Headphone Impedance relation to audio quality and amplifier

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What is headphone impedance and how is it related to audio quality.

I understand that at higher value we need an amplifier too. At what point or value do I need an audio amplifier for the headphone. Does the amplifier also improve audio quality.

Hope someone can explain this to me in layman's terms.
 
1) It is said that the amps output impedance should be no more than 1/8th of the headphone's impedance. So for a 32ohm hp you'll need an amp with output impedance <=32/8 ohms
However there is an exception where orthodynamic headphones are much less/not at all affected by the high output impedance due to linear impedance. Dynamic headphones on the other hand have much larger impedance variation hence it's recommended to follow the 1/8 rule.
From personal experience, i have driven 32ohm Shure 750dj from a Xonar STX with 10ohm output impedance. Result - Terribly rolled of bass

2) Does the amp improve input signal quality - No it does not. Amps are supposed to provide gain over the input signal.

3) Need of new amp depends on - Available spare cash ;)
 
Power into any load depends on the voltage across it, and the current through it. The second is dependent on the first, by a function known as impedance. The relationship is established by Ohm's Law, which you can find on Google.

Any equipment needs to deliver larger voltage as the impedance increases, to ensure similar power output. Inversely, the current through the load needs to be enough to deliver the stated output.

If you look at a 32ohm can versus a 600ohm can, the 600 will need more voltage to drive and the 32 more current.

For example, to get 100mW into the first you need 7.7V and 12mA current. For the second, you need 1.7V and 55mA. The current figures double for two headphones, but the voltage remains the same. As you can imagine, getting 7.7V is not possible from the ~3V batteries inside portable equipment and so an external amplifier is required. You can work out the required numbers basis Ohm's Law and P=((I^2)*R) but in general 64 and 32 ohm headphones are the practical limit for portable equipment.

An amplifier that cannot reach the figures above, either of them, will result in distortion (applies to internal and external amplifiers). Also, these are theoretical numbers, real world headphones require considerably more current as the impedance changes with power input and frequency.
 
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Forget the theory, In practice,

Headphone Impedance is crucial for its matching amplifier.

Example : an Senn HD600 sounds like a charm on an OTL amplifier, But an Audeze LCD2 sounds pathetic out of an OTL amp. because of amplifier's output impedance.

If Headphone and amplifier have good synergy (matching) then the sound quality will be optimal.
 
impedence for headphones or speakers is generally quoted at 1khz and its variable across the frequency spectrum.
 
Headphone Impedance of Sennheiser HD600, HD650, HD800 is 300 Ohms.

Output Impedance of headphone amplifier should be the lowest, to universally drive any of the headphone given; i.e, Less than 1 ohm.

Example : OTL tube amplifiers generally have higher output Impedances (120 Ohms) hence cannot drive lower impedance headphones like AKG Q701, Audeze LCD2, HiFiMan HE500 etc.

But NwAvGuy's Objective2 amplifier has output Impedance of 0.54 Ohms, hence It perfectly drives IEM's, Orthos, Dynamics with ease. or anything you throw at it.
 
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