| Flick, well done. this pic i allmost identical to my cones, the most critical section is the inner side ie; say you bore the 20 mm hole straight through inner to outer, what you must do to eleiviate the unwanted backpressure is to machine a progressive tapper to the inner side starting at 30mm and tapper down 35 degrees to meet the 20mm outer. by doing this will only assist in less power loss not noise volume. |