  We fabricated a double negative acoustic metamaterial which consisted of
Helmholtz resonators and membranes. Experimental data on the transmission and
dispersion relation are presented. The system exhibits three frequencies where
the acoustic state makes sharp transitions from density negative ({\rho} -NG)
to double negative (DNG), modulus negative (B-NG), and double positive (DPS) in
sequence with the frequency. We observed a wide range of negative refractive
index from -0.06 to -3.7 relative to air, which will allow for new acoustic
transformation techniques.
