Replies to This Discussion

Permalink Reply by Roadkill a.k.a. John Maw on January 20, 2011 at 11:55am

Hi Chuck.

 

That really does sound like the way to do it. How long have you been using that as a test?

Chuck Dubman said:

Build a tester, similar to a diddley-bow.  I took a 3 foot length of 2 x 8 and screwed a couple of raised blocks to the ends.  One block was drilled through, 3/32" bit, to act as a tailpiece, the other was drilled to accept the largest eyebolt / tuner I had available.  Boxes (or resonator bowls) get tested for sound and bridge placement by placing them under the string with a 2" piece of thin scrapwood acting as a floating bridge.  You'll find out very fast what works.  As per exact placement of a cigar box bridge, without exception, dead center puts out by far the loudest and the best sound.  Any deviation thereof is purely for looks.  Potential loss of volume is why we have amplifiers, anyway.

 

Permalink Reply by Chuck Dubman on January 20, 2011 at 6:52pm

John Maw said:

Hi Chuck.

 

That really does sound like the way to do it. How long have you been using that as a test?

About a month.  Works great, though, faster than solving complex equations.  One of the more useful tools I've made, plus it'll make tunes for whenever I get bored with the shop CD collection.

Permalink Reply by Mark Bliss on January 22, 2011 at 9:44pm

To me the ultimate question has been: why do some of these guys CBG's sound so much better (acoustics are assumed in this discussion) than others? And what baffles me, is that some of the ones that sound so good have construction details contrary to what makes any sense!

I could get deep into this discussion and question and still come out of it unsure. But to be clear, I have built and studied acoustic instruments for some time, and both understand most of the common theories and techniques, and have a few of my own theories as well. But its one of those areas where the more I learn the more questions I have.

There is certainly a relationship between the acoustic potential and the sound boards size/area, its freedom to vibrate, the bodys volume and the tension/preload placed on it by the strings. In my opinion, far too much attention or concern is placed on sound hole size and location, it is far less critical than these other areas.

The most amazing acoustic instruments in my experience all have very light construction, minimal bracing, and use the entire structure to best effect. They are also very fragile and prone to structural issues in the long term. For instance how a good violin effectively uses the front and rear of its tiny body to such amazing effect. Or how the legendary Martin tone so often results in bridge area failure on these beautiful sounding vintage instruments. Of course these flat tops use string tension instead of compression to transfer the strings vibration to the sound board, and thats a whole different area.... But I digress. Often. Sorry.

Working within the constraints caused by using a cigar box or similar body, I suspect that at best we are just likely finding the best comprimise. And of course on many of these builds seen here, acoustic sound is an afterthought, as its going to get plugged in and played in a crunchy state of tone anyway.

So the question remains for those of us who may desire to achieve the best possible acoustic sound, how to get the most response out of these boxes?

I suspect, just using what I know and logic, that the best bridge placement for maximum acoustic effect in this case is always going to be centered, all else being equal, to make best use of the limited area of the sound board. But there are comprimised to be made, for instance: with a body this small you might end up with the required picking area too far up onto the fingerboard area to be very effective, limited room for a pickup if desired, etc. But I think that ideal centered position may become far less critical than the balance of the whole design once you add in all the other construction factors and effects.

I suspect the best comprimise is going to be getting just the right balance of "free moving" sound board structure combined with as much string tension as it will structurally hold, but thats just an opinion I have been tossing about.

I see many attempts at using f-hole designs, but it seems to me they are often too big, or poorly spaced to have the desired effect. I am of the strong opinion that f-hole designs were originally used as much more than sound holes or to allow air movement from within the body. Proper f-hole designs effect the ability of the sound boards movement in acoustic instruments. As does bracing and other construction details. I also see a lot of boxes with what seems like far bigger sound holes or too many sound holes to be ideal. Or neck-thru builds where care was taken to allow the top freedom to move, only to add a solid brace under the bridge to neck area. Very flat string planes due to very low profile bridges creating very little string pressure at the bridge, and insufficient break over the bridge and nut. Playing hand resting on the soundboard or part of the bridge? Back of the body resting against the players body? Player wearing heavy clothing?

Despite all of this, some of these things ring out far better than others anyway, and I am really interested in why. And I must admit this is an area where some of the most accomplished CBG builders seem a bit tight lipped.......

Anyway...... Good discussion John.

Permalink Reply by MichaelS Country Boy Guitars on January 23, 2011 at 2:36am

Mark, I just joined this forum so I can fully agree with your ideas. Center may sound best but function is also important. I also need to add that some of the best sounding cigar box guitars have a lot to do with the fingers that are playing them. Mine all sound nice to me, but when a real player gets one, wow I'm impressed with what someone can do with my simple little guitars.  Very good discusion John, been reading since the start.

Permalink Reply by Mark Bliss on January 23, 2011 at 4:41am

After I wrote that, I went to bed with it on my mind and had many further thoughts. Some of which I might remember now........

First of all, on the tap testing or tuning fork testing, are you suspending the box/body by its ends as it would be when connected to a neck? If not, the tests usefullness may be comprimised.

Also I considered "What if my center bridge theory is wrong?" Well why would that be? Perhaps the ideal spot for transmitting the strings vibration TO the soundboard cannot co-exist with the same spot being the sweet spot for the soundboard to EMIT soundwaves into the air?

Then my train of thought wandered into comparisons of sound wave developement from bells, speakers etc. Obviously different size bodies and soundboards are going to resonate at different natural frequencies, just as say a different size bell has a different tone. (Then I thought of the fact that no matter the size of the bell, a bigger hammer makes it louder! Yes I was getting a little weird!)

Then I went on to thoughts that different areas of the box, speaker cone sizes, (or say a resonator cone) have different resonant frequencies, but yet as a whole they do pretty well at working over the entire range of desired sounds despite this, and then I started thinking about how amazing it is that all of these are pretty effective at transmitting so many frequencies and harmonics ALL AT THE SAME TIME!

Then I got a little sleep. But I am still thinking. Thanks a lot John.......

Permalink Reply by Alan Roberts on January 23, 2011 at 5:03am

I am NOT going to use a large hammer on my CBG. Not yet.

 

Any books you can recommend? I'm trudging through "The Luthier's Handbook: A Guide to Building Great Tone in Acoustic Stringed Instruments" by Roger H. Siminoff.

Permalink Reply by Roadkill a.k.a. John Maw on January 24, 2011 at 2:00pm

Hi Mark. Great to have your contribution. Just felt like batting this thought back at you. When testing with a tuning fork you are transmitting vibrations to the soundboard. The idea is that the tuning fork is a bridge substitute, possibly with the addition of a piece of wood to spread the vibrations in a more bridge-like way. Take the fork away and the box makes no noise. The energy comes only from the fork so in that sense the best place is the "sweet spot for transmission placement". The sweet spot for emitting may well be somewhere else or not, but how would we know and to some extent why should we care as long as it is nice and sweet.

 

Michael rightly points out that playability is also important. If you can't play it properly the rest is academic. The other issue is aesthetics. That won't matter to some but to others it will. Not only might this test reveal the location of the best place, but also give some indication of how rapidly the falloff occurs when moving away. In some respects I think that may be the most valuable part of the test and as far as my limited experience with this test is concerned that is the more variable aspect. Let's assume that the middle is almost always the sweet spot. Some boxes show a wide sweet area with little falloff of tone. Others show a very small sweet area (all this assuming that the test is a useful one). I think that that is the more useful bit of information.

 

Off to bed now. Sweet (spot) dreams.

Mark Bliss said:

Also I considered "What if my center bridge theory is wrong?" Well why would that be? Perhaps the ideal spot for transmitting the strings vibration TO the soundboard cannot co-exist with the same spot being the sweet spot for the soundboard to EMIT soundwaves into the air?

Permalink Reply by Tim Gale on January 24, 2011 at 4:37pm

I think you got it there.  Knowing how big your sweet spot is, so you know what your limits are aesthetically and still have the best sound is the most useful info here. 

John Maw said:

Hi Mark. Great to have your contribution. Just felt like batting this thought back at you. When testing with a tuning fork you are transmitting vibrations to the soundboard. The idea is that the tuning fork is a bridge substitute, possibly with the addition of a piece of wood to spread the vibrations in a more bridge-like way. Take the fork away and the box makes no noise. The energy comes only from the fork so in that sense the best place is the "sweet spot for transmission placement". The sweet spot for emitting may well be somewhere else or not, but how would we know and to some extent why should we care as long as it is nice and sweet.

 

Michael rightly points out that playability is also important. If you can't play it properly the rest is academic. The other issue is aesthetics. That won't matter to some but to others it will. Not only might this test reveal the location of the best place, but also give some indication of how rapidly the falloff occurs when moving away. In some respects I think that may be the most valuable part of the test and as far as my limited experience with this test is concerned that is the more variable aspect. Let's assume that the middle is almost always the sweet spot. Some boxes show a wide sweet area with little falloff of tone. Others show a very small sweet area (all this assuming that the test is a useful one). I think that that is the more useful bit of information.

 

Off to bed now. Sweet (spot) dreams.

Mark Bliss said:

Also I considered "What if my center bridge theory is wrong?" Well why would that be? Perhaps the ideal spot for transmitting the strings vibration TO the soundboard cannot co-exist with the same spot being the sweet spot for the soundboard to EMIT soundwaves into the air?

Permalink Reply by Mark Bliss on January 25, 2011 at 1:27am

I was just "supposin'"........

What I meant was that perhaps the box as a whole responds differently than just the top. Certainly these things sound different if they are suspended freely than when the back is muted and so on.

The "quick drop off" characteristic is interesting. I suspect the box with a larger "sweet spot" would be more desireable for acoustic response, no matter where the bridge ended up.

And my bigger hammer analogy was meant to infer, that if you generate a stronger input to the soundboard, it may matter less whether the bridge location is ideal, and transmit stronger output.

Certainly there is also a "sweet spot" in the amount of pressure applied to the top via string tension/bridge pressure. Too little is going to be inefficient. Too much is going to create diminishing returns as well as structural issues, as too much pressure may cause self muting of the soundboard, as would excessive bracing.

All of this is why I think the secret to good acoustic response is a balance of many conditions, not any one aspect.

I did not mean to detract from your thoughts on tap/tuning fork testing and considerations, I think it is interesting as well. I Just dont think it best to hyper focus on that and give too little consideration to the many other factors.

Now you have me thinking of a jig to measure bridge pressure. Damn it John I have enough to do! LOL!

Just for a heads up, I am currently putting together a quick and dirty prototype to test several different things, one of which is a slightly layed back neck set and taller bridge to increase bridge tension, to see how much it affects acoustic output. (This theory was already rolling around in my head, and the project was underway before this thread started actually). I havent had time to work on it much, but of course since some of us obviously share this interest, I will share any thing I find and further thoughts once I get it together. Right now the basic parts are chosen and layed out, neck is mostly roughed in, and maybe I will get a chance to work on it some more next weekend. My shop is in disarray as I have moved everything. I have to build a new bench, some tool stands and shelving/cabinets. But I got anxious and started this one on my shop-mate bench and a big box from my new table saw anyway. Too cold most of the days to get a lot done right now, and too many other responsibilitys.

Permalink Reply by MichaelS Country Boy Guitars on January 25, 2011 at 2:01am

I don't mean to put down this testing and hypothosizing stuff here, but.  I built 4 cbg's since this discussion started and they all sound pretty good, each one different of course. To quote Shane Speal " Don't over think it". now go out and build them cbg's.  

Just giving you a hard time.

Permalink Reply by Roadkill a.k.a. John Maw on January 25, 2011 at 3:05am

Look here young Michael. You stop causing trouble. Anyone who has seen your instruments knows what a lot of thought and trouble has gone into them. Anyway, you are now an old hand at this (in a young sort of way, of course) so you would be turning them out quite quickly.

 

Anyway, if we are quoting Shane he also said "There are no rules", so I will over think this if I choose.

 

Seriously though. You keep on making those wonderful guitars, but remember to make time to take lots of photos to inspire the rest of us.

 

P.S. As a serious point, when I started this discussion it was about a very simple, quick and cheap (free if you already happen to have a tuning fork) test. I thought some people might say that they were already doing something similar or someone might point out why it was of no use. I thought that would be the end of it. I thought the discussion would last less than a week. I didn't think it would go on so long or get so many comments. Just shows. You never know.

MichaelS Country Boy Guitars said:

I don't mean to put down this testing and hypothosizing stuff here, but.  I built 4 cbg's since this discussion started and they all sound pretty good, each one different of course. To quote Shane Speal " Don't over think it". now go out and build them cbg's.  

Just giving you a hard time.

Permalink Reply by Hellhound Custom Built Guitars on January 25, 2011 at 5:12am

It is all pretty simple really at least in my mind. The farthest point away from any support of the lid (meaning sides of box)will be your best point for vibration transfer from your bridge so dead center is the way to go.

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