Building a Subwoofer

Eldulcesol's suggestion is an excellent one. I sometimes use an NAD 2600A as a subwoofer amplifier with good result. This was their biggest amplifier of that iteration of the Monitor Series. 150 wpc continuous, rated extremely conservatively with the NAD Power Envelope that had either 4 or 6(?) of headroom. I have driven any speaker I have thrown at it, and in the late 80's, there were some extremely difficult loudspeaker loads out there.

The best thing about these are the low cost you can find them for, often under $200. And, if you ever want to use it as a full range amp, it makes very good sound.

Slappy, first off, GOOD LUCK!

You shouldn't have as much trouble as a lot of people will try and tell you.

Second, I am not so hot on using a car subwoofer for a driver, Infinity or otherwise. These drivers are normally 4 ohms, which may or may not be what you are looking for. They tend to appeal to a different sensibility, and often focus their performance in the 60 - 200 Hz band(mid and upper bass), which is at odds with the audiophile goal of producing low bass, under 60 Hz.

These drivers will make you happy if you are looking for what most people consider "good bass". Booming, shaking, mid and upper bass. As my friend Michael here likes to say, they rattle the guy three cars back. The box alignments they drivers are placed in, and are optimized for, play right into all of this.

Honestly, if you are looking for a pair of stereo subs which will produce clean, articulate bass, you can definitely do this project. You only need to do a little homework. Drivers from Madisound, Zalytron, Peerless, and Vifa are great for a vented box, and will fit well into your budget. Audio Concepts specializes in sealed box drivers, and are also a good move.

I would suggest that you find out whether your preference lies with the sonics of sealed or vented boxes, as there is a personal preference in most of us.

Other than that, look for a decent pair of plate amplifiers.

Since you are doing the cabinet work, it will cost not a whole lot beyond your own time and patience. 4' X 8' sheets of MDF and glue are certainly cheap enough.