1 XL â or EXL, Exploration Licence (United Kingdom), a type of onshore licence issued between the First Onshore Licensing Round (1986) and the Sixth (1992). 2  Xln â Crystalline (minerals). 3  XLPE-Cross-linked Polyethylene. 4  XMAC â Cross-Multipole Array Acoustic log.
When the frequency approaches 120 CPM (2 Hz), occupants perceive the ride as harsh. Consequently, the suspension of the average family sedan will have a natural frequency of about 60 to 90 CPM. A high-performance sports car will have a stiffer suspension with a natural frequency of about 120 to 150 CPM (2 to 2.5 Hz). Originally, human sensitivity to ride frequency was believed to be associated with the natural oscillations of an adult human body during a walking gait.
As many have stated they vary from 400 -1000 rpm , a lot varies on engine design , true they can idle lower , but the engine runs rougher, many older cars that did not have auto trans an power steering ,an AC , which of course had small 35 amp alt, would idle in the 400 rpm range ,most of the big truck eng use to idle in the 450 - 600 rpm range ,older cars with carbs use to use a step up solenoid that adj the idle do to engine demand, ie the AC cycling on an off , putting the car in gear ...