New PC sound system & Box size for 12" sub

There are loads of factors to consider when fabricating a box or cabinet for a subwoofer. You will need to learn lots about how a driver operates in various types of boxes. Or you can build a cabinet based on a template created online.
- http/homepage.ntlworld.com/intrelude/sub/boxtheory.htm
- http/www.bcae1.com/spboxnew2.htm
- http/www.freespeakerplans.com
- http/www.danmarx.org/audioinnovation/theories.html

** HEAVY theory regarding loudspeaker parameters, Thiele-Small Specs**
- http/www.loudspeakersplus.com/speaker_parameters.html


The amplifier you need must be chosen knowing certain key specs of the subwoofers you own. Namely the impedance, either 4 or 8 Ohms, and the speaker wattage. If possible, try to find the "RMS" wattage of the driver. That will be the actual wattage of the subwoofer, but is sometimes exaggerated by manufacturers. If you post the subwoofers make and model, we can help make a suggestion.

Can I ask why you want studio monitors? Are you producing or editing audio or music? Typically reference monitors reproduce very "flat" sound. Studio reference monitors may not be ideal in a home for playing back game audio, movies or music in a home setting. And given your budget, you have priced yourself out of any descent studio monitors. However, entry level studio monitors are available, such as the very popular Alesis Monitor One MKII passive studio monitors here:
- http/amzn.com/B0002A2RTU

Consider abandoning the desktop amp/speaker setup for active speakers. Active or "self-powered" speakers have an amplifier built-in to the speaker cabinet.