A cappella
The popularization of the Jewish chant may be found in the writings of the Jewish philosopher Philo, born 20 BCE. Weaving together Jewish and Greek thought, Philo promoted praise without instruments, and taught that "silent singing" (without even vocal chords) was better still. This view parted with the Jewish scriptures, where Israel offered praise with instruments by God's own command (2 Chronicles 29:25). The shofar is the only temple instrument still being used today in the synagogue, and it is only used from Rosh Chodesh Elul through the end of Yom Kippur. The shofar is used by itself, without any vocal accompaniment, and is limited to a very strictly defined set of sounds and specific places in the synagogue service.

Q: What is the one instrument still in use today by the synagogue?
shofar