Difference in source strength?

As long as it's not clipping or exceeding the power rating of your speakers, turn it up.  Some CDs (especially those made from older source material that was originally recorded with the old RIAA curve for vinyl) are recorded at lower levels than are newer ones.  I've seen as much as -10db from one CD to the next.  Same with the radio, broadcast is usually about -3db down from 0.  Just be sure when you jump out of your seat you don't cause an accident! Support the12volt.com

Different levels of recording on CD's is frustrating, and the lower level of volume and quality with FM is a pain, too.  The only thing that you have to make sure you do is play the CD with the highest dynamic recording to find the limits of the HU volume, and then set the gain for your amplifier to match that.  This will keep the system out of danger of clipping.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

most of the older stuff that is now on cd was remastered to be put on disc and still has a slight tape sound and it was processed with a noise filter,and it sounds lower than the new ones.if i can't make it sound good,then it is just a piece of crap anyway

You've just witness first hand the loudness war that has gone on in CD mastering for the past 15 years or so. When CDs were originally conceived, the average level was supposed to stay around -20dB, and thus you'd have 20dB headroom for peaks, resulting in a very clean and dynamic sound (once you turn the volume control up to compensate.) Nowadays, CDs are compressed to hell and back, and recorded as loud as the medium possibly can hold, and further still (clipping). There's a good web page on this here: http://www.loudnessrace.net/ Interestingly, Radio stations have been in similar loudness wars for even longer (40 years?) and this is why FM radio sounds like it does (like a cheap boombox turned up too loud).. It's generally worse in major markets - if you take a road trip to the boondocks somewhere, and tune in the local country station, you'll probably be surprised at how good FM can sound (once you get past the fact that you're listening to country!) That aside, turning up the volume control while playing a "quietly recorded" CD will absolutely NOT damage anything. However, switching to a loud CD without adjusting the volume (and blasting yourself out of the seat) COULD damage both equipment and ears. ///Leif