Seeing as he asked me this same question the other day, I think I know what he's getting at. First off, he's referring to flat top, steel string guitars. Secondly, he means the soundboard/top of the instrument. Thirdly, he's looking at it from the point of view of recording - in other words, which woods will give a brighter sound, better volume, etc...
I'd imagine it gets complicated, though, especially when you factor in things like body size/shape, bracing patterns, etc.
Ok I'll try and deal with that one first.
Keep in mind ALL this is dependant on just about everything else on the instrument, body size, back and side wood, neck timber, bracing style, soundhole size and placement (as mentioned), bridge size mass and timber, strings, the list goes on.
All things being equal then we can make some observations but first more caveats. As I've often said no two pieces of timber are the same even two pieces cut from a lump of wood that are right next to each other in the billit. Timber is an anistropic material, it's properties vary in all directions and are as unique as a fingerprint. One good way to look at it is that a specific timber species will have properties within a range and the resulting sound characteristics will form a spectrum. Its that spectrum that we can examine and use to our advantage when shooting for a certain sound.
The most common belly timbers used historically throughout history and today would be spruce, cedar, and to a smaller degree, cyprus and willow. Not used much these days on acoustics, but used for early fiddles and harp soundboards. I'll break down the different types within this classification in a bit but first why choose from a limited range of timbers and why don't we use others?
Acoustically the top has to have good strength to weight ratiois, or more correctly stiffness to mass ratio. We need a top that is fairly light so that the limited energy in the string can be efficiently used. That energy has to move the top and a lighter top needs less energy to start vibrating and less to change the frequency at which it vibrates. It also has to be fairly rigid to avoid collapsing. Bracing helps both these things and also contributes greatly to the way sound moves around the soundboard.
Sound waves in spruce for example travel faster and more effectively than many other timbers but only along the grain. It doesn't propagate well across the grain. Bracing helps overcome this as well. Spruce and cedar have proved to be excellent for the task.
OK onto types of spruce, but first a note on talking about timber. It is always best to describe timber in terms of it's botanical classification if you want to be specific. For the purpose of this debate I'll just deal with the common names we use. If I'm ordering any timber I'll qualify it with a botanical name, the same timber can have different names in different countries and the same name can be used in different countries.
Commonly three types of spruce are used in instrument construction. European, German, Italian, Carpathian, Swiss spruce all the same but grown in different regions (picea abies), Englemann spruce (Picea engelmannii) and Sitka spruce (Picea sitchensis). Both the latter are also grown in many regions but don't have quite the same range of confusing names. The quality and suitability do vary though as with all of them.
Cedar (Cedrus) is kind of cedar, and cyprus is also a cedar. You don't have the same range of cedars used. Cedar is closely related to the picea or spruce family.
So finally what do the sound like?
The most prized for years would be the European, it's that that started the whole thing off Strad used it and it's the most expensive today. Of them all it has a rich well rounded sound that is full and DOES improve with age. It is what all others are measured against. If you look at most handmade guitars from respected luthiers that would be the top of the range in most cases. Talking tone is hard but to my ears it is full, rich and almost bell like with good separation and projects excellently. We shall use it as the bench mark.
Engelmann has a good deep sound as well a bit less seperation but full none the less and sometimes lacking in highs. Commonly it does not improve with age, (neither does Sitka or cedar. Some say it does, trust me they don't, the sound you have once it's settled in is what you get).
Sitka spruce is the brightest and punchiest of the three with a good seperation and mid and top end. If anything it lacks at the low end and can be a little unresponsive to a light touch.
Cedar is the mellow one of the bunch. Many people pass it by as a poor mans timber. It doesn't have the punch and bite of the spruces but it makes an excellent instrument, especially for those Irish bazoukis, mandolas etc. Also good for shorter scale 12 fret guitars. They can be really sweet. The sound as a whole is mellow and even and it doesn't have the dynamic of the spruces.
I hate describing tone of timbers you need to get out and listen to a LOT of these woods to get the idea that it is both a tonal spectrum and you can't pigeon hole them and also to understand that there is so much else going on that it is hard to pin it down to one thing. You can get a feel for it the more you listen to them though. It's a bit like fine Scotch. The first time you taste it you think "yeh it's a whiskey", its not until you have experience and develop a palette that the subtle side of each comes out. At the end of the day though it is still a whiskey and no better or worse than an Irish or a Bourbon. Just different.
Did I mention this is all only general and it depends on everything else as well.
Pick the bones out of that.
