Sound hole size?

[viento]

How important is the size of the sound hole ?
It must be so big that I can put my hand through it.
But is bigger better?
I have two jumbos with almost the same dimensions but different top materials.
The western red cedar (6-string) is 11 cm or 4,33", the spruce (12-string) is 9 cm or 3,54331".

Are there any "recipes"?

[JonWint]

http://martinrep.com/dimensions.html

[Fathand]

The soundhole size is related to the volume of the body, The "martinrep" link given, is a good guide to start. I have noticed that a Gibson L-00 has the same 4 inch size soundhole as a Martin Dreadnought in spite of the body being smaller than a 000 so there is room for experimentation.

I typically read that smaller soundholes focus the bass response but I have played a Martin D-21 and D-28, both with Factory Large Soundholes that had great bass response to my ear so YMMV.

As for getting your hand through it, I can get my average size male hand through a 3 9/16" size 1-18 I built to bolt on the neck but smaller might be difficult for me.

[nikpearson]

Increasing sound-hole diameter will raise the air body resonance, reducing the diameter will drop the air resonance. This can have a significant effect on how an instrument sounds.

[viento]

The bass response of both of the mentioned guitars isn´t bad, cause might be the red cedar top of the 6-string and the other being a 12-string.Comparing both isn´t easy as they´re different.