Sealed versus Vented boxes for four #269-469 (69 cent wonder) drivers:
Predicted low-end response (anechoic).  Red is vented and orange is sealed.  The vented response is ideal for center channel duty as standard Dolby Digital setup cuts off center channel frequencies below 80Hz anyway.
Note:  the SPLs to the left are for single driver response.  The four driver response is 95dB/watt/meter.  The box dimensions are correct for four drivers.
Center Channel Usage