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xinze said:

So yes, on other devices such as Sansa Players, the Beyers would be so quiet that an amp would be needed to reach a decent listening level?

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It's not volume, it's the quality of sound, you can make a really cheap amplifier that can get something loud, but the sound quality would be so poor that you would not want to listen to it.
So on cheap amplifiers they can not let it get that loud or the poor quality would show.
Now most headphones sold in the world are around 32-Ohm to 45-Ohm, very easy to drive, most of these headphones are plugged into cheap low cost jacks.
People who do not know any better are going to be happy with the audio.
The DT770 Pro 80-Ohms are going to be a little bit hard to drive then the average headphone.
 
 
 

Cheap amplifiers add a lot of distortion to the sound, good amplifiers make it louder while preserving the input

Quote:

purpleangel said:

It's not volume, it's the quality of sound, you can make a really cheap amplifier that can get something loud, but the sound quality would be so poor that you would not want to listen to it.
So on cheap amplifiers they can not let it get that loud or the poor quality would show.

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With high impedance headphones, the main issue actually is volume, more specifically volume without clipping distortion (i.e. an amplifier may let you use a volume level it cannot output cleanly, it will then sound "loud enough", but distorted). As long as there is no significant distortion on even the highest peaks in the audio signal, high impedance is easier to drive than low impedance: it needs less current, typically reduces the distortion and noise of the amplifier (see this graph for an example), and is less prone to frequency response variations due to impedance interactions.
The OP is probably right, I also have the same headphone, and with the usual factors of clipping, lack of level matching, and placebo excluded, it really does not change much from different sources (except ones that are of inherently low quality driving anything).
 
The reason most portable players, cell phones, etc. cannot get very loud with high impedance headphones is not that the manufacturer wants to hide low quality (the same devices can be extremely loud with sensitive IEMs), but rather limited voltage due to being powered by batteries. Of course, in theory there are ways to work around that, but high impedance full size headphones are a niche market that is getting smaller, so the manufacturers do not see the extra cost as being justified.
 

Reviving dead thread, but I noticed something I had to point out:
 
I have both the Beyer Dynamic DT770 and 990s, both 250 ohm Pro version. Using them with a FiiO E11 amp and a 3.5mm 2 Female to 1 Male splitter, I can listen to both of the headphones and compare them at once. Thing is, there is absolutely NO DIFFERENCE in volume at driving one headphone vs driving two at the same time. Both of them play at high volumes even when the FiiO amp is on a low volume setting.
 
Question is: If I plug in another 250ohm headphone into one amp at a certain volume setting, shouldn't the volume for each headphone drop by a few decibels? Isn't this supposed to be like how the lights dim a bit when turning on a vac. cleaner, or do I have the whole concept of electricity mixed up?

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Question is: If I plug in another 250ohm headphone into one amp at a certain volume setting, shouldn't the volume for each headphone drop by a few decibels?

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No, since the headphones are connected in parallel, the E11 basically just has to output about double the current, which it is capable of. The voltage would drop if the E11 had high output impedance, but it fortunately does not.