Don Noon

Those numbers don't seem too crazy light, as that's about the same weight as my plates... for which I use good wood (medium low density, high stiffness). For student instrument regrads, the wood is usually quite high density and sometimes not very stiff as well, so I'd never go that light on a regrad. I don't think that worn edges are terribly sigificant in terms of weight. More important would be varnish, which can be a couple of grams... but most of the old ones have very little left, with only a thin French polish. One student instrument I refinished had over 10 g of varnish on the plates, a real tone killer.

Altering the arching is usually only done to restore the shape of very valuable old violins that have distorted over time. It's a big job. Regraduating the thickness is far less demanding and can be effective for student instruments that are often overly thick, but not something acceptable for valuable instruments. This is one example of a beefy German factory student violin that I regraduated several years ago. Unfortunately I don't have all of the details of thickness, only that the original top with bar was 82g. I probably took out 10g of wood or more. I do have before/after spectral plots of a bowed semitone scale. The results are typical... primarily power gain in the lower frequencies, but some in the upper frequencies as well. I think this would generally fit the description of "fuller". Thinning can be overdone to become excessively low-end oriented, or "tubby". Too bad I don't have a "before" video, but here it is after regrad:

Yeah, I guess that's a match, thanks. I was thrown off by how white the wood was, and thought it had something opaque on it. Looks very nice, but wouldn't feel comfortable with acid on the wood.

I haven't used nitric acid (and never intend to), but I'm curious how it could leave an opaque white surface that goes clear with heat. David's idea struck me as the most likely, and it seems different from anything else. I'd be interested in messing around with it... as long as it doesn't involve nitric acid or chlorine gas or phosgene.

Trying simple things is a reasonable recommendation, but my best bet would be that your violin was built that way, and any major sound improvement is unlikely without major changes to the way it was originally made. Not something to be undertaken lightly or without experience, unless your violin is of little value to start with... and not something to be undertaken just on the word of someone on the internet.

Longer answer: These observable features in themselves won't do much, but it is possible that they are correlated with other wood properties that might matter. Closely spaced rings I have not observed to be strongly correlated with relevant acoustic parameters, but I have not had enough samples to see if there is a weaker correlation. There could be. A knot indicates something about how the wood was cut (more likely slab), which can matter. Also, the knot has some local disturbance to the grain direction, which might do something. BUT... whatever these variations are in the wood, a good maker can compensate somewhat for them. And violins all turn out a bit different anyway, so in the end it's really, really difficult to say what causes what.

No.

If the grid is stiffening the plate to any degree, there will be local areas around the beams that are significantly stiffer than the areas away from the beams. This would be especially true for crossgrain beams, where the spruce is very wimpy. The mode shapes and frequencies will be different when compared to an unreiforced plate... unless the grid spacing is much closer that the higest frequency antinode patch, AND the grid is carefully adjusted to match the natural anisotropy of the wood. None of this is to say any of the effects will necessarily be positive or negative, although in general I would expect modes to be more widely spaced in frequency and more variable in amplitude. In my mind, that would tend to be undesirable... but who knows. Also, with glue and such, I would expect adding a reiforcing grid to increase damping.

Many years ago I experimented with silicates, and found it mostly added weight without stiffening very much. It didn't do anything that seemed promising. In general, water-based coatings that seal the wood I think will give the typical washed-out "glue ghost" effect. Casein seems a bit different in that it doesn't seem to totally seal the wood, allowing subsequent coatings to wet the wood (if the casein is thin enough). There are infinite possibilities that can be made to work, with testing and practice... and infinite possibilities that ain't so hot. Personally, I prefer to avoid water-based coatings on the visible surfaces.

My inclinations are the same for the TP/saddle, but I don't really care much about the afterlength. For violins.

A0 is not like the other resonances, and hard to affect much in a given instrument. The frequency is primarily determined by body volume and F-hole effective area (with length far more important than width), and secondarily by body flexibility. In this case, "flexibility" can be imagined as sealing the F-holes and pressurizing the body, and see how much the volume changes. Amplitude will be determined by how well coupled the string movement is to the change in volume. Again, imagine pressurizing the body, and see how much the G string moves. It will mostly be due to the top plate movement. I have done a number of regrads on various fiddles, with the most extreme effects coming from excessively thick student fiddles and taking them down to normal-ish grads. The most change I have seen in A0 is a gain of 1.7dB and a drop of 12Hz. These are not very big changes. Far bigger changes happen in the CBR adn B1- amplitudes... and you won't be able to just diddle with A0 without affecting other things. Anyway, if I had to guess, I'd guess that your proposed regrad of the back would lower the A0 frequency a small amount, and have even less effect on the amplitude.

With nothing else to go by, following the beliefs of someone with respectable results might be a good starting point. Then when you find out that others with respectable results believe something else, you have to start questioning. Like WHY they believe what they believe. I have mostly experimented with tailgut free length, where when you get 5mm or so free, then a TP resonance shows up noticably in the playing range. That's generally not good, but if it's tuned to a wolf note (usually the B1+ resonance), it can counteract the wolf. However, it also creates odd dynamics, which good players seem to find more objectionable than the wolf. For TP/bridge (i.e. afterlength), my playing isn't good enough to notice any big differences. Presumably, to some degree it might act like one of those sliding afterlength-mounted mutes. I just use an old Thomastik metal fine-tuning TP that has a far longer afterlength than "standard", and it's fine. I can measure narrow dropouts in the response at the frequency of some of the lower string afterlengths, but I don't find it bothersome.

If it was very dense, super-stiff spruce, maybe it could work. Perhaps SOME high frequencies would be strengthened... but you need patches of all size in order to get a wide range of frequencies. A large-ish patch will naturally subdivide itself into a variety of mode shapes depending on the input frequency. If you attach stiffening struts, it will likely result in less modal density and more uneven response.

Except for that one apparently chewed out by an industrious beaver. The ones that look OK, are set up well and sound good I think could sell for a few hundred $. For a professional shop that needs to cover expenses, that may be too close to zero to bother with.

I would say that the low strings are more smooth and round sounding, and the highs are very pure and clear. I suspect that the "Dunnwald dip" weakens the overtones of the low strings to smooth them out, and the solid "bridge hill" response gives the clarity to the highs. I don't have details on the setup, other that it's from the best luthiers around. It looks like your recent modification might have strengthened the highs a bit, but still somewhat the same basic shape. The big hill at the B1+ looks worrisome, especially with relatively weak response below that (A0, CBR, B1- resonances). I really don't like the top reinforcements, with multiple beams in several directions, and think it might be responsible for some of these issues. Struts tend to reduce the number of vibrating mode shapes, which in turn should give a more choppy response, with strong peaks and dropouts. A violin has a small soundboard to start with, and reinforcements just break it up into even smaller patches. I would try a normal bass bar, perhaps a bit heavy to attenuate the B1+ resonance.