a pick ...... it wasn't ....unless the action was more that 1/8" at 12th fret.

I now have a Santa Crus "RS" which whilst remarkably similar - it doesn't have the same problem.

I lost a lot of money in the deal,and was very dissappoinyted by the lack of support given to me and the dealer by the maker.

[mirwa]

Originally Posted by silverspear

So my question is: do you prefer to build with thick tops/thin braces, or with thin tops and thick braces, and why?

Everyone has there own recipe, there really is no right or wrong way about this.

Similiar to making spaghetti bolognase, everyone has there own version, but its still bolognase.

Once you have built a few guitars using the same wood, you get a feel for what you like. We all can hear different things during our tap testing of the tops whilst we shape them up.

For me I like a loose spruce top, which means thin but thin is not under 2mm, for woods like cedars I usually end up at around 3.5mm.

Thats a starting recipe, from there you shape the sound out as you build it.

Steve

[SiliconValleySJ]

Originally Posted by silverspear

I've not examined a Goodall yet, but I know that they don't scallop their braces, and yet their guitars are made loud. Makes me wonder if they thinned the tops to make it so.

James both thins the top to a certain degree (radiused) and scallops his braces selectively. I've seen it at his workshop. Just an FYI.