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whats the difference in ohms??? - Page 2

post #16 of 23
6/5/09 at 3:34am
Sarcasm of course...
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post #17 of 23
6/5/09 at 4:49am
Sorry for the confusion!

Removing my previous comment. Seems there are more forces at play than just hp impedance when it comes to driving cans effectively, ie: sensitivity, amp output impedance, etc.

OP: Maybe just research some headphones you're interested in to find out how hard they are to drive.
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post #18 of 23
6/5/09 at 12:51pm
I went to high school! Honest!
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post #19 of 23
6/5/09 at 5:34pm
Thread Starter 
thanks neko for the link a very good read
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post #20 of 23
6/5/09 at 7:50pm
This one is a nice read.
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post #21 of 23
6/6/09 at 12:42am
I didn't know AMP impedence mattered, I thought it all had to do with just enough POWER to the headphones with difference ohms, hence the high and low gain.
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post #22 of 23
6/6/09 at 12:51am
Thread Starter 
Quote:
Originally Posted by Tiemen View Post
This one is a nice read.
thanks for the knowledge tiemen..sweet beans
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post #23 of 23
6/8/09 at 10:46pm
Quote:
Originally Posted by NekoAudio View Post
DNA's new Sonett headphone amp provides a switch to raise the output impedance to 120 ohms. This is done in case you actually want the sound to be influenced by the headphone's input impedance.
I would like to explain the rationale behind driving some headphones with a higher output impedance:

To make a single transducer cover the entire audible frequency range, which is what the speaker in a headphone does, it needs to have a low resonant frequency, low moving mass, and low inductance. The resonant frequency is the determined by the moving mass and suspension compliance. You can achieve this through high moving mass at the detriment of high frequency extension and efficiency (how loudly it produces sound for a given amount of input power). The preferred method is use low moving mass with a soft suspension. Transducers with strong motors and low mass diaphragms + voice coils tend to be very over damped at their resonant frequency with falling SPL at low frequencies when powered by a voltage source (amplifier with theoretically 0 ohm output impedance).

If instead you drive this transducer with a high impedance (approaching a constant current source), the current from the amplifier sees the impedance of the transducer and produces a varying voltage across it, raising the SPL accordingly. By doing so, you can now get back the bass that was missing when voltage source driven.

This way, you can have your cake (low mass, high efficiency, good high frequency extension and energy time behavior) and eat it too (good low bass extension and SPL).

The IEC 61938 standard specifies 120 ohms for headphones. It also has the feature of delivering a more constant power into both low and high impedance headphones.

This same principle is done with single driver high efficiency loudspeaker drivers from Lowter, Fostex, among others. They need to be driven by an amplifier with higher output impedance if you want to get bass and a flatter frequency response from them. Nelson Pass of Threshold and Pass Labs fame developed and manufactures a specialty amplifier just for this application under the name First Watt.

6moons audio reviews: First Watt - An Introduction to the Concept by Nelson Pass
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