[Choobies]

Hey everyone,
 
I've spent the last eight hours or so browsing the Internet, looking up headphones, amps, and the like.  Lots of Google searches directed me to threads here, which have definitely helped a lot.  However, I'm still left with a lot of questions with which I'm hoping you guys can help me.
 
My current pair of headphones is the Sennheiser HD-448, which I've had for a year now.
I like the sound, but I'm looking to spend more money on more quality, so I'm thinking about upgrading to the Sennheiser HD-595.
 
It seems the general consensus is that while the HD-595's are 50 Ohms and can be decently powered by portable players, they would still benefit from an amp, which is what I want.
 
However, am I correct to assume that because their impedance isn't that high, I therefore don't need an amp with that much power?
 
Since my main listening will be on an iPhone 3G and an iPad 2, I'm considering getting the FiiO E1.  (It seems E1 vs. E5+LOD is pretty much a toss-up in terms of sound quality, leaving just convenience as the deciding factor.)
 
Now, I'm sure amps like the iBasso D2 and FiiO E7 would make my HD-595's sound even better, but are the benefits in sound quality due to using those amps worth the price increase when compared to the FiiO E1?
 
In other words, using a $500 amp for the HD-595's would be excessive, and using no amp would be suboptimal, so where is the balance?  What amp should I get to go with my iPhone3G/iPad2?
 
One reason I'm considering the E5 instead of the E1 is the ability to use it with a laptop.  However, I'm not quite sure how would I go about that.  Where would the line-out from my laptop be?  ('Cause using the headphone-out port wouldn't be advised, right?)
 
Thanks for your help guys!
-Preston

 

[scompton]

Not only are they low impedance, they're pretty sensitive too.  IMO, most portable amps have to much gain for them.  I just bought an HD595 so I've never tried it out of a portable amp.  I have tried other, similar headphones out of portable amps that people were raving about.  When I made sure the volume matched between playing directly from my iPod and from the amp, there was just a subtle difference.  For me, the difference is not enough to deal with a portable amp.  I have no experience with the Fiio amps, so they could be less of a hassle, but my main problems with portables amps are

1. One more thing to carry.
2. To much gain, ie, even at the lowest volume setting, they're too loud.  The line out of my iPod Classic is so hot, I really need negative gain in an amp.
3. It's to easy to bump the volume knob or dial and instantly have the music 5 times too loud, possible even into the levels that can damage hearing.

 
 

 

[Choobies]

What do you mean when headphones are too sensitive?
 
Also, does a headphone amp having too much gain mean it outputs the LOD sound from the iPod too loudly?

 

[scompton]

How loud a headphone gets is based more on the sensitivity than the impedance.  Impedance lets you know the resistive load of the headphone.  An amp, including the amp in the iPhone needs to be able to output enough volts to overcome the resistance.
 
How load a headphone gets is a function if the sensitivity, usually stated in dB/mW or dB/V.  The HD595 is 112dB/V.  From what I can find online, full volume on the iPod puts out 1V, so at full volume, the HD595 will be at hearing damaging levels.  This looks right to me because I listen at 65-70dB and I have the volume set at around 50% for the HD595.
 
The gain of an amp is the ratio of the input power to the output power.  The higher the gain the more it amplifies the signal.  A gain of 1 equates to no amplification.  The lineout voltage of an iPod is 1V any gain produced by an external amp is going to make it even harder to keep the volume down.
 
Even though 1 number is given for impedance, the true impedance varies by frequency.  Many headphone have an impedance hump in the bass so they actually require more volts if the music is very bassy.  If the amp can't supply the volts, the bass can get sloppy or even clip.  I don't really think this is much of an issue with the HD595
 
There is more to it than what I described here.  This is about the limits of my knowledge.