There are test discs with consecutive tracks with different test tone frequencies that go all the way down to 20Hz. Get one and see where you start to detect a falloff in output. More scientifically, you could see how they do with a SPL meter. All that being said, yes, a ruler flat response all the way down to 20Hz, while also being very, very unlikely, may also not sound "realistic", whatever that means.
Diagnosing inadequate bass in an audio system.
If you feel you have inadequate bass output from your audio system -
1) How do you confirm/quantify your suspicion aka what you think you hear as a problem?
2) How do you go about diagnosing the source of the problem, and how best to fix it?
Assume a CD source, DAC, preamp, power amplifier and floor-standing speakers.
Thanks,
Amit