In the process you raise the resonant frequency of the tap tone. Top wood, which is quite absorbent, will noticeably stiffen when treated by a number of materials. In so treating, the transverse velocity of sound will more nearly match the longitudinal. Norman has found lacquers and thin solutions of reasonably stiff resins to be effective, and make a great deal of difference in the finished instrument. The radiated sound field of an instrument is extremely complex.
Many players erroneously believe that most of the sound of an instrument comes out of the f holes.
Actually, just as much sound radiates from the back as from the top. Obviously the player does not have the same perspective on the sound he is producing as a listener would have. The player hears mainly the sound from the top. The complex sound field of a violin is not the same close to the top as it is say two feet or 50 feet away. This is why players cannot always judge what their instruments sound like.