Each one is unique.
It is important to know that no two trees are the same, each one is unique in its species, and although it is two trees belonging to it, the climate, diseases, age, the subsequent process of sawing and drying will define the face and the sound of it.
Wood cutting is a delicate process. It will define the direction of the veins and the drawing that will later be formed on the instrument. The veins are supposed to be straight, parallel and knotless, always as far as possible. This would be the ideal in the case of the soundboard, but in the case of the back and the sides we are often in the opposite situation.
The most expensive guitars tend to have very irregular and beautiful patterns. It would be very good if today’s guitarist understood that these drawings usually have more to do with aesthetics than with sound. In fact, only experts can tell by ear the difference between a Brazilian rosewood guitar and an Indian rosewood guitar.
Cedar vs Spruce
Soundboards are made of cedar or spruce.
It seems that the red cedar brings together better characteristics than the other to build a soundboard. Its weight is 320-430 Kg / m3 and the speed of transmission of sound waves in the direction of the grain is approximately 4100m / s.
Cedar is a very grateful wood when working with it, it does not present drying problems, it is more flexible and the grains are straighter, more parallel and more abundant.
Acoustically speaking, the results are usually quite good from the start.
In their eagerness to achieve generous bass, some Luthiers when thickening the wood, thin it too much, giving it very low profiles. This soundboard vibrates well from the beginning, and the instrument usually has enough sound power, but a few years later the guitar usually falls apart, presenting symptoms of acoustic exhaustion. It becomes deaf.
If we took a sample from this wood and looked at it through a microscope, we would see that the crystallized resin (during the drying process) found in the pores of the wood, is invoiced and ground.
The excessive vibration of the soundboard has broken its own crystal structure.
It should be mentioned that spruce is not exempt from this danger, but this is much less. Given these characteristics, many Luthiers choose to leave the cedar tops thicker, but this practice sometimes has very high acoustic costs, the bass is lost and the mid register is weak.
Anyway, cedar is a great wood and good guitar makers know very well how to take advantage of it.
The Spruce has a weight between 400-500kg / m3 and transmits the sound wave at approximately 3600 m / s in the direction of the grain. It is preceded by the reputation that its sound improves over time and that it cracks more easily due to its hardness. We can often find guitars whose spruce top is cracked in the central area.
This is due to excessive thinning when profiling the wood by the Luthiers, a sudden change in temperature or humidity. This wood is whiter and the grains are as parallel as in cedar. Since the soundboard is made of two pieces, the problem of symmetry between the rings is solved by leaving the narrower rings in the center. And this is what the guitarist often looks at when testing a guitar.
No two trees are the same and as we can see, the two types of woods have their pros and cons.