  We present experimental and theoretical results on an acoustic metamaterial
that exhibits negative effective modulus in a frequency range from 0 to 450 Hz.
One-dimensional acoustic metamaterial with an array of side holes on a tube was
fabricated. We observed that acoustic waves above 450 Hz propagated well in
this structure, but no sound below 450 Hz passed through. The frequency
characteristics of the metamaterial has the same form as that of the
permittivity in metals due to the plasma oscillation. We also provide a theory
to explain the experimental results.
