[koolkat]

Graphs of Sennheiser HD438, 448, Beats and Grado SR60.
I need help interpreting the info, I skimmed the 'wiki' on the headroom site and found it a little too vague, so I came here to see if anyone can tell me how these graphs work and answer some of my questions.

Impedance

From what I understand, the HD438, 448 and Grado SR60 all have the same impedance, but apparently (according to personal accounts) amping the SR60 would give more tangible results than amping the 438/448. The green line is the slightly higher on the y-axis than the red and blue line, and the red is just above the blue line. So wouldn't that mean that the HD448s require the most amping of the three?

Does the frequency response of the headphones play a role in amping? I've gathered the impression that headphones that are a little soft on the bass require more amping to improve the sound quality.. or do people interpret louder volumes as an improvement in sound quality? The higher the volume, the clearer the bass? The graph shows that the Grados require the least amping o_O

Also, just a little something I noticed on the way to/from school.. I've never seen someone using an amp on Beats before. They're not meant for studio use (we all know that's just a marketing strategy). They're actually targeted towards the youths who are always on the go. 200 ohms is a little too much right for portable use no? Maybe I should start a thread advertising the use of amps with Beats.

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Harmonic Distortion

Looking at the second image, the blue line(SR60) is slightly higher on the y axis and it has a lot more pits than the red line(HD438). Does this mean that there is a lot more distortion occurring in the Grado SR60s? I need to know because I'm thinking of rewriting my review on the HD438s to include some technical specs as well.

 

[xnor]

Regarding harmonic distortion, see http://www.head-fi.org/forum/thread/563141/question-about-harmonic-distortion
 
 
The impedance tells you how much current the headphones draw from an amp at a given voltage. The voltage is what you control with your volume control. How loud each of those headphones will play at a certain voltage is usually specified as sensitivity.
 
Generally speaking, high impedance means your amp needs to supply little current but higher voltages and vice-versa. Combine a high impedance, low sensitivity headphone with a portable devices that is very limited in voltage swing and you might have to add an amp to get the volume you're asking for.
 
The impedance curve can have an impact on the headphones' frequency response if the amp has as high output impedance.

 

[koolkat]

Hmm.

The best amps are supposed to maintain the linearity of the sound, to make it as close to the recording as possible, so the lower the impedance output on an amp, the better yes? How would you describe the impedance on the PA2V2 compared to the Fiio E7? Also, if you don't mind, can you explain what high gain/low gain amp means?

I think the public perception is that headphones that produce less bass need more amping to bring out the bass like for example the Beats. 200 ohms impedance, but I've never seen anyone pair them up with amps. :s

 

[xnor]

Quote:

The best amps are supposed to maintain the linearity of the sound, to make it as close to the recording as possible, so the lower the impedance output on an amp, the better yes? How would you describe the impedance on the PA2V2 compared to the Fiio E7? Also, if you don't mind, can you explain what high gain/low gain amp means?

Yes. I don't know the specs of the PA2V2 but the E7 was measured to have about 0.1 ohms, which is top-notch.
 
The gain is simply the amplification factor of the input. Lets say your DAP outputs 0.5 V max and your amp has a voltage gain of 5.
5 times 0.5 V at the input = 2.5 V at the output of the amp.
 
So if you have a 200 ohm headphone for example, you get 0.5 * 0.5 / 200 = 1.25 mW (milliwatts), but with the amp you get 2.5 * 2.5 / 200 = 31.25 mW.
 
Ideally you want such gain that you can use a big range of the volume control - if the gain is too high you cannot turn the control up without blowing your ears, if it's too low you don't get enough volume.
Also keep in mind that the amp also amplifies noise and high gain may result in hiss with sensitive headphones.
 
 
Quote:

I think the public perception is that headphones that produce less bass need more amping to bring out the bass like for example the Beats. 200 ohms impedance, but I've never seen anyone pair them up with amps. :s

 
There are a number of reasons for amping. One is the limited output power / voltage of portable devices, another one lowering (and flattening, since some devices have a rising impedance at low frequencies which causes bass roll-off) the output impedance. Also, if your source is weak you can reduce distortion and crosstalk by adding an amp.
And then there are amps that have bass boosting features or crossfeeding circuits.
 
The public opinion in the other sub-forums on the need for amping may reflect these technical reasons, but that's not always the case. For example, some buy amps for the prestige/image.
 
I don't see a good reason why the Beats need an amp. Their impedance is high and flat (so the output impedance of your source has little to no effect). Their sensitivity is 115 dB/V or 108 dB/mW which, if the specs are right, is quite high and you shouldn't have volume problems even with weak devices.

 

[koolkat]

I pmed one of the head-fi forumers regarding amping my HD438. His advice was, the amplifier will not do much other than allow me to increase the volume of my music player (PSP, motodefy, Acer laptop) since the headphones are fairly easy to drive. But I've seen others reviews where people claim that their SR60i's were better after amping, a fuller bass, and better highs.

Now from this chart we can tell that the HD438, 448 and the Sr60s have similar impedances so I got the impression that people mistook the increase in sound volume [which made the bass region more audible], to be an increase in bass quality. I'm thinking of investing in a portable amp, the PA2V2, but I'm not so sure if it's better to just save the money for something else.