The snare drum is a two-headed drum, as is the bass drum and other orchestral and band drums used in Western music. On the snare drum, eight to ten wire-bound gut strings, or snares, usually are stretched across the lower of the two heads; they vibrate against the heads as the membranes are struck.
The two membranes of the snare drum are acoustically coupled to each other, particularly at the low frequencies. This coupling via the enclosed air acts to double the modes. The lower frequency member of the mode pair involves both heads moving in the same direction and for the higher mode they move oppositely.