Official Luthiers Forum!

Hello. Brand new to the forum.

I probably got your attention with that subject line, but it's not what you think. It was actually somewhat of a joke, but, the truth is, I don't know how else to describe my question in 1 sentence.

Here is the long and short of it.

If you hold an acoustic guitar up to your face and you hum into sound hole, at some certain pitch, the guitar will inevitably start vibrating so hard that it feels like it is going to explode in your hands!

This is something I learned from my father when I was a kid, and was later brought back to my attention on "the red violin" when they put the violin above a speaker and played tones until it hit the perfect resonance and the violin went crazy.

Why do I bring this up?

I feel that the majority of factory line guitars are just assembled with some general tried and true formula that the manufacturer specifies, and maybe with some of the more expensive models, they MAY take this into consideration, but, I feel that any Yamaha, or Fender, Low end Gibson guitar etc dies not take this into consideration and just "puppy mills" these guitars in the millions. As long as they play, they are sold.

Now.... I know that what I'm saying is a "thing", and I know there is some sort of relevance and importance when building a guitar.

But how much thought (if any) do you guys as builders put into this?

To elaborate further:

If this IS to be considered, then think about the following. Noise canceling generally works when a sound, is played back over the sound within the troughs of the original sound wave (basically), and the pitch (frequency) may or may not be slightly different, I dont remember). So when you tune the low E string to pitch, but your guitar's natural resonance is E flat, there is a good possibility that the guitar will sound muddy or dead.

I have had several acoustic guitars over the years and have played more than I have owned personally. For whatever reason I almost always find it necessary to hum into the sound hole of a guitar I play. Couldn't tell you why.

Over the last 30 years of my playing, I have discovered one thing. If you find the key that the guitar is naturally tuned to from its build, and tune your strings to that pitch (which may be very flat, very sharp or even whole notes off from standard tuning) the guitar will EXPLODE with sound when you play it and will naturally drone the other strings. And if you tune it to a complimentary OPEN tuning... omg....

So... I've already convinced myself that this is something builders either do, or should look for when assembling and building their guitars, and there may or may not be ways to TUNE the tops (and now we come full circle to my subject line).

So... if this is the case, I assume that on a carved top, it has to do with where l, and how much material is removed from the top. On a flat top, it may be the bracing location, shape, top thickness, thickness of the bracing or who knows what?

My question though... if this IS actually a consideration in a build, would it be better to tune the top to, say "A" (most of them seek to be around there) so when the strings are tuned, it has more resonance, or is it better to tune it slightly out of pitch to keep some of the drone down?

Honestly I feel like almost no one has thought of this, there is practically (no... literally) no information online about this that I have found. Most things just show you how to make the guitar, how to add the braces or carve the tops etc. No mention is ever given to the tune of the top. At most, people Tap it to "see how it will sound" which I'm sure does something, but I dont know what for sure, besides make you feel like you're getting somewhere?

I know this is an odd rant, forgive me I've been up for a very long time and am rushing to write this before bed, after having just noticed that my acct has been activated.

But I hope someone can add some clarity to this for me.

Thanks
Mb

There is a lot of information on modal tuning and for hundreds of years instrument makers have been placing the instruments resonances so that they do not cause problems like wolf notes and to enhance the voice of the instrument. Most builder who care try to place the guitars resonances in between notes.

http://www.goreguitars.com.au/main/page_innovation_summary_modal_tuning.html

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http://www.Harvestmoonguitars.com

Thank you! See, I wasnt sure of it was on pitch or between. It makes more sense to me to be between notes. I'm just glad to know that my suspicions were right!

I will read the link. Thanks

Trever Gore's book covers this pretty well. IIRC The two options once the guitar is built to change it's resonant frequency is to change the size of the sound hole or add mass to the sides. From what I understand a lot of the classic Hawaiian slack key players would actually do what you said, tune the guitar to it's resonant pitch. So they would do it on purpose. Ideally a guitars resonant pitch should be a few cents flat or sharp of a major scale note or at least on or near a note that doesn't get played a whole lot. It's not at all easy to control and for the most part it doesn't cause a terrible problem, but it most certainly can especially in a well built very responsive guitar.

Man... this is some "next level" stuff here. Thanks for taking the time to explain.

"Man... this is some "next level" stuff here"

Welcome to Guitars in Black......

Also known as the "Rabbit Hole"

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Steve Smith
"Music is what feelings sound like"

Isn't the rabbit hole where the sound comes out? Oh wait. That's the sound hole. Nm lol

Thanks guys.

So far I'm enjoying the community here, I just hope I'll have advice to add at some point lol.

Good observation. It's less of an issue on cheap factory guitars that are usually overbuilt and less resonant. Resonant guitars resonate more readily at their "blowing-across-the-jug-neck" frequency, so they can be more sensitive to it. It's unlikely that any factory takes this into consideration given the time and somewhat subjective evaluation it would require on a factory assembly line.

The main air pitch you mention is just one of the frequencies. Responsive guitars "light up" to some degree—usually lesser—at other frequencies, such as the top, back and neck resonant frequencies, giving the guitar some personality. Guitars that don't light up anywhere, having even response to all notes, can be boring, so some of this unevenness is a good thing.

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formerly known around here as burbank
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http://www.patfosterguitars.com

Thanks.

And yeah I didn't think about the neck (etc.)

So realistically the neck material matters as much as any other material . I know that often times, the heck material tens to match the back and sides, but I always figured it was more of an aesthetics thing.

However there seem to be certain woods that I rarely see for use on the main part of the neck. I may be wrong but at the moment, I cant recall ever seeing a rosewood neck, only fretboard.

I sure it has been done, but I dont remember ever seeing one at a guitar shop.

The 'neck resonance' is generally too low in pitch to matter on most guitars, particularly steel strings. It can be up in the playing range on Classicals, and when it's high enough in pitch to match the 'main air' frequency does seem to produce a particularly good sound. Getting this to happen in a controlled way it not easy.

In general, guitars are complicated systems of coupled oscillators, where all of the parts are working more or less together to produce the sound. This sort of system is very tricky to understand; the response is far more than the sum of the parts. In many respects it seems to me as though the complexity of the guitar is deliberate: it's what enables a good player to draw out the wide variety of timbres by varying their playing technique. Many of the traditional aspects of the design, such as the outline and sound hole placement, seem to have been conserved because that's what you need to do to get a 'guitar' sound. 'Improvements' that eliminate these features, such as 'bell', 'lyre', or trapezoid shapes, may be popular for a while, but die out in favor of more traditional ones fairly quickly.

I'll note, too, that when you look closely at any of the constituent parts, they turn out to be less 'simple' than you might think. Strings, for example, do a few things that the ones in basic physics texts don't, and they're probably the simplest part of the system.

All of which simply means that it's dangerous to start to get too interested in all of this. You have been warned!

Alan.

So I need to learn string theory. Noted. Haha

Great info btw. Thank you

MythicGuitars wrote:
"So I need to learn string theory. Noted. Haha"

Well, actually....

I did a series of experiments to measure the forces that a plucked string exerts on the saddle top some years ago, and gave a talk on it at an ASIA Symposium. I've got the write up on my web site as a .pdf, entitled 'String Theory'. I just couldn't resist....

Nice!!!!

Actually I'd love to read that, can you link me?

Go to:
alcarruthluthier.com and look on the 'Acoustics' page.