if it is one of the older immortals.. they are impressive IMO.. I have 2 of the older 15s.. and haven't had any issues really.. threw my 2400 watt concept amp at one all day for over a year.. finally the sub popped on me but FI is reconing it for me.. and I got a steal on it in the first place.. they get loud but the sound quality isn't great.. i hit 143.9 with ONE off of 2400 watts in the trunk of my civic..
depends on what your looking for and/or how much u have to spend.. i got both of mine for cheaper than what you can buy one NEW on egay for..