  A soundproof window or wall which is transparent to airflow is presented. The
design is based on two wave theories of diffraction and acoustic metamaterials.
It consists of a three-dimensional array of strong diffraction-type resonators
with many holes centered at each individual resonator. The acoustic performance
levels of two soundproof windows with air holes of $20mm$ and $50mm$ diameters
were measured. Sound waves of 80dB in the frequency range of $400 - 5,000Hz$
were applied to the windows. It was observed that the sound level was reduced
by about $30 - 35$dB in the above frequency range with the $20mm$ window and by
about $20 - 35$dB in the frequency range of $700 - 2,200Hz$ with the $50mm$
window.
  It is an extraordinary acoustic anti-transmission. The geometric factors
which produced the effective negative modulus were obtained.
