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Is there a rule of thumb as to the area of a sound hole? Is it true that if the sound hole is made smaller you get more bass response?

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A higher purpose for wood.
Rich Smith
Issaquah, WA

Rich my friend I know of no rule-of-thumb for sound hole size. I simply take an existing design and tweak as I see fit or not at all.

And yes generally speaking if you reduce the sound hole size you get more bass. I had this wrong and thought it was the other way around and Al C. set me straight. Hopefully he will weigh-in here and tell us how this works.

It's also possible to get more bass by tapering the soundhole edges parabolically... I only know a few people who do this, but it is worth experimenting with...

As in make the soundhole oval?

No, think of chamfering the edges of the hole.

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Jim Watts
http://jameswattsguitars.com

A little bigger diameter helps get one's hand in for attaching/detaching the neck (if it's a bolt-on of course!).

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http://www.presnallguitars.com

Ricardo

How did you figure out the soundhole on your last few builds? Did you go off the plans?

PNJ, if I were to build a standard 000 from the plan I would make a sound hole 3.875" in diameter. Since I am putting my sound holes in the upper bout, I plan on copying a Grimes design that has a 3.25" dia hole on one upper bout, and a 2" dia hole on the cutaway bout. The area of hole for the standard guitar with a 3.875 hole is 12.18 inches whereas, the Grimes style has a total hole area of approx 16.5". So this leads me to the question what affect will hole size make on my sound?

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A higher purpose for wood.
Rich Smith
Issaquah, WA

The "sound hole" is a tuned port that affects the air-resonance of the contained volume of the guitar body.

A smaller hole will tune you lower, and a larger one will tune that resonance higher. This may seem counter-intuitive, but that's the way it works.

You need to take into account your plate tuning and all the other factors of instrument design to decide what effect your port tuning will have on the overall instrument.

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-donh-

Everything is a tone control!

As I understand it, the location of the hole also makes a difference in the pitch of the main air resonance. If I'm not mistaken, Al has explained how a hole in the upper bout (i.e. nearer the edge of the plate) will create a lower air resonance than the same size hole in the usual location, which may be why Steve Grimes' holes total a larger area.

Al or anybody, please correct me if I'm wrong.

I've always been curious about Tony Rice's big sound hole dread. I believe Martin makes a signature model like that, but I haven't heard one. I assume the main air resonance is higher than usual. I wonder by how much, and what effect that has on the quality of the low notes - and why he likes it that way. It's not something that comes across to my ear in any obvious way when I listen to recordings of Tony's playing, but microphones and EQ and reverb and whatnot play such a big part in recorded sound.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Another Myth.
IF shaping the edge of the soundhole parabolically vs rounded over effects the amount of bass, it will be inaudible. Let's face it here....this is grasping at invisible straws. This smells like an attempt at differential marketing.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Ya, I'm still at the very basic level. My first guitar is a prototype. So I am trying something unconventional. I want to find out for myself what affect the larger unbroken sound board with upper sound bout sound holes has on sound. It will be a short scale 000.

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A higher purpose for wood.
Rich Smith
Issaquah, WA

A=pi*r^2

'Way back in American Lutherie #1 William Allen published an article on the basics of air resonance. If you haven't got the mag, get the first 'Big Red Book' with that article in it.

Adding a 'port' in the side will raise the pitch of the 'main air' resonance. THe larger theport is, and the farther from the 'main' soundhole, the more it will raise the pitch. OTOH, as has been said, putting your soundhole in the upper bout will drop the 'main ar' pitch. Given all of the other variables, there's no way to calculate what's going to happen. I'd suggest making the hole(s) a little on the small side, and enlarging it/them later if you need to.

Dropping the 'main air' pitch is not the same thing as 'more bass', although that's the most likely outcome. Sometimes enlarging the hole can give you a stronger low end, simply because there's more sound coming from the hole, even if the pitch of the resonant mode is higher.

Alan, this is a grand experiment on my part. Hard to know if it will be a flop or not.

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A higher purpose for wood.
Rich Smith
Issaquah, WA

I built a thin bodied acoustic guitar based roughly on the size of an OM guitar for Miami. I didnt want any sound holes at all, but after I got it built, the guitar just looked funny so I added some "flame" inlays that I made with left over bloodwood and then drilled 1" holes inside the flame inlays on the top of the guitar. It turned out better than I had hoped for, but that was a pure stroke of luck.

I dont think the area is the same, but was close when you consider four 1" holes Vs. one 4" hole.

I had the same issue trying to figure out just how much area the holes should cover to give the desired sound, so I completely understand the question and would like to know a "rule of thumb" for figuring it out in the future.

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Reguards,

Ken H

Thats cool Ken, In what way did it turn out better than expected?

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A higher purpose for wood.
Rich Smith
Issaquah, WA

Search the archives: key word - Helmholtz resonance

Among many relevant GAL articles is one in American Lutherie Summer, 2005 by R.M. Mottola titled "The Helmholtz Resonance".

Welcome to the deep end of the pool.

Larry

Larry, I will. I definitely feel over my head.

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A higher purpose for wood.
Rich Smith
Issaquah, WA

I braced the lower bout of this guitar like a classical, but with an x-brace. I guess you could say and x-brace with fingers?

This answer is based strictly on the acoustic properties of the guitar. The guitar turned out to be MUCH louder than I expected it to be first of all. Because of the 2" body depth, I had assumed it would be rather quiet. It has a strong bass, but I wouldnt call it "boomy" by any stretch. Overall it turned out to be more of a mid-range strong guitar. Again, this is based on the acoustic properties, unplugged.

It is intentionally built a little on the heavy side (brace wise) because I wanted to market it toward electric guitar players who wanted to play an acoustic set and plugged in, not acoustically. It was built intentionally for a UST pickup to be installed and I sort of got the idea from the Taylor T5. The sustain on the guitar is better than I expected also, but I feel this is due to the solid maple neck. It also surprised me because it has a pretty strong bass response to it, which I wasnt expecting.

Plugged in, it sounds terrific! It has a true acoustic sound, which is what I was after. Playing it, it FEELS like an electric.

The down side of the guitar is that I left the neck too thick and at some point I may take the neck off and carve some more off of it to better match my other guitars neck profiles. It literally took me all day to install the pickup (B-Band) because you cant get your hands inside the guitar and I had to go fishing for everything to get all of the controls and electronics in the right places. The neck is bolted on with 4 wood screws like any other electric guitar neck.

It was a neat experiment, but didnt sell. I'll hang on to it and maybe some day somebody will come along that needs just this guitar. It was a fun experiment though!

As a side note, I got more compliments on the finish of this guitar than any other I have ever built. The finish on this guitar was done by Joe White and the finish is flawless.

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Reguards,

Ken H

I read in the Tap Tuning book you can tune the soundhole of a guitar by using a decibel meter then keep increasing the soundhole diameter by sanding doing this the sound level increases to a point, the optimum diameter then starts to decrease which you need to of stopped before or then bind the soundhole. True or not I don't know I don't own a decibel meter, but out of the hole book it'd been the only technique I may use depending in the price of the decibel meter

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Formerly JJH

I learn more from my mistakes than my successes

..it's nowhere NEAR close; 4 1" holes gives you an area of about 3.14 square inches, a single 4" hole has a surface area of roughly 12.5 square inches.

I found this info in the archives of a forum that gives a hemholtz formula to determine the ideal hole size for the top:
Any soundbox has a volume V which is equivalent to a sphere of radius R such that V=4/3 pi R**3. If I understood the explanation correctly the optimum soundhole surface area A for a Helmholtz resonator will be that of a circle of radius r such that r=R/4 where A=pi r**2. As long as the surface area of the opening is correct it can be any shape you choose."
Anybody else use this as a guide to determining hole size?

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A higher purpose for wood.
Rich Smith
Issaquah, WA

What if you made inserts for the sound hole ? Does the hole size also have some baffle effect? Does anyone know how sound hole(s) placement in the upper bout will affect the tone with the freeing up of the upper bout with the canterlever neck designs?

Chris I'm wondering the same thing about placement. The formula supposedly calculates ideal size for the Hemholtz but I have seen nothing about where the hole has to be placed.

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A higher purpose for wood.
Rich Smith
Issaquah, WA