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I have heard reference to a “sweet spot” for the bridge to be located on guitars.
For a flat top, is the “sweet spot” a subjective thing that will vary with design and materials or is there an actual place where the bridge should be located?
Is the bridge location always relative to the X brace and/or bridge patch?
Are folks making their bridge patches larger/wider than the bridge?
I apologize if these questions have come up before.
Thanks,
Wade

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Wade
Nashua, NH
http://www.wadefx.com

Yes I make my bridge plate wider than my bridge. I never really thought of locating the bridge indepently. but rather based on scale length and 12th fret to saddle slot. I slot my saddles prior to locating the bridge so I am pretty much stuck with the saddle locating the bridge.MichaelP38849.5285416667

Wayne,

"Allegedly" the bridge positioned nearer to the middle of the lower bout is supposed to be a good position and some models (particularly 12 and 13 fret clear of the body) are designed with such a position in mind. I think certain old Nick Lucas model's had this in mind.

That said the design has to function around scale length and appropriate brace positions (including the bridge) etc.

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Wade

Now there is an interesting question, are by sweet spot we looking for the most active part of the top, I think the principle behind some of the stuff I have seen on this was to seek a spot which is the least constrained by bracing so I guess the midpoint between the X brace Joint and the Rear of the guitar, and preferably in the center of the widest point of the body. First of all though is most active best ? surely that would have the same effect as a floppy top, secondly if you consider the bracing as a whole surely by moving the bridge back from the X Brace, it would require more force at the bridge to move the X (this is just based on my own thoughts so may not be true, maybe one of the scientific guys has measured this ?) and finally potentially it would cause problems with bellying etc.

Thanks Michael and Dave,
I forget that most folks work with a set of plans and that likely would dictate where to place the bridge.
I'm just wondering if it's a set in stone kind of thing or is there any lee way?

I have also heard that it is important for the "wings" of the bridge to cross over the X brace and if you set the bridge too far back, there would be consequences.

Lets say for a moment that you would like to shift the neck, fretboard and bridge forward or back relative to the body and bracing to make, say, a 13 fret to body or a 15 fret to body. What would be the consequence to making that shift?
Hopefully you can see where I'm going with this.

I guess I'm trying to hash out what the rules of thumb are.


Wade

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Wade
Nashua, NH
http://www.wadefx.com

Thanks Russell,
You snuck one in as I replied.
You seem to understand my query.
I seem to be generating more questions than answers.

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Wade
Nashua, NH
http://www.wadefx.com

Structuraly you need the wings to cross the x braces to prevent belling caused by string pull. basicly spreading the pull load into the x braces

Wade,

With me plans are what you make not what you follow

Golden principles still apply. You have usually a scale length and how many frets clear of the body in mind. This immidiately tells you where the bridge must be on the centre line down the guitar. If you are doing a pinned bridge, then it's a good idea to have the X braces going through the bridge wings with enough space for the bridge pins - so you would have to have an idea of the saddle string spacing you are going for. Then you probably have in mind the angle you want the X braces to make, so given the string spacing this will largely dictate where the centre of the X will be.

Then you can start to see what body shape will work around this - with lower bout, upper bout and waist width that you have in mind - where the soundhole will have to be (depending on the size of soundhole you want) and how the top arms of the X's fit with your upper bout bracing pattern and neckblock design. Assuming this all works then you can look at the bracing in the lower part of the X and any finger braces plus any soundhole re-enforcement you may do.

If it doesn't quite hang together adjust and iterate around until it works for you - functionally and aesthetically . . . or not as the case may be.

To me this is all part of the fun of designing and discovering guitars and what they can do. I've never ever built from a set plan (other than those that I draw out first using loosely the process outlined above).

Hope this answers some of your questions but probably will prompt a lot more Dave White38849.6098726852

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Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Wade

I believe Martin still make models with a forward shifted bracing system, that theoreticaly would open the top up.

I guess the position of the X in relation to the bridge plate, and in relation to the sides can be viewed as another parameter along with X Brace Angle, Bracing Design, Tone Bar Angles and Top Siffness as a method of influencing the end product.

For that very reason I guess there is no one sweet spot, it would depend on the sound you are going for.

I guess again, that doesn't provide too many answers.RussellR38849.613900463

I tend to think of the way the top works in terms of the resonant 'modes': the different ways it vibrates at different frequencies. The math guys tell me that once you've specified the mode shapes, masses, and losses, you've descibed the sound of the guitar. I can believe that, based on my experience: I sure can't do the math!

Most of the sound power of the guitar is produced by the 'main top' resonant mode, where the whole lower bout moves like a loudspeaker cone, flexing around the edge and in the center. This usually comes in around the open G string pitch. To get the most power out of this mode you want to drive it where it's moving: somewhere in the middle. _Exactly_ where that 'sweet spot' will be depends on a whole lot of things, like how you thickness the top and where the bracing is and how it's profiled.

There are lots of other modes as well, of course, and all of them effect the tone and power of the guitar. These modify the 'sweet spot' to some degree, but not all that much in general.

The deal is, then, that you locate the bridge where it _has_ to go: relative to the string length and how many frets you want to the body. Then you try to move the 'sweet spot' to where the bridge is.   

I _think_ that the size of the sweet spot is more or less determined by the bace profiles: it seems to me that 'scalloped' bracing will give a smaller sweet spot than tapered, for instance. OTOH, it may be less vital to hit the sweet spot exactly with scalloped bracing, since it allows for more motion in the center of the top. I'm not going to swaer to any of this, though.

A couple of years ago I built a guitar with a 20" string length. The bridge ended up about 2" below the edge of the soundhole, with a whole lot of top below that. It was not all that far from the waist. I managed to get the 'sweet spot' pretty close, and it sounded OK. you've actually got a fair amount of control over the thing.   

Thanks guys. You have given me way more answers than you likely know. It’s great to hear your thoughts because I know they are based on experience.

Dave, I can relate to your statement “plans are what you make not what you follow”. It is interesting how far from the norm an outline design can be and still make a good sounding instrument, As long as you fallow the Golden principles that is.

Alan, manipulating the “sweet spot” to where the bridge_has_to go was something I had not thought of.
Lots of food for thought here.

Thanks,
Wade

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Wade
Nashua, NH
http://www.wadefx.com

Gives me the will to abandon the idea of building with a plan for the next build and experiment with braces, bridge, soundhole placement, Thanks for a very interesting thread guys!

Serge

hey Wade, I admire the instrument designs that you have made, so i relate to your realating to Daves plans statement.(does that make any sence?)

I learned alot about the sweet spot when I made my first 12 fretter...which used the same scale length as my 14 fret models, and located the bridge further back over the lower bout. I was amazed at the power difference.


Matt

SWEEEEEET     

Go for it Serge!

Matt, Interesting about your 12 fretter.
The reason I started this thread is because of my latest build. I’m at a point in the build where I could shift the bridge placement and was wondering if there is an advantage to having it closer to the center of the lower bout. My body shape is a bit odd as well so I’m not sure I need to shift it anyway. I just thought I’d ask.
I came up with a body design/outline and applied a bracing pattern and sound hole placement that seemed to look right for the design. I decided on a 24.9” scale and when I placed the bridge/saddle at the usual spot, that placed the neck at a 13 fret to body. This seemed kind of cool but it started me thinking. Since it’s a cutaway anyway, I could go the 12 fret to body and shift the bridge further to the middle of the lower bout. We are only talking about a shift of the distance between 12 and 13th fret so maybe it doesn’t really matter. Or does it?

Wade

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Wade
Nashua, NH
http://www.wadefx.com

It seems to me that every shift or change in a design matters. Even the smallest. You are talking about pretty big changes. Like 12 or 13 fret to body. I've got to think that will make a big difference.

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Joe Beaver
Maker of Sawdust

yes! I believe it will matter. are you dead set on using a 24.9? I would go with a 25.4 scale 12 frets clear, which will really get you over the sweet spot.

Martin figured a lot of this out for us actually, and as you follow the progression of their designs you can see this type of experimentation going on.

I think you are right on track with your thought process....go man go.

Matt   

Serge I know you know this, but if expermenting and particularly without plans. Do one thing at a time IE braces, soundhole etc. I change things around but do it one thing at a time and after several guitars. The one on bench now was just a change in bridge plate.

Matt,
If I was to go with 12 fret neck with 25.4 scale I’d end up about here.

If I had not committed to the bridge patch, I would consider it.
This is what I am thinking.


This is with 24.9" scale, 13 fret to body.
Does this seem correct?
Thanks,
Wade

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Wade
Nashua, NH
http://www.wadefx.com

Go for it Wade!

Stan, i heard you my friend, yeah, it kind of makes sense, i'm gonna settle for brace experimenting and maybe a cutaway for the third, the cutaway is really something i long wanted!

Serge