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Headphone Systems Everything to do with Headphones 

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10th February 2013, 05:59 AM  #21 
diyAudio Member

LDRs aren't very linear as resistors IIRC. Why not just use a pot?
Any headphone which has an almost perfectly resistive impedance is basically operating in currentdrive due to its own internal resistance swamping out the coil reactance. So those AKG's probably tolerate high source impedances better than most headphones. On that note, current drive is supposed to be better for speakers, although somewhat more difficult to implement. So perhaps the same could be true of headphones? Just EQ out the impedance curve If you can measure the impedance of your headphones this should be easy. Unless your source impedance changes with volume, then the EQ would wander. The serious flaws of voltage drive  CurrentDrive  The Natural Way of Loudspeaker Operation 
10th February 2013, 12:15 PM  #22 
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Join Date: Oct 2010

Almost any dynamic headphone I've seen is underdamped, so any increase in output impedance makes this just worse.
Ideal output impedance = 0, but the rule of thumb is less than 1/8th of nominal impedance of the headphones. Some dynamic headphones have a fairly flat impedance response, but that's the exception... 
10th February 2013, 01:54 PM  #23  
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Join Date: Jun 2003
Location: Hamilton, was Ottawa (Canada)

Quote:


10th February 2013, 02:05 PM  #24  
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Join Date: Jun 2003
Location: Hamilton, was Ottawa (Canada)

Quote:
NwAvGuy summarizes and gives a practical example: THE SHORT VERSION: All you really need to know is most headphones work best when the output impedance is less than 1/8th the headphone impedance. So, for example, with 32 ohm Grados the output impedance can be, at most, 32/8 = 4 ohms. The Etymotic HF5s are 16 ohms so the max output impedance is 16/8 = 2 ohms. If you want to be assured a source will work well with just about any headphone, simply make sure the output impedance is under 2 ohms. http://nwavguy.blogspot.co.uk/2011/0...impedance.html Can you point me towards some data? Thanks, Jeff Last edited by AudioLapDance; 10th February 2013 at 02:10 PM. 

10th February 2013, 02:37 PM  #25 
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Join Date: Oct 2010

comparisonbeyerdynamicdt88032ohmdt880250ohmanddt880600ohmheadphones
.. and the countless headphone datasheets you can find on that site. (If the page is empty try another browser.) 
11th February 2013, 02:32 AM  #26  
diyAudio Member
Join Date: Jun 2003
Location: Hamilton, was Ottawa (Canada)

Quote:
Perfect, thanks xnor. I'll get to step response and damping soon, first I want to explore frequency response. I tried to model my AKG K301 as 300 ohm res peak at 80Hz, dipping to 120 at 2kHz and up to 200 at 20kHz. (Not in this case because I have no graph but ... what's cool here is that if you produce an electrical circuit that follows the impedance of measured headphones then the electrical circuit is modelling both the electrical and mechanical properties of the phones!) So ... you start with the nominal resistance 120ohm, then you add a resonator circuit that produces the peak at 80Hz [RLC res, 120+180=300], then you add an inductor to cause the hf lift: AKG K301 R series test circuit.png I just opened a Tina simulation and cut out the middle, here's the frequency response for a variety of R series Basic 2 ohm out for source then totals of 2, 7 [ipod], 10 and 20 ohm [standards], 50, 120 [standards], 500, and 909 ohm. AKG K301 R series 2 to 909 ohm freq resp.png Nothing significant for the lower output impedances but, of course, my crazy circuit produces a 6.5 dB hump at resonance (assumed 80ish) as predicted by xnor. Also interesting is that crazy old standard of Rout=120ohm (dark grey) produces noticeable boost and phase shift. Here's TINA SPICEBased Analog Simulation Program  TINATI  TI Software Folder And the circuit if you want to play: No Headphone Amp simulation.zip Cheers, Jeff Last edited by AudioLapDance; 11th February 2013 at 02:41 AM. 

11th February 2013, 05:54 AM  #27  
Lightning In A Bottle
diyAudio Member

Quote:
Some posts of Hifiman HE6 owners using transconductance (current drive) amps as headamp with great results. HifiMAN HE6 Planar Magnetic Headphone First Watt F1, F1J, F2, and F2J are transconductance amps from NP FIRST WATT PRODUCTS 

11th February 2013, 01:39 PM  #28 
diyAudio Member
Join Date: Jun 2003
Location: Hamilton, was Ottawa (Canada)

Here's a great book from 3 years ago and an inverted current clone from a decade ago!
current drive, inverted currentclone.jpg Current drive is confusing and turns everything 'upsidedown'. For those trying to get used to seeing things from a voltage perspective (even if idealized and inaccurate) ... Such confusions could lead to calls of reprehension preceded by explicit advisions! Please, let's start another thread! Last edited by AudioLapDance; 11th February 2013 at 01:51 PM. 
11th February 2013, 01:42 PM  #29 
diyAudio Member
Join Date: Jun 2003
Location: Hamilton, was Ottawa (Canada)

So does this curve remind anyone of anything:
AKG K301 R series 2 to 909 ohm freq resp.png I mean besides bad design and throwing explicit advisions to the wind. 
11th February 2013, 02:28 PM  #30  
diyAudio Member
Join Date: Mar 2004
Location: Budapest, Hungary

Quote:
http://en.wikipedia.org/wiki/Headpho...tput_Impedance Last edited by lcsaszar; 11th February 2013 at 02:31 PM. Reason: Found the reference 

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