We fabricated an acoustic composite structure consisting of a periodic array of interspaced membranes and side holes. Experimental data on the transmission, effective density, and phase velocity are presented. The system exhibits two critical frequencies, ${\omega }_{\mathrm{SH}}$ and ${\omega }_c$. Our metamaterial is double negative and transparent for frequencies lower than ${\omega }_{\mathrm{SH}}$. For the frequencies ${\omega }_{\mathrm{SH}}<\omega <{\omega }_c$, the medium is opaque and only the density is negative. For the frequencies above ${\omega }_c$, the system is double positive and transparent. The present medium exhibits a very wide double negative spectral range that opens the possibility of the application of metamaterials for “white lights.”

• Received 8 February 2009

DOI:https://doi.org/10.1103/PhysRevLett.104.054301