Double Bass Traeger's Soundpost Thoughts

[Chris Fitzgerald]

Too much "resonance" and a bass becomes wolfy and/or uneven, because the instrument has distinct pitches at which it resonates most strongly, and is therefore louder or more responsive or more wolfy (overblown) at that frequency. Many bass adjusters yank the soundpost far south of the bridge in an effort to stimulate resonance or depth. The result is almost always mud, wolf tones and unevenness. But at first glance it sounds deeper, which many equate to the player as better. "Better" to me is a bass that sounds clear, has depth, rings out, but most of all is even through all registers. Problems occur when we try to make a bass sound like a different bass. I hold to the traditionally accepted soundpost function: a piston to tie the top vibrations into the rest of the instrument; and a counter to the bass bar, acting as a pivot point. Moving the soundpost affects the swinging of the bass bar more than anything else, IMHO.

Posts like this one are a big part of the reason I come to TB. I may well frame this and hang it in my practice room. Thanks, Ahhnuld!

 

[godoze]

It reminds me of Harvard...

 

[godoze]

Arnold, Can you explain "swinging the bass bar" please ?

 

[Silversorcerer]

That is an excellent summary Arnold, and I think fulcrums and pivot points are the same thing.

I received the Traeger book just now, so I'm off to read a bit. I'll send it up when I'm done. It may take a few weeks because I have a busy reheasal and performance schedule over the next several days, so please be patient. I'll send you a PM.

 

[Ken McKay]

I hold to the traditionally accepted soundpost function: a piston to tie the top vibrations into the rest of the instrument; and a counter to the bass bar, acting as a pivot point. Moving the soundpost affects the swinging of the bass bar more than anything else, IMHO.

I think you and I mostly agree (and Traeger). I don't think of the post as a piston though it does couple with the back in some pumping modes. I am interested to read something regarding the post as a piston model. Can you point me to any source?

I said: The force exerted by the bowed strings causes the bridge to rock about the position of the post, causing the other side of the plate (east to west) to vibrate with a larger amplitude. This increases the radiating volume of the instrument and results in a louder sound.

Thanks for the insight on the bass bar which to my understanding, functions to dissipate high frequency partial resonances (spread the vibrating area) which use up energy but give little useful sound output.

Look here for violin acousics ... Highly recommended site.

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Traeger does not give a difinition of impedance.

 

[arnoldschnitzer]

Arnold, Can you explain "swinging the bass bar" please ?

The closer the soundpost is to the bass bar, the more the bass bar is impeded from "swinging" up and down with the bridge excursions (because if the post is near it, the top is stiffer there). Many people think that moving the soundpost toward the middle of the bass top (toward the bass bar)increases the "bottom", but the reverse is generally true. I personally like to set the post the same distance from the center as the bass bar, because I feel it gives the most even sound and response. Tom Martin likes a wide top and wide bridge, which allows the post and bar to be far apart. He feels this lets the bass bar swing more freely. His basses have a lot of bottom.

 

[Aroneng]

I think too much is made of the soundpost material and its affect on tone. It's only a piston.

I am not sure if piston is the right term here, at least as a gear head would imagine a piston moving up and down inside the cylinder of an engine. However, I am not sure of Mr. Arnold Schnitzer's intent of the word and possibly his ideas of the soundpost. Looking at the sound post in a string instrument it looks more like a round column (supporting the top of the instrument).

So tying the idea of a column or support between the top and back of the instrument, it has been mentioned that the sound post does not transmit the vibrations of the top to the back of the instrument. This seems plausible. But, if you envision on a different scale an apartment building. Imagine someone on the 3rd floor jumping up and down in their bedroom. Now think of yourself on the second floor holding a support column that is fitted between the 3rd and 2nd floor (the sound post). Surely the sound post is vibrating and the second floor is vibrating around the sound post (not directly underneath the column). Just a comparison of the 3rd floor as the top and the 2nd floor as the back.

Someone mentioned in an earlier post that the sound post acts as a filter, it's placement will tend to filter out certain frequencies or make others more pronounced. The intricacies of the sound post placement and its relationship to the bass bar, as Mr. Arnold Schnitzer mentioned, are also quite intriguing.

 

[Silversorcerer]

Ken M., I've seen that U. of New South Wales site before. While it is not exhaustive on the soundpost, it identifies it as primarily structural in function. That's a great site. Don't you just love the Helmholtz link. Pure mathematics!

Traeger equates node, pivot point, and fulcrum in one sentence. With respect to vibration, a node is a point that remains still with vibration radiating around it, like the nodal points that are determined by harmonics on the string. So if you think of the top and back as 3 dimensional strings, the soundpost produces a node on them that vibrates less than the surrounding surface. It follows that the amplitude of vibration increases farther from the post, but there could be other nodes as well, but the soundpost would be the determining one, the soul. I tried placing my finger on the soundpost spot and plucking the strings and yes, I could feel that the sound post spot doesn't vibrate as much as the surrounding wood.

"Pivot point" and fulcrum are essentially the same thing, and Traeger describes (like Arnold) the same effect on sound that positioning the post farther from the bass bar produces.

Traeger maintains that the ribs are responsible for the energy transfer between the top and back and provides an interesting reference to the testing of the soundpost as transferring vibration vs. acting as a node. Worth Reading.

The idea of it being a "frequency filter" of sorts would have more to do with its nodal function than it's density, or hardness.

As to leaving the definition of "impedance" out, and giving us no way to quantify that;- shame, shame. He's leaving that for someone else to do!

 

[iPlay15151515]

........

The idea of it being a "frequency filter" of sorts would have more to do with its nodal function than it's density, or hardness.

Now that might be an interesting concept, a tuneable soundpost to go with the adjustable bridge.




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[godoze]

This is OT but everytime i read this thread it makes me think of an aquaintances bass that has such narrow ff holes that sound post adjustments can only be made through the endpin socket.

 

[Johnny L]

No. Put two 2 ohm posts end to end.

LOL

But you guys bring up relevant points. Unless scientific reasoning is brought into play and shared on this matter, we're all riding in Nick's sound-quality boat and Arnold's top-damage boat down speculation river...

Tickets, please.

 

[arnoldschnitzer]

Perhaps I'm thick, but I don't get the gist of your post. Are you saying Nick and I are unscientific and are speculating?

 

[Bubbabass]

Now that might be an interesting concept, a tuneable soundpost to go with the adjustable bridge.




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The late Lou Savarino in the DC area was said to "tune" the post by drilling out a portion(longitudinally) to relate to some pitch of the body, or perhaps the air cavity. To my knowledge, he never showed anyone exactly what he did or how. Does this sound remotely legit to anyone?

 

[Damon Rondeau]

As to leaving the definition of "impedance" out, and giving us no way to quantify that;- shame, shame. He's leaving that for someone else to do!

From my reading of this section, it appears that the "impedance" concept is Carleen Hutchins'.

 

[mje]

The acoustic impedance of a material is the product of density and acoustic velocity of that material. Theactual acoustic impedance of a material used in a soundpost is less importance than the fact that there's a discontinuity, a difference in impedance, where the soundpost meest the top and the back.

Wherever you have an impedance mismatch in a system you will get less than 100% energy transfer; the energy that is not transferred will be reflected back, and dissipated there. So perhaps the technologically minded luthier could measure this match/mismatch, see how it affects tone, and then systematically vary it to obtain different results.

 

[Johnny L]

Perhaps I'm thick, but I don't get the gist of your post. Are you saying Nick and I are unscientific and are speculating?

I'm asking you guys to offer clearly composed data, terms, and results based on uniform standards. If you can't produce that and are offering anecdotal or common-sense instead, then my answer is yes.

And no, I don't think you or Nick are thick. Rather, I think you both are honest.

 

[Chris Fitzgerald]

The acoustic impedance of a material is the product of density and acoustic velocity of that material. Theactual acoustic impedance of a material used in a soundpost is less importance than the fact that there's a discontinuity, a difference in impedance, where the soundpost meest the top and the back.

Wherever you have an impedance mismatch in a system you will get less than 100% energy transfer; the energy that is not transferred will be reflected back, and dissipated there. So perhaps the technologically minded luthier could measure this match/mismatch, see how it affects tone, and then systematically vary it to obtain different results.

What? Please remember that some of the people who are reading your post might possibly be from Kentucky.

Are you saying that the post should theoretically be made of the same stuff as the top and back?

 

[Nick Lloyd]

I'm asking you guys to offer clearly composed data, terms, and results based on uniform standards. If you can't produce that and are offering anecdotal or common-sense instead, then my answer is yes.

And no, I don't think you or Nick are thick. Rather, I think you both are honest.

Well, honestly, the bulk of this thread is anecdotal.

 

[arnoldschnitzer]

I'm asking you guys to offer clearly composed data, terms, and results based on uniform standards. If you can't produce that and are offering anecdotal or common-sense instead, then my answer is yes.

And no, I don't think you or Nick are thick. Rather, I think you both are honest.

I believe that all the USABLE information about the soundpost and its affect on tone/response is based on common sense, experience and prior "fiddling" (bad pun intended). I suppose you are right that this is non-scientific, and most luthiers prefer it that way. There are no uniform standards and there is no way to measure results, tone being a subjective thing. I personally don't have a high opinion of the scientific types who try to boil our craft down to a bunch of numbers and formulas. I understand they are questing after repeatability but I think they miss the point.

 

[mchildree]

...There are no uniform standards and there is no way to measure results, tone being a subjective thing. I personally don't have a high opinion of the scientific types who try to boil our craft down to a bunch of numbers and formulas. I understand they are questing after repeatability but I think they miss the point.

Especially since "repeatability" usually leads to things like "mass production", "cost cutting", and other unpleasant non-magical things. I deal with the hard cold facts of technology every day in my career. I'd rather leave the fun stuff a little vague and mystical, if you guys don't mind.