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plywood ribs?

Edward Powell - 8-24-2012 at 03:43 PM

We are talking here about acoustic not electrical instruments. Veneered necks and pegboxes are, of course, traditional practice.

Plywood is a very stable material. The geometry of an oud bowl - is like an egg shell - very rigid and strong once assembled from individual ribs so I very much doubt if there would be any significant acoustic difference between one made from ribs of Beechwood aircraft plywood and one made of ribs from rosewood or any other materials all else - like the volume of the bowl - being equal (apart from the cost!). It is the sound board and bracing that are of primary importance acoustically.

I have heard of pine being used historically for lute bowls but have never found an extant example - probably because softwoods are more difficult to hot bend than most hardwoods.

For stability, 3 piece (3ply) plywood is usually constructed with the grain of the centre core at right angles to that of the outer laminations. Also when veneering a piece of wood both front and back faces must be veneered to counterbalance shrinkage forces and prevent 'cupping' of the work - at least if a traditional hot hide glue 'iron on' procedure is used.
Plywood can be hot bent.

Food for another topic, however, that I might initiate with my experience in building the 'Grobert' guitar - before memory completely fades.

I think u might have the answer there... when I veneered 3 (0.6mm) strips of mahogany into one rib they seemed a bit flimsy across the width. But the idea to make the middle layer a bit thicker and with the grain perpendicular to the outer layers - this would certainly stiffen up the rib for sure.

I tend to agree that the back material is not affecting the sound too much - otherwise how would those heavily jewelled egyptian ouds ever get a decent sound???

fernandraynaud - 8-24-2012 at 10:50 PM

I dunno, but I am not surprised the heavy backs can give a good sound. I've said this before, but here it is, for our newer members. I have two Sukars, a model 212 and a model 14. Sukar has worked out a template that his ouds generally follow. These two are very similar ouds, made around the same time, same dimensions, same bracing, same soundboard, fingerboard, same bridge, pegs, same paper strips inside, you name it. In most ways they are almost twins. I expected them to sound about the same. But they sound and emote very differently.

I've never weighed them but the 212 feels lighter, the 14 feels heavier. The 212 bowl is a medium colored grey walnut, not the reddish stuff, with, what do you call it, thin separating purfling(?) stripes between the ribs. The 14's bowl is a dark wood that some have identified as "pretty sure it's ebony", a Sukar reseller in Damascus identified specific Sukars as being ebony, while others have said Sukar never uses ebony except the pegs, and maybe those very dark fingerboards on the high end models like the 211, 212, 14, etc. On the Sukar site I could decipher it only as as "walnut of lions". Some have called it "oily dark walnut". I don't know. Who cares. The fact remains it's a much darker wood, and feels heavier. But the ouds are otherwise so similar it's a rare opportunity to isolate the effect of the bowl. Most comparisons are apples to oranges, altogether different instruments.

The 212 is at home in major chords, and maqamat like Ajam, Rast. The 14 is at home in deep soulful minor scales/modes, isn't so good with chords, loves Hijaz, Saba, Nahawand. The 212 is bright, shines and twinkles (as other 212 owners have agreed), the 14 bellows and moans, has a stronger bass. If you play the two you immediately feel it, it's intuitively obvious that one is "heavier and darker" in timbre and character, and what is most different in the construction is: the bowl material itself.

I don't think there's anything wrong with composite materials, or outright synthetics, but an Ovation fiberglass back guitar has a specific sound, and after my experience with these two otherwise so similar Sukars, I must reject the "no effect of the bowl material" story.

Edward Powell - 8-24-2012 at 11:07 PM

ragmakamtars version 9 and 12 are almost identical but the bowl wood is totally different - #9 is maple, #12 is merbou... merbou is extremely hard and hard to work with. There were enough differences in design to alter the sound - but in fact the sounds were WORLDS APART. I wonder how much the merbou changed the tone... I think I will not use merbou for bowls.

ragmakamtar #11 is rosewood and the bass is HUUUUUGE... but then the bowl is enormous also.

finally there are so many factors that we will never know for sure - that's what makes luthiery such a mystery.

PS - let me add that ragmakamtars 9 and 10 used exactly the same wood and body shape... but also had totally different sounds. The design differences were:
1) 10 had all round much lighter construction on everything
2) 10 had larger soundhole and 2 ribs less (bowl less deep)
3) 10 had one neck much longer

...so the wood was identical but sound totally different obviously from design differences.

fernandraynaud - 8-24-2012 at 11:21 PM

But my two Sukars are so similar that it gives us that rare opportunity to reduce the variables! Oh, and I even coated the soundboards exactly the same with egg white. I ordered them out of Damascus with the thought that I might sell one. But they are so different that THAT brilliant idea sure bit the dust. I kept playing them to try to decide which one to keep, after all it was too costly to keep both. But the more madly I played and compared them, the more they diverged! Aiii Caramba, dolor des dollares! Never do that unless you really want two ouds! So I kept them and ended up selling my Model 1 that was different yet, but sort of in-between. But there was something about a Shehata. Danger, danger! The number of ouds per household is mathematically almost impossible to reduce.

fernandraynaud - 8-25-2012 at 12:21 AM

"nnno!" he said, making little spirit-chasing-away gestures and looking about nervously for something to grab onto. (that was in response to Edward's question, as to whether I had a Faruk oud).

Aymara - 8-25-2012 at 12:25 AM

Quote: Originally posted by Edward Powell

I tend to agree that the back material is not affecting the sound too much ...

Sorry, Edward, but I highly doubt that. I believe, that the wood choice for the bowl highly influences the sound.

See what I reported about my personal oud choice in THIS thread at the beginning of page two.

So Fernand is not the only one with such experiences

fernandraynaud - 8-25-2012 at 04:00 AM

But I'll say one more thing. What I'm noticing most is the different "personality" of two instruments which are as close to clones as we get with ouds, because of Sukar's standardized production techniques. I don't think it's as simple as "heavier wood makes more bass". I don't know if it's something you'd immediately see on a spectrum. There's something about the overall "character" of a good instrument that is very strong, and if we think in terms of frequency response, we might say it's got more of this or that frequency spectrum, when in reality that's just part of a more complicated picture.

Those who say that technically the spectrum isn't as affected by the material of the bowl may be right too.

But the totality of the instrument forms that character, including the bowl. And maybe you even can't help but play each instrument differently, in accordance with how you perceive its character, and that might lead you to interpret, to abridge, that by saying this one is brighter, or bassier, or whatever. Then how you interact with it, how you play it, might also literally affect how the wood settles, how it, as we say, "opens up", so in a circular way your impression reinforces itself. And that's before invoking more metaphysical formulations (that we're not very well equipped to discuss), like "a player becomes his instrument", and vice versa.

jdowning - 8-25-2012 at 04:26 AM

Ho hum! So how about the practicalities of using plywood (either as a commercially available product or made up from exotic veneer) as a material for bowl construction? That is the question posed by Edward!

Edward Powell - 8-25-2012 at 08:49 AM

Quote: Originally posted by Aymara

Quote: Originally posted by Edward Powell

I tend to agree that the back material is not affecting the sound too much ...

Sorry, Edward, but I highly doubt that. I believe, that the wood choice for the bowl highly influences the sound.

...but read carefully, I do think wood choice affects the sound but "not too much".

I think saying that the wood choice (as long as we stay within the range of commonly used hard woods) "highly influences the sound" is an exaggeration. And furthermore, as John and I pointed out, your and Fernie's experiments, while very interesting, can't be held as conclusive because small variation in soundboard can alter the sound very much.

But this is a very useful dialogue and everyone's opinion and experience is valuable.

jdowning - 8-25-2012 at 12:18 PM

As I do not throw anything away that might find a future used I have this morning found my original molds as well as a set of laminated side rib blanks for a copy that I made of the circa 1820 Grobert guitar (Mirecourt 1794 - 1869) cat# E.375 C.278 that at that time was located in the Musee Instrumental du Conservatoire National Superieur de Musique de Paris. The Museum working drawing and notes by Pierre Abondance dated 1982 indicate that the guitar was once owned by virtuoso violinist and guitar player Paganini and then passed on to renowned French musician and composer Hector Berlioz.

The sides of the guitar body are made from sawn Rio Rosewood (Brazilian Rosewood) of thickness from 1.0 to 1.2 mm.
The back - of Brazilian Rosewood - is a laminate of 0.6 mm thick sawn rosewood veneer glued to a backing of 'mediocre quality' softwood - average total thickness of the back being about 2.3 mm.

I did not have any solid Rio rosewood for the sides so they were made up from a 3-ply laminate of Rio rosewood veneer with a mahogany veneer core. The glued laminates were then formed experimentally by conventional hot bending as well as by cold forming in a mold.

I have also used commercially available plywood - hot bent - to make lute cases.

More to follow on this experience.

fernandraynaud - 8-25-2012 at 01:36 PM

One man's ho' is another man's hum. I didn't realize the timbre of ouds had been fully elucidated and we were down to technicalities.

jdowning - 8-25-2012 at 02:56 PM

Then perhaps you did not read or understand the title of this topic fernandraynaud? It is all about the technicality of plywood ribs and not at all about elucidating oud timbre is it? The latter would seem to be part of the ongoing discussion that you are already participating in on the forum topic " which wood's the best "?

fernandraynaud - 8-25-2012 at 03:24 PM

Perhaps.

Aymara - 8-26-2012 at 12:16 AM

Quote: Originally posted by jdowning

I have also used commercially available plywood - hot bent - to make lute cases.

Is plywood more difficult to bend? I would expect that, but never tried.

jdowning - 8-26-2012 at 06:28 AM

Watch this space!

jdowning - 8-26-2012 at 12:15 PM

It is some time now since I have hot bent commercially available plywood so a quick trial was undertaken this morning to demonstrate bending of two strips of Meranti 3 ply of 5.2 mm thickness from my scrap pile.

Meranti plywood is about as cheap as it gets - a utility plywood for general purpose work.

Using a heavy duty propane heated bending iron and moistening the surfaces with water, the long strip (with the grain of the thin external veneers running longitudinally and the thicker core wood cross grain) the wood was bent very easily. Some compression damage (crumpling) of the internal veneer was noted.
The smaller sample with the external veneers cross grained and the core grain longitudinal was more difficult to bend - partly because the test piece was so short (about 5 inches in length).
The bent pieces remained stable after bending with no sign of delamination of the veneers.

I have used hot bent Meranti plywood 2.7 mm thick for making lute cases - see " Build an Authentic Oud Case" on this forum for the full story. Note that the bent staves of the lute case have the grain of the external veneers running cross wise.

Cheap Meranti plywood is, of course, not recommended for making oud ribs (this is just to demonstrate what can be done) - but high grade thinner plywoods such as those made from Birch (aircraft grade) or Mahogany (marine grade) - have not been tested but would likely give good results. The thinner grades might also be veneered with any type of hardwood veneer prior to bending into the ribs of a bowl.
Note that due to the thinness of the external veneers, bowl ribs would have to be accurately fitted with no significant 'step' between adjacent ribs and that it would not be possible to produce a rounded external profile of a bowl. The bowl would have a faceted profile like that of a lute - not an unattractive feature that would have the added benefit of reducing slipping or sliding tendency of a bowl when an oud is being held.

Next to review past experience in laminating Brazilian rosewood veneers in order to construct a 'copy' of the 19th C Grobert guitar that may also have some application to laminated ribs for oud bowl construction.

Meranti Ply Long and Cross Grain.jpg - 112kB

Edward Powell - 8-26-2012 at 07:50 PM

thanks John
this is cool and very interesting... I'm surprised that it is so easy to bend 5mm thick stuff!

My own idea was rather not to bend plywood but to 'make' plywood around a form, so the rib will end up having the exact shape it needs to be... thereby saving the builder the task of accurately bending the rib. I did this already and it worked really well --- I used contact cement but I think this is not a good idea because that glue does not dry brittle --- you mentioned using hide glue then ironing the veneer.... would this super heating of the glue cause an instant curing of the glue?

jdowning - 8-27-2012 at 05:14 AM

Hot bending of commercially available plywoods was just to demonstrate that it can be done.

I agree that a good method is to lay up the glued veneer on a caul or mold and then clamp in place (cold) until the glue dries.
This is the method that I finally used for the sides of the Grobert guitar as we will see.
However, I did also experiment with cold gluing the laminates as a flat sheet and then hot bending the sides in the usual manner - which also works. For this I used PVA glue for laminating as it is thermoplastic - temporarily softening with heat.
So it is possible to use both methods although if a 3 dimensional shape is required (like the back of an archtop guitar or plywood furniture), a stack of separate glued laminations would be required which are then formed on a mold under high pressure and temperature.

Hot hide glue was used for centuries past (and still is) for veneering. The glue will temporarily remelt as long as the temperature is not too high. This is the method that I used for laminating the back of the Grobert guitar.
A modern alternative is to coat both surfaces with PVA glue let it dry and then iron the the laminates together with a hot household iron.

Brian Prunka - 8-27-2012 at 06:30 AM

Would it be possible to use a vacuum press to assist in this process? I know in some archtop guitars they use a vacuum press and a mold to bend the plywood guitar top into the desired shape. I believe they do this during the gluing of the plywood.

Obviously, an oud has a much more dramatic degree of bending than an archtop guitar, so it may not be practical.

jdowning - 8-27-2012 at 07:49 AM

Yes a vacuum press can be used to apply a uniform pressure to laminates being formed over a mold.

For an oud bowl though we are here only considering forming the individual ribs from laminates that would then be assembled edge to edge in the usual way. That, of course, is a much simpler procedure than attempting to form the bowl as a one piece laminate (although it likely could be done by laying up veneer strips over a solid mold in the way strip built canoes are fabricated - rather like papier mache only using veneer instead of glued paper strips).

jdowning - 8-27-2012 at 04:02 PM

Here for information are some images of my 'copy' of the Grobert guitar made over fifteen years ago for a Canadian national 'live history' museum for performance of 19th C music.'

Note the beautiful figuring of the laminated Brazilian rosewood veneered sides and back and the spruce inner wood of the back.

Edward Powell - 8-27-2012 at 04:30 PM

this is a bit off topic, but John, I have a couple of old guitars I bought in CZ over ten years ago and they majorly resemble this guitar you have made --- I just wonder if you have any info on these guitars.... see pics

Edward Powell - 8-27-2012 at 04:35 PM

and this next guitar....

Edward Powell - 8-27-2012 at 04:38 PM

BTW... your 'copy' is amazing... did u use veneer simply to save $$$?

jdowning - 8-28-2012 at 05:20 PM

Nice old guitars Edward with some interesting details. They appear to be larger bodied and more heavily built than the French style Grobert guitar which was gut strung played 'finger style' with soft fingertips. These look as though they are more heavily strung intended for sounding with a pick or plectrum - either wire strung or heavy gauge gut/wound silk.
Interestingly the fingerboard of the first German guitar is 'scalloped' (between the frets) a feature seen much earlier on wire strung instruments like the cittern - in order to keep the action as low as possible and minimise intonation problems as the strings are stopped. The second guitar has machine heads of the type used for metal strings.
For these reasons I do not think that these guitars closely resemble the French style guitars and may be from a later period (late 19th C early 20th C ?) - but I do not know enough about this type of guitar to be sure.

For the Grobert copy I tried - as far as possible - to replicate the construction and materials of the original. The original has a 2 ply back of sawn Rio rosewood veneer on softwood about 2.4 mm total thickness and sides (ribs) of solid sawn Rio rosewood about 1 mm thick. I had to use knife cut Rio rosewood veneer for the copy because that is all that was available - although if I had been able to obtain sawn Rio rosewood at the time no doubt the cost would have been prohibitive (and its procurement illegal!).

So the compromise was knife cut veneer on Sitka spruce for the back and a double thickness of knife cut veneer for the sides.
More on that to follow.

Edward Powell - 8-28-2012 at 05:34 PM

i see... so you used veneer because the original used veneer?

jdowning - 8-29-2012 at 12:07 PM

Yes

jdowning - 9-5-2012 at 05:22 AM

The first (unsuccessful) attempt at making the sides of the guitar from veneer was to make a 2 ply construction - two veneers glued together with PVA glue (Lee Valley 2002 GF - high solids content and high viscosity to minimise chance of glue seeping through the veneer causing surface glue stain). The grain of both veneers was longitudinal.
After gluing the veneers were clamped between two flat boards to dry.
On release from the clamps - on further curing - the blanks became warped ('cupped') across the grain. This is likely because knife rotary cut veneer was used rather than quarter sawn.

The sides were then bent over a hot iron in the usual way. It was found that bending dry without dampening the surface with water caused 'blistering' - local separation of the laminates. This was avoided (and repaired) by first moistening the surface of the blank before hot bending with the bending iron held below scorching temperature.
However the bending process was still not completely successful as it was not possible to maintain flatness of the ribs across their width so this trial was abandoned.
I still have the test samples so can post the attached images. The total thickness - including the glue line - is about 1.05 mm equivalent in thickness to that of the original guitar (see the attached macro image)

In retrospect I figure that the hot bending would have succeeded had I made the blanks as a three ply construction with a thin cross grain core - which is what I did for the next stage to follow.

jdowning - 9-6-2012 at 11:53 AM

For the second (successful) attempt at making the guitar sides or ribs from veneer laminate, a three ply laminate was constructed using a caul or mold. The laminate was a 'sandwich' of two outside veneers of Brazilian rosewood (both with grain direction longitudinal) with a thin cross grain core of mahogany veneer. The core thickness was about 0.25 mm (they make modern veneer very thin these days!) - giving an overall finished rib thickness of about 1.3 mm.

The caul was made from layers of plywood glued together to a thickness of 3.5 inches (about 9 cm) and then accurately cut to the outer half profile of the guitar using a bandsaw to ensure vertical sides to the caul. Clamping blocks matching the inside profile were cut and then lined with foamed back carpet to provide a resilient surface over the laminate under clamping pressure.
I still have the original caul but cannot now find all of the clamping blocks. No doubt they will surface some time in the future (see attached image). The blocks were clamped to the caul using large 'G' clamps.
The depth of the caul was made oversize to allow trimming of the side blanks.
The sides of the caul were wax polished to avoid any risk of the veneer sticking to the sides should there be any glue 'leakage' through the veneer.

I cannot now remember exactly how I glued up the laminates but seem to recall that it was done in two stages - inner core to external veneer then - after the glue had dried - inner veneer glued in place.

The glue used was Lee Valley 2002 GF PVA and the laminates were glued 'cold' without need for application of heat. As the glue has an open time (before beginning to harden) of about 15 minutes there was ample time to align the veneers in the caul and clamp the blocks in place.

This custom made plywood is very stable and held its shape without any 'spring back' when released from the caul after allowing a few days for the glue to thoroughly dry.

Next to the veneering of the back of the guitar - a two ply construction like the original.

antekboodzik - 3-29-2014 at 02:47 PM

May I refresh this topic? Just in case that this topic turned out to guitars

Many modern classical guitars have solid backs and laminated sides (e.g. macasssar ebony for back and macasssar/ash sides). What is the difference in sound, or maybe to another material/techniques to be used, versus solid sides?

I was often thinking that laminated sides of contemporary guitars helps to create stronger "drum" like effect to the soundboard as a membrane. Laminated sides could then be made thicker (and thus much stiffer), as then solid sides of more than 2-2,5 mm would be extremely hard to bent.

Can laminating sides of veeners be considered as an (cheap, relative easy) option to make a guitar (for flamenco music (!?) ) by amateur like me? Veeners of different wood about 0,7-0,8 mm are widely available and cost a fraction of price of bookmatched professional sets. Do this technique apply to making backs of guitars?

Edward Powell - 3-29-2014 at 03:05 PM

Sides of guitars don't make much influence on the sound.
I would not recommend building with any plywood, like making your own with veneers - mostly because thin veneer is always a problem because if for some reason you need to sand more than half a mm. very likely if you are beginner, then you will sand all the way THRU one veneer and BINGO you have a big problem.

If you want to same money then just use a more common wood like maple... that's very cheap... or beech, ask, or even make the whole guitar from spruce - why not?

antekboodzik - 3-29-2014 at 03:20 PM

Well, here in Pomerania there is extremely hard to find even a single maple

Yes, this is a point with sanding, or scraping, thin veeners. But I can use same wood for both layers, even bookmatched pairs of dark in color timbre

Another consideration is about glueing along center line rather thin (not more than 2,5mm total), laminated back panels... Executing this precisely might be a challenge, if even possible.

Guitar made of beech? It would look like a piece furniture

Ash wood maybe a graet option, but again, I can get easily only veeners up to 2mm and planks of more than 4,5mm.

jdowning - 3-31-2014 at 12:03 PM

For some reason I gave up on this thread way back in 2012. I had intended to continue with information on veneering the back of the Grobert guitar copy.

According to the museum notes on the original instrument the back is a laminate of a softwood (spruce?) and Brazilian rosewood veneer. This is not a good combination as plywood is stable only if odd numbers of laminate are used. This is not a problem when veneering furniture, boxes etc where any stresses induced by the application of the thin veneer (glue shrinkage) will have no effect on the substantial underlay. Less so for the relatively thin back of this guitar.

The method that I used 18years ago when making the instrument was to support the spruce back on a plywood board prior to veneering (with hot hide glue in the traditional way). The method used was reported in more detail in the attached FoMRHI article.
An alternative to hot hide glue would be synthetic PVA carpenter's glue. Both surfaces being coated with glue, allowed to dry and then ironed together with heat from a hot iron. Another modern method would be to use a contact adhesive - no heat or glue shrinkage to deal with.

Note that veneer has a smooth surface so little sanding is required for finishing. An oud bowl made from laminated ribs would , however, have to be made with 'flat' ribs (like a lute) and could not be sanded into a smooth outer surface as noted by Edward due to the thinnness of the veneer.

antekboodzik - 4-1-2014 at 02:40 PM

Great article, thank you a lot.

Well, so summarizing (correct me if I am wrong):

- what many people say about tonewoods, and some aspects of construction, velocity of sound in materials, is a BS

- selection of wood for back and sides of guitars and lute ribs has minor influence to the sound (regarding apropriate construction methods),
- more important is general overall of construction, e.g. differences between flamenco and classical guitar, than the particular wood selection,
- in past years solid backs and sides for guitars (citterns, opharions) were simply easier to execute, but some top makers invested time in cutting own veeners and laminating them for tonal qualities,
- nowadays, with powertools, "veeners" are much more available to buy or make, and laminated guitars can be equal in tone quality than guitars made traditional way, however making laminated parts is quite sophisticated work,
- lute ribs would present certain difficulties to be made laminated, but it is not impossible.

Another issue is, that I tried several times to "laminate" two pieces of 1,5mm maple veener, by applying some hot hide glue and putting some weight on it until dried. But no matter which orientation of grains, it ended in less or more saddle like shape...

jdowning - 4-2-2014 at 05:25 AM

Instrument acoustics is not a generally well understood science - there are so many variables involved - so there is some (but not all) unfounded opinion about this and that concerning instrument construction and material selection.

Velocity of sound in instrument woods is one viable quantitative measure that may be used to judge the acoustic property of wood as an aide to 'tonewood' selection.

The flat back of a conventional 'classical' acoustic guitar does contribute to acoustic performance as it acts as a secondary soundboard. So wood selection and construction of the back, in this case, might be expected to be of some significance acoustically? On the other hand a heavily braced thick back would be less responsive in this respect.

Mass produced instruments of the violin and guitar family have been made from plywood for years. They are relatively low cost instruments and - as far as I know - of relatively low acoustic performance. This does not, of course, mean that a hand made instrument made from wood laminates by an experienced luthier would not perform well.

As mentioned earlier in this thread, a stable laminate (one that will remain flat and not tend to curl up) should be made from three laminations (or a greater odd number) the grain direction of the central 'core' being at right angles to the grain direction of the outer laminates.

antekboodzik - 4-2-2014 at 02:36 PM

Mass produced guitars, even with acceptable quality (at least to my eyes) of solid top have often very crudely executed bracings (not well shaped several bars at right angles to the bridge), and, what is horrible, a bridge supported by two screws... I would once take a risk and replace a top on a badger guitar to see if there would be an improvement.

There is a legible tendency to make sides and backs of CG very heavy (often up to 1cm!). And Smallman's guitars - with frames, lattice bracing reinforced with carbon fibre, and laminated tops - do they are guitars (or wooden drums with strings)?

If good, concert quality instrument can be made with quite big variety of woods for back and sides, and also with combination of spruce and cedar tops, AND, what more, using lamiantions or not, do it really matters? See that there are inconsistient oppinions which wood works better with spruce top or a cedar one (on guitars).

Also, I think that classical/flamenco guitars (and somewhat ouds too) are evolving nowadays like no other instruments at all. It would probably never happen to the bowed instruments. I wonder, if ancient oud and lute makres could play today's instruments, they would say "hey, that's exactly what I was looking for all my luthiere carrer"

narciso - 4-23-2014 at 11:52 PM

I have experimented quite a lot with plywood for soundboards on various instruments, since getting hold of spruce properly quarter-sawn and toned seems to be the principal cost factor in any project

The omnipresent cheap 3mm poplar laminates actually give a surprisingly resonant soundboard in my experience, although a bit cardboard-y ... as one expects.

It is fine to use no bracing at all with plywood, the conventional wisdom being I suppose that the function of the bracing is to stabilize against cracks along the grain and to distribute the sound perpendicularly. Both these roles are inherent to the cross-grained laminate structure of typical plywoods
(somebody has probably pointed this out already somewhere or other in this thread)

As a curiosity, just for fun I have also found it possible to make a viable 1mm thick lute bowl using birch strips steam-separated from old birch plywood
A bit pointless admittedly, as good quality veneers are cheap and straightforward to obtain
At the time, I was teaching in a Venezuelan outback far from any hardware store !