Replies to This Discussion

Permalink Reply by Hip Bone Bellaire on December 14, 2010 at 2:15am

Yep corners off the lid was the start of this... Still might look interesting...

• ▶ Reply

Permalink Reply by MichaelS Country Boy Guitars on December 14, 2010 at 4:39am

I like the idea, its got old world cigar box thinking to it, use the tools you got to make it work. Depending on how you cut or shape the cuts it could look nice too.

Hip Bone Bellaire said:

Yep corners off the lid was the start of this... Still might look interesting...

• ▶ Reply

Permalink Reply by carverman on December 14, 2010 at 6:29am

Hmmm...nested brackets are not the easiest formula to reduce to common denominators for a solution.

This is probaly high school level math and frankly, I haven't had the need to deal with Pi or 2PI since my

electronic math problems back many years ago.

I know you have to solve the innermost brackets first, then the the next set and then you can

solve for the outer set. Pi = 3.14       Area of a circle = PiR2

 

Trying to work it out on the box dimensions stated above. Converting a CB into a Hemholz

resonator sperical dimensions isn't exactly rocket science, but takes some disipline to solve.

Somewheres in that formula, you have to take the square root to get the radius of the circle..

I think.

 

Heck, a  CB is just a box with a certain volume.    The volume should determine the  fundamental

resonant frequency without any holes added. Add some holes,  which in essence should decrease

the resonant frequency.

So once we determine the area, divide it in half to work on the sound hole size....

or...just use an appropriate sized grommet and wing it.  

 

 

Rand Moore said:

There was a discussion recently on CBN's Super Advanced CBG Building group. They may have a formula. Not sure how valid it is. Could also search Google. I don't really know a formula, but if there is one and it has proved out by multiple CBG makers, then it's worth having. I'll look around a bit...

======

Comment by herb berwald on November 10, 2010 at 5:06am

1. Calculate box volume, LxWxH
2. Solve for the radius of a sphere of the same volume, ((3*V)/4*pi())^1/3
3. Divide the radius by 4
4. This is the new radius of the sound hole.
5. 2*r is the new sound hole diameter...
for this box it is around 5 inches...almost like a regular guitar. I must have done something wrong.

Assuming the box is 8.25" x 5.5" x 2.75", our calculated hole diameter should be:
    (2 * (((3 * 8.25 * 5.5 * 2.75) / (4 * 3.14))^(1 / 3))) / 4 = 1.55023303

======

Does that formula make sense?  I was never good at math.

-Rand.

• ▶ Reply

Permalink Reply by Rand Moore on December 15, 2010 at 2:03am

Okay, Guys... I built one. Here's the photo:

It's a 2 stringer, diatonically fretted using nylon tie-wraps, ukulele tuners and Aquilla Nylgut strings. From a players stance, it does not sound very loud, but if you bend over so your ear is over the soundboard, it's pretty loud. So it seems to project well into the direction of the audience. The box also has a pretty good sustain. I've written more about it on my personal CBN blog and have some more photos of it. Wish I had two identical boxes so I could do a more scientific comparison of this type of sound holes verses no sound hole, vs one or two traditional round sound holes. I also saved the corners of the soundboard with the idea of partially re-closing the sound holes to see if that makes a difference. Before I do that, though, I'll do more experimentation and use steel strings and frets to see how loud it can be.

 

-Rand.

 

• ▶ Reply

Permalink Reply by MichaelS Country Boy Guitars on December 15, 2010 at 2:31am

Wow you work quick.  Thats a lot more corner cutting off than I had envisioned, very bold. Nice job.

Rand Moore said:

Okay, Guys... I built one. Here's the photo:

It's a 2 stringer, diatonically fretted using nylon tie-wraps, ukulele tuners and Aquilla Nylgut strings. From a players stance, it does not sound very loud, but if you bend over so your ear is over the soundboard, it's pretty loud. So it seems to project well into the direction of the audience. The box also has a pretty good sustain. I've written more about it on my personal CBN blog and have some more photos of it. Wish I had two identical boxes so I could do a more scientific comparison of this type of sound holes verses no sound hole, vs one or two traditional round sound holes. I also saved the corners of the soundboard with the idea of partially re-closing the sound holes to see if that makes a difference. Before I do that, though, I'll do more experimentation and use steel strings and frets to see how loud it can be.

 

-Rand.

 

• ▶ Reply

Permalink Reply by Greg on December 15, 2010 at 3:04am

That's interesting. The soundholes really seem huge to me, but if it works...

• ▶ Reply

Permalink Reply by Hip Bone Bellaire on December 15, 2010 at 3:58am

No that's what I was talking about....

• ▶ Reply

Permalink Reply by Rand Moore on December 15, 2010 at 6:32am

Hi All...

I wasn't sure how big or small to make the sound holes (corners), so I took the extreme of trying to make the soundboard as octagonal and equilateral as possible. I was thinking maybe with less edge connection to the sideboards, maybe the soundboard would be more free to vibrate and have a bigger sound. I was also thinking that if this proved true, then the next step would be to build a box with the lid's side walls removed to a similar amount as this one, but to keep the full square soundboard. The other test I want to do is to build one with a smaller set of sound holes (corners), maybe half as big as this one to see how that affects the sound. But, before doing these test builds, I want to test this box with steel strings and metal frets as I know for sure the nylon tie-wraps used for the frets dampen the sound significantly. I also kept the corners of my soundboard and plan to glue them the the top edge of the bottom of the cigar box as shown in a couple photos (not yet glued in) on my personal CBN blog. The thing I do notice about the design is that it projects a lot of sound forward toward the audience, and has pretty good sustain (better than a couple other CBGs I've built).

 

-Rand.

 

• ▶ Reply

Permalink Reply by carverman on December 18, 2010 at 6:12am

Very neat design Rand. You know, this is what I like about CBG Nation..there are no limits

 in building them,  unlike conventional guitars where it" has to be done this way"

..or it's not going to sound the same as <whatever>.

The main thing is to experiment and find out how far you can go with what you have to work with.

• ▶ Reply

Permalink Reply by Shawn on December 18, 2010 at 10:34am

That's cool but what if you take the leftover corner lid parts ( just the lid wood without the sides) and reglue them to the base making it have side ports on all four sides. It would give it smaller sound holes and retaing the look you have going.


Rand Moore said:

Okay, Guys... I built one. Here's the photo:

It's a 2 stringer, diatonically fretted using nylon tie-wraps, ukulele tuners and Aquilla Nylgut strings. From a players stance, it does not sound very loud, but if you bend over so your ear is over the soundboard, it's pretty loud. So it seems to project well into the direction of the audience. The box also has a pretty good sustain. I've written more about it on my personal CBN blog and have some more photos of it. Wish I had two identical boxes so I could do a more scientific comparison of this type of sound holes verses no sound hole, vs one or two traditional round sound holes. I also saved the corners of the soundboard with the idea of partially re-closing the sound holes to see if that makes a difference. Before I do that, though, I'll do more experimentation and use steel strings and frets to see how loud it can be.

 

-Rand.

 

• ▶ Reply

Permalink Reply by carverman on December 18, 2010 at 5:08pm

I think the design looks pretty neat, even if the "sound holes" form open corner "reflectors"...almost

approaching a  CB guitar-banjo.  If he was to cut the corners on the bottom part and fill in 

the cuts, he might  be approaching an octogonal version of one.  

Shawn said:

That's cool but what if you take the leftover corner lid parts ( just the lid wood without the sides) and reglue them to the base making it have side ports on all four sides. It would give it smaller sound holes and retaing the look you have going.


Rand Moore said:

Okay, Guys... I built one. Here's the photo:

It's a 2 stringer, diatonically fretted using nylon tie-wraps, ukulele tuners and Aquilla Nylgut strings. From a players stance, it does not sound very loud, but if you bend over so your ear is over the soundboard, it's pretty loud. So it seems to project well into the direction of the audience. The box also has a pretty good sustain. I've written more about it on my personal CBN blog and have some more photos of it. Wish I had two identical boxes so I could do a more scientific comparison of this type of sound holes verses no sound hole, vs one or two traditional round sound holes. I also saved the corners of the soundboard with the idea of partially re-closing the sound holes to see if that makes a difference. Before I do that, though, I'll do more experimentation and use steel strings and frets to see how loud it can be.

 

-Rand.

 

• ▶ Reply

Permalink Reply by Rand Moore on January 4, 2011 at 7:25pm

Hi All.


I've built a second CBG with corner cut sound holes. It's a 3-stringer with a 20" scale, metal frets and steel strings. For more information about it, you can read about it on my personal account. Just click on this link and scroll down the page. Here's a photo:






-Rand

• ▶ Reply

• ‹ Previous
• 1
• 2
• 3
• Next ›
• Page