Official Luthiers Forum!
http://www.luthiersforum.com/forum/

bridge height
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=21759		 Page 1 of 1
Author:  J Hewitt [ Thu Apr 02, 2009 4:21 pm ]
Post subject:  bridge height
I would like to know if a 9/32 bridge height is to low? With a straight edge running down the center of the fretboard (fretted) I have a 9/32 of an inch gap from the bottom of the straight edge to the top of the top at approx. were the bridge will be. So that would be just kissing the bridge but actually it would be just a little less in height after the frets are filed.

The guitar still needs sanding and all but right now the neck fits pretty good to the body.


Thanks,
Jeff
Author:  David R White [ Thu Apr 02, 2009 4:38 pm ]
Post subject:  Re: bridge height
IMO that's a little too low, you want the strings to be higher. I like to be at 11/32.
Author:  Rod True [ Thu Apr 02, 2009 4:39 pm ]
Post subject:  Re: bridge height
I always try and build to my designs, so if you've designed the guitar to have a 9/32" tall bridge( which is very low), you'll still want to have at least 1/32" - 1/16" clearance between the plane of the frets and the top of the bridge. Set the neck right and you won't have to do it in 6 months when you have no saddle height left after the guitar has settled in.

If you intended to have you're bridge 3/8" than set your neck so it has clearance over the 3/8" tall bridge.
Author:  J Hewitt [ Thu Apr 02, 2009 5:07 pm ]
Post subject:  Re: bridge height
I've never went that low.....I was just curious?

Thanks,
Jeff
Author:  Rod True [ Thu Apr 02, 2009 5:35 pm ]
Post subject:  Re: bridge height
J Hewitt wrote:
I would like to know if a 9/32 bridge height is to low? With a straight edge running down the center of the fretboard (fretted) I have a 9/32 of an inch gap from the bottom of the straight edge to the top of the top at approx. were the bridge will be. So that would be just kissing the bridge but actually it would be just a little less in height after the frets are filed.

The guitar still needs sanding and all but right now the neck fits pretty good to the body.


Thanks,
Jeff

J Hewitt wrote:
I've never went that low.....I was just curious?

Thanks,
Jeff



Sounds like you're seriously thinking about it though :D
Author:  J Hewitt [ Fri Apr 03, 2009 7:12 am ]
Post subject:  Re: bridge height
Rod True wrote:
J Hewitt wrote:
I would like to know if a 9/32 bridge height is to low? With a straight edge running down the center of the fretboard (fretted) I have a 9/32 of an inch gap from the bottom of the straight edge to the top of the top at approx. were the bridge will be. So that would be just kissing the bridge but actually it would be just a little less in height after the frets are filed.

The guitar still needs sanding and all but right now the neck fits pretty good to the body.


Thanks,
Jeff

J Hewitt wrote:
I've never went that low.....I was just curious?

Thanks,
Jeff



Sounds like you're seriously thinking about it though :D


Just curious mostly.....what would it do to the volume? more or less volume? I think I will set the neck for a 5/16 -3/8 height.
Thanks for your replys,
Jeff
Author:  woody b [ Fri Apr 03, 2009 9:41 pm ]
Post subject:  Re: bridge height
It's my belief that the "magic" spot is when the strings are 1/2" above the soundboard. Less and the strings don't have enough leverage to properly move the soundboard. YMMV
Author:  David Newton [ Fri Apr 03, 2009 10:33 pm ]
Post subject:  Re: bridge height
I'm onboard with the other replies, but...

What kind of guitar are you building?
Author:  J Hewitt [ Sat Apr 04, 2009 5:10 am ]
Post subject:  Re: bridge height
David Newton wrote:
I'm onboard with the other replies, but...

What kind of guitar are you building?


A parlor size
Author:  bluescreek [ Sun Apr 05, 2009 8:17 am ]
Post subject:  Re: bridge height
When you do the math you want to have the string height to be about 1/2 inch above the top as stated above. In a perfect set up I like to have a 3/8 bridge with 1/8 saddle. My max bridge height is .410 and min is .312 . What you are proposing would be way too low to get the most out of your guitar.
Remember that the bridge , saddle and plate are the driver for your top. If the string height is too low regardless of the break angle you won't get the proper transfer of energy of the strings to the top. The bridge will work with rotational force to drive the top. The break angle is how much force is pushing down on the saddle. They are 2 different forces. The string height will get you the resultant force that is there to drive the top , the break angle what is there to push on the saddle. They work together . If you figure one is volume and the other tone ,that may help to give you an understanding of what is going on
john hall
blues creek guitars
Author:  J Hewitt [ Sun Apr 05, 2009 10:17 am ]
Post subject:  Re: bridge height
Thanks John :D
Author:  Ken C [ Sun Apr 05, 2009 7:12 pm ]
Post subject:  Re: bridge height
Very timely thread. I am at the point of making the bridge for my SJ. I took measurements last night, and my unfretted fingerboard provides a gap of 0.32". My frets look like they will add another .04" to .045", putting the gap at .036" or thereabouts. I don't know how much the top will rise under tension, so I'm thinking of making my bridge 0.34", which is pretty close to the Martin style bridges I have used. Those run around 0.36".

This will be my first foray into bridge making.

Ken
Author:  Alan Carruth [ Mon Apr 06, 2009 11:58 am ]
Post subject:  Re: bridge height
John at Blues Creek wrote:
"The bridge will work with rotational force to drive the top. "

Yes and no.

I spent 'way too much time a few years ago measuring the actual forces plucked strings put on the top of the saddle. The two main ones are a transverse force (the string goes up and down, and pushes the top down and up) and a tension change signal with frequencies that are double those of the transverse force (because the string gets tighter both when it's 'up' and when it's 'down'). The magnitude of these forces depends on the string construction and on how tight it is. Basically, for a plain steel string, the two forces are about equal when the string is tuned as low as G. The higher you tune it, the greater the transverse force; for a high E string it's about 6 times as great as the tension change signal. I did not measure a lot of wound strings due to time constriants, but would expect them to be far more like the plain high E than the plain G. You also have to think about two other things: how easily the string can drive the top, and how effective the top is in turning that force into sound.

We build tops to resist bridge torque. For the most part it is many times easier to push the top 'in and out' than it is to twist the bridge. There is one top resonant mode, usually at about 350 Hz, where it's possible to rock the bridge fairly easily, but otherwise the bridge rocking mechanism is not very effective. That resonant mode is often called the 'long dipole'. As the area behind the bridge is moving 'up' the area in front is going 'down'. At that frequency it's a bit easier for the air being pushed out behind the bridge to just 'slosh' up and fill in the area where the top is going down than it is to make sound, so there's a lot of cancellation involved. This action is not nearly as efficient at producing sound as the 'in and out' motion pushed by the transverse force.

I have read about the experiment done by one writer who feels the opposite, and I think he's made a mistake. The clue for me was that he stated that the string motion was predominantly 'across' the top. He then went on to pluck the strings very carefully and saw more output when the bridge was allowed to rock than when it was allowed to move in the vertical direction. This is the result one would expect if he carefully plucked the strings so that they moved across the top, since there would be no vertical component of motion to drive the top that way.

I think the problem is that he's assuming that the strings move in the same way the pick does; across the top. By analogy, I could assume that, since the cam shaft in my car goes around, the valves must move sideways. The pick is a sort of cam, changing at least some of that crosswise motion of the hand into vertical motion of the string. If the string did not move vertically, why would it buzz on the frets?

At any rate, I have done one experiment in which I used an electronic driver to push a string on a guitar both vertically and horizontally, relative to the plane of the top, and measured the output. Although I don't have the numbers handy, I did get far more sound from the vertical motion.

I wrote up all of the gory details of my string experiments in 'Guitarmaker' a couple of years back, although they left out a couple of the charts. It's not the most scintillating reading, but it has it's points.
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/