I just built my first CBG and am quite amazed by the sound that comes out of the simple design I used. It is a neck through the box, fretless design. I cut 4 1/2" f-holes near the top (neck end) of the box. I've been making modifications trying to increase the resonance.

First thing I did was to move the bridge from the junction of the box and the tailpiece to the body of the box. The second thing I tried was to remove 1/8" of the neck inside the box so the box top had room to vibrate.

These two things made a huge difference!

Another thing I tried was to turn the box upside down so the f-holes were closer to the tail than the neck. That also put the bridge between those holes. That seemed to help some but not enough to keep it that way, mostly for cosmetic appearances.

Does anyone have any opinions on how the size, shape, and location of the sound holes will affect the resonance? I'm looking for ways to improve the acoustic qualities.

Also, I have a nice sized cigar box. It is made of the typical Spanish cedar but the face of the box has a paper cover. Does anyone know how the paper will affect the resonance? Does anyone have any tips for removing that paper?

Thanks for any insight that anyone can give me!

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Unless the top is 1/8" or thinner, I'd be surprised if it made much difference

Addressing the paper question only:

It is, of course, impossible to say exactly what the effect of the paper would be without removing it.  PhlUSAFRet suggests that it probably would not make a noticeable difference on a top thicker than 1/8 ".  That's not a bad rule of thumb, but let's think about the physical characteristics of a piece of wood, plywood, etc., that affect its resonance.

-- Stiffness

The stiffer the board, the better it will resonate.  That's why tuna cans and dog bowls are popular additions.  Steel is generally stiffer than wood.  So, if the paper were stretched tight over the board and attached with a stiff glue, it could conceivably increase the stiffness.  But, my gut tells me you would have to take care to apply that carefully, and bulk industrial processes seem unlikely to produce this result.  So, I would expect the result, if measurable, to improve the tone.  Weigh this against the change in appearance.  For some boxes, part of the appeal is the graphics.

-- Size

Bigger lids seem to resonate better.  This seems counter to the stiffness argument, because larger boards are easier to bend than smaller.  If the lid were not constrained at the edges, a smaller one might well resonate better.  However, the sides of the box tend to damp the vibrations, reducing resonance.  Paper will not affect this factor at all.

-- Mass

In other words, for our purposes, thickness.  This is where Phil's comment comes in.  With thicker wood, there is more of it for the vibrations to move, so it resonates less.  It seems that removing the paper could reduce that mass to good effect.  But, most paper you would find on these boxes would be in the range of 1-3 thousandths of an inch thick.  An eighth-inch lid would be 125 thousandths.  Shaving off one or two would be unlikely to make an appreciable difference, especially if the lid were 3/16 " (193 thou) or more.

-- Coupling

The lid picks up the vibrations from the string via the bridge.  The complexities of that contact include the material, mass, stiffness, size, and shape of the bridge, the location on the top, the tension, mass, length, stiffness, and material of the strings, and so on.  The paper label is unlikely to be the limiting factor in the acoustic coupling between the bridge and the top.

Now, holes are another topic entirely.  My limited experience indicates that, if you want any kind of acoustic volume, you need at least one hole.  But, number, size, shape, location, and edge treatments affect tone and volume with crazy complexity.  Look for images of Chladni plates for inspiration to just give up and do empirical experimentation.

-Tommy Phillips

Thanks for all the information Tommy. There's a lot to think about there. I'm looking forward to trying some different things on the next CGB.

you  say  ...*** "First thing I did was to move the bridge from the junction of the box and the tailpiece to the body of the box. The second thing I tried was to remove 1/8" of the neck inside the box so the box top had room to vibrate.  These two things made a huge difference!""'***

  i'm  willing to  bet    only  the  first   part  made  the  difference  .  

contrary  to  popular  belief  ,   ( in my  opinion ) ,    gluing   the  neck  right to   the  box  lid  makes  the  entire  body  and   guitar   resonate    much better  .

some long time  builders  that used to  swear by  leaving a space ,    have now  changed  their  tune  .. after  playing    and  / or  building    one   glued  right  to  the  neck  . 

 (  pardon the  pun  :-)

 

Hmmm.... That's interesting. To be accurate, I didn't make both those moves at once, I did one (moved the bridge), evaluated it then did the other (make a space between the neck and the lid) and then evaluated that.

The creation of the space between the neck and the lid made the biggest difference.

It would be some way I could quantify the difference in sound. Maybe I need to make a video playing the same song every time I make a modification.

Anyway, you've given me more food for thought. Thanks!

humm  indeed,    .. i  didn't  take into account  the  f holes  ..   which sometimes act as a  sound  tongue    ..  and  heck  .  sometimes      many things  work  together  .  and all  guits  are  different  .  there are  many  variables .   anywho  ... 

heres some  more    chatter   on  this    very    topic      ;-)

http://www.cigarboxnation.com/forum/topics/neck-touching-inside-of-...

and some more  ..   considering    "caving "   etc 

http://www.cigarboxnation.com/forum/topics/time-to-go-super-advance...

Hey Thanks! Those are a couple of great threads there! More food for thought.

I'm pretty interested in the dowel under the bridge thing. I'll have to try that to see if that makes a difference.

Again, I wish I could quantify these changes with something like a volume meter. I do think I'll take a video of before and after.

I just did an experiment. After reading some of the threads that Swamp Witch posted, I decided to try installing a dowel between the neck and the lid (soundboard). Some had claimed that improved the sound and I thought that would be in between having a gap between the lid and neck and having the neck tough the lid through out the box.

When I installed the dowel, it dampened the sound tremendously. I mean day and night difference!

I took a video to show the difference... https://www.youtube.com/watch?v=F31SJo9Xd70&feature=youtu.be

hummmm.  you  should   post this  in the other  thread  also  ..  my  make   for some  good    convo  .  

Good idea, will do.

wait  ... did  you   put  the  dowel  between  the neck and the  lid  ?  or   from the  back  cover    to the  lid  ? 

it  seems  most were saying the  back and front  . 

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