Just to clarify, every ported enclosure (whether prefab or not) has a tuning frequency. This is its inherent nature. Just like a beer bottle will hum at a specific frequency depending on how full it is. That is its "tuning frequency" or resonant frequency. Most prefab enclosures are tuned very high, have very little port area, and have very little airspace as their main concern is space saving and not output.
There is more to getting the best sound than just throwing your sub in some arbitrary enclosure tuned to some random frequency you have heard other people mention. But even if you do throw it into a random enclosure that fits "recommended" tuning and size, it will sound leaps and bounds better than prefab garbage.