No. It depends on the amp. Some amps can run at lower ohms. Some amps are stable at 1 ohm, some at two ohms, and others at 4 ohms. For example, a long time ago when i had a punch 150, two 8 ohm subs were ideal for that amp. Bridged they ran at 4 ohms, and thats as low as you could go on that amp. If you bridged two 4 ohm subs on it,2 ohms total, the amp would not have handled it. It would have run hot, clipped off, blown fuses, etc.