Australian/New Zealand Luthiers Forum

I used the new 1.57 kg/m^2 number to update my 4DOF model of the medium falcate-braced steel-string. Based on the classical in table 2.4-1, the area inside the Chladni line (i.e. the top effective piston) is about 30% of the free top area, so I'm using At = 0.0416 m^2 (compared to 0.039 for the slig...

I have added to my spreadsheet an estimate of the whole soundboard mass of a medium steel-string with cut-away (per drawing #4), including the transverse brace, and head and tail block areas. I came up with 238 g. Pretty close the the numbers others have given here (229, 230, 239). For an area of 0....

AKEric wrote: ↑

Sun Aug 15, 2021 2:34 am

Length and width for my OM sized steel string guitars are 482mm x 382mm.

OK, I'm going to guess the area for the cut-away version is about 0.1390 then (vs. 0.1442, i.e. about 4% smaller), giving areal densities of 1.72 and 1.65 for the two cut-away ones.

Watch out for shear stresses as well as bending stress. I recall something in the books about balsa failing in shear well before the flexural limit was reached. Yes, this is discussed in section 4.4.6 (commonly referred to G), but it wasn't shown how to calculate or measure it. There was a formula ...

OK, now that I've calculated the rigidity (EI) of the soundboard, it seems like it should be possible the calculate the deflection (y) as a function of the force (F) applied, and therefore the spring constant, K = F/y. In Equ. 1.3-1 Gore shows the formula for deflection of a beam: y = FL^3 / 48EI Of...

Hello, I have data on three Falcate braced tops. All are standard OM sized, I don't have exact area measurements, but all have a 1/8" rim over hang for trimming and sound hole cut out. Tops thickness per my spreadsheet, all under 3mm. All Sitka spruce. #1 = 205g. No cut-a-way. This was an especiall...

Sorry thought I had said. It is steel string, based very closely on Trevor's design in the book for a mid sized SS. Assuming you have the book you can fairly easily work out the area since it is printed on a grid of squares. (and that takes me back a bit trying to measure the area uder curves on sp...

It's a long story but i have been able to get an approximate weight for a falcate top. This has approx 5 mm extra round the edges and does not have to cutaway removed yet. It is a little less than 3 mm thick Came in at around 230 g. Cheers Dave Thanks, Dave! Is this for a steel-string or nylon-stri...

OK, thanks to Richard, I found my errors. I'd failed to multiply by the quantity of braces (2) in some places. I now get the same numbers as in the book, Table 4.4-2. I'm looking for alternative species to use for braces. So I entered the 46 lightest species from my list on wikipedia (taken from the...

Thanks, Richard! I fixed the permissions on the spreadsheet, you should be able to see it now. Look at the "Braces" tab. I need to figure out what the curvature adds to the rigidity, as I plan to make an archtop with a top cylinder radius of 2 m perpendicular to the grain. I think the formula in Sec...

I'm new to this whole engineering thing, so I'm not sure what I'm doing when calculating soundboard rigidity and brace stress, as in Design section 4.4. Unfortunately, calculating the net second moment of area for the soundboard, Is, and flexural rigidity, EIs, was left as an exercise for the reader...

Thanks for that, Richard. 196 g for a classical top. If your guitar is anything like the one in the plans included in the book, then I'm going to guess that your top is about 490x370 and 0.1398 m^2 in area (I counted the squares in drawing #3, including the area of the head and tail blocks). That wo...

OK, my best guess for modeling the Gore Medium steel-string: Screenshot from 2021-07-24 17-11-15.png Screenshot from 2021-07-24 17-48-23.png If you want to see how I came up with these numbers, here's the spreadsheet . My technique is: I start by estimating the areas and masses by counting squares o...

Surely someone out there knows the mass of the top on the falcate-braced medium steel-string? Well, in any case, I've attempted to estimate the mass by adding up all the parts, and using their dimensions and density. Here's what I got: Screenshot from 2021-07-24 14-53-56.png This is just for the vib...

I'm trying to fit the 4DOF model to what I know about the Gore falcate-braced medium steel-string guitar, built as shown in the plans included with the book (drawing No. 4). There are bits of data on this guitar scattered throughout the book, but the main thing I don't know is the mass of the top. A...

I'd like to collect here in this thread any mathematical models people have made using the four-degree-of-freedom equations. This would be composed of input values and calculated results, having been measured from and/or fit to real guitars, as shown on page 2-37 of the design book. Unfortunately, a...

You might find this Master's thesis interesting. The author creates a new composite material for acoustic guitars using carbon-fiber filament, polyethylene tape, aluminum strips, and polyurethane foam, which he claims matches the mechanical and tonal qualities of Sitka Spruce. He has a spectrum anal...

I know this thread is really old, but I just want to give a big "thanks" to Jim Kirby and everyone else who worked on this. And if course Trevor Gore for writing the book in the first place! I installed the free open-source software GNU Octave (version 6.2.0 for Linux), copied the script Jim posted ...