Bridge design: What's tradition & what's physics?

[Fuzzball59]

On the subject of bridge design. My wife asked a question the other day---why the heart shaped cut out in the middle of the bridge? A good question I think for which I had no answer, and it piqued my curiousity about bridge design in general.

Anybody know of published analytical work that's been done on bass bridge design? Apart from it's function of transmitting string vibration differentially to the sound post and bass bar what part of that old familiar bridge shape is pure tradition--"because it's always been done that way"--and what part is purposeful design to enhance and maximize its vibration transmission function?

Can anyone here shed light on the subject?

[Jake deVilliers]

Google <violin bridge design> and pull up a comfy chair.

[Silversorcerer]

Probably better asked in the set-up and repair department. I know there are some who cut the wings off the bridge and report some improvement or at least some change in the sound. It is my theory that the bridge could look a lot of different ways as long as it has enough strength, but not too much mass. Not all have the same kind of cut out with the heart. The original bridge on my Kremona is quite different from the Despiau that I replaced it with, but the differences are not what I would think are substantial to sound, but there are other differences that probably do make some difference in sound. The wings are shaped differently and so is the heart cut out, but the biggest difference is the ratio of leg to top. And the wood is definitely not the same hardness.

Jim Hamm has made some interesting shaped bridges that still maintain the design but have variations on the shape.

I think I did see some analytical information on the vibrational patterns in a moving bridge, but it was a violin bridge. I don't remember anything significant related to various changes of the shape if there was anything.

The hard part about any meaningful analysis is that it would be hard to set up controls so that only the shape was different. Differences in the wood density, strings, etc. make such a study difficult if not impossible.

And even if one could draw some conclusion, put the bridges on a different bass and you are back at square one.

[Silversorcerer]

Originally Posted by Jake deVilliers

Google <violin bridge design> and pull up a comfy chair.

Please no, not the comfy chair!

[Fuzzball59]

Originally Posted by Silversorcerer

Probably better asked in the set-up and repair department.

I wondered where to go with this----Moderator? ya won't hurt my feelings if you moved it.

Thanks for the start guys. There does seems to be much more written for cello and on upwards (surprise surprise).

Now where in the heck did I put my comfy chair????

[arnoldschnitzer]

Draw an imaginary line down from any string to the top table of the bass (or violin, cello, etc.). You will notice the line always goes through a "hole" in the bridge, either through the heart or one of the side holes. Some surmise that this results in forcing the vibrations from all four strings down the same path and thusly makes the instrument respond evenly. I have noticed that when you bridge the gaps on the sides of the bridge, the acoustic tone suffers somewhat, especially when played arco. I've never experimented with bridges that do not have a heart cut-out, but I think it would be interesting.

[slight-return]

"well that's it, that's every shoe in the place. Unless, of course, you'd like to try...THE CRUEL SHOES"

[Silversorcerer]

Originally Posted by arnoldschnitzer

Draw an imaginary line down from any string to the top table of the bass (or violin, cello, etc.). You will notice the line always goes through a "hole" in the bridge, either through the heart or one of the side holes. Some surmise that this results in forcing the vibrations from all four strings down the same path and thusly makes the instrument respond evenly. I have noticed that when you bridge the gaps on the sides of the bridge, the acoustic tone suffers somewhat, especially when played arco. I've never experimented with bridges that do not have a heart cut-out, but I think it would be interesting.

On my 5 string, both the D and the E string are directly above wood and encounter no holes down to the arch between the legs. These have an uninterrupted path to the legs. The original bridge had different wing holes and a differnt shape at the heart, but not enough to change the situation. It doesn't seem unbalanced though. EE and BB are slightly less responsive unless you really punch them.

[arnoldschnitzer]

Yup, five stringers are different animals. Of course my comment pertained to four-stringed instruments only.

[MingusAmongUs]

Here's a potentially interesting layman's observation:
I have a student who's borrowing a horrible instrument from a school. The E string is totally falling apart where it meets the bridge, which I'm sure doesn't help at all. But a whole "wing" is actually broken clean off the bridge on the E string side. I don't know how much is because of the string and how much is the bridge, but the E string makes barely more than a dull thud. And, in fact, the A string isn't much better (even though the string itself is in decent shape). So that tells me that at least that part of the bridge is pretty critical.

I told the student and the mother that it badly needs fixing but they're not paying anything for the bass and I think Mom wants to make sure the kid is serious before she invests cashola. Can't say I blame her, but I have to keep pushing because the student means business. And I think it's really cool that a 10-yr old girl is interested in playing the DB! I suffered through a lot of wasted time and torture on bad instruments, I hate to see others do the same.

[Dr Rod]

Originally Posted by Silversorcerer

Please no, not the comfy chair!

Nobody expects the Spanish Inquisition !