Most frequencies below 30hz are not really that audible. But, when they are present you will feel them. Those subwoofers that can go below 20hz will not be audible at those frequencies, but you will feel their presence. That is what a great subwoofer is about. Many larger church and cathedral pipe organs can reach down to about 16hz or a little lower. That is why you feel the bass in going through your body, but you don't hear it. I learned this over the years when I was involved with some church music committees.