Alan Carruth and I discussed break angle on UMGF

[tippie53]

http://theunofficialmartinguitarforum.y ... K7pCK5_biQ
Posted this from a discussion about break angle .
Many misunderstand this and what it does in the matters of a bridge.

John Hall wrote:
"I agree that the break angle is little in the inference to tone. The big change is the overall string height of the bridge/saddle . I think slotted bridges don't add much unless the slotting is so great to move the ball ends considerably . I wonder if your findings, Mr Carruth, are the same as mine."

Alan Carruth wrote:
"I did a semi-full-blown study of this, and came to pretty much the same conclusions. I made a plucking machine that works by looping a length of magnet wire behind the string and pulling on it until the wire breaks. This gives a repeatable pluck in terms of force, location on the string, and the direction of the initial displacement. I recorded six plucks on each open string of a classical guitar for each of three conditions:
A - strings 11mm off the top and a 25 degree break angle,
B- strings 11mm off the top and a six degree break angle, and,
C- strings 18mm off the top with a 25 degree break angle (don't try this at home!).

I made up a 'strum' using .7 seconds of a randomly chosen pluck from each string, and played back random pairs of strums through good headphones for listeners who were asked to rate them as 'the same' or 'different'. With about a hundred examples of each possible pair, people were statistically unable to tell the difference between case A and Case B, but were very able to pick out case C.

My statistics guru and I spend a lot of time looking at the sound files, taking them apart in different ways and trying to see what might be different. It looks as though people were hearing two things that were different in case C from the other two cases:
1) there's more energy in the second partial in particular, and in some of the other even-order partials, when the string is higher off the top. This is probably the twice-per-cycle tension change of the string, rocking the bridge toward the neck.
2) there is also more energy in the 'zip' tone; a high frequency longitudinal compression wave that is driven in a fairly complicated way, but also acts by pulling and pushing the bridge top the same way the tension change signal does. Again, greater leverage makes it stronger. Since the 'zip' tone is not a harmonic of the string (usually) it would add a 'noise' component to the signal, and it might well stand out strongly since it's usually up around the 7th partial pitch.

You certainly do need to have enough break angle to keep the string from slapping. Benedetto shows a six degree break in his archtop book, and that's one reason I settled on that as the 'low' break. It's possible that's not quite enough, but it's hard to say: the data I have is not sufficient to see one or two 'jumps' that the start of the note. There was more variation in the signal in the low break case, so that's circumstantial evidence.

I'm trying to get a paper out on this, but need to break it up into several shorter ones: the project ended up generating a lot of data from multiple experiments, and it's sort of confusing. The two things I learned for sure were how to do it better next time, and that I'll need to do a much bigger experiment to really nail it down. Still, I'm pretty confident about the results I've got, as far as they go."

[Ben-Had]

So is this indicating that "higher" (to that point you mentioned) is better? And if so, in what way? Then if that is the case why wouldn't we want to have the fretboard fall off to a certain extent at the 14th (or 12th as the case may be) to gain increased string height over the top yet keep them close to the FB foe ease of playability?

[tippie53]

There seems to be a sweet spot. Alan and I both found that when you get over that 1/2 inch height the top becomes "locked" up or over stressed. This causes the top to rise more.
Also once you get under that 3/8 inch mark the top looses a lot of energy , and you loose the guitars voice. It is a balance to get into that butter zone. Early I thought that well if I use light gauge strings I could make the string height at the bridge and saddle even higher and with the lower gauge strings this would make the guitar feel softer and I would have more energy on the top , in essence fooling the top that it had medium gauge strings when using lights. Well that didn't work either. There is a point , like a see saw that you get over that point that becomes detrimental.
I kept logs on my guitars and the sweet spot is about .500 +/- .050. After .375 there is a significant fall off in amplitude of the sound waves. At the same over that .550 mark the top becomes muddled and the note clarity fall off much like when you exceed the headroom of the top.
Does than help explain things ?

[Ben-Had]

Yes, very informative and if I followed correctly as the guitar ages and the subsequent setup adjustments lower the saddle height, unless the break angle is less than about 6* + or - the tone should remain the same. So unless the action is really high the is no need for a neck reset unless break angle is less than 6*.

[tippie53]

has nothing to do with the break angle , as long as the saddle isn't into the bridge. In a perfect set up you will have 3/8 bridge 1/8 inch saddle.
Once the saddle has been cut down to adjust for the neck angle change and you are into the bridge , resetting the neck will reset that string height and all will be well with the world. Some people , to save money would shave the bridge to adjust the action , and now you need a reset and a new bridge.
The part most people over look is the attachment point. All they see it the break angle and assume that is the part that matters when in reality it is the overall string height of the bridge and the ball connection. The ball end is the point of fixation and the saddle is the point of direction.

[Ben-Had]

Yeah, I get that. I guess what I'm trying to say is there really should be no noticeable loss of tone until that point (where you are into the bridge) if you still have about a 6* break angle. I've often heard that as that angle approaches "flat" there is a loss of volume and tone but what you and Allan are saying is that isn't necessarily true. And the reason I ask is because I have adjusted saddles to that point (or near) and haven't noticed the change people talk about. I was wondering if it was my hearing perception.

[tippie53]

I try not to rely on ears . A spectrum analyzer will show the waves. Amazing what you think you hear and what you actually hear sometimes.