Replies to This Discussion

Permalink Reply by Steven Miller on July 23, 2009 at 7:01pm

I think in general a really wide bridge just adds mass to the top and damps vibrations. Violins have a really small bridge footprint on the top. Banjos also have a very small bridge foot print. Guitars with tailpieces also have small bridge footprint (except the Telecaster, but that is a special case related to the pick up.)

However if the bridge is glued to the top as in many acoustic and classical guitars, you need a glue patch large enough to prevent the strings from tearing the bridge off the instrument top.

Think of the top of your instrument as the cone of a speaker. You want it to vibrate as freely as possible.

Best Regards,

Steven
Diane said:

Well, thanks! That's very helpful. So how does a really wide bridge affect things? Lately I've got bridges several inches wide and am thinking that is making things louder. However, again, since I have never built the same thing twice, apples to oranges . . .

(My fiddle is coming along, slowly, but coming along . . .)

Permalink Reply by Bluesheart on October 2, 2009 at 11:40pm

Very informative. I tried a new (to me) pick up mounting in my recent 3 string. Piezo mounted by cutting a wine cork and sandwiching element between cork, top and back of box. After snooping around in here, I'll be removing that and freeing up the top I tried so hard to keep free in the first place. I think that will make it sound even better un-plugged.
Thanks!

Permalink Reply by Zandi Z on December 18, 2009 at 5:01pm

Amen, Steven.
What you said was elegant in its simplicity.
i am a novice player and a novice cbg builder. I am, however, in my Golden Years, as 'they' say.
To my eyes and ears, what you said was particularly profound...it is very commonly ignored, perhaps because of its very simplicity.

"Look carefully at traditional acoustic instruments that work well.
Notice the various dimensions mentioned above in relation to each other.
Try to emulate these proportions in the instrument you are building.

It is the relationships of these factors that count, not the exageration of any one of them".
thanks for voicing that...zan.

Permalink Reply by Zandi Z on June 17, 2010 at 9:58am

this is actually a response to Mark aka Junk Box Instruments.
i posted it as a blog, but it has not appeared...sooo...

Mark wanted to know more about what i said about proportions... and do i measure or eyeball it ?
I do measure, but eye-balling is ok, too.

My basic premises are these:
'the box' is an amplifier.
'the stick', with hardware, is The Machine.

Why Proportions ?
the most efficient way to get the Box and/or Stick to resonate or 'amplify,' is to 'feed' them 'vibrating lengths' to which they might be most sympathetic....
this minimizes the energy needed to 'push' them to getting them to vibrate and to keep them vibrating.

The Box:
the length of the box is my Basic Unit... i generally round that out to an average between the inside length of box and outside length.
my Scale Length is a WHOLE NUMBER multiple of the Basic Unit.
eg: if BU is 8 inches, Scale Lengths would be 1,2,3,4,5,etc, times as long as the box...... 8 inches, 16 inches, 24 inches,32 inches, and 40 inches, etc.

The Stick:
i choose, or calculate a Scale Length...
i divide that Scale Length value by 4 to get a Stick Unit.
eg: 16 inch Scale Length = 4 inch Stick Unit.

Total Stick Length is equal to 6 Stick Units.
1 Stick Unit is headstock.
4 Stick Units from nut to bridge...(Scale Length).
1 Stick Unit from bridge to tail end.

The Result:
Scale Length is both proportional to the Box and proportional to the Stick .
the possibility of resonance is enhanced;
the possibility of dampening is reduced.
.....resonance is the most efficient way to transfer energy.

To Finish:
a person could place the center of the box directly under the bridge.
i prefer to mount the box so that the bridge sits from 2/3 to 3/4 of the way down the length of the box towards the tail....

i use movable bridges...
experimenting is a great part of this adventure...
i measured LOTS of instruments to see what their proportions were... then, i experimented lots.

thanks for asking, Mark...........zandi z.




Zandi Z said:

Amen, Steven.
What you said was elegant in its simplicity.
i am a novice player and a novice cbg builder. I am, however, in my Golden Years, as 'they' say.
To my eyes and ears, what you said was particularly profound...it is very commonly ignored, perhaps because of its very simplicity.

"Look carefully at traditional acoustic instruments that work well.
Notice the various dimensions mentioned above in relation to each other.
Try to emulate these proportions in the instrument you are building.

It is the relationships of these factors that count, not the exageration of any one of them".
thanks for voicing that...zan.

Permalink Reply by Rob Ryan on October 17, 2010 at 10:38pm

I am on my 2nd guitar and wanted to try and make it louder unplugged and to try and improve the tone quality. I have seen classical guitars with a double top. SSOO I made a frame out of paint stur stick wood and used mono kote to cover it..like a membrane ,I drilled some small holes under the saddle thru the top of the box. i glued two small dowels in the holes so that they would contact the bridge..and attached the membrane box to the dowels on one end and the neck on the other. We will see if it makes it louder..or changes the tone quality.

Permalink Reply by Rand Moore on October 19, 2010 at 3:10am

This advice of keeping the components of a CBG in proportion with each other makes sense to me at a gut level. After all, the head, neck, and "tail end" of the "stick" are like the transmission medium and when the wave reaches the end of the stick, it is reflected back and this can, at various points along the neck make the signals add together in strength (creating a standing wave) or it can wipe out the signal, or (usually) do something in between -- usually either degrade the signal a bit, or just not be strong as it could be (compare to the points where there are standing waves). In computer/network cabling situations, we need to terminate the cable with resistors that closely match the impedance of the cable to minimize the reflection, as it tends to degrade the basic signal strength (and we basically ignore the signal boosting additive effect that reflections can also give us). With a guitar neck, I don't even know how one would go about terminating them to effectively eliminate the reflection, and for amplification reasons, we may decide that we don't want to. The trick then is to find the right length of the "stick" (head, neck and tailpiece) that will set up a standing wave in the area of our resonator (cigar box) so that it can be experiencing maximal signal strength (vibration) when we pluck a string. But, then with CBGs, we are talking 3, 4, or 6 stings all tuned differently, and our model suddenly gets too complicated for my simple mind to comprehend. Well, I wish I were better versed in physics so I could give you an answer, but perhaps that's what this proportion formula is trying to do. Does this supposition create any more ideas we can discuss?

-Rand.



Zandi Z said:

this is actually a response to Mark aka Junk Box Instruments.
i posted it as a blog, but it has not appeared...sooo...

Mark wanted to know more about what i said about proportions... and do i measure or eyeball it ?
I do measure, but eye-balling is ok, too.

My basic premises are these:
'the box' is an amplifier.
'the stick', with hardware, is The Machine.

Why Proportions ?
the most efficient way to get the Box and/or Stick to resonate or 'amplify,' is to 'feed' them 'vibrating lengths' to which they might be most sympathetic....
this minimizes the energy needed to 'push' them to getting them to vibrate and to keep them vibrating.

The Box:
the length of the box is my Basic Unit... i generally round that out to an average between the inside length of box and outside length.
my Scale Length is a WHOLE NUMBER multiple of the Basic Unit.
eg: if BU is 8 inches, Scale Lengths would be 1,2,3,4,5,etc, times as long as the box...... 8 inches, 16 inches, 24 inches,32 inches, and 40 inches, etc.

The Stick:
i choose, or calculate a Scale Length...
i divide that Scale Length value by 4 to get a Stick Unit.
eg: 16 inch Scale Length = 4 inch Stick Unit.

Total Stick Length is equal to 6 Stick Units.
1 Stick Unit is headstock.
4 Stick Units from nut to bridge...(Scale Length).
1 Stick Unit from bridge to tail end.

The Result:
Scale Length is both proportional to the Box and proportional to the Stick .
the possibility of resonance is enhanced;
the possibility of dampening is reduced.
.....resonance is the most efficient way to transfer energy.

To Finish:
a person could place the center of the box directly under the bridge.
i prefer to mount the box so that the bridge sits from 2/3 to 3/4 of the way down the length of the box towards the tail....

i use movable bridges...
experimenting is a great part of this adventure...
i measured LOTS of instruments to see what their proportions were... then, i experimented lots.

thanks for asking, Mark...........zandi z.




Zandi Z said:

Amen, Steven.
What you said was elegant in its simplicity.
i am a novice player and a novice cbg builder. I am, however, in my Golden Years, as 'they' say.
To my eyes and ears, what you said was particularly profound...it is very commonly ignored, perhaps because of its very simplicity.

"Look carefully at traditional acoustic instruments that work well.
Notice the various dimensions mentioned above in relation to each other.
Try to emulate these proportions in the instrument you are building.

It is the relationships of these factors that count, not the exageration of any one of them".
thanks for voicing that...zan.

Permalink Reply by Dustin Smith on October 25, 2010 at 12:45pm

I posted yesterday in another group discussion about this exact topic, strange I found it here. Anyways this is what I've noticed. My first five builds, I glued a 1x1 to the inside of the bottom of the box, then inserted a 1/4x2 on top of it, running the length of the box and cut slots...action is lower than usual. The next five builds I cut the slots the "traditional" way but cutting from the top inside of the box and glued directly to the body. On the first five, the body is supported by the bracing as I thought this may reduce neck tension by distributing it through the body and in turn what I have noticed is that the bracing supports extra tone even though it reduces the inside airspace of the box.

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