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"Testing" a box for bridge placement

I've been searching through the articles on this site for information on selecting the position where the bridge should be. Obviously on an unfretted instrument you can move the bridge and experiment, but on a fretted guitar, once the frets are on and the neck is fixed that's it. You have committed yourself.

So is there any way to know on a box for box basis (not using formulas because I'm pretty sure that they are worthless unless you always use identical boxes) where the bridge should be to get the best results?

Now I've already done some test, but I don't know if they are the work of a visionary (don't laugh) or a pointless waste of time (odds on the latter). I was thinking that as far as the box is concerned it gets most of the string vibration through the bridge. If you want to simulate vibrations coming from the bridge can you use something else that will transmit vibrations and see (or rather hear) how they sound and make a choice based on that. I found a tuning fork and tried it at various places on three boxes that I intend to use soon.

The results from the three were quite different. Not surprisingly all gave the warmest and clearest sound in the centre of the box. The top one gave quite progressive results getting better quite gradually towards the centre. The left hand one was very even across it's width until right near the edge. The right hand one was a surprise as it sounded best right in the middle, tone falling off and getting soft of nasal even an inch away from the motif. Shame as I don't really want to put a bridge right on the motif but my tuning fork test suggests that it may be the best place.

So, finally, to the question. Has anyone done any tests - similar or otherwise - that give a good indication of where to put a bridge and that do not rely on ratios or formulas, but take into account the different characteristics of each box?

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Replies to This Discussion

Permalink Reply by Ron "Oily" Sprague on August 13, 2011 at 11:55pm

Also also wik, there's this little gem to keep in mind / confuse your noodle from the developer of RainSong graphite guitars:

http://www.guitarmasterworks.com/about-guitar-acoustics-101.html

Permalink Reply by Mark Bliss on August 14, 2011 at 3:22am

Well holy Hades, this thread just goes on and on and yet remains fascinating! No appology necessary John!

Oilyfool, thanks for the links. I esecially liked the music box mechanism test, even while accepting the results may not mean much at all, it is interesting.

And the last one, guitar acoustics 101. I had seen that and forgotten all about his contribution. His comments and experiments with top bracing (and the lack thereof) are right up my alley. Exactly what I wanted to see.

"Start with maximized stiffness with minimal mass". (More or less quoted) Didnt I reckon that a while back in this thread?

But the best things he says in the whole paper-

Guitar Acoustics theory is complex to the point of being unsolvable – the theoretical description of the vibrations of a guitar soundboard leads typically to a set of a thousand simultaneous nonlinear partial differential equations; and
Measurements tell one almost nothing useful – what one hears when a guitar is being played -- and measures on an oscilloscope or frequency analyzer – is usually dominated by the excitation mechanism, and the frequencies used by the human brain to determine “quality” look like white noise to laboratory instruments.

And there it is. The human ear test is the final determination no matter the complexity of the calculation.

Thanks again Oilyfool, I really enjoyed that!

Play nice,

Mark

Permalink Reply by Ron "Oily" Sprague on August 15, 2011 at 12:28am

Mark, et al,

I'm truly glad you found my search contributions useful / entertaining. The whole idea of testing hypotheses is obviously near and dear to my heart, as is bringing information to people who might find it useful. And I love the fact that John's original question has led to exposure of all these variations of thought and experience.

I think the best thing I got from the RainSong guitar acoustics 101 site is the second point you quoted above, about the frequencies the human brain uses to determine "quality" looking like white noise to lab instruments. Like you, Mark, that's precisely why I keep telling people, whether they are testing guitars, amps, speakers, mxing boards, etc., "Let your ears (not mine, or anyone else's) be the judge."

Sometimes, we will differ on what we think sounds good. That's because our brains are different. That, and many sound-related things exhibit non-linear behavior.

So I guess my science degrees didnlt go completely unused ;-)

Permalink Reply by Mark Bliss on August 15, 2011 at 6:07am

I also enjoyed the comments on comparing sound. He points out that hearing memory is notoriously bad, and recording back to back trials, even on basic cheap equipment, often reveals that the one you THOUGHT you liked best doesnt really sound the best at all!

Good stuff.

Permalink Reply by Rand Moore on September 18, 2011 at 10:06am

I second Chuck Dubman's idea of adapting a diddley-bow into a cigar box sound tester. It seems like a really simple solution to the topic of this thread: how to test a box for "good sound" and optimal bridge placement. Here are Chuck's photos of the one he's made:

Chuck Dubman had this to say: "Speaking of diddleybows, this "diddley tester" saves a lot of time and hair pulling when figuring whether a given box or bridge location sounds "right." Makes a fun noisemaker in its own right, too. Poor man's Theremin! ". Here's the link to the thread where Chuck originally posted these photos.

Hopefully, this will help put to rest the "thread that will never die".

-Rand.

Permalink Reply by Mark Bliss on September 18, 2011 at 12:06pm

Put it to rest? Whatchu talkin?

Now wait, I have this link to a modal vibration analysis I have been holding out on, I am NOT done! LOL!

Put it to rest, not gonna happen. Well maybe for brief periods........ I am doing my Banjo practice and putting up firewood here!

Now that said, I am digging the monochord test bed theory, and if nothing else, that tailpiece is awesome! LOL! Oh and the banjo bridge, good stuff!

Dont mind me, I blame the Tequila.

Permalink Reply by Roadkill a.k.a. John Maw on September 18, 2011 at 12:14pm

Just thinking. If you substituted the banjo bridge for one with a couple of piezo discs embedded into it you could try the amplified sound. Just a thought.

Permalink Reply by Ron "Oily" Sprague on September 18, 2011 at 9:58pm

OK, so now we have a test bed. Thanks, Rand; I'd not seen Chuck's DBCB tester (hey, how would that tuning sound?...CBGB's on a Friday Night...hmmm, might be a song title lurking in there...)

This thread, dead?

But there are so many variables left to consider: string gauge, bridge height, properties of the test bed itself (metal versus wood - yes, I just know someone will be coerced into repurposing an old shotgun cleaning rod into a CB test bed ;-)... hey, waitaminit!), atmospheric conditions, amplification types as John sez, influence on slide technique while under the influence, playing "Tequila" in slidetime...

Thomas R. Marshall, 28th Vice President of The United States

"What this country needs is a good 5-cent guitar"

Permalink Reply by Roadkill a.k.a. John Maw on September 18, 2011 at 10:13pm

Re. amplification. How about a bracket for a mag pickup inverted over the strings on a sliding mechanism so you could also test for different pickup positions (and pickup types). Once you have a signal to work from you could link it to all sorts of measuring equipment to analyse the signal. Of course one could just spend the time learning to play better. Just a thought.

Permalink Reply by MichaelS Country Boy Guitars on September 19, 2011 at 2:40am