Headstock angle and break angle at bridge on an archtop

[Robert Kroon]

So this morning i was figuring out the neck angle on a archtop im building and i got to thinking.
Why do violins and upright basses have such a high bridge? Is it for bow clearance? Thing is i've owned a couple of les pauls and all the ones that sound good had a healthy amount of break angle at the bridge. Does anybody have a theory on this? I'm entertaining the idea of making a high bridge and mounting the pickup to the pick guard.

[Dave Stewart]

Break angle absolutely affects the acoustic properties of an acoustic archtop (changing the downward component of string tension). Forget about violins and solid-body LesPauls ....different parameters going on. If you are building an archtop, I'd strongly suggest Bob Benedettos' book before get too far.

[Patrick Hanna]

Hi, Robert.
I suspect your hunch about high bridges on bowed instruments is correct. Remember that those instruments have internal soundposts, which acoustic archtop guitars do not have. String break over the bridge of a hollow body archtop guitar is sort of a balancing act. You need sufficient angle to create downforce and drive energy into the top, but not so much downforce as to collapse the top. Dave's advice is good.

[Robert Kroon]

It's actualy a gretsch style guitar. This might be the wrong part of the forum for this discussion but i guess this section has more acoustic experience. I've built an acoustic archtop before and this is a laminate. The top with bracing feels very stiff to me. To me it would indeed seem that there's and ideal amount of downforce/deflection and was woundering what your experience is. I recently swapped a normal tail piece for a bigsby and noticed a dramatic increase in sustain/tone. The break angle increased by about 5 degrees. The guitar used to sound quite weak but really came alive after the swap. To me gretsch style guitars sound great but sometimes a bit weak also. I'd like to experiment with these factors a bit. Is there a formula for this?

[Dave Stewart]

Well, I've never dealt with laminates, but I expect they're stiffer. Regardless of construction, if you have a very stiff top combined with a low breakover (ie without the power to drive it) the results will be less than ideal. You can increase the breakover, tune the top to best use the breakover you have, or a combo. (eg calc the downforce needed to get the desired deflection via a jig, then calc the breakover needed to get that force, then find the bridge height needed for that breakover.)
The formula for downforce is Downforce = 2 x T x sin(breakover/2) where T is total string tension.

[Barry Daniels]

The change in tone with the swap to the Bigsby tailpiece probably has more to do with the mass of the unit instead of a slightly different break angle.

[Mark Swanson]

It sounds like you are talking about an electric archtop guitar. If that is true, then there is some confusion and you are getting information that doesn't really apply to you- electric archtops like the Gretsch hollow bodies are really completely different from acoustic archtop guitars, and you'll never get the same type of acoustic tone or power from them as you would an acoustic guitar.

[Michael Lewis]

Mark is right. They are different animals and have different design needs.

Acoustic archtops that are amplified are more suited to more intimate settings like a solo or small combo that is not loud. If you intend making a lot of sound you need to have a less acoustically alive instrument. That is why solid bodies are so popular for rock, and acoustic archtops more popular with intimate jazz settings. Semi hollow guitars fall somewhere in between.

[Robert Kroon]

I agree with everything being said here .

I know that a laminate will never sound like an acoustic archtop. The lack in body size and the complete lack of a recurve alone make it pretty much
impossible. The bracing/soundpost's i've seen on gretsch's are all quite big "quenching" the acoustic properties to prevent feedback from a big amp.
I'm just trying to make the best instument i possibly can. I think i'll give Dave's idea a go and see what i come up with. Is there a certain amount of deflection i want to be looking for? That old instument i was talking about earlier is alot looser when i "thumb press" the body compared to the one i'm building.

Thank for all the info guys! There's not alot of people around where i live to talk shop with and this place always seems to help alot.

Happy building!

[Mark Swanson]

Fine- you agree. But you still haven't told us what it is you are building, and what kind of guitar you are talking about. If you would please explain what you are trying to do with what kind of guitar and pickups, that would help us talk with you.

[Robert Kroon]

Mark,

I wasn't trying to be a smart-ass or anything. Anyway. It's a Gretsch style guitar. Laminated top/back and sides and two tv jones pickups.
I'm trying to get a bit of extra tone out of the guitar and thought it could mabee be won by playing around with the break angle to " drive" the top a bit more.

[Beate Ritzert]

I own an old Isana thinline - a german archtop.

It is one of Josef Sandner's simpler guitars built fully laminated. Otherwise it is built like an acoustic archtop - V-bracings and, imho, really nice teardrop f-holes. Its acoustic sound is surprisingly strong and full, especially if the pickups are not mounted and the holes act as additional resonance holes. So if You are able to built a few prototypes or at least can build one You might experiment into that direction.

As far as i understand the matter You cannot reach the warmth and responsiveness of a solid stop with a laminated arched top. It will always have a sound of its own. But please be aware that such a guitar will be as sensitive to feedback as any other acoustic archtop. As a rule of thumb: the better the acoustic tone the larger the sensitivity to feedback.

[Robert Kroon]

Thats great Beate!

The instrument i put the bigsby on is acually an isana!. It's an acoustic archtop and far as i can tell its made to be one. It's very old and unfortunately
some one drilled a bunch of holes in the top for pickups. I played it acousticly for about 2 years but im using it now for a rock-a-billy band so i mounted a pickup and the bigsby. It's a lot louder acousticly than say a Gretsch 6120 and doesn't have alot of feedback. Wounderful instrument. Best 100e i've ever spent. There are a whole bunch of factors to a great guitar and the whole loud acoustic/low feedback thing kinda puzzeles me thats why i started this post.

[Dave Stewart]

Dennis Durross correctly pointed out an error in my "downforce" formula above.
Use the online version at http://liutaiomottola.com/formulae/downforce.htm
Sorry for any confusion.

[Alan Carruth]

I did an experiment years ago with a 'hook' type tailpiece that was set up so that I could vary the contact point on the side of the guitar fairly easily. Since the line of the strings goes from the bridge top to the contact point, moving that point up toward the edge reduces the break angle, and lowering it raises the break. What I found was that increasing the break angle beyond a certain point killed the sound. Although I could not try too mane different angles, the effect seemed to be rather sudden; below a certain point the sound was fine, and above it it just died.

Given that you don't need a lot of break angle to ensure that the strings stay in good contact with the top of the saddle, I've taken to minimizing it. Benedetto shows a six degree angle in his plans, and data from another experiment suggests that this is about the practical minimum.

And yes, violins are a whole different beast. The bow drives the strings _across_ the top, but the top wants to be pushed vertically. The sound post 'nails' the treble foot of the bridge, making it into a bellcrank that converts crosswise force at the top into vertical force at the bass side foot. The bass bar then helps spread that motion along the length of the top.

[Dennis Duross]

Alan:

I had wondered about doing something like that---setting up the tailpiece in a fashion so it could be raised/lowered. The drawings I did suggested that for every 3/16" you raise or lower the tailpiece's point of attachment at the heelblock you change the break angle by one degree.

For what that's worth.

Did I misunderstand or are you saying that 6 degrees is a sufficient break angle?

[Alan Carruth]

As far as I can determine, six degrees of break angle is _just_barely_ sufficient.

[Michael Lewis]

I find that about 12 degrees works very well. It provides firm contact of the strings with the saddle and plenty of down force to drive the top, but not too much.

[Alan Carruth]

How does increasing the break angle serve to drive the top more effectively? Once you've got enough angle to maintain contact between the string and the bridge, all of the signal should be transmitted.

[Michael Lewis]

Alan,I can't explain the specific interactions of the parts but I know what has worked well for me and what I measured from some nice older vintage guitars.