It’s not Qts, the figure that determines a drivers enclosure characteristic is the EBP (efficiency bandwidth product). The EBP is calculated by dividing the Fs by the Qes.
As the books generally go, 0-50 is sealed enclosure territory, 50-100 is okay for either and over 100 is strictly ported.
edit: Well leave it to M5 to jump in whilst I was held up finishing my post to make me look foolish...