06-18-12: Suteetat
Drew, thanks for your information. I certainly don't disagree that giving bass extension can help to improve midbass performance as well. However, I don't think that it would answer my question regarding playing music that contains fundamentals that are only 50Hz or above as to what kind of sound, information or contents those recording contains that are below 50Hz?
You make a good point that if speakers are strong, linear, and honest down to 40 Hz (not 50--it's just not low enough), you are going to hear most of the music and the system will come across as having excellent bass. However, a great number of speakers actually start rolling off around 100 Hz and have pooped out around 50-60 Hz and they are definitely missing something. Even augmenting such a system with a sub that itself rolls off at 36 Hz will make a positive and noticeable difference.
Furthermore, not all kick drums' fundamental tone is around 50 Hz; it depends on the drum size and the tuning. My vintage Slingerland 14"x22" has a lower thump than that, and many kick drums today are much larger, like 20"x24". Even the fundamental on a snare drum can provide a workout for a good woofer.
Another thing: the low E of a 4-string electric bass is around 42Hz, but many rock/pop bass players use a 5-string, whose lowest note is about 32 Hz. It's just one whole note above the bottom A of a standard piano. If you have a system that's truly flat to 40 Hz it'll sound strong on rock and pop, but if it's flat to 30 Hz you'll hear the difference on many recordings, especially later ones.