Replies to This Discussion

Permalink Reply by Tim Gale on January 25, 2011 at 6:47am

I think what I am going to do is generally place my bridge in the middle or close to.  If I want to place the bridge in a different location for aesthetic purposes, it would be handy to have a tuning fork to check the box for sweet spot size.

Permalink Reply by Fitzhugh on January 25, 2011 at 7:07am

I've built each of mine with a tilted back neck, enough to get 3/4 inch of biscuit and bridge all together under the strings on the ones with lowe cone resonators. I did make a quick test case first with a straight neck and wasn't happy with thesound, when I built a "real" one I found the angle made a big improvement. It wasn't a good test case since that first one was disposable and sloppy (re-used the cone, had fun sawing a neck off ), and those cones seem to really like a lot of pressure to drive them.

 

 

Permalink Reply by Mark Bliss on January 25, 2011 at 7:49am

Alright MichaelS, you made your point..... LOL!

I figured a few more experienced CBG'rs were probably following this thread and laughing at us. But thats ok, its imaginative mental research. Though I do want to follow up on this point, and hope to develop at least a small amount of empirical data on some of this. All my experience has been with big old conventional acoustic guitars.

Backing up a little, Chuck mentioned his testing with what I will call a "modular diddly bow". His reply was interesting and seems to verify my thinking on bridge location. But I still contend, center often simply isnt practical, unless you want to play on top of a bridge mountain dulcimer style. That can work, but it makes for odd construction and positioning. It would look like you were playing a neck with a box hanging off the back end or something........ So the 1/4 to 1/3 "rule of thumb" seems a practical comprimise to me, but I still want to explore how to get the most acoustic response out of whats left.

I picture using a test bed similar to what Chuck describes, but with the following modifications:

I would set it up to take multiple strings and experiment with sets of three and four to start with.

Add a scale, possibly one of those little 4" X 4" digital jobs, and measure the pressure generated at different bridge heights, relative to the nut and tail peice/anchor end. (A picture or drawing would be worth a handful of sentences here.)

Add a variable scale length to the equation, and test different string sets, different string guages and different bridge heights, maybe a few different common tunings, at least to see how much difference in overall pressure there is, in general.

Using this data I would then go foward with tests to add some actual findings to what Fitzhugh said, that increased pressure "woke up" his Lowe cone set up, just as I believe it would any soundboard, to some degree. Then I would find out at what point more bracing is needed, and then at what point you hit the point of diminishing returns.........

Did someone say shut-up and get building? LOL!

Like I said before, I'm just supposin'

 

Hey, does a "rule of thumb" mean you shouldnt strike your diddly bow with a stick any larger than the diameter of your thumb? Oh nevermind..........

Permalink Reply by MichaelS Country Boy Guitars on January 25, 2011 at 8:59am

LOL, I'm just giving you guys a hard time, keep overthinking it and I will keep reading and maybe something good will come of it. Its really an interesting thread. I'm only able to read this now because I am waiting for the tung oil on 2 more necks to dry, lol some more. My compromise has been about 2 1/2 inches off the back which gets me good string tension on the bridge and room to play in front of the bridge. Life is all about compromises. 

I think the best test would be to build 2 identical cbg's but put the bridge middle on one and back on the other. The scale would need to be the same so the neck would be longer on one, tailpiece would need to be altered for proper string tension. Hmm, I'm going back to my little shop now.

 

New can of worms, what do you think of the idea of the strings going thru the body like a telecaster, good or bad for sound vibration? (should have used a new post for that one.)

Permalink Reply by Rand Moore on January 26, 2011 at 1:51pm

Yes, let's throw gas on the fire!

Hoov said:

Interesting discussion!

I am a newbie coming from the visual arts and from that realm the Greeks came up with the "Golden Mean" as a way to find dimensional "harmony" in a rectangle.  It works for the rectangular top of a CBG too.  First determine the (inside...unglued) corners of the rectangle.  Use a straightedge to determine the diagonals. Then use a square or compass to strike a line which squares one diagonal and intersects the opposite corner.  (You may want to duplicate your box on a piece of paper to do this rather than poke holes into your box.) The intersection of that line and the diagonal it squares will be a potential sweet spot for your bridge.  Run a line square to the centerline of your box through this point and this line will be the dynamic centerline of your bridge.  Then determine neck length and position it from this sweet spot based on your fretboard (nut to bridge) dimension.

Can't hurt to try it. Pull out your drafting tools (and a tuning fork) and go at it.

The biggest problem that arises with this method is that the folks who decorate the boxes often key off of these same dimensions and you often engage key graphic elements of the box cover as a result of finding this sweet spot. 

Next approach is to extend the bridge base or bracing to engage (activate/vibrate) the "diagonals" or some proportional segment of the line length (space) between them. 

Good fodder for experimentation.

 

 

 

 

 

Permalink Reply by Rand Moore on January 26, 2011 at 4:24pm

Hi Everyone.

I agree, this is a very interesting discussion. But it's getting so long I thought it needs to be summarized. This is my first pass, so I'm open to suggestions/comments.  The finished version I'll add to my CBN discussion group "Home Made Resonator Boxes 101". I already have a link to this thread in my "Useful Links" list.

 

Here goes...

------------------------------------------------------------------------------------------

 

Useful Advice Regarding Bridge Placement

1.) It seems each cigar box has a unique "sweet spot" and this is the best place to put the bridge.

2.) You need to know the bridge location before you can figure out your neck length and nut position as this defines your scale length and ultimately where each fret will be located for proper intonation. So, CBG builder should use some test to locate the "sweet spot" of the box they are planing to use so they can first locate where the bridge will be placed before deciding on neck size, nut placement, etc.

3.) The "sweet spot" is generally in the middle of the box, but many other variables can come into play to make the "sweet spot" move to some other place. Things like internal bracing and sound hole placement should ideally be complete before the final "sweet spot" test as doing them afterwords can move the "sweet spot".

 

{ I also assume that the neck attachment method may also be a factor (neck-thru verses bolt-on, and whether the bolt-on relies on an external heel, or heavy internal bracing. Pretty paper labels, the addition of pickup controls (cable jack, switches, volume and tone pots) and other decorative items will likely also adversely affect the "sweet spot" and the optimal bridge location. For this reason, a "clean/plain" design with pickup controls on the side (and maybe sound holes on the sides) of the cigar box may prove better than placing all that "junk" on the soundboard.}

4.) Putting the bridge in the middle of the box doesn't give you much space to pick or strum the finished guitar. For this reason, the bridge is pushed back toward the tail end of the box (usually 60% to 75% of the way across the box). This is the likely the original reasoning behind the often cited CBG builder's rule-of-thumb: "Place the bridge about 2/3s to 3/4s across the box (down from the point of neck attachment)."

5.) Should have a way to test the "sweet spot" of a box.

Method 1: Use a tuning fork.  Maybe you can use additional tuning forks (each tuned to a different note) to test the frequency response of the box over a wider range of frequencies. Marking the various sweet spots on the sound board and then figuring an "average sweet spot" and placing your bridge there.

Method 2: Build a "test jig" composed of a head and neck assembly (with machine tuner(s), string(s), nut and tail piece already in place) that can be easily attached to a box. (I'd like to see some pictures of one of these.) It can (should?) be fretless. Use it along with a movable bridge to find the "sweet spot", then plan your scale length, neck length, nut placement and fret spacing based on that "sweet spot" as the bridge location.

6.) Try to increase the break angle of the strings over the bridge by increasing the bridge height. This will put more force on the bridge and theoretically make the box sound louder. But, doing this will also raise the strings off the neck/fretboard resulting in "high action", which is likely something you don't want (unless you are a slide player). So, to compensate for the high bridge design your neck so it tilts back a few degrees so the "action" (string height off the fretboard) will be lower.

7.) Other tips for building a better CBG:

• Choose a large (length, width and depth) wooden cigar box with a thin lid top (soundboard). The thin top will allow your soundboard to vibrate more readily.
• Often times the bottom side of the cigar box will be thinner and so will make a better soundboard than the top side.
• Choose a box without paper artwork on the soundboard as this just will dampen the sound.
• Consider rebuilding the box so that all the mating surfaces are tight and well glued.
• Consider removing the top (or bottom, which ever will be your soundboard) and replace it with either a thin (1/8") veneer or with real sound wood. With sound wood, you will likely need an electric planer a (power tool) to plane it down to such a thin size and then maybe some light bracing to strengthen the soundboard, the way luthiers do when building real guitars.
• Consider building with a home made box rather than a cigar box, using more of the techniques used by professional luthiers when they make their sound boxes.
• Consider building with a metal resonator using a thin metal resonator cone such as those made by Old Lowe.
• Consider adding a magnetic or piezo pickup and go electric.

------------------------------------------------------------------------------------------

Any constructive comments are welcome...

-Rand.

 

Permalink Reply by Mark Bliss on January 26, 2011 at 4:49pm

MichealS says:

"New can of worms, what do you think of the idea of the strings going thru the body like a telecaster, good or bad for sound vibration? (should have used a new post for that one.)"

 

First of all, no fire here Rand, just What I would call an interesting Discussion on theory and opinion. I havent even noted a strong disagreement anywhere within this discussion. Thats one of the things I enjoy a great deal about this site, and this group. Unlike many other online forums on various topics and interests I have been involved with in the past where the debates and one-upsmanship (and typically the lack of maturity) gets totally out of hand, and people with little or no experience or real knowledge clog the discussion with nothing less than crap and spam. If someone here disagrees with me, or I with them, we can still have a civilized discussion about it and keep it fun. Thank goodness for the cigar box nation. Very cool stuff.

 

MichealS, as far as the thru body stringing goes, I dont think it is off topic whatsover, and maybe even is a logical next step to the discussion, which in my opinion, (correct me if I am wrong on your intentions at this point John) could be summerized as "How to get the most acoustic response out of a CBG"

My first two thoughts on thru the body stringing is that within the context of CBG's it presents the challenge of setting it up so restringing isnt a hassle thru a box that has open internal space, and more to point relative to the present discussion, would require added structure or reinforcement that may negatively effect acoustic output by reducing already minimal box volume and sound board effectiveness. and for those two reasons alone I feel that type of bridge might really be best suited for solid body (or semi-solid body) builds with mag-pups. Another thing to perhaps consider relative to acoustic concerns, is the overall mass and weight of typical examples of the type of bridge you brought up, and also how they might effect the transfer of string vibration into the soundboard. I may be way off the mark, but I doubt it is a good choice for any build where you are trying to get good acoustic output.

When I first started looking at these modern versions of the CBG, my first impression of the thru body neck builds with the little stump sticking out the back with the strings attached thru that piece was that it was a little odd, but upon further consideration I see it now as a brilliantly simple and effective solution. The other tail peices for string attachment that we also commonly see attached to the end of the box, and most often to the base of the neck that lies within, also often make a lot of sense for acoustic purposes. Some of the other solutions I see are hit or miss for acoustic purposes. The less common build that looks to be more like a small standard acoustic instrument with internal braces/tone bars and such are a whole different situation, kind of a sub-genre of their own.

I kind of look at the thru neck designs that are acoustic or acoustic/electric as a modular design, where the string tension over the length of the neck is potentially optimized for sustain and simplicity of structure, and the box/body can be used primarily for acoustics, as well as a place to mount the necessary additional parts. Simple beauty by design. Have fun! 

Permalink Reply by Mark Bliss on January 26, 2011 at 5:17pm

All right Rand, I think you posted while I was typing..... LOL!

 

I dont think any worthwhile thread ever gets "too long" if the additions are on topic and contribute something.

 

You kind of hit on it at #7, but before you can begin the search for the combination in #2, you first need to select a "sweet box" and I dont mean Swisher Sweets.

 

Seriously, I think you summerized the thread well, but I dont think we can rule out the possibility of further useful contribution. Or just some fun thinking out loud.........

Permalink Reply by Hellhound Custom Built Guitars on January 26, 2011 at 6:01pm

I have done a few string thru body designs and I think they have all sounded and looked great. Just remember to thicken your neck at the point of the string thru right to the base of the box. It also helps to put a piece of metal or rivets where the string ball comes in contact with the back of the box. These are both preventative measures so you dont rip through the back of the box.

Mark Bliss said:

MichealS says:

"New can of worms, what do you think of the idea of the strings going thru the body like a telecaster, good or bad for sound vibration? (should have used a new post for that one.)"

 

First of all, no fire here Rand, just What I would call an interesting Discussion on theory and opinion. I havent even noted a strong disagreement anywhere within this discussion. Thats one of the things I enjoy a great deal about this site, and this group. Unlike many other online forums on various topics and interests I have been involved with in the past where the debates and one-upsmanship (and typically the lack of maturity) gets totally out of hand, and people with little or no experience or real knowledge clog the discussion with nothing less than crap and spam. If someone here disagrees with me, or I with them, we can still have a civilized discussion about it and keep it fun. Thank goodness for the cigar box nation. Very cool stuff.

 

MichealS, as far as the thru body stringing goes, I dont think it is off topic whatsover, and maybe even is a logical next step to the discussion, which in my opinion, (correct me if I am wrong on your intentions at this point John) could be summerized as "How to get the most acoustic response out of a CBG"

My first two thoughts on thru the body stringing is that within the context of CBG's it presents the challenge of setting it up so restringing isnt a hassle thru a box that has open internal space, and more to point relative to the present discussion, would require added structure or reinforcement that may negatively effect acoustic output by reducing already minimal box volume and sound board effectiveness. and for those two reasons alone I feel that type of bridge might really be best suited for solid body (or semi-solid body) builds with mag-pups. Another thing to perhaps consider relative to acoustic concerns, is the overall mass and weight of typical examples of the type of bridge you brought up, and also how they might effect the transfer of string vibration into the soundboard. I may be way off the mark, but I doubt it is a good choice for any build where you are trying to get good acoustic output.

When I first started looking at these modern versions of the CBG, my first impression of the thru body neck builds with the little stump sticking out the back with the strings attached thru that piece was that it was a little odd, but upon further consideration I see it now as a brilliantly simple and effective solution. The other tail peices for string attachment that we also commonly see attached to the end of the box, and most often to the base of the neck that lies within, also often make a lot of sense for acoustic purposes. Some of the other solutions I see are hit or miss for acoustic purposes. The less common build that looks to be more like a small standard acoustic instrument with internal braces/tone bars and such are a whole different situation, kind of a sub-genre of their own.

I kind of look at the thru neck designs that are acoustic or acoustic/electric as a modular design, where the string tension over the length of the neck is potentially optimized for sustain and simplicity of structure, and the box/body can be used primarily for acoustics, as well as a place to mount the necessary additional parts. Simple beauty by design. Have fun! 

Permalink Reply by Mark Bliss on January 26, 2011 at 6:54pm

Heres something for you to mull over John, about half way down the page........

http://frets.com/FRETSPages/Luthier/Technique/Structural/ToneBarFit...

Permalink Reply by Mark on January 27, 2011 at 9:21am

This certainly is one of the most thought provoking threads I've read in a long while. I've only just happened upon it because I got distracted away from the 'Nation' by mundane matters over Christmas and I've only really just got back to checking in on a more frequent basis. I've got the following initial thoughts and observations - but I'll probably have more in due course as this has really got me thinking and doing a bit of background reading.

First thing to say is that the tuning fork test is interesting and probably one of the few practical ways of testing a box prior to construction. The question is, what does it actually tell you? Is the "sweet spot"  at which you get maximum response with a tuning fork actually the best place to put a guitar bridge? - by which I mean we need to question whether it is best from the purely acoustic point of view as well as question it in terms of the playability and other practical issues already mentioned.

The meaning of your findings depend to some extent on what you actually mean by words such as "warmest and clearest sound". It seems to me that a term like "warmest" inevitably involves some subjective aspect unless you are defining it in terms of the harmonic composition of the sound and measuring it with some sort of frequency analyser. If all you have available is your ear then I guess that's all you can use - but perhaps I can try to get you to describe what you hear in more precise language. For example, when you talk about the sound being clearest, is part of that down to the volume being loudest (ie. so that it's easier to hear)? I'm kind of assuming that's the case but I feel we need to be clearer.

It could be that what happens when you find a "sweet spot" is that you are at or close to a point where you induce resonance in one of the modes of vibration of the box and/or its top. For example, the centre point of the lid would tend to be an anti-node for the fundamental frequencies in both the lengthwise and widthwise axes of the lid (and also for the odd harmonics). When you drive a resonator at such a point it would tend to produce a louder response than at other points.

I'm asking myself if driving the box at such a point is necessarily the best thing to do if you want it to sound good across a range of frequencies. (And with guitars we're potentially dealing with a range from around 82Hz for the fundamental of an open low E string up to around 660Hz for the fretted note at the 12th fret of the top E string - and much higher for the harmonics). There are reasons why a bridge located at your "sweet spot" might not produce the best sounding guitar. It might, for instance, produce an instrument that has a brilliant response at some notes and a poor response at others, or even an instrument that suffers from wolf tones. I cannot say for sure - the more I think about it the more complex it becomes. And that's before you add in the additional complexity of what happens when you connect the box to the rest of the guitar (and what happens when you put soundholes in boxes).

It seems to me that it's more important to ensure efficient transmission of energy from the string to the box (and then from the box to the air). From what I've read this is heavily affected by acoustic impedance, which is a different matter from what you seem to be measuring with the tuning fork. It has more to do with materials, string loadings and other constructional details.

Having said all of that, it feels, on instinct alone, as if the positioning of the bridge must surely play some role in the efficiency of energy transmission and the tonal balance of the instrument. A bridge located at the very edge of the box would surely be different in efficiency terms from one located several inches inwards - but at the moment I'm unable to offer any scientific proof or explanation for this. What I am sure of is that none of the explanations I've read here really give a good answer either.

It might be more useful to look at what you need from a box in terms of its general characteristics as a resonator. It seems to me you want it's principal resonant frequencies to be nicely within the frequency range of a guitar (see above but also remember a CBG will have a narrower range than a 6-string and the exact range will depend on the tuning). You also want it to have a response that is broad and flattish - ie. you don't want it to have extreme resonant peaks combined with areas in between where it responds poorly. It seems to me this type of characteristic is something you could usefully test with appropriate tuning forks (fancy electronic equipment would be better but I don't think most of us are in that position). Of course, you could try doing calculations based on the theory of Helmholz resonators to work out optimum box dimensions - but frankly, when working with cigar boxes, this sort of property is something much better left to simple empirical tests - and especially ones that can be done without fancy apparatus.

(NB. There is, of course, the difficulty that putting a soundhole in a box changes its characteristics, so you can't do a really good test until you've already plumped for a particular size and shape of hole - but I'll leave that for another time or another place).

The bottom line is that what you've opened up here is a very complicated set of problems and there probably is no simple and easy answer. That's why so much of the best musical instrument building has depended on instinct and on designs that have evolved through trial and error (and often on traditional ideas that have developed over many decades or centuries). It really is true that you can over think this stuff - and that's not just instinct it's a conclusion that I'm led to by rational analysis.

 

 

 

 

 

Permalink Reply by Roadkill a.k.a. John Maw on January 27, 2011 at 10:50am

Hi Mark.

 

Mark aka. Junk Box Instruments said:

This certainly is one of the most thought provoking threads I've read in a long while. I've only just happened upon it because I got distracted away from the 'Nation' by mundane matters over Christmas and I've only really just got back to checking in on a more frequent basis.

 

• What are you doing letting Christmas get in the way of the serious stuff. Actually, I only started this discussion to keep Michael amused ;^)

 

First thing to say is that the tuning fork test is interesting and probably one of the few practical ways of testing a box prior to construction.

 

• It may also be a way to test prior to purchase if you buy in person rather than mail order. Just a thought.

 

The question is, what does it actually tell you? Is the "sweet spot"  at which you get maximum response with a tuning fork actually the best place to put a guitar bridge? - by which I mean we need to question whether it is best from the purely acoustic point of view as well as question it in terms of the playability and other practical issues already mentioned.

 

• I think that there is no doubt that this is only a crude acoustic test. Other factors (playability and aesthetics) will rightly influence placement. I would like to stress again that I did not intend this as a way of finding the one and only spot where the bridge should be. What interests me much more is "sweet spot falloff". This has been covered previously, so I don't think I need to elaborate.

 

The meaning of your findings depend to some extent on what you actually mean by words such as "warmest and clearest sound". It seems to me that a term like "warmest" inevitably involves some subjective aspect unless you are defining it in terms of the harmonic composition of the sound and measuring it with some sort of frequency analyser. If all you have available is your ear then I guess that's all you can use - but perhaps I can try to get you to describe what you hear in more precise language. For example, when you talk about the sound being clearest, is part of that down to the volume being loudest (ie. so that it's easier to hear)? I'm kind of assuming that's the case but I feel we need to be clearer.

 

• Not volume, although in most cases in increase in volume seems to go along with the nicer sound. In some cases it is just that the sound becomes muffled away from the suggested sweet spot. In other cases it actually seems to be polluted by other notes and resonances or even slight buzziness.

 

I'm asking myself if driving the box at such a point is necessarily the best thing to do if you want it to sound good across a range of frequencies. (And with guitars we're potentially dealing with a range from around 82Hz for the fundamental of an open low E string up to around 660Hz for the fretted note at the 12th fret of the top E string - and much higher for the harmonics). There are reasons why a bridge located at your "sweet spot" might not produce the best sounding guitar. It might, for instance, produce an instrument that has a brilliant response at some notes and a poor response at others, or even an instrument that suffers from wolf tones.

 

• OK, but back up a little. What are we comparing it with. It's not as if I am suggesting this in place of a tried and tested method. I think that for most people there simply hasn't been a method. Put it where it looks good and you have enough room to beat hell out of the strings (which is fair enough or course). What you have to ask is why is this more likely to produce patchy results than something that has little more logic to it than pinning the tail on the donkey.

 

From what I've read this is heavily affected by acoustic impedance, which is a different matter from what you seem to be measuring with the tuning fork.

 

• Indeed, but do remember that this was conceived as a simple cheap/free and quick test for those who didn't want to get too involved with rocket science. It has it's limitations. That is part of the deal.

 

The bottom line is that what you've opened up here is a very complicated set of problems and there probably is no simple and easy answer.

 

• I think there is. It is simple. If you like the idea and have a tuning fork (or fancy paying a couple of squids to buy one) have a go and see if you like the idea. If not, move on and hack hell out of a piece of wood. This was meant to be simple. I think it still is. The only unanswered question is weather it can tell us anything useful at all. I don't know and it remains to be seen (or rather heard).

At this point I have a question. Nobody has owned up to trying the same thing since this discussion started. I can't be the only mad idiot out there and I certainly can't be the only one with a tuning fork. I would love to know what other people think once they try it.

 

Lastly, this wasn't supposed to be the "be all or end all" of test. Just something quick to contribute a little to how you lay out the guitar.

 

PS. Thanks to Mark B for the link. Useful things tuning forks. Now, how about using it to test glue joint integrity on a box. NO. NO. NO. NO. NO. NO. NO. NO.

 

 

 

 

 

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