hey guys i need ur help. My friend has recently purchased 2 alpine type r swr1221d subwoofers and needs to make a box. They each have 330watts rms and 1000 watts peak. Not sure if they are spl or sq...... but do know they are recommended for a sealed box with .7- 1 cubic feet each. If he is to make just one sealed box, does that mean he needs to have 2 cubic feet. Thanks in advance.