mijostyn
You have to forget about fundamentals. Things like the thumb striking low E produce a thump that is below the fundamental. Percussion will do this also.Huh? Unlike harmonics ("overtones") that occur naturally in music and nature, undertones generally do not. You've previously noted that your audio system requires a subsonic filter to avoid your woofers "flapping," so once again I suggest you examine what is going on there that is amiss.