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Weight of braced soundboard?
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=12878		 Page 1 of 1
Author:  CraigSz [ Thu Jul 19, 2007 12:35 am ]
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I have just weighed by braced soundboard minus the bridge at 328 grams. It is Adi with Adi bracing and maple bridgeplate. I was wondering if anyone could tell me if this was somewhere around useable or still too heavy. It is for a dred sized guitar. I know the question is a little like how long is a piece of string but I would appreciate some comparisons with others that keep track of all the details.


Regards


Craig.
Author:  Michael Dale Payne [ Thu Jul 19, 2007 12:43 am ]
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I would not QC a top by weight. Deflection and tap tone will tell you more about the top. If your top is in the .110-.120 range on nominal thickness and your braces are of a proven design. I would pay more attention to tap tone and deflection Than a specific weight to shoot at. Over all weight does not know where the mass is. It only knows the total of the mass.
Author:  Alexandru Marian [ Thu Jul 19, 2007 1:01 am ]
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Still, the weight considered together with the deflection test results could tell something.

For example, if one makes two tops, and shoots for a certain deflection result. (he heard from X that 5mm at 1Kg is best etc. ) The tops are sanded until they both match.  Then they are weighted.  The lighter top should be better, right ?

In any case, I plan to weight everything in the future, besides testing deflection.  Might be useful in the long run.

If anyone has such weights for classical guitars, I would be grateful.  Sorry Craig if i am jacking your thread :(
Author:  Alexandru Marian [ Thu Jul 19, 2007 1:29 am ]
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Here is some interesting statistical data I've read yesterday.   I have no idea how accurate it is, and if he used 1000 tops or just a couple (that would render it useless)  but anyway, some food for thought.

http://www.larrystamm.com/wood_testing.php
Author:  Alan Carruth [ Thu Jul 19, 2007 7:59 am ]
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Thanks for that link. I'd bet that Larry has used a pretty large sample: he's got it handy, after all, and he knows a lot about the science end of it. I note that his numbers agree pretty broadly with mine, although I'm sure my sample is much smaller.

328 grams seems on the heavy side for a Dread top, but I can't say by how much. I don't build Dreads, and am extrapolating from a few OMs with Red tops that I have weights on. Also, of course, there's no way of knowing just where the 'extra' weight is. If you used a 2x4 for a shoulder brace, and that's where all the excess is, then it's unlikely to effect the tone much. If, OTOH, your tone bars are too deep or wide, that could make a difference. It's most liely that the majority of the excess is in the top plate itself; that's usually 3/4 of the total or more. Also, the final purpose of the guitar has to be taken into account. I'd think that, for a fingerstyle box, it would be over built, but if it's going to Rory Block, or some Bluegrasser who likes to use havy strings and play with a quarter for a pick, then you might want to beef it up.

Ultimately any method of QC you use, be it top weight, static deflection on or off the box, tap tones, Chladni patterns, thickness, or clairvoyance, you're going to have to compare apples with apples. Nobody else makes them quite the way you do, and the most meaningful data you can get is that on your own guitars. My own opinion is that it's hard to have too much information, but that has to be balanced with the amount of time you can spend getting it, filing it, and looking for relationships. I can see the utility of top deflection measurments, for example, but I don't do them consistently, simply because I've already got a lot of other data that, I hope, will fill in that gap.    
Author:  CraigSz [ Thu Jul 19, 2007 11:51 am ]
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I suppose because I have nothing to compare with being my first instrument I am just after some general guidelines. I have got absolutely no idea what is a good tap tone and even less how to go about getting one. When I tap the top I,m getting slightly different tones depending on where I tap. Around the bridge area is brightest.Thanks everyone for your thoughts . I realise this process will become easier the more instruments I build . I will see how this one sounds and work from that.


Regards


Craig


 
Author:  Jim Watts [ Thu Jul 19, 2007 12:42 pm ]
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Well, I have to agree with everyone here that deflection and tone are the way to go.

I don't know the size of your instrument or anything but I'll give an example of my last top, 15.5 inches lower bout, 20 inches long. Fully braced weighed in at 230 grams. I've had lighter and a little heavier, but not much.

As a side note, there's a strong correlation between density and stiffness. Denser woods are TYPICALLY stiffer. FWIW.

I'm not in any way saying that yours should weigh that. I do think however that 330 grams is a lot of mass to set into motion.
Author:  John Mayes [ Thu Jul 19, 2007 2:17 pm ]
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just weighed a 13 fret Grand parlor of mine (00, L-00 size). Lutz spruce,
average braces, very stiff top. Weighed in at 205g
Author:  CraigSz [ Thu Jul 19, 2007 2:54 pm ]
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A little more info on the top. It is 16 inch lower bout 20 inch length.I have thaken it down  to .115 inch thick. I have left the top flat ,no radius . The bracing is all 1/4 x 3/4 inch except the bracing between the sound hole and neck join which is 5/16 x 3/4 inch.


Thanks for the reply's.


Craig.
Author:  Jim Watts [ Thu Jul 19, 2007 3:10 pm ]
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Craig, is your bracing 3/4" tall everywhere?
Author:  CraigSz [ Thu Jul 19, 2007 4:48 pm ]
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Jim the main x brace and the 5/16  braces are 3/4 tall .The main tone bars and smaller braces are about 1/2 inch tall.


 


regards


Craig.
Author:  Dominic [ Thu Jul 19, 2007 9:44 pm ]
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Ive been recording top weight in the few OM style guitars I have made. The last two come in at around 280gm and 300gm so far. Not sure what it means yet but it is a base from which to work and experiment.
Dom
Author:  Blanchard [ Thu Jul 19, 2007 10:59 pm ]
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I don't build dreads so I can't comment on that...

My Om sized tops usually end up between 230 and 250 grams.
The bracing, including the bridge plate usually accounts for about 50-55 grams of that.

Weight does matter, I think. I have built a couple of guitars with tops close to 280 grams and there definitely seemed to be something holding those guitars back. They just sounded heavy to me.

These days, I look at the weight vs. stiffness (as indicated by Chladni patterns) of the unbraced plate. If the weight is above a certain threshold, I don't use that top.

Mark
Author:  Brock Poling [ Fri Jul 20, 2007 12:00 am ]
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[QUOTE=Blanchard]If the weight is above a certain threshold, I don't use that top. Mark
[/QUOTE]

I am curious, what is that threshold weight?
Author:  CraigSz [ Fri Jul 20, 2007 12:19 am ]
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Thanks everyone for your responses. It really does help reassure me that I'm not going to end up with something that will need fencing wire to get the top moving. By the way Alan I do love bluegrass and will probably end up with medium's on it at some stage


Craig.
Author:  old man [ Fri Jul 20, 2007 12:46 am ]
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That is very neat work. That's the first time I've seen a tone bar originating from the center of the bridge plate rather than from the X-brace. Interesting.

Ron
Author:  Blanchard [ Fri Jul 20, 2007 1:52 am ]
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[QUOTE=Brock Poling] [QUOTE=Blanchard]If the weight is above a certain threshold, I don't use that top. Mark

[/QUOTE]



I am curious, what is that threshold weight?[/QUOTE]


Brock

For an OM ish guitar,  unbraced top with soundhole and rosette, thinned and graduated until I get a certain stiffness....... the threshold weight would be about 190 grams. I'm generally a lot happier if the weight is under 185 or less.

I run my tops pretty thick so I generally like very low density wood, Euro spruce and Engelmann are my favorites. .130 - .140 is a common thickness for me in the bridge/soundhole area, thinning to .105 - .115 at the edge. Spruce has to be pretty light to be that thick and stay under 185 grams !!

Mark
Author:  CraigSz [ Fri Jul 20, 2007 11:27 am ]
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Thanks Hesh for your encouragement and explanation of tap tuning.I will give it a try. Ron the bracing layout I got from a picture that Rod True posted on the forum a while back. He based it on Jim Olsen's design. I really like the sound of Olsen guitars so thought I would give it a go.


Regards


Craig.
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