| 摘要 |
<p>A sounder is disclosed which has walling (36, 38) defining a first air column (26) leading to a first sound aperture (34) through which the first column opens to atmosphere, and walling (40, 44) defining a second air column (60) leading to a second sound aperture (64) through which the second column opens to atmosphere. A diaphragm (16) is between the air columns and means are provided for causing said diaphragm to vibrate.</p> |
