Double Bass Weight & stiffness effects of carbon fibre soundpost?

[swingingoodtime]

So (being the overly impulsive tinkerer that I am), I decided to try a carbon fibre sound post in my bass as I wanted a slightly longer one given that I find the best placement about 12mm further in towards the centre line & therefore needs to fill a bigger gap. I had some 16mm solid rod left over from my endpin experiments, so I cut the rod about 1mm longer and reshaped the ends to match the angle on my original (19mm wood; spruce?).

After some sanding & fitting it's now in place and the bass is restrung. I also changed strings from guts to Helicore Orchestrals on a whim, as I was starting to tire of how much amplitude the previous guts exhibited & the work required to control them (that & my D was starting to sound a little whiny). To my surprise, the bass doesn't sound as choked as it has with the Helicores in the past; it actually sounds really good. I'll admit it's been a while since I tried them, but I'm pretty sure that it's better (better sustain & clearer tone).

I'm not sure why, though; I've changed too many variables in one go to isolate the changes to just the post material. Any thoughts or previous experiences in this? To summarise, the new post is 16mm solid CF and double the weight (80g) of the wood version (19mm spruce (I think), 39g). The fit is tighter (gently snug) compared to before, which probably requred the top to sink under string tension about 0.5-1mm from unstrung position in order to hold the ends of the post.

Thanks!

 

[JKoehler]

You may want to be very careful with a soundpost made from anything other than spruce. I work at a violin shop in Austin Tx. that had a luthier, no longer at shop, that would use maple or oak dowel rods on rental instruments for soundposts. Every instrument that had those posts developed soundpost cracks in the top. I think spruce has a certain amount of "give" to it, where cabon fiber has little to none. The fit of the post is also inportant, but the material is crucial also.

 

[Matthew Tucker]

I think that rather than there being magic in the new sound post, it's more likely you are playing steels with a gut technique and getting a better sound out of them! If you've been using the bass a fair bit, it's quite likely that the bass has "played-in" a bit, too, since the helicores first went on.

 

[swingingoodtime]

@JKoehler, thanks for that. Did he ever fit spruce soundposts and did those instruments ever crack? If the answer is no (and no) or yes and yes, then perhaps he was doing something else that was a problem (ie, too tight etc). I’d like to find out more about why material is so important (if it indeed is); maybe it’s something to do with, as you suggested, simply about it being ‘not spruce’, rather than the specificity of the different material. If both post & top are spruce, then the ‘wear’ factor in each is equal, so neither will break the other under normal conditions, whereas something harder will stress the spruce and something softer will give out before the spruce. Hmmm, food for thought…

@Matt, (Hi! How's life?)
Hah, I’m happy with that logic! Although, out of interest, what difference if any would the increase in soundpost weight make? I’m assuming it would have to have some kind of impact (good or bad).

 

[Andrew McGregor]

CF has zero response to humidity, wood does respond. If you're in one of those places where humidity changes with the seasons a lot, I'd be somewhat worried about that fact.

 

[Matthew Tucker]

BUT wood shrinks almost imperceptibly along the grain compared to cross grain.

So thats not going to make any difference compared to the movement of the top and back.

There is usually a very good reason why certain materials are used and cost ease of working is a big factor. Unless the difference with a carbon soundpost is MAJOR you wont find many luthiers willing to forsake a cheap and relatively easy solution. Paul what will you do if your bass expands with humidity and the post needs to be replaced? is it worth buying another CF Rod and fiddling around to find out? probably not i'd say. but its your bass and you are a fiddler ;-) so go for it. but next time change one thing at a time!

 

[swingingoodtime]

BUT wood shrinks almost imperceptibly along the grain compared to cross grain.

So thats not going to make any difference compared to the movement of the top and back.

There is usually a very good reason why certain materials are used and cost ease of working is a big factor. Unless the difference with a carbon soundpost is MAJOR you wont find many luthiers willing to forsake a cheap and relatively easy solution. Paul what will you do if your bass expands with humidity and the post needs to be replaced? is it worth buying another CF Rod and fiddling around to find out? probably not i'd say. but its your bass and you are a fiddler ;-) so go for it. but next time change one thing at a time!

You're certainly right; the CF was hard work to shape due to it's incredible denseness. I could have used a rougher rasp I suppose, but was worried about tearing the fibres around the end circumference of the post. I only tried it out of curiousity and the fact that I had the rod lying around as spare material. If I need to make a new post, I'll probably make it out of spruce, although it's tempting to make an identical post in spruce now to see if there is an appreciable difference or not (which will be a single change!).

Stay tuned...

 

[1st Bass]

It isn't dense--it is hard and tough. Density is a ratio of mass per unit volume (pounds per cubic foot, etc.) Carbon fiber is very light for it's size...and incredibly stiff, as well as hard, which makes it ideal for certain things. Soundposts might not be one of them.

It does occur to me that if the main caveat in using it for a soundpost is the possibility of damage to the plates, would it be of any use to cap the two ends with spruce, as pads, so that you have the low density, high stiffness and strength of the CF, and still have some give at the ends? Or would that defeat the purpose?

 

[swingingoodtime]

It isn't dense--it is hard and tough. Density is a ratio of mass per unit volume (pounds per cubic foot, etc.) Carbon fiber is very light for it's size...and incredibly stiff, as well as hard, which makes it ideal for certain things. Soundposts might not be one of them.

It does occur to me that if the main caveat in using it for a soundpost is the possibility of damage to the plates, would it be of any use to cap the two ends with spruce, as pads, so that you have the low density, high stiffness and strength of the CF, and still have some give at the ends? Or would that defeat the purpose?

You're right; I didn't pick my words properly. I was just recalling in my mind's eye what a b**** it was to work.

The notion of capping the post is something I've also considered, but am unsure of the effects. Maybe (whilst probably more work) a patch on the belly & back at either end would be better in terms of reinforcement. And if they were shaped such that the ends of the post could be cut perpendicular to the length, then this would reduce 'fit' issues...

However, my question remains, though: if carbon fibre is a poor choice, in what ways is it verifiably bad and why? So far, we've only tossed around anecdotal notions & hypotheses (not that I object to the input, of course!)

Oh, and what difference if any would the increase in soundpost weight make?

 

[Matthew Tucker]

As you've discovered, carbon fibre works just fine as a soundpost material. I think you'd probably find that plastic, glass, ebony, bamboo, ivory, aluminium etc would all work as well. But like all these alternatives, CF is a verifiably bad choice of material for the simple reason that it is so hard to work!

 

[robobass]

It does occur to me that if the main caveat in using it for a soundpost is the possibility of damage to the plates, would it be of any use to cap the two ends with spruce, as pads, so that you have the low density, high stiffness and strength of the CF, and still have some give at the ends? Or would that defeat the purpose?

Using anything harder than spruce for a soundpost seems like a bad idea simply because of the risk of damaging the top. Take a piece of spruce dowel and press it hard against a flat piece of spruce, then do the same thing with a much harder dowel, and look at the mark it leaves. However, capping the ends would eliminate this problem, as well as the difficulty of shaping a hard material. Also, if the post needs to be shortened or lengthened, then the caps could be refit to the cf post instead of cutting a whole new one.

Would it sound better? No idea, but it would certainly sound different.

 

[Matthew Tucker]

Actually I kinda disagree that a harder material will damage the plate; if it is well fitted, not too tight, not at an angle, not too narrow, *I* think it will be fine. But a spruce endpin, badly fitted, too tight, or tilted at an angle, will be just as likely to dent or crack the wood. It happens all the time. But I have never seen a well-fitted soundpost do any damage, unless the bass gets a hard knock - in which case all bets are off no matter WHAT the soundpost is made of!

 

[swingingoodtime]

Thinking about the notion of wedges on the plates to keep the ends of the soundpost square (see pic; dimensions are exaggerated for clarity):

I appreciate that this would add a little more material to the plates, but given the use of cleats, braces and patches, surely not a gross amount, no? Would this approach be preferable in that it would allow a proper post fit everytime? Or would humidity changes cause problems for carved plates (ie, differences in changes between plate & wedge)? If so, how about deliberately carving those shapes as part of the plate itself?

 

[james condino]

The original post mentions a solid carbon fiber rod; that is a pretty important point in the discussion. Given the many different ways that you can use carbon fiber- hollow tubes, solid rods, laminated layers, bladder formed internal modlings, open weave exoskeletons over a spruce core....the list goes on. Universally most us agree that it is an incredible structural material and it has been proven in many different forms that it can hang with the big boys in terms of tone, volume, and response.

Rather than a dogmatic yes / no definitive answer, I more like the idea of it being a viable option among your list of tools for potentially getting more out of an instrument. On some basses it may work well, on others....not so well. Even when I fit a traditional wooden soundpost for a customer, I generally offer them in 4-5 different types and grade of spruce, a couple of hardwood materials, and I'm always experimenting with other options- like variations on your carbon fiber ideas. What I hear and how I play is different than any customer's, so I offer a bit of perspective, let them hear all of the options, and then they chose which one we'll use first. If they have questions or want to try other posts, I don't really have any issues if we cut, fit, and tryout ten different models until they feel the option is the best fit for them. They also understand that the meter is running, so every new test still adds to the final bill, but it gets all of those undecided "what ifs..." out of their head and they can get back to practicing and playing....

j.

 

[Jake deVilliers]

Thinking about the notion of wedges on the plates to keep the ends of the soundpost square (see pic; dimensions are exaggerated for clarity):

I appreciate that this would add a little more material to the plates, but given the use of cleats, braces and patches, surely not a gross amount, no? Would this approach be preferable in that it would allow a proper post fit everytime? Or would humidity changes cause problems for carved plates (ie, differences in changes between plate & wedge)? If so, how about deliberately carving those shapes as part of the plate itself?

Two square soundpost ends would be terrible! Its bad enough getting a soundpost to sit correctly on a flatback... I find it much easier to get a nice, snug, wedged fit with an angle on both ends.

As to the material, I've made maple soundposts for a few basses, and they improved the sound markedly. Like James, I try to keep an open mind - if you don't try different approaches, you're limiting your knowledge.

 

[powerbass]

Thinking about the notion of wedges on the plates to keep the ends of the soundpost square (see pic; dimensions are exaggerated for clarity):

I appreciate that this would add a little more material to the plates, but given the use of cleats, braces and patches, surely not a gross amount, no? Would this approach be preferable in that it would allow a proper post fit everytime? Or would humidity changes cause problems for carved plates (ie, differences in changes between plate & wedge)? If so, how about deliberately carving those shapes as part of the plate itself?

From my largely uneducated perspective I like the concept of parallel surfaces for a soundpost to contact. Just say you have parallel top/bot plates wouldn't it be easier to adjust the post? If the surfaces are not parallel and you rely on wedging the post wouldn't this result in varied tension whenever you move the post?

 

[Matthew Tucker]

A platform for the soundpost is not a new idea. A number of luthiers have tried it. But like a lot of good ideas there's probably a reason why it hasn't exactly caught on. Another idea which i like better is a maple veneer at soundpost position. And the best idea, I think, is a proper inlaid soundpost patch put in by the maker at time of manufacture. This would virtually eliminate any possibility of a SP crack and I doubt very much whether the sound would be adversely affected.

All these ideas are extra work. Will the customer be prepared to pay the extra? Dunno.

Powerbass, if you have a classic top/back and you want soundpost a little bit tighter fit you just move it towards the edge a mm. If you have parallel surfaces and you want a tighter fit you need to make another post! It's six of one and half a dozen of the other.

The other thing is that to get a "flat" on the top you need to thicken the top at what is probably quite a sensitive part of the plate. Not sure this is a good thing acoustically, just so a tinkerer can adjust the post a little more easily. Finally, remember a flatback bass has a "flat" at the back brace. And a roundback with a centre brace, same same. You're halfway there!