D. Noon's Trashbin

[Don Noon]

I have done a number of sadistic things to unfortunate cheap fiddles in the past, usually trying to test some acoustic idea or get some practice in varnishing or antiquing where I don't want to risk ruining my own stuff.   I have previously put them under separate topics, such as the recent old Maggini model rework, $44 violin, and slab top experiment.  These are the links to them, respectively, for anyone interested:

http://www.maestronet.com/forum/index.php?/topic/331823-what-does-the-back-do/

http://www.maestronet.com/forum/index.php?/topic/330559-the-44-fiddle-another-silk-purse-project/

http://www.maestronet.com/forum/index.php?/topic/331372-slab-cut-spruce-top-another-whacky-experiment/

 

I have been accumulating a few more cheap fiddles to replace the ones that have pretty much died on the operating table, and thought I'd just have one thread for all the carnage and autopsies.  Easy to find or ignore... and I don't want to post this unprofessional stuff in my "Contemporary Makers' Gallery", which I'll use for the stuff I'll put my label in.

 

I have one on my bench now... an inexpensive Chinese model, complete with varnish and everything.  From the $44 white fiddle experience, by the time I put in fittings and add a case, it's cheaper just to get an equivalent package and strip it.  I'll post more later.

 

 

[Marty Kasprzyk]

I have done a number of sadistic things to unfortunate cheap fiddles in the past, usually trying to test some acoustic idea or get some practice in varnishing or antiquing where I don't want to risk ruining my own stuff.   I have previously put them under separate topics, such as the recent old Maggini model rework, $44 violin, and slab top experiment.  These are the links to them, respectively, for anyone interested:

http://www.maestronet.com/forum/index.php?/topic/331823-what-does-the-back-do/

http://www.maestronet.com/forum/index.php?/topic/330559-the-44-fiddle-another-silk-purse-project/

http://www.maestronet.com/forum/index.php?/topic/331372-slab-cut-spruce-top-another-whacky-experiment/

 

I have been accumulating a few more cheap fiddles to replace the ones that have pretty much died on the operating table, and thought I'd just have one thread for all the carnage and autopsies.  Easy to find or ignore... and I don't want to post this unprofessional stuff in my "Contemporary Makers' Gallery", which I'll use for the stuff I'll put my label in.

 

I have one on my bench now... an inexpensive Chinese model, complete with varnish and everything.  From the $44 white fiddle experience, by the time I put in fittings and add a case, it's cheaper just to get an equivalent package and strip it.  I'll post more later.

Sounds like your shop is an above ground mausoleum.

[Don Noon]

Sounds like your shop is an above ground mausoleum.

 

More like...

[Don Noon]

A little digression into the current state of "The $44 Fiddle" (see link in post #1):

I didn't like the straight varnish, so I took to antiquing it.  Not a great recipe: trying out several different new kinds of varnish and colors, and trying to antique it.  Anyway, this is the result so far, and I think I'm quitting:

 

Now onto another one, a not-quite-bottom-of-the-line student model.  I kinda like the back figure.

I did play it in the original condition and take some measurements, and it was good and bad-

-Good:  well, at least it didn't sound horrid.  Not really up to the level of good, though.

-Bad:  signature modes were extremely low (B1+ ~515 or maybe less, and overly resonant), indicating that it might already be too thin (and verified by measuring thicknesses)

-Bad:  440g without chinrest; very heavy

I don't know how much weight is in the varnish, or whatever thick plastic was sprayed onto it.  I'll take it off and see what happens, later.  The primary intent is to practice varnishing and antiquing, but it's disappointing as to its acoustic potential.

 

A pattern seems to be emerging:

My measurements are the red squares, and the low-cost modern Chinese tops are all in the oval.  The points immediately to the left (but to the right of the blue RR=14 line) are "after modification" , including a 100 year old German cheapo.  And my violin #1.  None of these have any hope of getting to the taptone/weight region of the good stuff, which essentially means the stiffness/weight ratio of the wood is not very good.

 

I am picking up a couple of mid-level German fiddles, a few decades old, and see if they are any different.

[MikeC]

That's a nice looking finish for a $44 piece of trash!

[Don Noon]

Another item entered the trashbin today:  a Pfretzschner student violin.  It's a large brick:

 

360 x 210 body

504g without chinrest 

 

Body resonances:

A0  285 Hz (amplitude ~10 dB below normal)

B1-   490 Hz (also extremely weak)

B1+  607 Hz (extremely high amplitude, even affects the open E)

 

CBR is at 429 Hz

 

It sounds horrid, as you might expect, with no power on any fundamentals until you get to the E string.  And the overtones are pretty weak, too.

 

Exactly what I want:  some roughed-out plates that have been aging for 52 years.

[Dwight Brown]

Can you just treat them as having been "roughed out" for you to use as raw material?

 

DLB

[Don Noon]

I haven't decided yet exactly what fate awaits this specific fiddle, but at least there's enough material there to start with, and it's aged well.  Most likely I'll just regraduated it into a more functional fiddle.  The varnish doesn't seem too bad, so I am hesitant to practice varnish/antiquing work on this one (for that I have another cheap Chinese fiddle, pictured above... and another German student instrument coming in soon).

 

These projects will have to play second fiddle to my #18, which I am finally getting back to working on.

[Don Noon]

I'll leave #18 strung up in the white for a week or two to see where it stabilizes; meanwhile:

 

First out of the trashbin is the low-density Sitka top graduation experiment.

 

As is my usual custom with experiments, I like to state the objective and expected outcome before seeing what the outcome is.  That's a very effective way to be wrong most of the time, as I have found out.

 

The main objective of this test was to see the effects of full arching... very narrow channel, with the plate rising as steeply as possible from there.  As a consequence, the arching becomes relatively flat across the center.  I didn't use templates, other than a 2m radius template to start the long arch, and a 130mm radius template to shape the crossarch under the bridge (so some of my existing bridges will fit without adjusting them).  Everything else was by eye.

 

This arching should stiffen the top in the low frequencies, particularly in the 600 - 1kHz range where plate rocking appears to be significant.  If this happens, it might be observable as an upward shift in the "transition hill" frequencies.

 

The center of the plate would then be less stiff.  My working theory has been that a tighter arch in the center area would not only shift the "bridge hill" toward higher frequencies, but also generally make the acoustic output stronger across the high frequency range by increasing the size of the mode antinodes.  So, by this logic, the bridge hill on this experiment should be shifted to lower frequencies and perhaps be weaker.

 

There are some conflicting aspects in this test, though:

- The top is extremely low density, high radiation ratio, and it is relatively thick, so all frequencies might be pushed upward

- The back is strongly involved in the transition hill, so any influence by the top might be obscured

 

Here are some details:

 

Wood

.33 density Sitka, processed VERY strongly (too brittle for anything but testing; OK stiffness but very low breaking strength)

5500 m/s speed of sound

~17 Radiation Ratio

164 Q (very ringy, although not the highest I've seen)

 

Plate without bar (but with 2 thin applications of my ground)

60.6 g

94 Hz M1

177 Hz M2

334 Hz M5

 

With bar (bar from .42 density ponded Sitka, moderately processed, C=6070 m/s, slab cut)

65.1g

100 Hz M1

201 Hz M2

387 Hz M5

 

Graduations were between 3.0 and 3.5, which would be ridiculously thick if you didn't consider the low density.

 

The rest of the instrument is a Chinese fiddle, decently made, and presently graduated to near what I normally do now.  Nothing strange.  If you think you see a faded out area on the centerline of the top, you're not mistaken.  That's where I scrubbed off the glue from when I had to glue a major crack caused by light carving on the inside.  The plate almost broke in half.  

 

One expectation I failed to mention... it should be very loud.

 

edit:  and another one:  B1- frequency might be higher than usual, due to the high crossgrain stiffness of the top.

[DGV]

Why did you think it should be very loud?

[jezzupe]

Why did you think it should be very loud?

I surmise...super low density wood, super processed {plato}, big radiation #'s with a bouncey top and bar...a weak breaking point translates to high cross grain stiffness which translates to super stiff flabbiness or the ability to have a large "throw" when set in motion, assuming he undermined the top stiffness correctly with his ff hole size and placement.

 

No purfling? or going in later?

[Don Noon]

Why did you think it should be very loud?

 

High RR, light weight, low damping... the string energy has nowhere to go except into the air.  The wood won't eat up much of it.

 

No purfling? or going in later?

 

This is an acoustic experiment only, where I'm not going to waste any time on aesthetics.  

[DGV]

This is an acoustic experiment only, where I'm not going to waste any time on aesthetics.  

 

If the experiment is successful, maybe you can sell it at a decent price with the added aesthetics.

[Don Noon]

I wouldn't want to sell this, for a number of reasons.  The main one is the low-density, brittle, weak wood.  Way too prone to major damage.  This wood is a good demonstration that stiffness and strength are two separate issues, even though they usually go together for most materials.  

 

Plus, once you do crude work, you can't rehabilitate it completely.  And this was done crudely (but a little better than some of my other experiments).

[Michael_Molnar]

Don,

 

Have you considered post-processing your wood, namely infusing it with some kind of stiffening resin for instance?

 

Mike

[Don Noon]

Mike,

 

I have tested quite a few coatings, and have decided that wood is good.  Instead of a coating, you could leave the wood a tiny bit thicker, and you'd have a better stiffness/weight ratio.  Less coating is better, I think.

 

Of course, I haven't tried everything... I'll bet a sputtered beryllium plating would be pretty good, if you want to get higher stiffness/weight.   It might poison the player, though.

[Don Noon]

Preliminary results:

 

It is very loud, and B1- frequency is rather high.  All the other "expectations" look wrong, but that's OK...if  those concepts were wrong, I don't want to hang onto wrong thinking.

 

Generally, my impression is that it's a little too stiff and harsh for my tastes, but you can play very close to the bridge. I want to do some adjustments before concluding anything further; only one of my old bridges fit, and it was really oddball.  So I'll cut a new bridge and mess with the soundpost to see what I can do.

[Evan Smith]

The increase in the hz. Of the modes is a bit abnormal.

The increase in 1 is low 5 is high. 2 is stiff.

Are the upper and lower bouts extremely full and round and puffy.

The shear is all I’m really concerned about.

Without a bar 82 or so works good, and if the arches are right and the wood is sufficient,

with the bar it will increase to about 92, sometimes I go to 94, but I have found that 100 is way to stiff,

No matter what the density happens to be.

I like 1 around 92-94,sometimes down to the upper 80's. 5 around 370-400 or so though sometime 5 will be as low as 330, it doesn’t seem to matter as much as getting 1 right, the shear mode makes the biggest functional difference from my observations.

[DGV]

Interesting. According to platetuning.org, mode 5 is more important. That is why I stopped tapping for mode 1. Maybe I should try to tap for mode 1 as well.

How does one bring down mode 1 without affecting the other modes much?

[Don Noon]

Are the upper and lower bouts extremely full and round and puffy.

 

I should have mentioned... the wood I started with wasn't very thick, and the arching I could get out of it was only 14.7mm.  I did attempt to get the arching as full as possible (no effective recurve at all), but with the shallow arching, this necessarily meant that the cross arch in the middle was relatively flat.

 

I generally find my M1 frequencies in the 70's without the bar, and in the 80's with the bar.  Specifically, M1 frequencies without and with bass bar:

96 - 103 2011 VMAAI 2nd place tone steel

73 - 82  2012 VMAAI 1st place tone steel

76 - 83  2013 VMAAI 1st place tone steel

80 - 89  2014 VMAAI 2nd place tone steel

 

Going by these results, the lower M1 appears to do better.  However, I should also note that the first on the list (with the really high M1) was my "Snakefiddle", with ultra-low density wood, and the lightest top I have ever made... definitely not stiff, though, as the assembled signature mode frequencies were quite low

 

For the current experiment, I thought I'd leave it stiff for starters, and thin it out later if necessary.  I'll probably do that soon, after I live with it for a while.  There's also a 830 Hz semi-wolf on the E string, which I have traced to an excessive back resonance that I'd like to try to kill off.

 

 

Interesting. According to platetuning.org, mode 5 is more important. That is why I stopped tapping for mode 1. Maybe I should try to tap for mode 1 as well. How does one bring down mode 1 without affecting the other modes much?

 

I always try to discourage people from trying to tune free plate taptones to any prescription by diddling around with graduations.  Taptones of the free plate don't exist when the instrument is assembled, but the graduations DO.  The graduation pattern seems much more important to me than the frequency of the flapping plate edges, but the flapping plate edges can give a general clue about stiffness and when it might be a good idea to stop removing wood.

 

That said, I do record M1, M2, and M5 for everything, because it's easy, and I also measure absolute plate stiffness by deflection under weight.  So far, it has all been only a vague indicator of overall stiffness of the assembled instrument. 

[Evan Smith]

That would explain the high 2 and the lack of gain in 1.

The curve in the length of the arch with the b-bar added give a fairly predictable increase.

A low arch won't accommodate that.

16 mm arch has become my bass line for observation, with density around 36 to 38 at least.

So what was the density of the snake fiddle?

31,,32,,

I have a lot of 33 and 34 but I'm feeling that this too low and possibly is not suitable for long term fiddles,

at least in the form of Engelman. I am liking the high 30s to the low to mid 40s.

I have some Sitka in the 50s, I would like to try an experiment with that,, just because it would be

a challenge.

On how to lower mode 1,, the fastest way is to vibrate the plate arch up,, draw mode 1 on the outside of the plate,

then scrape it back off going completely across it and a bit further, ,by lowering the arch and removing stiffness in the area of the greatest shear,, it will go down the quickest. Doing the same thing on the inside of the plate will keep 5 up a bit more in relation to lowering 1.

However as a disclaimer,, I agree full with Don that the free plate modes have next to nothing to do with the completed

instrument,, other that giving an estimate of overall wood stiffness,and for that I prefer mode 1.

I have gotten 1 down to the low 90s with 5 at 400 on a finished plate a few times, and while I think that is good,

it is not the answer.

[Don Noon]

So what was the density of the snake fiddle?

 

.31

The top plate was originally 51g without the bass bar, prior to varnish.  I later pulled it apart and took out another gram of wood.

[Don Noon]

While waiting for some ground to dry, I suppose I should tie up this low-density Sitka experiment (see post #9 for most of the details).

 

I played around with the setup, which greatly reduced the harshness, but decided it was way too stiff for me, and since I'm not selling it, I might as well tune it down to my tastes.  So I ripped the top off and hogged out a bunch of wood.

 

I only used gouges for the regrad... no scrapers or even fingerplanes.  My wide, flat gouge got it close enough, I think.  

I did not remove the bass bar (or take any wood off of it), so I don't have bare plate taptones. 

 

Top plate, with bass bar:

Mass:  57.0g (8g reduction; note: calculated bare plate = 52.6g)

M1:  94Hz (6Hz lower)

M2:  174Hz (27Hz lower)

M5:  366Hz (21 Hz lower)

 

Final Signature Modes, with chinrest:

A0:  280Hz (1Hz lower)

CBR:  382Hz (2Hz lower)

B1-:  442Hz (6Hz lower)

B1+:  557Hz (22Hz lower)

 

And the response spectrum: 

 

Reviewing my pre-test expectations...

 

Upward shift in transition hill frequencies:  nope.  They are about the usual places, and didn't move much in the regrad.  I do know that the back is involved, and may be the major controlling item... but it is also possible that the lower arch height is a factor.

 

Bridge hill shift to lower frequencies, and weaker:  no and yes.  The bridge hill (if you can call it a hill) isn't particularly shifted, but it IS relatively weak.  I can't call the second item a successful call, though, as I seem to notice weakness in the higher frequencies associated with lower density wood.

 

Attempt to reduce 830Hz resonance:  not great.  It's still there, and strong, but at least it doesn't seem to be as wolfy as before.  Another of many unsuccessful attempts to target a specific resonance for modification (other than the signature modes).

 

It is pretty loud, though.  The frequencies below 1kHz are quite strong, with no major dropouts.  Even above 1kHz, it's relatively even, without big dropouts, so it is very nice as a fiddle...  but you can come to your own conclusion about that:

LD Sitka regrad.mp3

 

Bottom line on the arching:  Nothing outstandingly better or worse than other violins where I used templates from known Cremonese violins.  For me, at least, templates are not required.

 

 

 

 

 

 

[Don Noon]

Just one or two more observations before moving on to the next one...

 

The results of the regrad, other than frequency shifts noted above:

 

-Below 500 Hz, there was a fairly uniform gain of ~3dB

-Above 3500Hz, there was a similar increase in amplitude

 

Although I would consider these to be significant improvements to the sound, measurement-wise, I was surprised by the before/after recorded scale comparisons.  They sounded the same at first, although with closer listening, I could hear the fuller, brighter, snappier sound of the regraduation.  

 

12.5% weight reduction in the top seems like a lot, but acoustically it's not huge, I suppose.

 

Hopefully my next regrad (a Pfretzschner, already nearly complete) will have a larger effect.  It sounded positively horrid initially, and I have taken out 26% of the top wood (and I still left it heavy).

[actonern]

Macbeth act 5 scene 5