If you connect a subwoofer without an amplifier, the subwoofer will not produce any sound. The subwoofer relies on the amplifier to provide it with power, so without an amplifier, thesubwoofer will not be able to function. This is why it is important to make sure that you have an amplifier when you are setting up your audio system. If you are using a home theater receiver, then this will typically have an amp built-in, so you won't need to worry about buying one separately. However, if you are using a separate stereo receiver, then you will need to purchase an amp in order to power your subwoofer.