what are the characteristics of rosewood in terms of tonal quality?
how about sapele? i'm not too familiar with this type of wood. 
Maxi, here's something from my compilations of tonewood info....
re: Rosewoods (genus DALBERGIA) -Brazilian, Cocobolo, Honduran, Madagascar, Bolivian (Pau Ferro), Panama, Amazon, Bubinga, Camatillo, and a most recently introduced South East Asian Rosewood (Dalbergia Bariensis)....almost forgot the most availble - East Indian.
Dalbergia is reported to be a large genus, consisting of about 300 species of trees,
Remember the term - "Q factor" for tonewoods...Brazilian is reputed to have the highest "Q". I have been told by US luthiers that Cocobolo has an even higher 'Q' than Brazilian....here....
1) ROSEWOOD (genus Dalbergia)
Rosewoods are more consistent from sample to sample than spruces and cedars and one piece is much more like another in behavior, if not appearance. Of the rosewoods used in guitarmaking, Brazilian rosewood has traditionally been the best wood of choice. This is partly due to tradition and partly due to its phenomenal "Q", which makes it a very acoustically active material. When struck, a properly cut sample rings like a plate of glass. This quality contributes to sustain and projection in a guitar, because those are the chief functions of the back. Sustain, because it rings a long time; and projection, because the back’s movement can be coupled in vibrating activity to the movements of the face, boosting the directional power of the activity of the guitar. Because of its high "Q", Brazilian rosewood is both vitreous and brittle, and therefore prone to cracking and checking. East Indian rosewood, the alternate wood of choice, is comparable to Brazilian rosewood but simply not as beautiful nor as "live", by a factor of some 10% to 20%. This is not a huge difference, and there are plenty of excellent sounding East Indian rosewood guitars around. Also, East Indian rosewood is an attractive choice because it is much less prone to cracking and therefore generally less problematic to work with. Other rosewood-like woods which have a high "Q" are wenge and padauk (both of which crack very easily) and certain Asian and Central American rosewoods, which do not have the beauty of Brazilian or East Indian. While I haven’t worked with all these woods I’d expect them all to be brittle in direct proportion to their liveness and be prone to the same mechanical failures. Removing their brittleness would in fact remove the factor that is responsible for their characteristic tone.
2) MAHOGANY AND KOA (Sapele is a Mahogany which I believe comes from South American, while Koa is in the Acacia family, the Philippine Acacia could be what they call Black Acacia, check with our Forestry Bureau)
Mahoganies and koas are very variable in physical properties. That is, whereas one piece of rosewood is much like another in this regard, these woods range from light to dense, and stiff to loose, while all looking the same. Accordingly, they will behave differently as tonewoods as they exhibit different degrees of "Q" and a guitar’s sound will be colored by the specific selection of koa or mahogany used. The denser and more brittle the wood, the more it will ring; the lighter and looser the wood is, the more it will be an acoustically passive part of the guitar. Heavy koa, mahogany and walnut are all comparable in their tone. Everything else being equal, it is generally recognized that mahogany and koa will produce a "warmer" sound in a guitar than the more brittle rosewoods can.
