Double Bass slight bridge repositioning method

[moles]

Hi all,
Been lurking for a couple of weeks. Been dying to tackle the upright for quite some time - got ahold of a czech carved top that I'm renting til I decide if I like it enough to go ahead and buy this one, or keep looking for something else.
So far so good - I love the way it sounds - almost bought a chinese Hofner from another shop around here, and I'm glad I didn't. That was an alright bass, but the Schoenbach is Much Livelier sounding..
There is one small problem - I had asked the sales guy at Long & Mcquade if they had set it up and was told it already had been (usually they're pretty good for being honest about that stuff, and they know me - heck I spend enough there After a day of noodling around on it, I started to really noticed what I thought was a setup issue: really high G string, and the E was way too low to pluck reasonably hard - I figure now the bridge probably just shifted treble-ward.
I really don't want to haul the thing down and lose it for a few days while they look at it if I can get away with it - so whats the best way to reposition the bridge? I mean I know *where* it should go (f-hole notches and dead center) but can I just loosen the strings and give it a tap with a rubber mallet? Do I need to loosen the strings right to slack and get a helper to hold it in place while I re-tension them?
Seems like a pretty simple job - just don't want to blow it - I've done just about everything you can think of over the years to my EB's, and I'm wary of getting cocky with my repair skills..
Thanks all.
Miles

 

[toman]

With the bass on a table or bench, just loosen the strings fairly well, grab the bridge and wiggle it around to where you want it. No big deal, really, there's nothing you can hurt. Worst you can do is accidentally knock over the soundpost, and even that's not serious. You'll just have to have your luthier put it back up...

 

[Michael Eisenman]

Hi, Moles.

I'm not a luthier. I'm about to tell you what I did; if you aren't comfortable with my suggestion, please don't follow it. I assume that this is not an adjustable bridge.

When you say the G is too high and the E is too low, do you mean the string height from the fingerboard? If so, check to see that the bridge is installed correctly; that is, the flat side should face the tailpiece.

The center of the feet should center on the inside f-notches and be equidistant between them (side to side). The flat side of the bridge should be perpendicular to the body.

On my bass, the top of the bridge (at the strings) drifted toward the fingerboard due to tuning, etc. As a result, when I played the 7th position ("12th fret") harmonic followed by the fingered note at the same position, the fingered note was higher in pitch. This indicated that the string length needed to increase, just like when you adjust the saddles on an EB. The bridge had to be persuaded away from the fingerboard.

My luthier assured me that I could knock it back with a narrow hammer without doing any damage to the bridge, which is made of hard maple. So I got a tack hammer and stuck a piece of felt to the face. Without loosening the strings, I held the feet firmly in place with my fingers while I gently rapped the bridge between and just below the A and D strings. I repeated this until the harmonic and fingered notes were the same.

That's how I did it. I hope this was helpful.

Regards,
Michael

 

[Matthew Tucker]

I repeated this until the harmonic and fingered notes were the same.

Thats wierd because on a fretless instrument the harmonic and the stopped octave should be exactly the same position for ALL string lengths, by definition. The only thing that can change that, is increasing string tension as you press down the string, which will sharpen the stopped note.

you can adjust an EB bridge like you did because the 12 fret is fixed relative to the string length. On a fretless instrument the stopped octave position will change with the string length.

 

[moles]

"When you say the G is too high and the E is too low, do you mean the string height from the fingerboard?"
-- Yes. Well, really because you're dealing with a curved surface, I mean the G is too far away from the board, and the E being too close. So not vertically speaking, as in 'up' being away from the body, but left-right on the plane of the fingerboard....

As far as the bridge being reversed - there's an obvious shape to the end of the board that matches the bridge perfectly - so I think that's all good..

Well, I managed to get it centered last night while I was home for a bit. The E and G play beautifully now. It might take a bit more adjusting though - the A and D strings now have some slight buzzing around the octave position, which wasn't there before. It's a bevelled board, and I can see the A string isn't quite running parallel to the bevel edge between the E and A strings. Couple more hairs either way should do it. It's much nicer playing already.
Thanks guys.

 

[Michael Eisenman]

Thats wierd because on a fretless instrument the harmonic and the stopped octave should be exactly the same position for ALL string lengths, by definition. The only thing that can change that, is increasing string tension as you press down the string, which will sharpen the stopped note.

Good point, Matthew; I didn't think of that.

Suffice it to say that I adjust the bridge until the tension is optimized for the notes to match. It appears that changes in tension have a more noticeable affect than changes in string length.