Goodvibes? I have no idea ...

[matthew]

Lads and lasses, guys and gals ...

I have NO IDEA what I am doing here yet, but for the fun of it, I'm now trying to map some chladni patterns on the cornerless bass top i am graduating now, and annoying the neighbours with loud sweeping tones when all good citizens are tucked up on the sofa watching the footy ...

but it seems to make a big difference where I place the speaker, and how I suspend the plate. Not sure I have a good technique yet!

So far I have suspended the plate with strings either end and the speaker directly under the bridge point. But if I change either of these, the patterns and response changes! So i changed the suspension system to foam pads under the shoulders. Seems better.

This is what I have so far. Not really sure what it means. They're not very good patterns

96Hz -This one could be a mode 1 or 3 I suppose?

134 Hz - not sure what this one is ...


170 Hz - this could be a mode 6??


hell, the neighbours are complaining of the noise. I'll have to do some more tomorrow in the daytime ...

[Bob Connor]

Matthew

The only bloke I know that has lots of knowledge of Chladni patterns is Al Carruth. He uses them for acoustic guitars but is well regarded as THE expert in this area.

I sent him an email with a link to this thread so I'm hoping he might drop by and may be able to assist you or point you in the direction of resources that deal with Chladni patterns that are specific to Double Basses.

Cheers

Bob

[Allen]

What are you using to generate the tones Matthew? I'm on a Mac, and have found a few tone generating programs, but the wimpy speakers in a notebook computer aren't going to be enough to drive a top.

[matthew]

freeware thing called sinegen

i couldn't find anything for mac either so i dragged out the ol' PC

I was using a small 15w guitar amp but I think I need my bass amp to do it properly. More today I hope.

[matthew]

Here are some better results by using my 180W roland amp. Seems I need a lot of power to get the thing moving. My daughters complain of painful ears ...

66Hz: 71Hz: 91Hz:

93Hz: 96Hz: 98hz: 133Hz:

They don't really seem to conform with any conventional violin plate modes except maybe Klingon mode 6.

Almost got a mode 2 at 71Hz but it looks weird.

At 71 Hz I thought the plate was going to take off!

Conventional modes for violins are show here http://www.phys.unsw.edu.au/jw/patterns2.html


The lines indicate antinodes, or points of least vibration. Anyone give me an idea of where I remove wood to "move" the antinode? My instinct would be to remove wood from the side of the antinode I want it to travel to ... is that right?

(By the way i'm prepared to accept that this is all bullsh1t but I'm giving it a go )

[matthew]

I have finally (almost) figured out what they mean:

1. witch on broomstick
2. ballet dancer leaping
3. sad face?
4. dog lying on its side
5. klingon warship
6. no idea
7. I think this one is on the way to being a prehistoric "white horse"


__________________

[Allen]

I'm with you here Matthew. I've got absolutely no idea, but I'm sure hoping someone with more knowledge on the subject will weigh in here so we can all learn a little more.

One thing I'm interested in is why some notes when played up the neck aren't quite as strong or vibrant as others only one fret away on my guitars. Will the Chladni patterns help to determine what needs to be "tweaked" to get a more even response?

I suppose it would be the same with your bass. Just need lots more knowledge and insight to develop our building skills.

[matthew]

I'm sure hoping someone with more knowledge on the subject will weigh in here so we can all learn a little more.

We can hope, but I'm not so sure, judging by the reaction I've had on other forums. Either people dismiss it as quackery and guff, or they know something and keep their cards close to their chest.

[Bob Connor]

One thing I'm interested in is why some notes when played up the neck aren't quite as strong or vibrant as others only one fret away on my guitars.

Carbon fibre re-inforcement in the neck will fix that Allen.

We're putting it in all our necks now for that very reason.

Bob

[Allen]

Matthew, I suspect that just about everybody knows sweet F all about it and just are hoping that someone will let the penny drop. I've tried reading up on it, but I end up getting bogged down in the descriptions, explanations etc. and it just seems to me that the people writing about it either don't really know either, or worse yet, don't want the rest of us to know. Hoping that I can be proved wrong.

[matthew]

One thing I'm interested in is why some notes when played up the neck aren't quite as strong or vibrant as others only one fret away on my guitars.

Carbon fibre re-inforcement in the neck will fix that Allen.

We're putting it in all our necks now for that very reason.

Bob

do you put CF in neck AND a truss rod? If so, doesn't the truss rod prevent the truss rod from altering the neck straightness?

MT

[Allen]

I've used CF rods in a Cypress neck and a Aust. Red Cedar neck, along with a LMI truss rod. Now that you mention it, the Cypress guitar doesn't have any weak notes. I can't say about the other, as that guitar has a different home. I only use the CF in these necks because of the nature of the wood. Much lighter than traditional neck woods.

[Bob Connor]

Two strips of 1/8 x 3/8 carbon fibre on each side of the truss rod.

You can still adjust it with the truss rod but you probably won't need to.

I put them in the two 12 strings we've just finished.

One of them went to a mate of mine. I took it around to him so he could hear what it sounded like before I'd even dressed the frets. That was a month ago and he won't give it back for me to finish it off .

The neck is still as flat as a tack, action is reasonable with no buzzes and very consistent notes all the way up the neck.


Bob

[graham mcdonald]

I have been away for the week-end, but I might be able to cast a little light on this.

Exciting the chladni patterns is dependant on driving the soundboard in the right position (with the speaker) while supporting at near the edges along the lines of the antinodes (where the lines appear). Using the rubber suuports on the shoulder is about right for exciting the lowest mode (can never rememeber what it is called), but it is the same one that you get holding a guitar soundboard upside down and holding it around the 10 o'clock position and tapping it at the 4 o'clock. The other important mode to get going is the one that happens when held at the end and tapped in the middle.

For a bass soundboard I would suggest that you find out where the violin makers do it and go from there. The UNSW site is very good at explaining what you are seeing, but even the people who do it lots often can't explain why a soundboard does what it does. Even more confusingly what a 'free plate' is doing sometimes has little to do with what happens once that plate is glued to sides and the back is glued on.

Australian violin and guitar maker Graham Caldersmith has written a number of atricles for American Lutherie over the years and they are well worth reading. He knows as much as just about anyone about this stuff.

cheers

graham

[matthew]

So, you don't just excite the plate and find out where the modes are; you set up the foam supports along the lines where you think the antinodes will be, for each mode? in other words, you are targeting a known mode? I didn't know that. I just thought the modes would reveal themselves. Hmmm I must try again.

[graham mcdonald]

The modes will only really show themselves when the plate is supported along the antinodes and driven in one of the areas of most movement (where the glitter isn't), so you have to have a pretty good idea of what you are looking for before you start. There is much divination of the shape of the modes as well, but I never got that far into it. It is being able to selectively adjust the graduations to get the optimal shape of the patterns which is the trick to learn, but it takes quite a bit of experience.

I have watched Graham Caldersmith do a violin top a couple of times and tested one of my flat-top lattice braced bouzouki soundboards in an anechoic chamber with Prof Neville Fletcher a few years back and he explained to me what was going on up to the point where the speaker blew out. It needs a fair bit of sonic power to drive a soundboard and it can be pretty destructive on a cheap speaker.

And of course, what the freeplate does is only one bit of the puzzle. By itself it doesn't tell you much, but if the patterns are clear and distinct at particular frequencies and the finished instrument turns out well, there is a good chance that another instrument where the soundboard vibrates the same way will be good as well. It is a matter of building up a body of information about how soundboards and backs work as free plates and then trying to duplicate the good ones.

The other area to consider is the resonances on the finished instrument. The soundboard behaves rather differently when it is glued to the rest of the body and will have another sequence of frequencies where resonances occur. The first half dozen of these are the important ones and will have a radical effect on how the instrument works. If one of those resonances is right on or close to a note on the fretboard that note will tend to leap out and the ones on either side noticeably weaker. I have watched Greg Smallman use blobs of Blutack to shift a resonance by a fraction of a semitone to get a resonance between notes where it is not so obvious.

Stiffening up the neck will have an effect on some of the lower body resonances because the neck will resonate at higher ferquencies and will not interact with the body frequencies as much. There has been the interesting computer modelling done which shows the enitre guitar flexing and resonanting at particular frequencies. If the soundboard resonances are not right in the first place nothing you can do to the neck will fix it, but it can certainly help.

There are folks out there like Al Caruth and Graham Caldersmith who do a lot of testing on their instrument, and lots of people who do none of it and still make great instruments. It is a tool which can be useful, but it does take time and experience to get useful information out of it. At the very least it is good practice to measure the first couple of tap tones on soundboards and backs and then try to work out the resonances of the finished body and write it all doen in an exercise book or similar. after a few instrument you should be able to see patterns and it might help you make a better instrument, or at least have a little better understanding of why a good instrument is a good one.

cheers

graham.

[matthew]

Well this one is interesting:

114Hz


this may be on the way to a mode 2 at 36Hz


and this is what I get at 70Hz ... nothing again until 91Hz



91Hz


It doesn't really seem to matter where I place the foam blocks. I tried many positions, but I get the same patterns more or less.

[sebastiaan56]

Hi Matthew,

well i just looked up my interpretations on a Rorschach testing site and well... you guessed it.... i need therapy.. again. I love the pictures of Marilyn Monroe and Madonna, although the beer bottle one looks half empty, you have a talent mate.

Sebastiaan

[Kim]

The one piece in the first image is nice, the frocks in 2 and 3 are very stylish, but the naughty little number from Reo in 4? Well ding dong baby that's just ring'in my bell...ooooow!

Sorry Mathew, I am sure it is trying to tell us something but I don't know what, certainly worth while research if you keep images from each top and note how variations affect tone.

Cheers

Kim

[kiwigeo]

Looks like someone tripped and spilt the contents of their coffee perculator onto a bass top.

This Chladni stuff is fascinating though....must get into it myself at some stage.

Something else that might be interesting is looking at chladni patterns on luthiers. I wonder what sort of patterns we'd see??

[matthew]

Actually, jokes aside (is that possible here?) if you think about it, there is a good reason why many of the patterns resemble womens' clothing. Look at the shape of the plate. What am I asking it to do? Then imagine a dress with the straps balancing on the edge of the shoulders. Would it work?

[matthew]

This one is for you guys

[Kim]

That'll be Tassi oak eh Mathew ?