Bass top vibration video

[Matthew Tucker]

Though some might be interested in more hocus pocus ... it's quite spectacular!

http://www.youtube.com/watch?v=aHbpC_0E7wM

[MIKMAN]

Matthew i was always particularly keen to study the nodal points of a vibrating top in any instrument of the violin family. When i bult my first violin i tested the top over a speaker, watching the vibrations of the tea leaves, in order to improve the graduations. Mrs Hutschins from the CAS has published some excellent articles on this theme and as an engineer i spent hours reading them. When my arthritis will allow me to built my first bass i'll check this aspect meticulously. As you know it's not hocus-pocus bat pure science.
Mike

[Matthew Tucker]

it would be pure science if we could control all the variables ...

[bigolbassguy]

That's cool. Thanks Matt.

[Andrew McGregor]

Originally Posted by Matthew Tucker

it would be pure science if we could control all the variables ...

We can. Trouble is, we don't know what values we're trying to control them to, nor are all the combinations necessarily possible...

[Jay VandeKopple]

Carleen Hutchins' articles do give some guidance on the effects of modifying the bassbar, showing the changing nodal patterns. She liked to end up with a very clean shape to the sprinkles. It's associated with getting a nice ring when you tap on the plate.

On the other hand, it is quite complicated and you can't control everything. It's just one tool in the kit, but gives a nice visual of these ring tones (particularly modes 2 and 5).

[rgarcia26]

Originally Posted by Matthew Tucker

Though some might be interested in more hocus pocus ... it's quite spectacular!

http://www.youtube.com/watch?v=aHbpC_0E7wM

Mat, let me start by saying that I am a big fan of yours…  I’ve seem your work here in TB and in the Australian/New Zealand Luthiers Forum and its amazing, I hope one day I can do half you what you do…. I see the patens but I don’t understand what they are suppose to mean, are they showing symmetry from left to right, and if I want to build an DB I have to test the top for this?... this is way beyond my area… where I can find information about I my quest for DB building knowledge, I only fond one book about DB building sold by this Canadian Website ($70)… and very little info on the web.. there are tons of books about violins making.. but very few about DB

[drurb]

Cool video , Matt.

For anyone interested in learning more about Chladni patterns, click here.

[1st Bass]

"I only found one book about DB building sold by this Canadian Website ($70)… "

That's the one! Matt used it, as I did, and others...along with Chuck Traeger's book, and all the support from TalkBass you can get.

Matt made a bass as his first instrument, so it can be done, but I recommend building a smaller instrument first. It gives you a chance to get familiar with some of the procedures using less costly materials, and less space. OTOH, he and others have built basses or cellos as their first, so...take your pick.

As you say, there is a wide variety of instruction manuals, videos, forums, etc. for building violins, but not much on building basses. Much of the information is usable on basses, so it is good experience. BTW, Matt's website is a huge help.

Chet Bishop

[forester]

what if you left it on for days,or weeks.would it open it up,or wear it out?

[powerbass]

I am not sure what to make of this video. It is obvious to see that the black particles run down hill and that the lower bout moves more being the larger and more flexible portion of the top. Seems to me that to truly get a sense of how vibration works you would need to have the top attached to the bass. Since the perimeter of the top is fixed while attahed the vibration would primarily occur in the center?

[rgarcia26]

Originally Posted by 1st Bass

"I only found one book about DB building sold by this Canadian Website ($70)… "

That's the one! Matt used it, as I did, and others...along with Chuck Traeger's book, and all the support from TalkBass you can get.

Matt made a bass as his first instrument, so it can be done, but I recommend building a smaller instrument first. It gives you a chance to get familiar with some of the procedures using less costly materials, and less space. OTOH, he and others have built basses or cellos as their first, so...take your pick.

As you say, there is a wide variety of instruction manuals, videos, forums, etc. for building violins, but not much on building basses. Much of the information is usable on basses, so it is good experience. BTW, Matt's website is a huge help.

Chet Bishop

Thank you! That's make me feel better about spending $70 in a book….. , I was thinking on building an archtop guitar/bass… not 100% related but it should be somewhere close, of couse a violin would be better, but it doesnt motivate me that much as an archtop….I just a litle overwelm with all the information that it takes to make one…. I planning on taking an guitar building workshop at woodcraft ($600) it can give me some inside before getting into the DB buiding PS I don’t want to hijack Matt Threat

[Jay VandeKopple]

Originally Posted by powerbass

I am not sure what to make of this video. It is obvious to see that the black particles run down hill and that the lower bout moves more being the larger and more flexible portion of the top. Seems to me that to truly get a sense of how vibration works you would need to have the top attached to the bass. Since the perimeter of the top is fixed while attahed the vibration would primarily occur in the center?

Yes, what's happening in this one is not so clear. They're showing primarily the movement of the edge. With the "shaker table" the interest is usually with the pattern of glitter.

What happens there is that the glitter jumps away from the vibrating parts to the stagnant parts - creating the nodal lines. The glitter will really go uphill to reach a nodal line.

You're right that the ultimate interest is in the assembled instrument. However, the luthier is interested in how the plates are going during the process of building. In the old days, makers would tap at several locations on a plate. We still do that, but the shaker table can give us a nice visual of what's going on with the frequencies we'd hear with the taps.

There are other techniques used for assembled instruments. Most of them are quite expensive and impractical for a shop (requiring the use of lasers, etc.). You CAN actually use glitter on the outside of an assembled instrument (the glitter will climb up toward the nodal lines), but it can be quite a mess (and is not used much). The most promising now is some new modal analysis software that will animate the vibrations of an instrument.

Since the ribs move as well, the edges of the plate do move as well as the center. The nodal lines actually seem to have some similarity in shape to the shaker table figures. The top and back will have different shapes for a given frequency, though. There's a lot to learn yet.

[Matthew Tucker]

i'm making no attempt to predict how the top will vibrate once it is attached to the ribs. I am merely making a flexibility measurement. The nodal (no vibration) lines in this case demonstrate mode 1 - a twisting movement - and is the most easily demonstrated and lowest frequency mode. If I work on the top and re-measure and the frequency at which this mode appears is lower, it means the top is more flexible in that mode, and vice versa. There is nothing to say this is better or worse in itself. it is only a measurement.

[powerbass]

I see what is happening now, thank you. Does this kind of vibration testing steer the graduating process? Is this a standard practice for graduating or are there other techniques luthiers employ?

[Matthew Tucker]

Some luthiers use it, some don't. Some swear by it. Some think its rubbish. I don't think it's necessary to get a good result nor does it guarantee a good result. I do it because I have an open mind about it and it's fun and cool and because i can. s far as graduating is concerned, there's more to making the plates than just the thicknesses; the arching shapes make a huge difference and that's a whole other subject. Although, because the arching shapes do affect the stiffness, the result will be reflected in the flex measurement.

[powerbass]

I had an opportunity to check out a Prescott bass recently and noticed the top thickness at the F holes was about 3/16". Does the top thickness vary greatly throughout the plate on an average instrument?

[Matthew Tucker]

3/16 seems pretty thin at that point but quite often the FFs are chamfered on the back to give the impression that the plates are thinner than they really are; this makes the FFs look more elegant. Some basses have graduations that vary, some don't. Usually though, the tops are thicker where they need the strength and thinner where they need to be flexible. Kind of obvious, really. Ply basses are usually even thicknesses, for obvious reasons.

[Matthew Tucker]

Originally Posted by Jay VandeKopple

Since the ribs move as well, the edges of the plate do move as well as the center. The nodal lines actually seem to have some similarity in shape to the shaker table figures. The top and back will have different shapes for a given frequency, though. There's a lot to learn yet.

Another observation I might make is that the modal frequencies of an assembled instrument are quite a bit higher; when you're doing this sort of thing on an assembled bass you need quite a lot of audio energy to get glitter things happening. From a practical standpoint this means a very loud BAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA
blasting at the instrument which is quite unpleasant for neighbours to deal with, let alone the luthier!!!

[William Hoffman]

Originally Posted by Matthew Tucker

i'm making no attempt to predict how the top will vibrate once it is attached to the ribs. I am merely making a flexibility measurement. The nodal (no vibration) lines in this case demonstrate mode 1 - a twisting movement - and is the most easily demonstrated and lowest frequency mode. If I work on the top and re-measure and the frequency at which this mode appears is lower, it means the top is more flexible in that mode, and vice versa. There is nothing to say this is better or worse in itself. it is only a measurement.

Matt, what does this "twisting movement" -- so clearly visible in your YouTube video -- mean for the way a bass top will vibrate? do all or most top plates exhibit this twisting motion? is it true that a sound post, if narrowed towards the top end, frees up the top to twist more freely?