[paulguru]

  They sound very similar but to me the 400i has better bass and highs and are more efficient. The 650 has incredible mids, great headphone. But the 400s sounds to me like a crisper cleaner 400i with better bass quality not to mention it is 200$ cheaper. They both sound great. Can't go wrong with either.   

what means "better highs" ? ... treble most enphasized ?
this dont make the 400i less relaxed and most fatiguing ?

 

[Tunkejazz]

what means "better highs" ? ... treble most enphasized ?
this dont make the 400i less relaxed and most fatiguing ?

Only less relaxed, but by no means fatiguing. These are not bright headphones. The 400i are very clear without any glare in the treeble. I think you will love any of the two, and in both cases you will need a decent amp to drive them PROPERLY.

 

[chowmein83]

  They sound very similar but to me the 400i has better bass and highs and are more efficient. The 650 has incredible mids, great headphone. But the 400s sounds to me like a crisper cleaner 400i with better bass quality not to mention it is 200$ cheaper. They both sound great. Can't go wrong with either.   

 
Also agree with this. @Bri-Fi I'll be looking with interest at your impressions over at the 400s thread, as I am curious to see how they will stack up to the 400i (since I own the latter).
 
@money4me247 since you said you also agreed, have you had the chance to listen to the 400s?

 

[paulguru]

Only less relaxed, but by no means fatiguing. These are not bright headphones. The 400i are very clear without any glare in the treeble. I think you will love any of the two, and in both cases you will need a decent amp to drive them PROPERLY.

is not the 400i easy to drive ?
i thinked it can be drive also with smartphones .....
 
Is not particularly sensible headphone right ?
You must to use an highter volume setting compared to HD6xx, right ? ( 97db vs 102db )

 

[Tunkejazz]

You can use a phone and barely get enough volume, but the sounds won't be very dynamic and the bass will be soft. Add a decent amp, and they will sound much better. At least that was my experience going from the headphone jack of my laptop (macbookpro) to a Vali. That's why I said "drive them properly"

 

[paulguru]

You can use a phone and barely get enough volume, but the sounds won't be very dynamic and the bass will be soft. Add a decent amp, and they will sound much better. At least that was my experience going from the headphone jack of my laptop (macbookpro) to a Vali. That's why I said "drive them properly"

Ok but this is the case of this Hifiman ?
400i is not extremelly easy to drive ?
I'll drive it with a discrete sound card

 

[tinyman392]

Ok but this is the case of this Hifiman ?
400i is not extremelly easy to drive ?
I'll drive it with a discrete sound card

The 400i can be driven from my iPhone at around 50-55% volume. The iPhone is a colder source and the 400i is a colder 'phone that definitely benefits from a warmer source.

 

[snellemin]

I agree, the 400i really shines with an amplifier.  My phone is barely enough and I use a small amp for decent sound.  For the full potential and subwoofer deep bass that vibrates your skull, I use solid state amplifier on the cheap.  I'm really surprised what this headphone can do with the right equipment. In my eyes the 400i is not really a "mobile" headphone, unless you have some badass DAP.  My unscientific method shows an average of 4W rms before I start to overdrive the headphone.  Now this is with the 31.5hz increased.  It can get really painful when I lower that down a few notches and crease the gain back up.  Please be kind and don't laugh too hard at my headphone setup.
 

 

[chowmein83]

  Ok but this is the case of this Hifiman ?
400i is not extremelly easy to drive ?
I'll drive it with a discrete sound card

 
Like @tinyman392 said, the 400i can be driven okay with more powerful smartphones or DAPs (the iPhone is powerful enough, in my opinion) but the 400i will definitely benefit from an amp.
 
Basically, the 400i is easy to drive for a planar magnetic headphone, but among all headphones it's not the easiest to power.
 
EDIT: Sorry, I originally tagged the wrong user.

 

[Airlight]

Snapped a beauty shot of my HE-400i today, and felt like sharing.
 

 

[money4me247]

  Also agree with this. @Bri-Fi I'll be looking with interest at your impressions over at the 400s thread, as I am curious to see how they will stack up to the 400i (since I own the latter).
 
@money4me247 since you said you also agreed, have you had the chance to listen to the 400s?

@chowmein83, nope not yet. I was agreeing with the HE-400i vs HD650 comparison. sorry for the confusion. cheers!

 

[paulguru]

The HE400i sensitivity ( 94db/mw ) is  expressed in Vrms or SPL ?

 

[john57]

  The HE400i sensitivity ( 94db/mw ) is  expressed in Vrms or SPL ?

This is efficiency at 93dbSPL per mill-watt according to the HifiMan web site.  
http://www.head-fi.org/t/168037/db-per-milliwhat-efficiency-vs-sensitivity-vs-how-loud-do-they-really-go/15#post_6431953
http://www.head-fi.org/t/463983/what-determines-how-sensitive-a-headphone-is/30#post_6304937
 
On the new HE400S there is two ratings.
 
SENSITIVITY: 98dB/V
EFFICIENCY: 93dB/mW
 
Noticed that both headphones have the same efficiency but the 400S has lower impedance at 22 ohms vs the 35 ohms of the 400i
This means that the 400S can be a bit louder than the 400i on the same SS amp.

 

[Bri-Fi]

  This is efficiency at 93dbSPL per mill-watt according to the HifiMan web site.  
http://www.head-fi.org/t/168037/db-per-milliwhat-efficiency-vs-sensitivity-vs-how-loud-do-they-really-go/15#post_6431953
http://www.head-fi.org/t/463983/what-determines-how-sensitive-a-headphone-is/30#post_6304937
 
On the new HE400S there is two ratings.
 
SENSITIVITY: 98dB/V
EFFICIENCY: 93dB/mW
 
Noticed that both headphones have the same efficiency but the 400S has lower impedance at 22 ohms vs the 35 ohms of the 400i
This means that the 400i can be a bit louder than the 400i on the same SS amp.

I Have both headphones here right now, and on my Schiit Asgard 2 the Volume knob in the same place, the 400s definitely plays louder. No doubt, it is more efficient then the 400i for sure. 

 

[tinyman392]

  The HE400i sensitivity ( 94db/mw ) is  expressed in Vrms or SPL ?

Sensitivity is a measure of dB per x amount of power or dB per x volts.  In this case, it's expressed in SPL / power.  
 
Keep in mind that a lower impedance (see it loosely as resistance) will lead to a higher power output for the same amount of voltage (V = IR; lower R -> higher I; since P = VI, higher I -> higher P -> higher SPL).