Perpendicular bridge?

tinyd · #1 12-04-2008, 04:51 AM

Hi all
I finally took the plunge and bought my first DB - a used Shen SB180 - to my novice eyes and ears it seems like a great buy, but I have a question about the bridge. Basically, the guy that I bought it from got a new bridge fitted by a well-respected luthier in Dublin (can't remember his name, but it's stamped on the bridge). I thought that the bridge was supposed to be perpendicular to the bass body, but there's a slight angle towards the tailpiece if you see what I mean. It looks like the angle is deliberate as the base of the bridge seems to have been sanded to give the angle, rather than the bridge being warped. So I guess I'm trying to find out if this is OK, or should I get someone to take a look at it?

Thanks for any insights

Dave

Steve Clark · #2 12-04-2008, 05:37 AM

New guy here. The back of the bridge should be square to the top of the the bass. Check it with a right angle. I thought the same thing after a few days of having my bass but it was an optical illusion. More experienced voices may chime in.

drurb · #3 12-04-2008, 07:50 AM

The "tailpiece side" of the bridge should be perfectly perpendicular to the top. It is quite normal for the other side of the bridge to be tapered.

tinyd · #4 12-04-2008, 09:12 AM

Thanks for the replies. Not sure if the diagram that I've included will show up, but I think I understand how it's supposed to be - I'll take a look at the bass when I get home.

Thanks again

drurb · #5 12-04-2008, 09:13 AM

Yup--that's it!

GerardSamija · #6 12-04-2008, 10:09 AM

While as a general rule, the perpendicularity of the back side of the bridge to the local arching is solid enough, it has a point beyond a sort of rule of thumb. This intention is to as nearly as is practical divide the angle of the strings over the bridge in half, to match the more rapid drop of the strings behind the bridge to the saddle (through the tailpiece) against the longer, more gradual drop to the nut. The wide range of bridge heights, neck angles, neck projections above the belly, and saddle heights mean that bisecting that angle is a bit complicated. Not always easily accomplished by simply standing the back of the bridge straight up, though that is often close enough.

Sometimes a tailpiece riser is called for to enable putting the strain of the strings directly downwards, through the centre of the bridge to the belly. That's the whole point. If you drew a line down the side of a bridge, from the centre of its top to the centre of the feet, this line measured against the fore and aft angles of the strings over the top should be identical - a bit variable here, owing to the curvatures of various tailpieces, especially so with the MarvinUSA endwire, or perhaps I should say that this innovation makes for more predictability. The reason for this matching of angles is so as to equalise stresses, to most efficiently put the direction of pressure, and thereby the shortest, least wasteful path vibration, directly through the middle of the bridge and into the belly. Through well-fitted feet, of course.

While it's a bit of an aside, I see so very many bridges with incorrectly fitted feet that this needs mentioning. There is no excuse besides the luthier's laziness to hollowing out bridge feet, and yet I see this constantly from many respected shops, as well as from the cheapest of overseas factories. It's a shortcut, and a rather painful one in terms of both sound production and damage to the delicate spruce and varnish of the belly. Why bother going to all the labour of fitting a bridge to the right angle, carving it to tune its responsiveness, and then fit only 50% or often much less of it to actually contact the belly? Rant over. Majority of luthiers, consider yourselves admonished.

tinyd · #7 12-04-2008, 10:37 AM

Thanks for the detailed reply GerardSamija. I think I understand what you're saying - that the angles X and Y in my diagram are equal? Apologies for the diagrams, I've been helping my daughter with her geometry homework a lot recently

GerardSamija · #8 12-04-2008, 10:45 AM

No apologies needed for the drawings; they are providing excellent clarification. And your understanding of what I wrote is just fine.

drurb · #9 12-04-2008, 11:11 AM

Quote:

Originally Posted by GerardSamija

While as a general rule, the perpendicularity of the back side of the bridge to the local arching is solid enough, it has a point beyond a sort of rule of thumb. This intention is to as nearly as is practical divide the angle of the strings over the bridge in half, to match the more rapid drop of the strings behind the bridge to the saddle (through the tailpiece) against the longer, more gradual drop to the nut. The wide range of bridge heights, neck angles, neck projections above the belly, and saddle heights mean that bisecting that angle is a bit complicated. Not always easily accomplished by simply standing the back of the bridge straight up, though that is often close enough.

I understand what you are saying with regard to the angles. As I understand it, the ideal situation is for the bottom side of the bridge to be perpendicular and that if that does not bisect the angle, then other adjustments should be made. It would seem that the alternative you are alluding to would be to carve the bridge at a slight angle but that the feet must, of course, be in full contact with the top. Yes?

Quote:

Originally Posted by GerardSamija

Majority of luthiers, consider yourselves admonished.

Majority? Really?

GerardSamija · #10 12-04-2008, 11:31 AM

Quote:

Originally Posted by drurb

I understand what you are saying with regard to the angles. As I understand it, the ideal situation is for the bottom side of the bridge to be perpendicular and that if that does not bisect the angle, then other adjustments should be made. It would seem that the alternative you are alluding to would be to carve the bridge at a slight angle but that the feet must, of course, be in full contact with the top. Yes?

Exactly. Though it is with some reluctance that I have fitted bridges at angles other than 90 degrees on the back side, and usually do find that a given nut/saddle/projection of neck relationship allows for compromising at that angle to come close to bisecting the string angle across the bridge top. I have improved the sound considerably on a number of basses by adding wooden saddle risers. (And in another aside, per an older thread here on TB; I have settled on a clean wood-to-varnish contact on the belly rather than any sort of 'pad' material, with wood causing the least varnish or wood damage. I will be developing an endpin-mounted solution in the coming couple of years as time allows, something to offer better control of endwire height. I know of a couple of existing adjustable saddle riser solutions, but find them unsatisfying.)

The danger of a bridge slipping out from under the strings increases with divergence from vertical, so any compensatory tilt here ought to be quite minimal, within a degree or so.

Quote:

Originally Posted by drurb

Majority? Really?

Unfortunately that has been my experience. Of the 8 or 9 luthiers working full-time in the Greater Vancouver area on doublebasses and other instruments of the violin/viol family (there are probably a few more working part-time), only 3 do not routinely hollow out the feet of their bridges to give the appearance at the feet edges of full contact. A similar ratio seems to apply nationally, though obviously I see fewer instruments from other cities. And of those instruments coming to me from shops in the USA, I have seen about the same ratio as well. So about 60% of luthiers, a majority, seem intent on appearances over performance and instrument safety.

tinyd · #11 12-04-2008, 01:47 PM

Quote:

Originally Posted by drurb

I understand what you are saying with regard to the angles. As I understand it, the ideal situation is for the bottom side of the bridge to be perpendicular and that if that does not bisect the angle, then other adjustments should be made. It would seem that the alternative you are alluding to would be to carve the bridge at a slight angle but that the feet must, of course, be in full contact with the top. Yes?

I'm at home now and it seems to me that this is what my bridge looks like. The feet seem to be in full contact alright, but the bridge has a very slight curve, and where the bridge meets the strings looks like it bisects the angle. So I'm thinking that this is either intentional, as described by GerardSamija, or that the bridge has become warped. Maybe I should try and post a photo...

GerardSamija · #12 12-04-2008, 04:58 PM

Owing to some focus of interest in the bridge foot fitting area (and a private message asking to elaborate some on my views), I've thrown together a little picture essay on my site. It's not the most exhaustive which might be done and sometime I may use a different bridge and do a more thorough job, but for now this is all I have time to share. It just happened that a cello was dropped off today with an ill-fitted bridge, needing lowering overall and to have the hollows of the feet tidied up. The angle of this bridge was actually just fine, but little else about it was so. Enjoy.

http://www.luthier.ca/tutorials/brid...e_fitting.html