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All-mahogany Martin-1 top thickness
I’m planning to build an all-mahogany Martin-1 (parlor) guitar. My question is; what about the top thickness? I have some older Honduran mahogany I’m gonna build with.
.12″
That’s what I was thinking of… Curious what you can advice me.
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8 Replies
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That is a good safe number for spruce. Are you going to be doing any resonance testing ? This might be an interesting question for @giulianonicoletti .
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Thanks! I don’t even know how to test for resonance. I’m just starting, studying and learning and really can use some advice.
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Finding the resonant frequencies is not that difficult, and well worth your time and $ investment. You will need a computer, some software, and a measurement microphone. I recommend you start by watching Guiliano’s first video on this site regarding testing.
For measurement, the UMIK-1 works (USB connection) and costs about $130 or so. The Behringer ECM 8000 also works well, but will require a preamp. It is on sale right now at Sweetwater for $20 with free shipping. I have used both and both work well.
There are several free software options. Guiliano likes REW which works fine. https://www.roomeqwizard.com/. Trevor Gore likes Visual Analyzer 9.0.6 (not the later versions). https://www.sillanumsoft.org/download.htm. A third option is Guitar Tap. https://github.com/dwsdolce/guitar_tap. All these do is take the tap signal and do FFT (fast Fourier transform) on it to get the resonant frequencies.
You will first need to make sure your top panels are planed, not just rough sanded at 80 grit (the smashed rough sanded wood fibers add mass but do not contribute to stiffness). Cut the panels to true rectangular. Then measure dimensions, thickness, and mass.
There are three different tap tests to measure the elastic properties of the wood. We will need these three numbers.
The first is the long grain Young’s Modulus. Hold a plate at 22.4% of length downwards, and tap in the middle. The tap frequency will give the long grain Young’s modulus. Write this down. I haven’t tested Mahogany, but for Spruce this number is generally around 60-70 Hz.
Second is cross grain YM. Measure 22.4% along the width of the wood and hold at 22.4% in from edge about 40% down the length of the wood. Write down that tap tone frequency. As above, I don’t know the likely range for Mahogany, but for Spruce typically around 100-110 Hz.
Third is shear/diagonal YM. Hold along the length at node (about 50% down) and tap in lower corner. Put microphone directly behind the tap area in lower corner. Write that one down too. It will be about 40 Hz and is sometimes hard to get (and not all that critical for the formula). With larger plates it can be lower and really hard to get.
If you decide to do the testing, report back with the data points (x/y dimensions of plate, thickness, mass, and the 3 resonant frequencies) and I’ll do the math for you and get you a suggested top thickness.
Best,
Michael Minton
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Thanks so much Michael. This is all so valuable info. I’m gonna dive in and will come back to this topic!
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Just a couple of comments on this. Robbie talks about using the ‘sheet metal sound’ to determine the stffness experientially rather than from measurements.
And another option for the top thicknessing is to use the web fft software I put together as an alternative to REW and the python packages and web calculator that implement gore’s formulas in his book.
These are located here:
Robbie talking about the sheet metal approach:
https://www.youtube.com/watch?v=JHs7s1_pbAgMy FFT software & thickness calculator:
https://www.celestialinstruments.com/blogs/calculators/thickness-calculator
-Rick
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Thanks Rick. Really helpful. I’m gonna digest this first before I come back to this topic!
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Already a lot of info there, what a great group!
I can add the link to my book, that will give a nice overview:
Cheers,
Giuliano
a.co
Mastering the sound of the acoustic guitar: Nicoletti, Giuliano: 9791041512539: Amazon.com: Books
Mastering the sound of the acoustic guitar [Nicoletti, Giuliano] on Amazon.com. *FREE* shipping on qualifying offers. Mastering the sound of the acoustic guitar
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Thanks. I will look into it ! And I agree, what a great group!
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