Back in the 80's, I had signal generator access and rooms full of brand new speakers for play-time fun. I discovered that I liked two-way bookshelf speakers that could produce a clean 40hz, but that was asking a lot. Fifty hertz was more like it for those type speakers, which by-and-large were... well, larger than many of that genre today. These days I expect to hear a clean 30 from my floor-standers, and even though I use dual subwoofers, they are compact in size and don't go appreciably deeper than 30. However, if 40 is good, I'm satisfied. I know some of you need to get down more deeply to really satisfy your ear-bone (maybe sternum, too). Especially you pipe-organ lovers. So how low do you need it to go?