Australian/New Zealand Luthiers Forum

I stopped using it and run REW, I still look at it sometimes, but it’s never clean like Trevor’s graphs and I have it spec’s to his settings I like Room EQ Wizard too. It's free and it runs on Windows, Mac, or Linux. Also supports the UMIK-1 USB measurement mic ($130), and can import the calibratio...

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

As described in the Design volume, the natural resonance of the top, the back, and the air are coupled together. It's easy to calculate the uncoupled frequency of each. For example, the air resonance depends on the volume of the cavity and the area of the soundhole. But calculating where they end up...

Thibaud-- I think these folks provide a similar grading service in your part of the world: https://woodntones.com/the-abies-project They work with Rivolta Woods in Italy (outside Milan). https://riwoods.com You might also contact Giuliano Nicoletti at https://www.iuliusguitars.com/ in Sorbiers, Fran...

Thibaud-- It makes me happy to see my spreadsheet being used! I had the same thought about that paragraph. He seems to be implying that for this guitar, a 390x490mm OOO size, that 169g (the POC, #11 and #12) is too much. Also, he said that sample WRC #17 was too heavy at 165g. The Engelmann averaged...

Here's my spreadsheet (google docs).

I have used average values for many species listed on wood-database.com.

Section 11.2.2.2 states New Guinea Rosewood for transverse brace, I looked for it on Wood Data base, for the properties, weight/density/ym,, etc, it’s not there. Is there another name for this wood? I searched for it on wikipedia and found this: Pterocarpus indicus , commonly called Narra (wood dat...

Thinking about it more, the problem with this guitar is that it's just too darned stiff! First, I should have done the calculation in newtons, not kg. In which case, this top has a stiffness of about 490,000 N/m. I think a typical stiffness for a steel-string flat-top is about 47,000. So this top is...

Here's my very crude rig. It can be adjusted for both height and width via slots in each member. It works, but I think there's room for improvement. :? PXL_20221005_040959121.jpg For a weight I used a 1 kg lead diving weight (1006 grams, actually). On this Ibanez archtop (the top of which is greatly...

Says the calculations, as in the book, Table 4.4-2. I posted an extensive spreadsheet (80 species) a few days ago in this thread. Did you see it? Here it is again in case you missed it: spreadsheet Specifically, for these species: 1. stresses do not exceed the breaking point, 2. due to their stiffne...

If you don't need to bend your braces, some of the best species appear to be: Obeche Western Red Cedar Sugar Pine Coast Redwood Eastern White Pine Okoumé These are all better than Sitka Spruce, Engelmann Spruce, or Norway Spruce for braces. Top panels are a different matter, of course. Silver Maple ...

To answer the original question: Mediteranean Cyprus was one of the few species that exceeded the allowable stress. It's at 130% of the allowable stress. The other species that exceeded the allowable stress are: Balsa Paulownia Gore's Western Red Cedar (but not average WRC according to wood-database...

This is an old thread, but I thought I'd pass on the results of my search for a brace wood. Note that this is just calculations, and I haven't actually tried any of these species. First, the species must be bendable. I found this report that lists steam-bendable species. Machining and related charac...

Here's the Hearmon paper, in case any one wants it. The Fundamental Frequency of Vibration of Rectangular Wood and Plywood Plates R. F. S. Hearmon, 1946 Proc. Phys. Soc. 58 78 One thing I learned from this paper is that the constants shown in the book, Equ. 4.5-6 (126 and 4/7=0.5714) are for a clamp...

In section 2.4, the book references two papers by Ove Christensen. I managed to find these on the internet, in case anyone wants to read them. Simple model for low-frequency guitar function, 1980. Found here: https://www.iuliusguitars.com/portfolio_page/my-research/ An oscillator model for analysis ...

I applaud any effort in guitar building of measurement and being more scientific! The book covers how to determine the thickness of the top panel based on the properties of an individual piece of wood. You have to measure it, weigh it, and find the frequencies of its natural resonances. It takes jus...

Yes, you need to use values in the formula in Pascals and meters. The values in the table are mm and GigaPascals. So divide the mm values by 1000 and multiply the GPa values by 10^9. I.e 11.84E09.

Greg

Well you might be right but...arch action comes from inducing compression in the arch and thus relies on support at the spring of the arch which is questionable on something as light as a guitar. Its not flexural so vibration modss will be very different. Think Hoover Dam versus Tacoma Narrows Brid...

Just read through the posts. I am not sure it is addressed, does the mass of the top only include the vibrating area of the top not the weight of the top itself. That thought always kept me from weighing the top. Well, I've asked poeple for the weight of the whole top, since that is really the only...

How have you incorporated the curve in the top into your calculation of I? I cant see it in the spreadsheet. A 10mm rise will make a big difference. I assume you are using your I value to derive your K value?? Also, I re read your previous post and I don't understand this This would bring the long ...

OK, I've modeled a large acoustic archtop, 17" x 3.3". Pretty close to a Gibson L-5. I came up with an 80 mm sound hole, top stiffness 55,000 N/m, back stiffness 137,000, no added side mass, producing resonant frequencies of 90, 180, and 227 Hz. This gives me targets for the cylindrical archtop I wa...

Oh, yes. This report, commissioned by Pacific Rim Tonewoods, compares the 4 extant techniques for thermal modification of Sitka. It examines changes in stiffness, density and damping. As with everything else, technique matters, and a mere label of “Torrefaction” does not suffice. The outcomes vary ...

Here's another report on torrefied wood. This is by the International Thermowood Association in Finland, 2003. While engineering tests of the ThermoWood method indicated increased resistance to humidity, they also showed a significant reduction in strength (ultimate breaking point), while stiffness ...

All good points, Richard. I'll take them in order. Yes, it would be difficult to calculate I for such a complex structure as archtops usually have. Varying thickness, complex shape, holes in inconvenient places. I'm thinking I'll create a cylindrical top with a constant thickness. I hope this simple...

Reminder: all this data is in the spreadsheet.