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 you 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 Resonator Boxes Group, but I would like to see the discussion take place there.
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
The Heretics Guide to Alternative Lutherie Woods, by John Calkin
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?
Thanks for the post. It interests me a great deal. Whether I will do anything with it is another matter...
Check the comments on this cross-posted thread in the Resonator Boxes group.
One of my comments links to this page, where guitar tops are specifically tested. (If you are like me you will skip the theory and formulas and go straight to "The Equipment" and "The Method" sections.) :)
Thank you Darren. That was rewarding and I'm sure if I get around to acoustic body building, I'll look up your book.
Wait a minute-i've got Audacity, a microphone and a rubber hammer right here!
I normally test pre-built boxes and tins just by tapping out the hollowist 'Tok!' and the mellowist 'Bong!' with my fingers for optimum bridge placement... but until now i've been at the mercy of random chance with my Tennis Racket Dulcimers, never knowing what i'm getting until the glue has dried in the frame. I could see the Tap Test working with the 1/8' Birch Ply and the 1/8' Cedar plank I normally face and back with...but do you think the Tap test would be worth trying on the rather flexible 1/16' birch I use for the sides, or would it be useless until i've glued the frame in place?
Here's a consideration..
I thought this was a bit dumb but started doing it anyway "just because"
When I've built my through neck design I hold the neck by the sides at various places along its length and tap the bottom of it. There are two sweet spots that make a pleasing ring from the wood. I try to get my bridge and my 4th or 5th fret to sit as close to these spots as possible (although it's not always practical). It probably makes no sense whatsoever as the saddle will be siting on the soundboard.. But I still do it anyway.
Incidentally, there is no ring from the middle of the neck. The place where I thought the best ring would come from.