Sunday, December 16, 2007

 

Bridge Check


As promised, here is a photo-documentation of my bi-weekly bridge check. With all the drastic temperature and humidity changes this time of year, I've found my bridge alignment varies quite a bit. It also could just be that my bridge has weakened over time and needs replaced. When I bought the cello I also asked them to fit a spare bridge (just in case) but I've not yet used it.




The humidity indicator card that came with my dampits is a perfect tool for checking to see if the bridge is square to the face of the cello. The tailpiece face of the bridge should be exactly perpendicular to the cello, (the fingerboard face of the bridge is beveled). The side of the card against the face of the bridge shows that the A/D half of the bridge is almost exactly perpendicular...




At the G/C part of the bridge, there is a noticeable gap along the upper edge of the card, showing that this part at least, is somewhat out of square. I'll have to (carefully) pull the top of the bridge towards the tailpiece. (Notice that my humidity is in the "Danger" zone, despite a room humidifier adding gallons of water into the air each day.)



Careful... with one hand bracing the bottom part just above the feet to keep it from slipping on the cello, I use the other hand to pull the top towards the tailpiece. I press my thumb against the middle of the tailpiece side and pull the top with my fingertips from the fingerboard side. A surprising amount of pressure is needed to make this adjustment - so I have to also apply an equal amount of resistance in the other direction with the thumb and other hand to avoid too much movement. If the entire top part of the bridge needs adjusted, I'll use both hands, with the thumbs both providing a counterforce as I pull with the fingertips.
If it's way out of alignment, I would loosen the strings a bit first. However, re-tightening the strings risks pulling the top of the bridge back in the other direction. A little graphite from a pencil on the bridge's grooves is supposed to help let the strings slide rather than pull when tightening.




Rechecking with the card shows the bridge is now properly aligned. I also rechecked the A/D half to make sure it didn't slip during this procedure (it was OK).



Now, I check to see if the bridge remains properly aligned to the strings. (Actually, this step ought to be done first). The "fingerboard" side of the feet should line up with the center point of upper notch in the "f-holes". If it's not aligned it will make intonation more difficult and it might be harder to tune to perfect 5ths. Mine has only shifted once, when I first changed strings (teaching me to do them one at a time and bring each new string almost up to full tension before doing the next one). Today, the alignment is perfect.



And the alignment is also perfect at the other "f-hole".

Now, if I could only apply this same basic geometry to my bow placement and arm/hand/finger angles....

Comments:
You do great Public Service Announcements.
 
I was surprised to find that I had a good millimeter gap at the top on my bass side. Well, not entirely surprised, given how many times my pegs have popped out this month. The moral of that story is that once there is space under the foot of the bridge, the bridge is *way* tipped forward. Incredible improvement in sound once I adjusted it to completely perpendicular - my cello really opened up. Thanks.

I wonder if the f-hole notches don't vary from cello to cello, or at least maker to maker, though. Based on the varnish, my bridge has not moved, but the inside notch points to the middle of the foot, and if I align a card across both notches the line isn't parallel to the bridge, and the edge of the card extends to the tailpiece side of the bridge. Sounds like a good thing to ask the maker, since I can.
 
I wasn't very clear on this point... what I was trying to say was that if you lay a sheet of 8" x 11" paper across the face of the cello so that the paper's edge forms a line between the outer notches on each f-hole, the front (fingerboard side) of the bridge's feet would just touch the edge of the paper. On my cello, like yours, the inside notches point to the middle of the foot.

What's more important, though, is establishing the correct string length [or "stop"] between the nut and the bridge [on modern cellos, this distance should be 27.36" or 695mm]. It may be that the final bridge placement by the luthier might have to be slightly in front of or behind this "line" between the outer notches in order to ensure proper string lengths.

What is most important, though, is that the front of the bridge's feet should be perfectly parallel to that line between the outer notches.
 
Great info, thanks! Where/how did you learn this?
 
I should have realized that by "upper" you meant "outer," looking more closely at the picture, but the extra explanation helped. Now as to string lengths... I have specifically searched for cellos that have a string length not longer than 27" over the last few years (big difference in my overuse issues), and find that while lengths around 27 1/4 in. are the most common, there is a lot of variability in the 27 to 27 3/8 in. range, with occasional outliers. We're talking mere millimeters here, but I think the f-hole/bridge relationship had less variability than the string length, which was generally proportionate to the body length of the cello, also variable.

Dealers must think I'm a little nuts, as I measure the instruments before I even try them. It's worth it, though. I'm convinced that limiting my instruments to the shorter string length is a major component of my ability to play pain-free now.
 
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