Official Luthiers Forum!

Hello, first post for me here,
I am not a luthier and would appreciate any advice and knowledge you could share with me.
My luthier came across some planks of very old mahogany ,probably Honduran and we decided to make an OO acoustic. Being a fan of all hog guitars i asked him to make the top mahogany too but he is worried the wood is too hard and he has never used mahogany as a top.
He supposed that the mahogany used for the top of a guitar would be softer? So my question is ,since I have nothing to compare and draw results, is there specific conditions and prerequisites for mahogany wood to be used as a top?

Thanks in advance, I hope my question makes sense.
Alexandros

I built a 000 12fret all mahogany, which turned out great, so much so my brother and nephew asked me to build one for them each. So 3 in total and all were fine. I used the Stewmac plans and didn't alter the bracing or anything else, tops were about 3mm or a shade less. Hope this helps. Mike

Gibson and other makers have created guitars with mahogany tops. It's quite a valid choice.

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Thanks for your replies, I know mahogany makes great toos, I have a guild all hog guitar and love it. My question mainly is about the hardeness. Would you use a hard mahogany for a top or would it need to be a softer plank of mahogany? And is there such a thing? Don't know how to phrase it properly. Will a hard mahogany plank used for a top, "sing"?

I built an all mahogany L-00 style guitar that came out very nice. I used standard bracing but made the body extra deep on mine.

Dave

The Mahogany tops on the Martin guitars I once owned (an O from the 30's and an OO from the 40's) had fairly "hard" (dense) tops, but were also fairly thin. They sounded O.K. , but I will admit - mahogany is not my favorite top wood.
The old mahogany seems to be somewhat more dense than what you find today, but that is what they built the old guitars with.
Thin it down, tap on it a bit, and then decide if you think it will work. If your luthier still has doubts about using it, and a mahogany top guitar was not your original choice you may want to let him decide. He may be more comfortable using materials he is familiar with.

Alexandros, welcome to the forum. I have built an all mahogany double ought guitar and it is one of my favorites. The top plate was thicknessed sanded to 0.110 and bracing is fairly heavily scalloped 1/4 wide spruce. Short Martin scale, 12 frets clear.





A number of people have played my guitar and seem to speak highly about it. It is a tribute to the wonderful inexpensive mahogany guitars of the Depression era, think of the original 00-17 and similar. If your luthier would like any other information about how it was built I would be happy to answer questions

Tens of thousands of Martins have mahogany tops right now and they are great guitars.

Tone is subjective so what I experience and what you experience may not be the same. But I hear a bit of a darker tone from hog guitars that I like a lot especially for alternative music such as Alice In Chains unplugged, etc.

Welcome to the forum too!

And, forgot to mention you do't have to wait 5 - 10 years for the bass to develop nicely either like you often have to do with spruce.

I would not be afraid of it. But I’m pretty mathy in my process. I would simply thin it til it deflects to the same amount as a spruce top and go from there as normal.

^^ Wot meddlingfool said.^^
I'm a deflection man too.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

The latest addition to the Marvel Universe canon: Deflection Man! Raised on tap tuning and Chladni patterns, he developed extraordinary powers of deflection after exposure to mass quantities of nitro, epoxy, and CA fumes. Making the guitar world safe for luthiers and players alike from those who would build lackluster sounding guitars. Coming soon to a cinema or streaming service near you.

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If you measure the properties of the wood it turns out that most mahogany will need to be about the same thickness as spruce to be stiff enough along the grain. Since it's usually denser that produces a heavier top. It's harder to drive a heavier top, particularly sat high frequencies, so mahogany tends to have a 'bassier' or 'warmer' sound, and a bit less power. You could go thinner with the top and make it up with taller bracing, which saves some weight, but I always feel that you lose 'clarity' that way because the brace and top stiffness don't match as well.

I did as Alan suggested, in fact I think I asked the same question here back before I built it and followed Alan’s advice.

I just went with the same deflection figures I used for Spruce.

It was well received and I was happy with it. It’s an OM.

ABEBADCF-A10B-44C4-A49F-6602CBCE748C by Terence Kennedy, on Flickr

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Exactly what I would do too.

These are all great answers, thank you so much! I happen to really like the mahogany sound , dark sounding is what i want my guitar to sound like, not very fond of the spruce brilliance in the sound. From our answers i draw the conclusion (and correct me if I am wrong)that mahogany IS expected to be harder and denser than spruce and it is nothing to worry about soundwise, it will still play as mahogany is supposed to. Not as loud and hi-range but darker, mid-rangy and bassy. Can you please clarify (so i canmake the translation cuz my luthier doesn't understand english) what is the meaning of deflection rates and how to measure it so i can explain it to him?

If this luthier doesn't already use deflection then it's kind of a moot point. In order to use deflection testing you have to have a lot of data or at least a few good guitars at those deflection values.

For example, I use a standard red brick and place the weight right over the bridge footprint and measure deflection at the X-Brace crossing. I found that for an OM size guitar a deflection of .3in works really well so for a responsive guitar that is what I go for. I have built 15 OM guitars so that is why I know this value works. They are remarkable consistent at that deflection value.

Other luthiers have their own methods of doing it and their own data sets. So again if he is not already doing this than it's sort of useless on the first guitar.

If you trust this luthier then just let him/her do their thing.

Deflection is just a way to get a more or less 'standardized' measurement of the stiffness of the wood. Many makers flex and feel to do this. In one test I was told of a very experienced violin maker was able to sort out small slips of wood with an accuracy of 3% or so compared with 'lab' measurements. I'm also told that, in similar tests at violin maker's meetings, most people are nowhere near as good at this as they think they are...

A lot of folks do more or less what jfmckenna does; use a standard (for them) setup with the same handy weight every time. This gives a number for the deflection that can be compared with other instruments you've made, so that, over time, you can home in on what will work best for you. These sorts of measurements can also be done in ways that give standardized numbers, particularly the 'Youngs' modulus' for bending along and across the grain. With this sort of information you can tap into other people's experience, which is a considerable shortcut. Both David Hurd in his 'Left Brain Lutherie' and Gore & Gilet in 'Contemporary Acoustic Guitar' (two volumes, and much more expensive) go into this in detail, and there have been articles in other publications as well. As with any measurement, there are some pitfalls you should be aware of if you want to get useful information, and these get covered in both books.

I use a vibration test to get that sort of data, along with some other information that is useful. Gore & Gilet cover that too. Haines published a number of articles on this in the Journal of the Catgut Acoustical Society, which is available on line. See, in particular, "The Essential Mechanical Properties of Wood Prepared for Musical Instruments", JCAS Vol 4, Series 2, pp 20-32, Nov. of 2000. With current technology this sort of thing is actually fairly simple to do, and very useful.

I agree with the above statements. Trying to instruct your Luthier on how to build a guitar can only lead to frustration to the both of you and probably be detrimental to the outcome. If he has built a number of guitars I'm sure he will come up with something nice.

What Clay just said.

As I said earlier, I built one a few years ago and did not do any deflection testing or anything like that - I'm not smart enough. I had built a few smaller bodied guitars (single and triple ought, never a double) and they had all turned out just fine with spruce tops between 0.095 and 0.100, and scalloped braces. Since I had been told mahogany wasn't as stiff as spruce (Sitka and Lutz) I simply made the 00 top about 10 percent thicker.

As I was building the guitar I did my rudimentary tapping and flexing, but remember that I really don't know what I'm doing. I must be very lucky because the guitar sounds quite fine.

I'm quite sure your luthier has a method of selecting wood and another on how to work with it, it would be totally wrong of me to try to convince him/her to use mine. I did, however, do a build thread at another forum, if you would like I can PM you the link and you can share that with your builder.

The guitar itself is remarkably well balanced. I would say the notes tend towards the fundamental but there are certainly overtones there. Its got a huge bass for a little box. Because I have several acoustic guitars I tend to leave this one strung a little more heavily and tuned to an open chord - its a heck of a great little blues box and handles the slide very well.

I am not insinuating that Alvaf is in any way like that but I have had that experience once my self and if anyone ever 'instructs' me to build a guitar again I will fire them

I built a OO 12 fret all hog guitar for my son and it turned out very well. I only used one tone bar off the x brace and two finger braces, one on each side.


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That's my intuitive take. Factory built guitars are overbraced, says me, so as to limit warrantee activity. We home builders don't have the same needs.

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Peter Havriluk

If that because most of us will be dead before the top pulls up and the guitar needs a neck reset?