I'll start off by saying that this may not be everyone's "cup of tea" and that some people might consider this "overthinking". To that I will simply say that one person's overthinking is another person's "understanding".
Let's start with something we can (probably) all mostly agree with: Different boxes (CBs or built boxes) have different sound qualities based upon: the type of wood, the thickness of the wood, joint construction, size, proportion (including depth), etc. (feel free to add more considerations).
For building our own boxes, we have control over every one of those aspects. Wouldn't it be cool to test the individual wood components going into our boxes and then the assembled boxes to see how each choice changes the resonance? If your answer is "no" then move along. If your answer is "maybe", then read on.
This is not a tutorial. It is a set of links us to consider and discuss in this thread. I'm going to cross-post this on the Advanced Techniques board, but I would like to see the discussion take place here, if possible (we'll see how it goes, organically).
This began for me with an investigation into how the various components affect the acoustic properties of a guitar (and then how these might apply to CBGs). Invariably, the question of solid wood vs plywood will come up (or "laminates"). For example, let's say I have a cigar box that has a 1/4" thick solid wood lid and a 1/8" plywood bottom. What sound qualities will I get using one for the soundboard over the other? Another (related) question is: Where do I place the bridge for the maximum resonance for this particular box/soundboard?
Exercising my Google-Fu, I found this interesting article on tonewoods and
It was in the aforementioned "where do I place the bridge" thread that someone mentioned "The Art of Tap Tuning: How to Build Great Sound into Instruments" by Roger Simonoff. The "Tap Tuning FAQ" is here: http://siminoff.net/tap-tuning-faq/
For a video introduction to what is possible on the subject, I suggest Mr. Simonoff's "Intro" video on YouTube:
It was the comment below that video that got me next. The commenter suggested that Simonoff's approach was too complicated and linked to this PDF entitled: "What you can find out by hitting things, by Don Noon, a retired NASA engineer." (Don Noon's bio here.)
The beauty of THIS approach is that all you need is the freeware audio editor program Audacity and a computer/laptop and a microphone. (I wonder if one could test piezos or other pickups in a similar fashion).
I think that someone who builds a ton of CBGs (and pays attention) comes to understand a lot of this just through experimentation. But I think that this testing method might help someone "get there" a lot sooner by narrowing down what works (better) than other approaches - for the particular sound that they are going for. In particular, figuring out what pattern on the graph (or maybe the total length of the graph, or the amplitude of certain points on the graph) correspond to the low end, high end and midrange, etc.
I might equate this to the different ways that homebrewers make beer. I knew one guy who loved to make up his own "recipes" (by varying ratios of different grains, and throwing in this or that and experiementing with different hops, etc.) But he never wrote anything down. So if he got something particularly good, his chances of replicating it (ever again) were somewhat reduced. This is sort of the point of recipes. Keeping track of what materials we use, in what proportions, and what thicknesses, etc. seems to me to be similar. Being able to graph the sound qualities of different designs seems to me to be something that might be helpful in replicating, or fine tuning the direction of our successful builds (or experiments)
Does this interest anyone besides me?
You're right....it IS overthinking. :P
I'm sure that is what some told the Stradivari (Stradivarius) family too. :P
Yup, cool, I'll check this out.
If you are like me, you will skip the "theory" and complicated physics formulas, but this page may still be helpful. (Skip down to the "The Equipment" and "The Method". While Don Noon originally formulated this for violins, this page is specifically about testing guitar tops.
It shows a little preamp that one can make (between the mic and the laptop) and describes how to test long grain and cross grain (among other things):
The link above is the download page for Audacity (for Windows, Mac, OR Linux - so everybody can play). :)
If you wish to export Audacity files as mp3s (not necessary for this usage, but still handy) then you will want to also install the LAME extension: http://lame.buanzo.org/
Alternative page for installing the LAME extension:http://audacity.sourceforge.net/help/faq_i18n?s=install&i=lame-mp3
Count me in, Darren. One of my disappointments about this community is that many builders are going strictly for amplified sound. I carry a guitar with me often, but never an amp. That stays home....so far. I prefer my guitars/ukes to sound good unplugged. I haven't mastered the art of tapping yet, I even carried a tuning fork around for a few days with no results.
I have had to scrap 4 nice looking boxes because I found out when cutting the sound hole that the tops were made of MDF.
One of my questions is whether to glue or screw. I hate the thought of glueing a box together and never being able to open it again without a lot of grief.
I'll take a look at those links you posted.