What makes Coptic hymns with the use of the triangle and cymbals unique compared to other Christian hymns?
Coptic hymns are prayers and praises that are chanted. The focus is on praising God wholeheartedly. Cymbals and triangles are used to keep the pace of the tunes.
It is not known exactly when the cymbals and triangles were introduced into the church but they are used to keep the pace of the tunes. In the early days, musical instruments were frowned upon by the church and many early church fathers wrote injunctions forbidding their use. Yet some early church fathers such as Clement of Alexandria, Origen, St. Athanasius I, and St. Cyril I tolerated certain instruments such as the cymbals because King David's use of them and the spiritual qualities to the sound of certain instruments. Origen stated that " the cymbals expressing the eager soul enamored of Christ."
The cymbals date back to the Old Testament and is mentions in the New Testament in 1 Corinthians 13:1. In the Old Testament, the cymbals is confined to religious ceremonies such as bringing back the ark of the covenant of the Lord (1 Chronicle 15:16,19,28), at the dedication of Solomon's temple (2 Chronicle 5:13), at the restoration of worship by Hezekiah (2 Chronicles 29.25), at the laying of the foundation of the second temple (Ezra 3:10), and the dedication of the wall of Jerusalem (Nehemiah 12:27).
In Psalm 150 two types of cymbals are pointed out: "Praise him with the clash of cymbals, praise him with resounding cymbals." The "clashing cymbals were of a larger diameter than the "resounding" cymbals, and were two-handed cymbals. The resounding cymbals were much smaller and were played by one hand—the cymbals being attached to the thumb and the middle finger.
In the time of David and Solomon, much stress was laid on the cymbal and percussive instruments. The chief singer of David, Asaph, was a cymbal player (1 Chronicle 16:5). However, in the last century of the second temple the percussive instruments were restricted to one cymbal, which was used to mark pauses only, not to be played while the singing and the playing were going on.
Today, two percussion instruments are used in the rites of many of the Coptic churches: the small hand cymbals and the metal triangle each played by one of the deacons and/or the cantor. Providing a rhythmic accompaniment to specified hymns and responses sung by the choir and/or congregation, they signal the congregation to participate and unify the singing.
"I will praise You, O Lord my God, with all my heart, ?And I will glorify Your name forevermore" (Psalm 86:12).
Atiya, Aziz S. (ed.), The Coptic Encyclopedia, vol. 6, (New York: Macmillan Publishing, 1991), p. 1738-1741.