[Levaix]

I'm not sure if this is a newbie question, but I couldn't easily find it. Headphones have a listed frequency response, and so do source components. However, generally speaking it seems as if most source components do not have the same range as top quality headphones. Just an example, my Ultrasone Signature Pro's are rated at 8Hz-42kHz. However, my Aune T1 is rated for 20Hz-20kHz. Does that mean I'm missing the entire range that the Ultrasones are theoretically capable of? And I understand that the Aune is not flagship material. But even something like the WA7 is rated for "only" 11Hz-27kHz. (It also looks like frequency response is sometimes different between the amp and DAC portions of a device, eg. FiiO E17.)
 
So I guess my question is, is that going to be noticeable? Am I reading this right as many source components aren't driving some headphones to their full potential? Or are these numbers only a minor part of the overall picture? In other words, is this something to be concerned about?

 

[NA Blur]

The numerical report of the frequency response is not entirely telling.  Some companies report the frequency response where the gear is above a specified dB level while others report where they tested it.  I typically look at anyone listing 20Hz - 20kHz as an untested listing.
 
In many cases most gear extends pretty well to both sides of the frequency spectrum.  Many amps have a hard time with the really low bass say frequencies below 50Hz.
Take a look here for more detail:
http://www.innerfidelity.com/images/AllAmpGraphs.pdf
 
The frequency response of a headphone, without some sort of HTF ( Head Transfer Function ) really does not tell the whole story as to how a headphone may sound.
 
This is partially why so many of us want vendors to actually supply their measurements with their gear.  Take Audeze for example.  Each pair of LCD-2/3 headphones comes with a graph of how that headphones measures.  The same should go for every piece of gear sans cables.
 
I would not worry about it, but most inadequate amps will have an audible absence of low end kick.  My Grace Design m903 is audibly less punchy in the low end than my Headphone.com BUDA for example.
 
I always say that the easiest way to change the sound signature is typically by changing headphones ( if EQ is not used ).  Often headphones are less expensive than a DAC or AMP.

 

[edstrelow]

Added to which the standardly reported range of human hearing is 20 Hz to 20kHz.  With men the upper limit is lower and for all persons tends to go lower as we age, and can get really bad with some medical conditions. Kind of like the old counterculture refrain "don't trust anyone over 30."  I would say don't trust their hearing.