First of all, The Concerti Armonici lack the typical contrasting setting of a few concertino players accompanied by the ripieno players. Although the first and second violin and the violoncello have the most soloistic parts, especially in Concerto III, they are not the obvious soloists throughout all the Concerti.
Secondly, the form and markings such as Da Capella follow the late 17th-century sonata di chiesa and sonata da camera traditions. He avoids symmetrical phrases or the ritornello-style of writing that we often see in concertos by Vivaldi and Valentini, in which the whole ensemble repeats a solo line.32
Furthermore, he uses the string instruments in an unconventional way by joining and seperating lines on unexpected moments, so that the music varies from being a three, four or five-partpiece. The melodies often meander through different parts, instead of being started and finished by the same instrument. Perhaps the idea to have four different violin parts could have derived from the concertos by Valentini and Vivaldi, but Van Wassenaer's writing for the third and fourth violin and the viola give the whole ensemble a colour that is different from their Italian style. Unlike his contemporary Willem de Fesch, Van Wassenaer was just a bit influenced by Vivaldi's music: Van Wassenaer's violin parts are less virtuosic in the sense that they do not have a lot of fast runs and jumps that can only be played on a violin. The melodies are written more vocally and are therefore closer to the style of Corelli but Van Wassenaer's use of harmony and dissonants resembles more late-baroque style.33 Nevertheless, De Fesch' twelve concertos op. 2 and op. 3 (Amsterdam, 1717) could have been an inspiration for Unico van Wassenaer, as they are a relatively early example of concerti grossi from the Netherlands.
Another interesting aspect of Van Wassenaer's music is his use of counterpoint and the way he constructs fuges, which both relate to the late 17th-century church and chamber sonata. This can also be an indication of some German influences such as Georg Muffat's concerti grossi from Außerlesener mit Ernst und Lust-gemengter Instrumental-Music. Although this music also clearly has a French influence that Van Wassenaer's Concerti Armonici lack,34 and it is uncertain if he knew Muffat's concerti, it could nevertheless explain his attention for the middle voices and his use of counterpoint.
Other concertos that Van Wassenaer probably knew are the concertos by Johann Christian Schickhardt (c. 1681 - c. 1762),35 Henrico Albicastro (c. 1660 - 1730)36 and Francesco Venturini (c. 1675 - 1745).37 Stylistically, there is also ressemblance with the Twelve Concerti Grossi op. 6 by Georg Friedrich Händel (1685 - 1759), but since the first publication was in 1739 (London, Walsh) it is not possible that Van Wassenaer used this piece as an example.
Although the VI Concerti Armonici seem to be Dutch concerti grossi, there are indications that the piece does not completely fit in that genre. Thus, the Concerti Armonici do not have the logical moments for a double bass to drop out or join in again, such as many concertos and concerti grossi do.