Sound Post Free Design

[gbaker]

Ever wonder what a bass would sound like without the sound post dampening the top plate? I have for years so I set up a test to find out.

I *know* it is traditional and all but I always thought the sound post was, well, primitive, a hard-to-adjust stick and worse, that it probably kept about 1/2 of the top plate from vibrating freely.

Shown is West German 3/4 laminated I have been rebuilding. The experiment is in place, held by string pressure.









Rather that building a special sound post (platform) from within and put a hole in the top plate, I constructed a hard maple cross-bridge to fully support the bridge G foot by the ribs without touching the top plate center area. There is no sound post to impede the vibration of the top. The E foot drives the top/bass bar in the normal fashion.

Mechanical Result - It is harder to tune because the top is more compliant and pressure from one string effects the others more than usual, particularly the E-D side but once set it stays. Surprisingly string height didn't change much if any. I expected the top to drop with string pressure without the sound post bearing it up and that it would require string height be increased. Not.

Acoustic Result - a very loud and open low end starting at D and increasing toward low E. Like maybe 3 times as loud at low G. Remember this is a ply bass, but typical. There may be some loudness decrease above the D but it is hard to reference and say for sure.

Has any one else experimented with or seen a free-top design?

All rights reserved.

[moles]

My understanding of the physical mechanics involved in a DB (or other, similar stringed instruments) is limited at best...
But, it is my understanding that the soundpost does not dampen half of the top, or prevent it from vibrating. Rather, it creates a fulcrum to the top's vibrating, similar to placing your finger at a harmonic on a string and creating two opposing vibrating lengths.
Isn't this function required to give any harmonic complexity to the sound? Otherwise you're just dealing with a big box... An increase in volume sounds good - but I can get volume out of my bass - if I put plain guts on, the E and A literally shake the windows. Those notes aren't so easy to hear when all the ear is getting is fundamental...

Anyway, colour me genuinely curious where this all takes you.

[MrSidecar]

Plus,

a traditional soundpost has some advantages in terms of optical sexiness :-)

Sidecar

[Fletcher Lanning]

Now IANAL but I thought one of the main functions of the sound post was to spread vibration coming down from the bridge to the back, in essence reflecting the sound off the back so that it will project through the sound holes in the front. The top is not the only thing making sound on the bass, it takes the whole body vibrating to make that sound. If you have a good instrument (even a good plywood instrument) you want to hear what the properly carved and treated wood sounds like, not what a 1" solid beam sounds like.

Lastly, it seems that your particular solution has, essentially, added significant mass to the bridge and, by proxy, the top of the instrument. From what I understand about sound waves and vibration, adding to much mass in that area will cause you to actually lose sound as it takes more energy to make it physically vibrate (a problem that would be exacerbated by the fact that part of the bridge is basically suspended between two pieces of wood that will flex).

That's all from a purely theoretical standpoint and, as I said, IANAL.

[uprightben]

Cool, what does it sound like with an ungalvinized metal brace? Seriously, you just invented the acoustic bass guitar with a db sized body. You could probably get a similar sound in a more economical design with the mexican guitarron, which is pretty cool.

[drurb]

Indeed, the sound-post does not "dampen" the vibration in some undesired way. With all due respect to the OP, I'm always a bit amused when someone eschews centuries of knowledge and study and basically starts from scratch. This is especially true when the endeavor proceeds from a false assumption. The soundpost creates a vibrational nodal point in addition to transmitting energy to the plates. The function of the soundpost is fundamental (pun intended) to the what has become the desired sound of stringed instruments. Of course, one is free to invent his/her own instrument and experimenting can sometimes yield insights, even if only to the experimenter.

The links below present the tip of the iceberg re the soundpost.

Take a look here, here, here, here.

[robobass]

Hmmm...Nothing if not creative. You could refine the rig further by having the cross brace rest on posts which go through the F Holes and rest on the back. Then the energy transfer from the G-foot would be more in keeping with a traditional setup. If you really liked the result, then the last step would be to bore a 1/4" hole through the top in the center of where the G-foot used to sit, and mount a steel rod to the back, coming through the hole, and holding up the G-leg. By doing this, you could still set up the bass normally later. Interesting idea anyway. Could you post some audio comparing your invention to a normal setup on the same bass?

[drurb]

Originally Posted by robobass

...If you really liked the result, then the last step would be to bore a 1/4" hole through the top in the center of where the G-foot used to sit, and mount a steel rod to the back, coming through the hole, and holding up the G-leg.

Then the real last step would be to shorten that steel rod (soundpost), craft it out of wood, close the hole and let the bridge sit on the top where it will rock on the fulcrum of the soundpost. Hey wait-- that's the design we've had for centuries.

[Jake deVilliers]

Originally Posted by gbaker

Ever wonder what a bass would sound like without the sound post dampening the top plate? I have for years so I set up a test to find out.

I *know* it is traditional and all but I always thought the sound post was, well, primitive, a hard-to-adjust stick and worse, that it probably kept about 1/2 of the top plate from vibrating freely.

Shown is West German 3/4 laminated I have been rebuilding. The experiment is in place, held by string pressure.









Rather that building a special sound post (platform) from within and put a hole in the top plate, I constructed a hard maple cross-bridge to fully support the bridge G foot by the ribs without touching the top plate center area. There is no sound post to impede the vibration of the top. The E foot drives the top/bass bar in the normal fashion.

Mechanical Result - It is harder to tune because the top is more compliant and pressure from one string effects the others more than usual, particularly the E-D side but once set it stays. Surprisingly string height didn't change much if any. I expected the top to drop with string pressure without the sound post bearing it up and that it would require string height be increased. Not.

Acoustic Result - a very loud and open low end starting at D and increasing toward low E. Like maybe 3 times as loud at low G. Remember this is a ply bass, but typical. There may be some loudness decrease above the D but it is hard to reference and say for sure.

Has any one else experimented with or seen a free-top design?

All rights reserved.

Nice going G!

There was an inquisitive Frenchman who performed a series of similar experiments on violins 75-85 years ago. Pretty interesting stuff really, but if the fiddles sounded better you'd think there's be a strain of them with different top support strategies.

I noticed you are saying that the E, A and D strings are louder - what about the G string? How does it sound up at the octave on the G? And are you talking arco or just pizz?

[arnoldschnitzer]

G, that's an ambitious experiment and I tip my hat to you. However, to really hear the sound of a bass with no soundpost, you will need to remove the top and install a second bass bar, or put in an x-brace like some archtop guitars have. That way the g foot of the bridge can rest on the bass' top, where it belongs. The rocking of the bridge will then affect the top table more realistically and efficiently. There is a guy down south somewhere making plywood basses with two bassbars. I have been told they are very loud pizzicato, but don't respond well with a bow.

[Greg Clinkingbeard]

Arnold,
I seem to remember the guy's name is Luke Medley and he is in southern Missouri.
KC Strings had one of his basses a year or so ago and it had a big booming pizz tone. It would be a good choice for grassers or similar but the tone was very raw. The workmanship wasn't to a high standard.

[1st Bass]

You can read about him here-- even has his phone number. :-)
http://www.ruralmissouri.coop/05pages/05MayBass.html

Also, on this link, if you scroll down, you can see photos...and the price.
http://www.bluegrassbassplace.com/ph...0ae67e660d6814

[robobass]

Originally Posted by arnoldschnitzer

G, that's an ambitious experiment and I tip my hat to you. However, to really hear the sound of a bass with no soundpost, you will need to remove the top and install a second bass bar, or put in an x-brace like some archtop guitars have. That way the g foot of the bridge can rest on the bass' top, where it belongs. The rocking of the bridge will then affect the top table more realistically and efficiently. There is a guy down south somewhere making plywood basses with two bassbars. I have been told they are very loud pizzicato, but don't respond well with a bow.

True, with only the E-foot vibrating the top, it's hard to imagine any kind of useful tone quality, especially on the G-string. I bet it is loud as heck, though!

[Pentabass]

The only problem, the number of variables you have changed - - it is not just a matter of no soundpost. No, you also pretty much fixed the G side of the bridge (in the bridge leg at the level of the adjuster screw) for most horizontal and vertical movement, thereby creating a new pivot point for the bridge.
Intuitively that should pump more energy into the E-side of the bridge.

If you want to hear how the instrument sounds with it's "natural voice" , why don't you just simply take the soundpost out and leave the bridge normal. Sure there is the risk of damage, but most instruments will tolerate a brief period of no soundpost, not so?

[Mike Arnopol]

Paul Toenneges tried that years ago.(two bass bars, various other types of bracing) The results were that the basses sounded better with the soundposts. My previous EUB was the Alter ego which had a vibrating top with two bass bars. The two bass bars yielded a certain openness and sustain, but the basic attack and thump weren't there. My current EUB ( Volante) has a vibrating top with a bass bar and a sound post. The attack and envelope are just like a regular bass. The description of the sound post as a fulcrum is correct in my opinion. With designs that could use other types of bracing is is certainly possible to get a bass with more sustain and other positive attributes, but for the attack and control (function) of a double bass---if it ain't broke-----
To me it's like comparing a NS EUB and my Volante. The NS is a cool unique instrument, but can't function as a substitute for a Double Bass. I'm not saying that one is better or worse, but they don't perform the same function. It's like Eberhard Weber's bass.It works amazingly well in contexts designed around it. But you couldn't walk on it, or use it as a substitute for a slab.

[gbaker]

Thanks for the comments and the links.

I have created some confusion. I need to better explain what I am trying to do.

First let me say I have never played a high quality carved top bass. I also have never used gut strings, just Spiros, so I may not know what I am missing. I don't want to offend the DB community, I just like to experiment and I got tired of bumping the SP around with little result.

Opinion - An instrument the size of a DB (as I know them, right?) should have a better bottom end. More bass. One of the possible reasons it is lacking is because the top plate is dampened by a post that sits about 1/3 into the field of possible motion and limits the potential. One objective of this experiment was to test this.

The mechanics -

See diagram:
http://www.soaap.com/music/images/guides/violin_02.gif

The violin family instrument bridge translates string movement (mostly sideways with some up-down relative to the plate) by a fixed pivot of the G foot. This translates to a up-down force and motion at the E foot which drives the top/bass bar assembly. Normally the sound post provides the fixed pivot of the G foot. Note that the G string is operating the same way as the E string - sideways movement translating to up-down movement at the E foot.

Opinion - The sound post, essential to the G foot pivot also traps the top plate, restricting movement.

Test objective-
I wanted to separate the support of the pivot G foot from the dampening of the top. One way to do it would be to provide for the pivot foot an access hole in the top to a stable platform (like a stationary sound post end) that does not touch or impede the top. This approach required some irreversible destruction and internal SP bracing so I decided to build an external support instead. The external support is not practical for a traveling instrument and is a test bed.

Observation - The sound post dampens (the vibrations and) the sound output of the top, particularly at the lowest frequencies. With this test setup you have to back off rather than dig in as you play down the scale to keep the same perceived loudness.

I have read (Traeger?? or someone) that stated that the sound post contributes little or nothing to the radiated sound of the bass. Opinion - I tend to think this is true based on my test.

Opinion - I am now thinking that some top dampening would be beneficial particularly if it is adjustable.

I will try to address some individual's questions and comments in a separate post.

Thanks again for the comments.

[gbaker]

Originally Posted by moles

My understanding of the physical mechanics involved in a DB (or other, similar stringed instruments) is limited at best...
But, it is my understanding that the soundpost does not dampen half of the top, or prevent it from vibrating. Rather, it creates a fulcrum to the top's vibrating, similar to placing your finger at a harmonic on a string and creating two opposing vibrating lengths.
Isn't this function required to give any harmonic complexity to the sound? Otherwise you're just dealing with a big box... An increase in volume sounds good - but I can get volume out of my bass - if I put plain guts on, the E and A literally shake the windows. Those notes aren't so easy to hear when all the ear is getting is fundamental...

Anyway, colour me genuinely curious where this all takes you.

Opinion - As for the divisional properties of the post, if a node is created by the post then the secondary movement is 180 degrees out of sync with the primary movement and acoustical cancellation occurs.

Loudness - you are fortunate. I am looking for more bass myself.

Why? Why not? As my granddad used to say "Nothing beats a trial but a failure."

Thanks.

[gbaker]

Originally Posted by uprightben

Cool, what does it sound like with an ungalvinized metal brace? Seriously, you just invented the acoustic bass guitar with a db sized body. You could probably get a similar sound in a more economical design with the mexican guitarron, which is pretty cool.

I don't know how the bridge functions on a guitarron but this is not a acoustic BG I built. The ABG has a guitar bridge (what torsion?) rather than a rocking bridge like a violin or DB and this one.

And the ungalvanized clip angle sounded tinny and I would have to change it every 120 years.

Thanks.

[drurb]

Originally Posted by gbaker

Opinion - An instrument the size of a DB (as I know them, right?) should have a better bottom end.

Should? Based on what? For example, think about the wavelengths involved.

Originally Posted by gbaker

Opinion - The sound post, essential to the G foot pivot also traps the top plate, restricting movement.

Traps the top plate? Again, based on what?

Look, these are not matters of opinion. They are matters of physical acoustics, specifically the vibratory patterns of the plates. You may wish to visit your local library and check out the Journal of the Acoustical Society of America beginning in 1929, Research Papers in Violin Acoustics 1975-1993 published by the ASA, and the publications of the Catgut Acoustical Society for starters. It's all well and good and fun to experiment-- I don't mean to throw a damper on that spirit but there's something to be said for consulting the existing knowledge base.

[gbaker]

Originally Posted by Jake deVilliers

Nice going G!

There was an inquisitive Frenchman who performed a series of similar experiments on violins 75-85 years ago. Pretty interesting stuff really, but if the fiddles sounded better you'd think there's be a strain of them with different top support strategies.

I noticed you are saying that the E, A and D strings are louder - what about the G string? How does it sound up at the octave on the G? And are you talking arco or just pizz?

It is a fun experiment for snowed-in day, Jake.

Pizz only.

I will have to raise the G string to get a good reading as it's buzzing above high C. I had it set close with a SP and it probably dropped 2 mm because of the cross-bridge flexing. I'll have to get back to you on that. Thanks.