Sound Post and Bass Bar for Dummies

[ii7-V7]

I've read alot of old post regarding the Bass Bar and Sound Post. There doesn't seem to be much concensus on the purpose of these components, but agreement that they are one of the most critical components of a DB.

What does the Bass Bar do? What does the Sound Post do? And what would a bass sound like without one or the other? Or without both?

I've heard that the Sound post is supposed to act like a piston, that it stops vibrations of certain frequencies, or that it stifles vibrations in certain areas of the top. I've heard that it allows the Bass Bar to move. Whats the real story.

And what is the purpose of the bass bar other than structural?

Please try to write your answers in English...as opposed to Engineerese!

Thanks,
Chad

[mchildree]

http://www.davidgage.com/z_david_archive3.htm

[M_A_T_T]

I believe the bassbar helps to transfer the bass frequecies across the top, and the soundpost transfers some of the frequencies and vibrations to the back.

[ii7-V7]

Thank mchildtree for the link. I"ll copy the pertinent parts here.

The bassbar runs along the length of the top and has the same function and design found in all the violin family. The function is to support the top from collapsing under the string pressure and it 'tunes' the top to reproduce the most desirable resonance. It helps dictate where the top vibrates.

In a sense, the sound post is the antithesis of the bassbar in that it dictates where the top doesn't vibrate. At the point where the soundpost touches the top is a nodal point or a spot of no vibration.

The soundpost's fit is crucial. It should be flush to the inside of the top and the back of instrument. This improves the linkage between the two plates and helps generate the maximum resonance from the whole box.

Good stuff. Thanks.

Chad