bridge advice please

[murrmac123]

Originally Posted by Tygrys

Am I correct thinking that bigger brake angle will increase "volume" of the instrument.

No, break angle has little or no effect on volume. What does have an effect on volume is the torque exerted on the bridge, which in turn depends on the height of the top of the saddle from the soundboard ... the higher the saddle, the greater the torque. It is generally accepted that a height of .5" is the height to aim for.

I posted volume in the bracket as I know that this is not best description, but there were information in the net that strings should have as little contact with saddle as possible

Maybe you're not phrasing exactly right what you actually mean to say, but in fact the reverse is the case...the strings should be supported in the breakover portion by the curve of the saddle, otherwise you will get premature wear on the saddle at the point where the string makes contact.

and also that saddle should be as tide as possible to improve instrument tone.

Within reason, yes. It should be a push fit, but should not have to be forced in, not so tight as to cause stress on the bridge.

[Alan Carruth]

tygrys asked:
"Am I correct thinking that bigger brake angle will increase "volume" of the instrument."

No, it won't. That is a common misconception, but from the experiments I've done it seems to be false, assuming you don't only changed the break angle. Here's why.

If you pluck a string in a certain place with a given amplitude, the actual forces it imposes on the top of the saddle are easy to figure out, and much less than the static tension of the string. If the string has 10 kilos of tension on it, the maximum force up and down on the top of the saddle as it vibrates will be no more than about 1 kilo. Think about it: when you pluck the string you don't pull or push it with a force anywhere near the tension, and the force on the bridge top can't be any greater.

So long as the string stays in contact with the top of the saddle throughout it's whole vibration cycle, it will transmit all of the vibrating force to the bridge. The down force on the saddle only has to be great enough to do that; about 10% of the string tension. The down force is the sine of the break angle times the tension, and .1 is about the sine of six degrees, so that's all the break angle you should need to keep the string in contact. Increasing the break angle beyond that won't put any more signal into the top. It will increase the tipping force on the saddle, which is trying to break out the front of the saddle slot, but you don't want that.

So much for theory.

I ran a fairly long experiment on this a few years back, using a Classical guitar. I set up the bridge so that I could have either a 6 degree break, or a 25 degree break, with the same saddle height. I also made a tall saddle that gave a 25 degree break angle with the strings set up as they had been for the low six degree break, to see if string height off the top made any difference.

I rigged up a mechanical plucker that plucks the strings with almost exactly the same force in the same place and direction every time. I plucked each open string six times for each of the three setups, and recorded the plucks.

I strung together a set of plucks for each case to make a 'synthetic strum'. These were played back in random pairs through headphones to see if people could hear any difference. Basically, they could not hear any difference from the simple change in break angle, but easily picked up the change when the strings were raised off the top.

In addition, a student helped me do statistical analysis on the actual sound of the plucks. We found no difference in the 'rise' or 'fall' times or the maximum amplitude: in other words, no one case was any louder or more powerful than another. We did see a difference in the harmonic content of the sounds, but, again, only when the string height off the top was changed.

Thus, on the basis of this experiment, it seems that increasing the break angle by itself doesn't make the guitar louder. There is a change in timbre when you raise the strings higher off the top, assuming you're using a bridge that is glued down, rather than a tailpiece. This may sound louder to some people.

Of course, all the usual cautions apply. One would like to have a lot more data on this instrument, and on other guitars as well, to be sure. That would take a lot of time, and I don't get paid to do this stuff. What we saw made a lot of sense in terms of the physics of strings, but, as usual, there were a few surprises that would be nice to track down in more detail. I don't think a better experiment would reverse the finding, but it might refine it a lot.