主题：箱体的QA，QB，QL解释

where Q_L is the “leakage Q”, considered as a parameter of the driver.  In the 1961 paper, Thiele calculated a
similar parameter Q_B, the “box Q”, as a parameter of the box.  When Small showed later that such leakage
losses were much greater in the driver than those in the box, so much so that they could be virtually ignored,
he still called the changed parameter Q_B initially, but later called it Q_L. Thus in the expression above, Q_L is the
loss parameter for the driver, as calculated below. If Q_L is not known, it may be taken as 7 without too much
error.