Gore plate thickness maths help

[Luke72]

Hi All. I have been putting this off for a very long time because the maths does my head in. I am trying to understand how the maths works for plate thicknesses as per the formulas in the Gore/Gilet book. i have my timber dimensions and density, and the frequencies FL, FC and Fd, but how do i transform that into a plate thickness. The math seems beyond me. I see people are using excel spread sheets, but having never used excel, that is making no sense to me either. I am sure this has been extensively covered on the board so if someone could point me in the right direction, i'd be grateful.
Cheers

[Dave M]

This is mainly covered in the Contemporary Acoustic ... section of this forum. There is a lot of it! And you will find that many others have struggled with this so you are not alone. I seem to remember that someone even offered a copy of their Excel spreadsheet.

Good luck Dave

[Luke72]

Hi Dave. Thanks for that. I did notice, but only after i submitted the initial post, that there was a section of the forum dedicated to this topic, to which i am grateful and not at all surprised. I've read and re-read the books, but at the moment i find the equations difficult to understand. Hopefully it will all click into place at some point. It would have been most helpful to see the formula applied to an example. I'll check out the dedicated section.
Cheers

[GregHolmberg]

Here's a Google spreadsheet that shows how to calculate thickness using the book's equations. The thickness is in column T.

Hope this helps,

Greg

[Luke72]

Here's a Google spreadsheet that shows how to calculate thickness using the book's equations. The thickness is in column T.

Hope this helps,

Greg

Thankyou very much. That helps immensely!
Cheers

[joel]

I have to say thank you too Greg. I downloaded your spreadsheet a while ago and then used it to step through the calculations in the book. I then made my own version using the constants and values in the book. Extremely helpful thanks.

[aflint]

Good day all,
Firstly, I have greatly appreciated this forum. I am currently commencing my 3rd build, which is a 12 string guitar and I have decided to go with an X brace system on this build, despite talking with and considering John Parchem's experience with his falcate 12 string.
My question is, ......
"what is the ideal thickness that should I make my sound board utilizing the calculations from the Gore/Gilet text. The calculation from what I see, has no factor in the formula allowing for a 12 string. Is there a factor to add in or is it just in the brace heights/thicknesses that make the difference?"
My Sitka spruce has a target thickness of 2.9mm.

Look forward to hear from the group.

Cheers

Antony

[GregHolmberg]

Well, with the caveat that I've never built a 12-string, I have these observations, based on my calculations:

• The panel is 60 to 70 % of the mass of the active area of the sound board.
• Mass is the #1 priority in a good sound board (other than not breaking, of course).
• Braces are 75% of the rigidity of the sound board; the panel is only 25%.
• It's the braces that will break if the string force is too high, not the panel. Peak stress is at the top of the main braces.
• I would think you want the same frequencies from the panel in a 12-string as in a 6-string, so the vibrational stiffness parameters in Table 4.5-2 would still apply.

So, if it were me, I'd go with the thickness calculated for f=75 Hz and do the stress calculations to size the braces appropriately for the tension of 12 strings.

It would be interesting to hear from someone who's actually built one though...

Greg

[kiwigeo]

My last 12 string build was basically based on a 6 string dreadnaught but with an extra tone bar across the lower bout. All other dimensions were kept the same.

The only significant difference as far as I can see between a 6 string an 12 string is string tension and a bit more fiddling around with saddle compensation for the lower string pairs.