So you want to test your subwoofer to see how deep it goes, but you don’t have a room analyzer. No problem!
Use a test track like the ones below and watch the response numbers. Most unexceptional subwoofers really start to fade around 30-40 hertz, in some cases almost becoming silent under 30. Be careful, if you run this test it can damage subwoofers that are not meant to handle sub 40 hertz sound, and even those that are if you turn it up too high. You may also hear chuffing, rattles, or other undesirable noises.
The subwoofers on The List are relatively free of such problems, and the coolest thing is that you can hear a clear difference from something on the list vs a $300 subwoofer you would typically find in a big electronics store.