why do bridges go across? How should they relate to bars? More.

[Stephen Perry]

Why do bridges go across? The issues arise when they move back and forth, getting unseated.

How are they supposed to relate to the bars?

Wouldn't a bridge that had feet that ran right on top of the bars be good? There's a bit of an acoustic and engineering challenge there!!

Wouldn't a bridge with feet that ran fore and aft, rather than abeam, be more stable? Has this been tried?

Wouldn't the posts work better if between the courses rather than at the ends? I've done this one with success. Some issues to work out.

Why is the bridge so wide? Wouldn't a full contact in the middle do the same or better? Perhaps an oval contacting the surface, or an approximation thereof.

[billhay4]

These are good questions that probably will need experimentation to answer (insofar as they can be answered). Are you experimenting along these lines? I hope so. It's good to see a good luthier asking such questions.
Bill

[MikeEdgerton]

Non-tip.

[mandroid]

& Fan fret, the bridge is at a specific Angle..

[Tobin]

Wouldn't a bridge that had feet that ran right on top of the bars be good? There's a bit of an acoustic and engineering challenge there!!

If the bars were only structural braces, I could understand the logic of it. Taking the load directly to the supports would be a good thing. But the tone bars are there specifically to shape or balance the tone, by adding mass and stiffness in particular zones in relation to the bridge, sound holes, and edges. Despite the claims by some that the top moves as a rigid plate mounted at a flexible edge support, it seems clear that the tone is indeed affected by variations in mass/density and stiffness within the center area of the plate. Otherwise, tone bars would serve no purpose.

You could certainly try making a bridge that is only supported directly over the bars, and see what it does to the tone. But I would imagine that when Lloyd Loar did his own testing and came up with the tone bar design that's still copied today, it was based on a bit of studying and experimentation.

Wouldn't a bridge with feet that ran fore and aft, rather than abeam, be more stable? Has this been tried?

I don't remember seeing one with feet running fore-and-aft, but some of the Weber bridges have 'turns' at the ends of the feet which do make them more stable against tipping. This is what my Bitterroot mandola has on it:

[bernabe]

I would think the bridge design has structural aspects intended. If smaller [or shorter in length], then downward pressure on the top wouldn't be as dispersed and could indent or cause damage from concentrated pressure on a smaller area. As far as being supported on vertical feet, pressure would run along the grain lines rather than perpendicular to the grain which could possibly cause a crack or indentation as well. Cant comment on tone and can only assume the structural opinion as it makes sense to me. Just my opinion.

[AndyPanda]

I would think the bridge design has structural aspects intended. If smaller [or shorter in length], then downward pressure on the top wouldn't be as dispersed and could indent or cause damage from concentrated pressure on a smaller area.

Violin bridges have much smaller feet ... however if you look at how narrow the violin top is at the waist, perhaps the ratio of foot to width of top is similar. Also the violin has a rocking action, due to bowing - I'm not sure the mandolin has that rocking action going on(?) or does it?

[fscotte]

I think if you took away the bridge feet between the tonebars, you have to beef up the center of the top plate to keep it from bulging up. The feet there, like a full contact bridge, help support the top from deforming and cracking.

Secondly, you'd be putting more force directly onto the braces, thus beefing those up may be required as well.

I believe the tonebars are just braces and nothing more, allowing you to make the top thinner overall, offsetting some of the force onto the braces. Those braces also help keep the top from bulging out as well.

Overall, I think Loar got it right.

[Stephen Perry]

I've just had so much fun with my odd bridges!

Imprinting and pressure distribution across the top isn't an issue. Can be addressed. I might pull together additional designs in my "free time"!

Aspects that are useful to incorporate include "tuning" options - i can already adjust individual courses on conventional bridges. Just did two today.

[CES]

Keep thinking outside the box, brotha! That's how innovation happens...

[fscotte]

Instead of conforming the bridge to the tonebars, why not just conform the bars to the bridge? X brace, Y brace, z brace, whatever brace configuration. Then you could imagine any bridge you need.

[Bertram Henze]

I can see where this leads...

[Stephen Perry]

One of the issues with product development is conforming the product to the existing market. Like my various acoustic optimization things. There are certain principles that guide both manufacture of violins (which I still do slowly) and which I apply to an existing range of instruments (application to guitars is coming along very well). The application differs and I add other steps when building, with much more control. But that's not really a product-based system.

So. The product I have now is my modified conventional bridge. In working on a lot of bridges, I face or detect the same issues:
1. bridge wants to dig into the top at the inside edge of the two feet.
2. ends of the feet tend to lighten up pressure and lift
3. saddle rotates forward towards neck
4. signs of greater pressure at forward edge of feet
5. complex array of facets and shapes on saddle
6. E and G courses closer to posts than D and A courses (figures into voicing)

I suspect the current system is a combination of history and practicality. History is an easy piece across, simple to make. Practicality is the wheel adjust. Sensible, crosses lots of grain lines.

Brekke bridge does some interesting stuff to counter some of this. The heart cutout improvement reported makes sense in an intuitive way.

I'm not at all convinced that the relationship of tone bars to bridge feet is crucial. My experimental bridges with the posts between the A & E and G & D courses worked fine on a relatively narrow platform, but the two-foot approach presented difficulties in getting what I considered to be sufficient area of contact without some design weirdness. I'm no longer convinced that one troubling design consideration was necessary. So I'll try more of that kind of thing.

There are also ways of breaking up a single foot into multiple feet without allowing much or any distortion. Must ponder.

Just breaking in from outside the box. Ideas very welcome.

[Tavy]

Banjo builders have been there already:

From http://banjobridge.com/stu.htm

[fscotte]

Some mandos don't have tonebars, and they sound as good as any mando with tonebars. So I'm not sure what the fascination with tone bars is all about. There is a certain mystique about them of course, cause they have the word tone (oh my! That's where the tone is!) in them, so that's gotta be good right??? Dave Cohen has built mandos with weird tonebar placement, more than two tone bars, etc.. And you guessed it, sounds like a mando.

I say just design the bridge you want and forego the tone bars altogether.

[Stephen Perry]

Makes sense to me.

I had a violin experiment once. Pure structural, without the bar extensions north and south (which aren't needed really). Very pure and loud. Didn't actually sound that much like a violin! I put in separate "tone bars" in spots that seemed to respond appropriately and got a very nice, very clean sounding violin / fiddle. Probably still out there somewhere! Was putting the top on with glue stick for testing. Worked fine, for limited periods!!!!

[AndyPanda]

Non-tip.

That non-tip bridge reminds me of this:
Attachment 154264

[Jim Garber]

Wouldn't the posts work better if between the courses rather than at the ends? I've done this one with success. Some issues to work out.

I am not 100% sure what you are describing above, but here is some pics of the original bridge from my Weymann Style 25 mandolin-banjo.

[Steve VandeWater]

That non-tip bridge reminds me of this:
Attachment 154264

The opti-grab! Opti, for eyes, and grab, for where you grab it! Classic