Senn HD 558 imedance range
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dirkpitt

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Hi all, I have been reading the forum for several days now - contemplating different debates and discussions. 
 
I have a set of Sennheiser 558's which I enjoy because I get fatigue pretty quickly listening to music. I run them at very very low volume on home PC, work laptop and ipod touch 3g.
 
DAC aside or a moment... I know there are mixed opinions about amping these headphones with many stating there is limited improvement because they are relatively low impedance anyway.
 
My phones seem to have a slightly fuller low end running from my yamaha home receiver than anything else  I have listed.
 
So I just wondered about this chart?
 
I think the chart shows more impedance required in the ranges of 40Hz to around 120Hz for the 558's, which is the frequency range of most subs. Does that also mean that an ipod (intended for 32Ohm headphones) will struggle to drive the headphones within the 40-120Hz frequency range? Or does this balance out somehow?
 
 

 
 
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john57

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With my tube headphone amps that tends to like higher impedance sometimes I noticed a bit more dynamic range in the low frequencies with some types of  music with my Sennheiser  headphones. I do not have a Ipod but a Sony Walkman MP3 player that I used with a special kind of headphones that is tailored to my needs and gives full isolation of outside sounds. My Sennheiser   headphone models  are too bulky to used in the public for my needs. You seems to noticed a difference using your home receiver amp which answers your question if a home amp can make a difference in sound with Headphones.  There maybe some portable amps that could handle the impedance peaks with different results.
 
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dirkpitt

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Thanks for the response John. This can't be limited to Senns though huh? with a wide range of impedance on many headphones... how does any source that cant supply 300+ Ohms (intended for 32OHms for example) cater to that? Or am I over simplifying things? Is anyone familiar with the math behind it..? (not my strong point)

 
 
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dirkpitt

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Bump .. I listened to this again quite closely comparing the tones that I think are missing between the 3rd gen touch and my receiver.
 
Its the range of 60-90Hz that is all but non existent from the touch that can very clearly be heard through my receiver. I am assuming that anyone using 32Ohm and below phones might not hear this because their cans are being powered adequately?
 
I guess the main thing that I am trying to determine is .. that its not the DAC that is processing poorly, but from what I have read the touch has a wolfson DAC that is respectable.. and I think I subscribe to the notion that most reasonable DAC's will be doing the the same job as long as they fall within certain thresholds of key specifications and don't introduce errors in the music as they are reproducing a waveform from a digital representation and can do so accurately. (provided that my music is of reasonable quality of course)
 
Failing confirmation, I guess I will purchase a cheap amp and see if I can get more out of the ipod and laptop within the 60-90Hz range. 
 
I notice that a lot of people claim that some DAC's/AMP's sound brighter than others. I get that impression between my ipod and receiver, BUT for sure it would sound brighter IF half the bass is missing 
 ..?! 
 
 
 
 
 
 
 
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john57

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[size=medium]A basic rule is that according to ohm law if the impedance goes up you would need higher voltage to maintain the same power level which is watts. Tubes tend to like to operate in higher voltages.  It is harder for a battery operated device to have large voltage swing at the output.  Also with higher impedance current tend to go down which tubes like better. This also depends on the headphone efficiency as well. Some Solid State amps usually have 10v peak to peak operating voltage and a few like the Hybrid Schiit Lyr have 20v peak to peak operating range making it able to better cope with higher impedance cans plus huge current reserve. This is an over simplification on what happening. [/size]
 
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dirkpitt

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A more direct question - What does "nominal impedance" mean in terms of headphones. Specifically... not "impedance" .. but "nominal impedance" and can this measure be reliably used for any impedance matching at all when we have variations like this chart? I have read a few posts on this with no real answer.
 

 
 
 
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john57

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[size=14pt]The nominal impedance rating official rating of the headphone in question is 50 ohms but with the chart it is about 52 ohms. Your apple touch seems to design for 32 ohms since that is that comes with it. I could not find any more information on your touch amp but usually with the IPod there is just one volt of operating voltage which about make it harder to handle any impedance swings. In addition a high sensitivity headphone with your touch is going to help as well. My tube amps has no problem handling the impedance swings and either your receiver or my stereo amps which has about 50 volts swing will not have any problem handling the impedance swings within that range either with the HD558. The good sensitivity rating is going to help as well. I also gave specific Solid state desktop amps that will not have any issues with that impedance swing. That impedance peak is at about where the frequency curve will start to drop a bit as well.[/size]
[size=14pt]If you have amp that cannot handle the higher impedance it will generally sound weaker depending on the sensitivity rating for the headphone. Amps that are designed for higher impedance will generally have specs that will tell the current rating at 300 ohms as an example. [/size]
[size=14pt]Some additional examples:[/size]
[size=14pt]Post 2[/size]
[size=14pt]http://www.head-fi.org/forum/thread/564793/how-much-difference-does-a-portable-amp-make#post_7640453[/size]
 
[size=14pt]http://www.head-fi.org/forum/thread/246424/benefits-of-high-impedance-headphones/30#post_7266161[/size]
  
 
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dirkpitt

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Thanks again for the quick response John, much appreciated and thanks for the links I will have a read.
 
 
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