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I'm trying to make an Excel spreadsheet for some basic math calculations. I can make excel do the simple arithmetic but I would like to have a line of cells for the Helmholtz Resonance in which if the volume is entered and the port size is entered the basic pitch in htz is delivered. And then a line of cells that would figure the approximate sound hole size for a given volume if a certain pitch is desired. I'm thinking that it might be useful not so much on my standard builds but for cigar box ukuleles that come in all sizes as a comparison starting point to other successful cigar box builds.

I can find the formula buy my excel skills are't good enough to make it work.

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Michael F Smith
Goat Rock Ukulele
http://goatrockukulele.com

My excel skills are strong. If you have a sheet laid out with your desired table, and the formula(e) in math notation, I can likely make it work.


Sent from my iPad using Tapatalk

Excel is a breeze to use. As Tim said, provide the math notations and it can be done easily.

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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."

Here is the basic formula for sizing sound hole size. I tried plugging it into excel and it didn't work for some reason. Thats how daft I am with this stuff. Also below is much of the text from the source where I got this formula.

R = (V/(4/3*PI))^1/3

So, we take the number we got for the volume of the psaltery, (91.36 in^3) and plug it in as V in our equation.

First we divide it by 4/3 PI, or ~4.1888 and get 21.811

Next, find the cube root, which means 21.811^(1/3)

And we get ~2.79″

So, in a nutshell, the volume of our psaltery is equal to the volume of a sphere with a radius of 2.79 inches. And now for the final payoff, dividing by four to get the size of the soundhole:

So, 2.79/4 = .6975″

So, the ideal soundhole size for this instrument is a circle with a radius of .6975 inches, or a diameter of 1.395″. Overall, a 1 3/8″ (1.375″) hole would do nicely. Now, you’ll notice that I used a triangularsoundhole, so it will help to know the surface area of our ideal hole size, which can be found with the equation for a circle’s area: A = PI * R^2

.6975^2 * PI = ~1.528 in^2

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Michael F Smith
Goat Rock Ukulele
http://goatrockukulele.com

I put V in cell B1, then wrote your formula in cell B2
=(B1/(4/3*PI()))^(1/3)

When V = 91.36, that should generate the 2.79. Is that the part you were struggling with?

The rest of the manipulations are
soundhole size in B3:
=B2/4

and surface area in B4
=B3^2*PI()

Yay!! that works Tim Thanks. What about this one. 1237.917 is the speed of sound @ 70 degrees at sea level. It is in km/h. I assume that I will need to do measurements in km. or mm

Thanks

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Michael F Smith
Goat Rock Ukulele
http://goatrockukulele.com

So does this calculate the hole size for a certain frequency you are trying to match?
Would this opening size be optimal for sound projection?
Not sure I understand.
Thanks,
Dan

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wah
Wah-wah-wah-wah
Wah

The last equation theoretically will give the cavity frequency of a given cavity with a given port size and tube size. Tube size being the top thickness at the sound hole. Most guitars from what I have read come in at around 55htz. I don't know what ukuleles come in at and that is one thing I hope to learn. It isn't that simple though and I plan on using these numbers as a reference and not to size sound ports. If you make the sounhole the size these figures would guide you to a ukulele will tend to bark in a very unpleasant way. Least that is what seems to happen if the sound hole is too small for the cavity volume.

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Michael F Smith
Goat Rock Ukulele
http://goatrockukulele.com

Most guitars come in between 90-110 HZ
But they are Not true Helmholz resonators anyhow because they are comprised of flexible plates rather than being a rigid chamber and this lowers their resonance from the theoretical Helmholtz calc.

Thanks Mike,
I understand now.
Dan

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wah
Wah-wah-wah-wah
Wah

The speed of sound you gave would be in feet/second. At 20°C at sea level (standard temperature and pressure, STP), the speed of sound in metric units is 340.29 m/s -- I expect those are the units you want, but I'm not sure. As for the ratio S/(VL), the units shouldn't matter, as long as they are all the same.

As far as writing your equation in "Excel speak", if you put c, S, V and L in cells B1, B2, B3 and B4, respectively, the equation can be written:
=(B1/(2*PI()))*SQRT(B2/(B3*B4))

Again, not sure about the units, but if you have a reference with a worked out example, you can tell soon enough. Hope that's of some help, but I have no idea about the validity or application of the equation.