Bracing Ottomans :)

[Hesh1956]

I have been wanting to start a thread to discuss bracing and more specifically NOT over bracing for a while now. I decided that the ANZLF might be a more harmonious place for this discussion in as much as we tend to be more respectful of each other.

The statement was made on another forum by a highly respected and perhaps in some cases feared builder that you could stand on one of his tops....... It took all the restraint that I had and more to not post in reply - what are you building ottomans or guitars.........

Anyway my point is that a guitar top is not something that I would expect to be able to stand on if it was a guitar that was responsive, loud, and with a quality tone.

For me building and bracing a guitar top is an exercise in brinkmanship. You want the top light and responsive with little if any mass that does not provide value like tone and strength.

I sometimes think that it might be an advantage to have never worked with wood before which is my situation, when it comes to tops. Having never built anything from wood when I brace a guitar top I am not thinking so much about the strength part of the equation as I am the tone part of the equation. Ask me how I feel when one of my lightly braced guitars folds in half at 3:00 AM...........

Anyway I would be very interested in two primary things in the ensuing discussion that I hope will occur here.

1) Are you over bracing, underbracing, just right and what makes you come to the conclusions that you do.

2) Traditional bracing with Martin coming to mind - when considering the traditionally braces Martin "X" braced tops AND the materials that they had in the day to work with is this design efficient, very efficient, or does it suck.

thoughts please - I am off to get off my feet and put them up on a factory guitar.....

[Dennis Leahy]

I'd love to enter into this discussion, but will wait for a while - because my perspective is from so far out in left field (or maybe the 3rd ring of Uranus.)

I will say that you won't be using my guitars as ottomans - well, that is, they won't last long as ottomans.

Dennis

[Alain]

Hesh, good thread idea.

I too believe that we're trying to balance a fine line between building light so as to have responsive and vibrating tops and structural integrity so they don't implode on themselves...

I believe that my first guitar's top was too thin but the bracing was pretty much in keeping with the teachings of Cumpiano/Nathelson (scalloped). I know the top was way too thin because I over sanded that guitar ad nauseum. In the end you could/can see the tail block. Just the other day, my girlfriends daughter managed to punch a hole through that area of the guitar and I figure the top must be no more than 35-40 thou, plus, it received 2 neck resets in as many years... Still, it plays very well... LOL

No.2 received a much thicker top. Adi at about .110-.115 but with very minimal bracing (parabolic). It has held up for over a year now and hasn't budged at all... Sides where in the .120 range.

No.3 is sitka at about .100 with minimal bracing (parabolic) and she's the one I prefer so far. I haven't even strung her up yet but I can tell just by the decay when I give her a good tap where the bridge is that she should ring like a bell and have great tone...that's the plan at least... sides .125 as well on that one...

So, I think the braces should be tall and narrow and the top should be on the thin side of things. HHG for braces probably also helps.

This also begs the question: How long should a good guitar last? 30 years? 50 years? 100 years? I'm sure that a guitar that implodes after 30 years would sound better than one that lasts 100...

Some of those older 'golden age' Martins are close to a hundred years old now and some of them have X's no wider than .25 as well...

Which brings me to the idea that I wanted to build a test guitar. I wanted to use just plain (read cheap) hog and go absolutely crazy on it. Sides in the .05 range, the back too... The top in the .075 range with very very light bracing. I wanted to do this just to see how 'low' you can go and how long it would take to fold on itself.... I will get around to doing it one day and I'm sure it will be a great learning experience...

[Allen]

My first Dread was definitely an Ottoman. I didn't have a clue. It's scalloped and thinned, but the bracing dimensions where just so large to start with that in hindsight it was just to hard to convince myself to remove all that wood.

With each successive build they have been getting lighter. The Cypress 000 that I built was the first guitar that actually came alive when it's played. Probably mostly due to the wood being so light and responsive to start with rather than a conscious effort on my part, but this got me thinking about building lighter.

After watching the Ervin Somogyi video's that Bob put a link to, I've got a whole new impression on how light we are aiming to build. As well, the physics behind brace hight vs. stiffness was something I had a vague idea about, but he explains is so well, that even a dolt like me had the penny drop.

On my current build I'm really focusing on building light and responsive as the primary goal. It may work out to be just right, but I suspect that it will still be over built. I think that most of us without a dozen or so guitars under our belts find it difficult to build so it just holds together.

On a recent thread on the OLF I saw that quite a few builders were taking their back and sides down much thinner than I have been as well. If a great deal of the weight in a guitar is in the body plates, then this would be a huge weight savings. We would loose some stiffness in the plate itself, but is this a bad thing, or is this just one more area that is overbuilt? Does this translate into a plate that is going to be more responsive?

So many things to consider and learn. Looking forward to others thoughts on this.

[Bob Connor]

Horses for courses methinks.

The last six instruments we have built have been OM's. Basically a fingerstyle guitar.

The tops have been thicknessed based on to things.

a) the stiffness of the piece of wood

b) the playing style of the guitarist who is going to play the thing.

The last Myrtle/Engelmann OM we did had the top thinned to 2.2mm(.086") the braces weren't taken down as much as we normally do, and a Mario brace was chucked in behind the bridge plate. And it ended up being a very nice sounding and responsive instrument.

But it is useless to someone who plays with a heavy pick and strums like a threshing machine. The top will overdrive too easily.

A previous one was built from Hard Rock Maple/Engelmann for someone who does play like a threshing machine so the top was thicknessed to 2.7mm (.106"). Not as responsive a guitar but certainly stands up to a player who is more aggressive and uses a pick.

We've got 5 x 0-18s and 5 x Dre@dnoughts under construction which will again take two different trains of thought when voicing the tops.


The 0-18's. because of their smaller size should be stiffer so they'll be built with that in mind. Plus most 0-18's would be used for fingerstyle so that's what we'll aim for here. I've laid out a bracing pattern for these and it is forward shifted to try and induce some bottom end into a small guitar.

They'll also have different timbers for the tops so it'll be interesting to note the differences in them.

The dreds, on the other hand, will be built with hard pick, hard strumming players in mind so the top will require some more mass so it won't be overdriven. Depending on the stiffness of the wood I'll start at around 2.8mm(.110) with the perimeter thinned down to 2.3 to 2.4mm.(.090- .094)

One of the early dreds we built has a top which is 1.8mm(.070). After a year it is bellying slightly behind the bridge but it is still playable and hasn't needed a neck reset yet (I'm sure it will eventually)

Does it sound or play like a Dred - NO.

It's a great fingerstyle instrument and very responsive but it ain't no dred.

All of these measurements are starting, ballpark figures. They'll change as the the top is checked for stiffness.

I might add that all of these are fairly standard Martin style X braced instruments.

Bob

[Serge]

Having in mind that each piece of wood is different from the next, that each top is different and that we have to tap tone and measure the flexibility/stiffness of each top, i'd say the the first ten guitars are a real school in itself, personaly, i like a top that's thin but sometimes, tops are more responsive to tap tone on the thick side(thinking of red cedar here) but in any case, i love my braces tall and thin when scalloped but had a marvelous experience with parabolas on no 3 which turned out to be really responsive thanks for the parabolic bracing (lower and thin) on that one, i'm not sure if the scalloped bracing would have done the job. No 3 was as light as a feather.

Excellent question which can lead us in many directions, i'd say that Somogyi's approach is interesting in regard to obtaining some sort of light and responsive vessel and i'm sure by what Hesh has observed that his guitars are something out of this world but for me, once the top and back are glued to the sides and the sides have reinforcement, the sides get all the stiffness needed to let the plates vibrate freely. I would rather go for an option a la Dave White with his bars leaving the neck block and reaching the waist if i wanted ectra stiffness for the sides without adding too much weight. Afterwards, i mean, everything is possible for the thickness of tops before implosion IMHO.

Not sure if i made any sense

[Allen]

You're in a great position Bob to be able to see subtle differences in small changes doing productions runs like you are. I bet you must observe and learn in a few months what it will take many of us years to achieve.

I haven't got them to the point where they will be overdriven, so I guess I've got some leeway yet.

[joel]

OK, I haven't built one yet but I'm with Ervin on this one. Those were good little video's. Monocoque construction is the way to go. Build it just stong enough for it's intended purpose and no stronger. If you want a light responsive fingerpicking guitar, make it light. If you want a heavy metal acoustic, build it heavy enough to survive being smashed over a speaker stack.

I guess that's were the skill and experience comes in. Knowing where the 'strong enough for intended purpose' line in the sand is. So, I'll probably build a fallout shelter as my first 'guitar'.

[Rod True]

I'll have to say that Bob and John K are our resident "experts" as they probably have the most completed guitars of the group.

Having said that, I'll jump into the blue.

An old gentleman engineer I worked with on a project at my previous employment use to say this about how tight to tighten a bolt "turn it till it just starts to strip, than back it off 1/4 turn, that's when you know it's tight enough." I use to get a good laugh out of that.

Now, I don't have many answers at all, and I've built a couple of good sounding guitars. I'm also very afraid that my ears in their youthfulness were much better hearing than they are now (sad to think I've killed a lot of my good hearing from turning up the stereo to loud) so my subjectivity is realy worth the price of admission here. Having said that, I'll share my "wisdom".

Build it lighter than you think you should. Take a look at any of the plans out there, you'll find that the brace stock of overbuilt for the most part.

I like Hesh's post over on the OLF in the Somogyi thread and the reminder by all the veterans of this craft. The top and braces are all a system and a few go on to say that the top, braces, back, sides, neck block, neck are all a system.

It's really hard to talk about one aspect of the guitar without really having to think about all the others (structurally that is) and to do so would be IMO a dis-service to the instrument.

As Joel just mentioned, the intended purpose of the instrument is vital to the construction of it.

I know that my car is not meant as a race car, but I try and prove that it is ever chance I can . What I mean is this, if we want to build a tank (Landcruiser for you Aussie's and me) that can take a good amount of abuse, we brace the top a bit heavier to withstand the heavy strumming.

If we want to make a Porsche', something fast and responsive yet smooth in the corners, we brace the top a little bit liter and caress the instrument more than pound on it.

Now having said all this, what does all that mean? Hell if I know

No.......I know a little bit more, but not much. Because we need to think of the top (one part of the system, maybe the most important) as one system, lets look at the factors.

first, it needs to be able to withstand the pull of the strings so it doesn't torque out of shape, causing the action to drop down onto the frets. Or so it doesn't just rip to pieces (I won't use the word implode because that's not what it would do, sorry Al buddy) and send the bridge flying at the head of the player. So I see the bracing directly behind and in front of the bridge as the key components to making sure the top does not distort or come apart at the point of highest load, the bridge.

This is really why I've adopted this bracing pattern. I believe that it adds a great amount of strength right behind the bridge without adding any additional weight which would dampen the vibration of the top.



I am going to try a different bracing pattern on the next two guitars as I have an idea which I think will really stiffen up the top in both of these critical locations AND I'll be dropping the weight of my braces which should allow the top to respond more freely. Just my theory though.

Now by stiffening up the bridge area, not dampening, just stiffening (making those areas stronger) there may be more tendency for the neck block to want to rotate and add more torque to the system. My plan for this is to add a foot on both the bottom and the top of the head block. These "feet" would couple the neck block to the top and the back more than they do already and would help reduce the torque from the neck to the neck block. I know quite a few guys do this already, I'm just thinking I'll join the club.

But this is about tops. Take a read on Ervin's website in the articles section, I don't really think there is to much magic there, but there certainly are a lot of good articles on what should start to produce a good/great sounding guitar.

This stuff isn't rocket science you know.........it's much harder than that

[Rod True]

Oh and Serge, what Dave White does is called a flying buttress (sp?).

What this does is reduces the rotational torque of the head block, It's not there to add stiffness to the sides.

Somogyi's theory is that the top and the back are air pumps and I have to agree with him. When the string vibrates the top it causes the top to move in many different ways, one of the most obvious movements is up and down (if your looking down on the surface of the top), like a speaker or air pump.

The back does the same thing as the air movement from the top bounces off the back. So the two plates can be made to compliment each other (al'a Alan Carruth's theory) or the back can be made stiff to reflect the air of the top (I think this is more of the Charles Fox theory but don't quote me on it).

Think about a speaker for a minute. there are basically two important parts to a speaker, the cone and the rim. If the rim is really floppy and loose, it won't support the cone very well right. Which part of the speaker is producing or translating the sound? It's the cone. So for the cone to be the most effective that it can to translate the energy out to our ears as music, it must be supported. The stiffer the rims of that speaker, the more efficient the cone will be to send out that sound.

Same thing with the guitar sides. We want the coupling of the top to the sides to be as stiff as possible to allow the top to move as efficiently as possible. If we were to make really flimsy and loose guitar sides, they would rob some of the energy from the top and the guitar just wouldn't sound as good as if the sides really supported the top so that the top does it's job as efficiently and effectively as possible.

Make sense? Heck I may have convinced myself there

[Bob Connor]

I've been looking at Rod's top and Ervins top and it started me thinking which is always dangerous.

I'm not having a go at your bracing either Rod because it's essentially what we, and most other people do. It's just that your pic was handy.

I've drawn some circles on the two following pictures to show where I think the stiffest parts of both tops are.

There's also an arrow on Rod's to show a great swathe of the lower bout where there are no braces.

I've assumed that the stiffest area on Rod's top will fall around the peaks on the side braces, tone braces and the X brace.

The intersections of the side and tone braces with the X brace will also be stiffer.

It's a fairly wide area across the soundboard. If this top had standard scalloped tone braces, that stiff area would move further down into the lower bout.

There is also an area on the treble side of the lower bout where there is no bracing. Just an open area of floppy soundboard.



Ervin's top has no peaks in the X brace or side braces. The side braces look as though they are flat.

I don't know whether stiffness or mass is the right concept to use here but Ervin seems to be trying to centralise that mass/stiffness in the centre of the soundboard and trying to provide a uniform or more evenly graduated stiffness all the way out to the rims.

This is very apparent with the lattice bracing in the lower bout and probably gives him much more flexibility in eliminating dead spots while tuning the top.

His bridge plate is also very wide. Possibly to stop the bridge belly syndrome and allow him to use those lattice braces more as a tuning tool and less as a structural element in the lower bout.





Then again I may be talking through me bum. I won't know 'til I try it so it's going to get put into action very soon.

I've always been concerned about the open area in the lower bout that has no bracing on it on traditional Martin style X bracing.

The Somogyi bracing would give more accuracy in controlling cross dipole and long dipole responses from a top than traditional bracing.

Now you blokes can stick the boots in

Bob

[BillyT]

Ha! A Guitottoman!!

Great furniture idea!
Bad musical instrument!

I'm took a look at another of those Somogyi videos and I have to admit, it does get one thinking. His bracing, comparatvely, is downright puny!

There's this guy that builds named Turner, he's kind of liked the feared builder you mentioned, does anybody have pics of his bracing just to compare.

As mentioned, on another forum, it's difficult to compare small/custom builder work. It is kind of a dream of mine to have everybody's guitar in one room and try them out! Wait! I think it's called Healdsburg! I'll have to go next year.

Are you going to display next year Hesh?

[sebastiaan56]

A question,

So what about this bracing system, www.kinscherff.com/BracingSys.html has anyone had the chance to evaluate the guitar. I must say that it fascinates me from a geeky engineering perspective. As mentionted in another post I spent an hour going through the concepts with an architect friend. It shis bread and butter but he is not a luthier,

Sebastiaan

[Hesh1956]

Sebastiaan thanks for the link.

In my way of thinking the holes are not productive and may in fact inhibit the braces ability to act as unencumbered meridians for vibration.

A guitar top will weigh typically between 200 and 250 grams. The bracing only weighs in, for bracing such as what we are seeing at the link, 40 grams or less. Look at the mass of all the braces and then at the holes. the holes probably only provide a few grams of weight reduction but again with a potential price in the transmission of vibration.

I could see drilling out braces in place of scalloping them and letting the holes weaken certain braces in certain areas. But then why not just scallop?

With no disrespect intended to the builder and I admit that I have never played one of his guitars this looks like engineering of say a bridge being applied to a guitar.

Even the guys who spend their lives scientifically measuring guitar top response will freely admit that wooden musical instruments rarely will react exactly as a mathematical model would suggest. It is this unpredictability that fascinates me to no end. Reminds me of when I was married.......

We do have a great deal of control in the potential response of a guitar but we don't have total control. This is partly the nature of working with wood and partly that a guitar is a "system" and to some degree ALL things will interact, or not, and vary the results of the individual parts of the system.

I am just beginning to understand how a guitar works and it has blown my mind in many ways. For example most believe that sound comes out of the sound hole when in fact the majority of sound radiates off the top of the guitar........ Yep, right where your arm as the player is blocking the sound off the top for the listeners......

Its all very interesting, ever changing in some ways, and offers an opportunity for learning that one will never fully be able to master in a single life time.

[Allen]

Well stated Hesh. That's what's so fascinating. The more we learn about building an instrument, the more we realize we don't know yet.

The braces with all those holes sure look purdy though .

[BillyT]

Actually, the holes are probably a good idea!

Holes spaced and sized appropriatly do not change the stiffness of the beam and substantially decrease the weight. I remember discussing this with my Dad who was trained as a civil engineer. There is a loss of lateral strength but not in the plane desired. The same applies to "I" beams.

The thing that concerns me is the thickness of the braces, have you seen how thick they are! They look like there ½ inch (12.7mm)! That would completely offset the weight savings considering hole size and how few holes are in the X brace!




As for sound coming off the soundboard, perhaps that's why Townsend used to windmill!

[Paul B]

I was thinking of putting holes in braces a few years ago, but Billy hit the nail on the head - there's a loss of lateral strength. What happens if they get a good sideways bump, say when someone has their hand inside the guitar.

Oh, and Townsend was still doing that windmill thing when I saw The Who a couple years ago.

[Kim]

I have not seen nor played one of these either but like my mate Billy I question the need for 1/2" thick braces, why not just go with 1/4" and spare the drill bit? Seems more of a gimmick to me than a sound engineering practice.

Cheers

Kim

[Alain]

...a sound engineering practice...

Kim

Kim, a double engendre?

[Hesh1956]

Billy my friend thanks for posting the picture in the thread so we can discuss it easier.

Here are some more thoughts that I have about this top.

We can't know if this is a work in progress or a completed top. If I had to guess a craftsman would not post a picture of their top on a web site unless they wanted to put their best foot forward. So I would guess that this is the completed top. With this said here is what I see.

The braces are not tapered at all toward the highest parts or peaks. This in and of itself leaves a massive amount of brace material on the top that provides virtually no strength or additional stiffness. Triangular profiles are widely known to be the most efficient shape for a guitar brace. In fact I have never seen anyone brace without narrowing the tops of the braces with a finger plane or a chisel, some even use a special bit in a hand held router.

So the holes as a mechanism for weight reduction look like the right idea but the wrong way to get there to me. This is not unlike a person who is overweight ordering a diet drink with their ice cream.......

Yes the braces look excessive thick to me too. Tall and thin braces are far stronger and instead we see fat and scalloped braces.

I see no cap over the X brace intersection. The cap is very important in as much as it supports and distributes the stresses that act on the X-brace intersection.

Notice how tall the finger braces get right next to the X-brace legs? It makes no sense at all because the finger braces intersect a portion of the X-brace that has been radically scalloped to a very low height. This scalloping is a deliberate effort to make the top more flexible in these locations. But then the builder places radically jutting high finger brace peaks right next store to where they weakened the top, again deliberately..... It makes no sense at all to me. Also where two braces intersect are known problem areas on a top and frequently these areas don't resonate very well until you pare back the braces to nearly nothing.

One of the reasons that Martin's X-braced system was so very successful is that with the shapes of the braces a guitar could be assembled in a factory with no fine tuning from a luthier. Some would sound great, some average, and some not so good. It was more an assembly process then a process where there was any crafting and individual adjustment for optimization. And there is nothing wrong with this either because they were very successful, a legend in fact, and it made guitars affordable to produce in mass quantities.

But those of us who build guitars are generally looking to optimize each individual guitar and not just assemble a model airplane kit from a box.

Also looking at the finger braces - where they end they are tapered but not tapered away to nothing. This creates stress risers and could potentially result in cracks in time.

So sports fans I see a bracing system that although it would certainly hold up a bridge if scaled it is not efficient by any means. The opportunity to reduce excess mass which is far greater an opportunity by tapering the tops of the braces is lost in favor of holes...... the holes had to have been drilled before the braces were installed because the drill chucks would hit the top otherwise. So the holes have nothing to do with the idea of "tuning" the top. The braces were probably prepared off the top and simply glued on - assembly again.

You know one can make a guitar from a kit where the braces are pre-carved and have the guitar sound great. But it's still not individually optimized which is the difference between a Luthier built guitar and a factory guitar.

[Hesh1956]

I forgot to come to the conclusion that is most on my mind here.

I believe the holes to be an effort to reduce the weight/mass of the braces that is necessitated by the braces being to massive to operate efficiently because they are not tapered, they are to wide, and the peaks and valleys and their respective locations actually conflict with each other.

[Kim]

Yep, a gimmick.

[BillyT]

I didn't think that these were unfinished braces/yet to be triangulated! But I think they are! The mechanics of the holes is a "sound concept" (no pun intended but realized and exploited shamlessly as per Kim, nice catch Paul! )

I've never really heard of this guy as a builder and have no reference for his work. There's a lot of ways to do virtually the same thing without the holes, it's just poorly executed IMHO.

[Allen]

For those of you that have placed pickups in your guitars, do you brace any differently? I must admit that I'm completely clueless when it comes to pickups. Never used one or installed one for that matter. I'm only guessing here, but I imagine that feedback could be a problem for a acoustic?

[Bob Connor]

Allen

Absolutely.

I've been experimenting with a couple of OM's we built earlier this year.

Some of the blokes will remember these as Trev and Cheryl, the OM twins. One is parabolic the other scalloped. Lightly built and braced EIR/Engelmann.

I've been using Trev the parabolic both in the acoustic duo and band I play in using a K & K pickup for the last six months.

It's great for the acoustic duo but hopeless with the band.

It just doesn't cut through particularly in the top end as the K & K's have a slight rolloff in the top B and E strings. So any lead that I do just gets swallowed in the mix.

Feedback is not a problem particularly when using feedback busters in the soundhole.

I've just replaced the K & K it with a Fishman T4 so we'll see how that goes.

I've used a Takamine for live work for a number of years. Built like a tank, sounds crap acoustically but works brilliantly in the context of an acoustic guitar in a full band with bass and drums.

I really am wasting my time building a really nice acoustic instrument
just to wack a pickup in it to play with a band . But it is a form of advertising to have your own instrument on stage so I persist.

Your standard factory built Maton, Taylor etc will perform the dual role but won't be great at both.

One of the projects that's rattling around my brain at the moment is to prototype an instrument that's suitable for loud live work. Thinner body, a top that's braced in between the Takamine and a "real" acoustic guitar, stiffer back and a blender system with and under saddle pickup in conjunction with the K & K minis.

A few years back Glenn Frey and Don Henley bought a guitar each from Spud McGrath who lives in Geelong.

I saw the Eagles last year in Melbourne. One of the best concerts I've ever been to.

Were they playing the McGrath's. Nope. They all play Takimines on stage.

Horses for courses.

Bob