593aac@houxa.UUCP (S.JOHNSON) (10/29/85)
Loudspeaker sensitivity is typically determined by the mid-band sensitivity of the woofer, which is independent of enclosure choice if a direct radiator design is used (horns excluded). The efficiency is usually highest with large magnets and light cones. The tweeter and mid are usually chosen to be slightly more sensitive than the woofer, and padded down to match. It is true that there is a trade off at the low end between enclosure size, efficiency, and bass extension, however, once a driver is chosen the efficiency is fixed. For example, if the box size and magnet structure are known, you can use a heavy cone ( low resonant frequency and efficiency) or a light cone ( high resonant frequency and efficiency). This example ignores suspension compliance, but in many cases, the stiffness of the air in the enclosure dominates. I haven't the quoted formula to determine whether a driver is better in a closed or a sealed box. You can use Thiele/Small to predict the performance for each case. Generally, I look for a fairly low QTS for ported designs, otherwise the volume of the box is huge. I have built ported designs with drivers with QTS values of .29 to .4. If QTS is larger than .4, I would stick with a closed box.