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Message started by Acabooe on Feb 14th, 2008 at 2:48am

Title: Question about sound hole size
Post by Acabooe on Feb 14th, 2008 at 2:48am
Here is a good question for all of you scientific approach builders out there.

The size of a normal sound hole on a tenor is about 2 1/2" diameter, right?

This size sound hole would have a specific circumfrence, and area, right?

Here is the question:
If a luthier wanted to make multiple sound holes, how would they know what size to make them?

I was thinking that if you measure the circumfrence of the normal size sound hole, and make it so that the sum of the circumfrences of the multiple sound holes, add up to the single sound hole's circumfrence, then it should still have optimum results.

Would my theory be correct?

If not, is there any one who can explain?

Mahalo for any help that you can give.
Bob 8)

Title: Re: Question about sound hole size
Post by Don_Orgeman on Feb 14th, 2008 at 3:38am
Bob:

I think you want about the same amount of surface area open as on the 2 1/2 inch hole.  Surface area is pi R squared, or 3.14159 X 1.25 inches X 1.25 inches = 4.9 square inches.  Adding up the circumferencs does not get you to the same ratio since the circumference is calculated by 2 X pi X R (a single value of R not squared).

I don't think this is an exact science, so start with less area for the multiple holes and gradually sand to increase the sizes until you get to the right sound volume.

Don

Title: Re: Question about sound hole size
Post by Jeff B on Feb 14th, 2008 at 7:44am
Don is correct.

Though I couldn't quote the physics of it precisely, I'd venture that the opening's area is just one factor. Placement of the pukas relative to braces, strings, and bridge, etc. would also seem to be important. Maybe not...

But, with our relatively insensitive ears (compared to a dog :)), would we be able to really discern the difference? Put your pukas where YOU like 'em!

Jeff

Title: Re: Question about sound hole size
Post by Acabooe on Feb 15th, 2008 at 1:43am
Thanks guys,

Although I didn't exactly understand the math of it ( was terrible in math at school ) I am very thankful for all the help I receive.

My dad is great at math, I will ask him to go over it with me, and look at the math application. I would still like to put my pukas where I want them though :P

Mahalo
Bob 8)

Title: Re: Question about sound hole size
Post by konacat on Feb 15th, 2008 at 2:02pm
Bob,

You have already received some good information on this subject. You might also try searching under the word decibel for some past posts. And of course, I have some thoughts to add.

I think that Don is correct in that you are looking at the total area of the puka or pukas. Jeff is also correct about placement of the holes. Put them wherever you like but keep in mind the structural integrity. My thinking is that you would them on the sides or above and horizontal bracing. You certainly would not want them on the sound board below those braces where sound is being generated from the sound board. In fact, today I saw a photo of two pukas on top of the upper bout that were near either side of the neck. I didn’t really care for the look but whatever you like.

Now if you were creative and mathematical you could use some geometry and do something a bit more exiting. I have often wondered if you could treat sound the same way we energy is transmitted. If you created a dish on the back that was mathematically shaped to receive the sound transmission from the top and then focus it to a specific location such as your sound hole. An example would be a satellite dish. When the dish is lined up properly to receive incoming signals the dish then can focus those signals to the receiver end of the unit. I don’t see why you couldn’t use the same geometry to focus the sound directly to the sound hole. Of course it might make the back very round and misshapen. It’s just a thought


Philip

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