aja
Concerning acoustic guitars: Is solid wood really necessary/better?
If a tighter (closer) wood grain makes for a better sound due to increased rigidity, then surely a ply/bonded wood would be even better because of the even higher rigidity? The same goes for older wood - dried out so more rigid, right? Keira will attest to the fact that she has found amazing tone in some entry level guitars with almost no solid wood on them at all.
Surely, from a materials engineering perspective, a ply wood is better because the luthier has much more control over the characteristics of the material, especially concerning its consistency. Take for example Takamine - almost every one of their guitars has bonded sides and most have bonded backs. Very few have solid backs. Surely a manufacturer of such high standing will get their ducks, erm, woodpeckers in a row and make sure that solid wood is not always the best way forward for certain parts?
This comes back to the age old question of what sound is a good sound. To me the most important things are:
1. Flatness of frequency response - not too bright, not too boomy.
2. Overtones and general complexity of tone
3. Sustain
As far as my engineering minded brain is concerned, all three of these factors are limited, or enhanced, by the design of the guitar and choice of materials. Furthermore, if I were a luthier, I would choose a material and modify the design accordingly, not the other way around. But that would take many many hours of scientific research since resonance chambers and vibration theory are complex to say the least. So, if you were to stick with the generally accepted guitar designs available today, you have to modify the materials you use in order to get the right characteristics you need to get the sound you want. So ply wood is an option, yes?
EDIT: this is just my mind digitally doodling - tell me if I'm on the wrong track here! ?
Gearhead
I do not think plywood is full of advantages, especially for tops.
To me in an acoustic there are parts that are mostly meant to transfer vibration and parts that are mostly there for structural reasons. You want the vibrating parts to resonate with the strings and the structural parts to selectively absorb some vibrations. The way I look at it is that in reality the vibrant parts also absorb and the structural parts also vibrate and that the overall balance of those will determine the character of the guitar.
Now for vibrant parts, it is important that the speed of sound is consistent through the material. If it is not, sound waves will scatter and the resonance is hampered. A solid wood has the edge here: the speed of sound, although not the same in every direction, is as consistent as the grain density in the wood. A joint perfectly perpendicular to the wave front should not disturb the vibration, but strength wise this is worst case. All joints between the nut and the bridge will have their own scatter effect. Especially the top, with its complicated vibration pattern, will be affected by the joints in and around it. The back and sides may not be affected the same way, in fact they might even benefit depending on the absorption that results from the joints.....
zohn
Grading of tone wood is based upon evenness of the grain and colour, tightness of the grain and most important minimum grain run-out and perfect quartering. To find a board with all those qualities is rare, and thus the reason why they are in demand for more expensive instruments - these are typically classified as AAAA or "master-grade", and very expensive.
Fact is though that wider grained billets often yield stiffer boards along and across the grain than the "perfect" ones. Jean Larrivee, Dana Bourgeois and Del Langejans are builders known to prefer the stiffness and "organic" appearance of wider grained, multi-coloured tops.
If you imagine a bunch of straws laid out and stacked on top of each other in multiple layers, that is in essence what a piece of wood or a soundboard's structure looks like, with all the straws bonded together . Vibration is transmitted across the walls to the surrounding ones and along the length of the "tubes" or grain. The more these walls are allowed to vibrate freely, the better it will resonate. I believe that the top is the primary and most important part of a guitar. Bracing and the rest of the body is constructed to assist or dampen the top to vibrate in a pre-determined way to produce a sound that is pleasing to the human ear. Cross ply construction inhibits the free movement of the wood grain significantly.
As Gearhead explained the sides-construction holds the whole system together, and allows the top to vibrate, while the back also reflects sound towards the sound hole. It is however not only the sound hole that "releases" the sound, but in fact the vibration of the whole soundboard.
Laminates do in fact add strength to the sides because the layers are glued in a cross-grain fashion. It provides "bullet-proof" tenacity and is mainly the reason why the best guitar cases are constructed from it and not guitar tops.
Greg Smallman's guitar bodies (back and sides) are all laminates constructed to support a very resonant lattice braced top - John Williams plays his guitars.
Del Langejans uses solid sides, but almost twice as thick as the top to provide a rigid structure for the body.
Mervyn Davis' Smoothtalkers are also solid, but with very thick rims. Other brands like Martin "brace" their solid sides to provide a strong and stiff structure, in contradiction to the belief it is done to prevent cracking, although it does that as well..
EDIT - a very clever title to this thread Aja - I like it!!
Wizard
Maybe the one that works is just the one that works ... and mankind is still trying to figure out the mystery?
