[Suopermanni]

Quote:

 
The low impedance of your can is the problem. The efficiency is not relevant to the ME's output impedance potential problem (the efficiency is more related to the ME's power output, but it's not an issue here).
 
If the Samson SR850 have a (relatively) flat impedance response across the audible range, then the high output impedance won't change the "intended" (original) frequency response of the cans.
If their impedance response varies a lot with frequency (as occurs on Balanced-Armature IEMs, which have cross-over network with complex impedance, that by nature, varies with frequency), then the intended frequency response will be modified (in general, for the worst, but not always).
 
The amp's output impedance also determine electrical damping. Simply put, the higher the damping factor, the quicker the driver "reacts" (= the more the amp has control over the driver). If the damping factor is too low, the driver will be "loose" and bloom will occur (e.g. in the bass).
The damping factor is defined as DF = Zcan / Zamp. As rule of thumb, DF should be >8. Which means, if the amp has an output impedance of 50R, the can should have an impedance of (at least) 400R.

 
Wow, thank you for the detailed explanation. I actually expected something something a little less....expansive? Oh well, it's a good learning experience. Anyway, thank you for telling me that, now I know not to get low impedance cans for that device.

 

[netdog]

Oh.  Now I feel thick.  But informed anyway.  I'll start looking through the HeadFi guide for good low impedance headphones.

 

[citraian]

You should start looking for high impedance headphones instead 250 Ohm should be a minimum if the Explorer's output impedance is indeed 50 Ohm

 

[teofilrocks]

Quote:

If their impedance response varies a lot with frequency (as occurs on Balanced-Armature IEMs, which have cross-over network with complex impedance, that by nature, varies with frequency), then the intended frequency response will be modified (in general, for the worst, but not always).
 
The amp's output impedance also determine electrical damping. Simply put, the higher the damping factor, the quicker the driver "reacts" (= the more the amp has control over the driver). If the damping factor is too low, the driver will be "loose" and bloom will occur (e.g. in the bass).
The damping factor is defined as DF = Zcan / Zamp. As rule of thumb, DF should be >8. Which means, if the amp has an output impedance of 50R, the can should have an impedance of (at least) 400R.

 
I guess the real question is, how audible is the impedance mismatch? I'm guessing it varies even among equally resistive headphones and also among different sets of ears.

 

[Clemmaster]

Quote:

 
I guess the real question is, how audible is the impedance mismatch? I'm guessing it varies even among equally resistive headphones and also among different sets of ears.

 
One cannot really predict the behavior of the cans, unless both the Frequency and Impedance Response charts are available.
Once you get the corresponding data, it's fairly easy to derive the FR chart for various amp's output impedance.
 
Again, the frequency response deviation might even be "for the better" to some users.

 

[teofilrocks]

Quote:

Again, the frequency response deviation might even be "for the better" to some users.

 
Exactly. That's why I'm not worrying about high output impedance (and because I don't use IEMs). I'll just wait for my ME to arrive on Thursday and give it a listen.

 

[Clemmaster]

Quote:

 
Exactly. That's why I'm not worrying about high output impedance (and because I don't use IEMs). I'll just wait for my ME to arrive on Thursday and give it a listen.

 
The reduced damping factor is, objectively, for the worst though
 
If you look at some FR chart for BA IEMs driven with high impedance amps (as provided by Purrin), the FR can become really funky

 

[Tyll Hertsens]

Quote:

 
So what cans would fare well with the Explorer as I already have it?

Any with over 300 Ohms.  HD580/600/650, HD 800, Beyer DT880-600 Ohm, etc.
 
Ummmm...if I were interested in an ME for low impedance headphones, I'd wait a couple of months. Jus' sayin'.

 

[teofilrocks]

Quote:

Ummmm...if I were interested in an ME for low impedance headphones, I'd wait a couple of months. Jus' sayin'.

 
Uh-oh spaghettios. 

 

[netdog]

Is there any chance that Meridian can fix this with a firmware update?  I know that they designed it so that the firmware could be easily updated by the user.

 

[vrln]

I don't think so, output impedance changes require hardware modification. The Explorer is just simply not suited for driving IEMs. My guess looking at Tyll's comment is that Meridian plans to launch an IEM edition eventually. It would be good damage control too as the facts are now out. Ideally Meridian should have been honest about the specs all along and not hide them instead. Those looking for a portable product like this for IEMs should take a look at the HRT MicroStreamer, output impedance quoted in the specs is 0,5 ohms.

That being said, I'd still be interested in an IEM edition of the Explorer despite all the drama.

 

[Tyll Hertsens]

Quote:

Ideally Meridian should have been honest about the specs all along and not hide them instead. 

 
Oh I don't think they were being dishonest.  I think they were simply not intimately familiar with the new market they were getting into and made an understandable misjudgement of what was needed to cover the all the headphones of interest. 

 

[telecaster]

Maybe some claims should be taken, as always in all things audio, with a pinch of salt:
My take on this is is that damping factor, reguarding the looseness of the diaphragm in dynamic headphone is close to nill.
But damping factor affect the frequency response, and it may be that HD800 will sound better to most with low damping factor.
The norm is high impedance output for headphones (120ohms) and manufacturers may well tune their headphones to accomodate this. i.e the akg 701, but many more are succeptible to be designed that way.
 
My Balanced armature xba4 sound shrill with my low impedance phone output, but with the explorer it sounds really good.
Remember that in audio you have your tastes as well as measurements, and outlandish claims comes to make you buy the new best thing.
 
http://rockgrotto.proboards.com/thread/7589
http://www.head-fi.org/t/598565/damping-factor-why-it-is-not-always-as-important-as-some-make-it-out-to-be
http://www.head-fi.org/t/340327/damping-factor-for-headphones
http://www.head-fi.org/t/617902/effects-of-damping-factor-on-planar-magnetics-orthodynamics
http://www.head-fi.org/t/602788/damping-factor-impedance-response-can-any-amp-drive-a-headphone-with-flat-impedance-response
 
Meridian may have choosed this output impedance to permit the use of the explorer to drive powered speakers with the quiet analogue volume control of the 47ohms output.
 
Sound is really good with my HD650.

YMMV!!!!!!!!!!!!!!

 

[estreeter]

Quote:

Meridian may have choosed chosen this output impedance to permit the use of the explorer to drive powered speakers with the quiet analogue volume control of the 47ohms output.
 
Given that Meridian's own expertise seems to be in 'enhanced' active speakers (DSP and DAC built into the speaker enclosure), there may be something to this - in any case, I suspect that they put more time and effort into the DAC section than the headphone amp, but that's pure speculation. The electronics experts can comment on this, but I dont think any of the aforementioned issues around the output impedance on the headphone out will impact the ME's utility as a DAC in a speaker rig. Everything I've read on the line-level output seems to point to happy campers in the speaker world.  

 

[vrln]

Quote:

 
Oh I don't think they were being dishonest.  I think they were simply not intimately familiar with the new market they were getting into and made an understandable misjudgement of what was needed to cover the all the headphones of interest. 

 
Good point, but then it seems they didn´t do their homework properly. If they had consulted even a few enthusiastic hobbyists they would have known that output impedance will be scrutinized just like on every other portable amp device these days. The choice of optimizing for 300 ohm or so headphones is fully ok, but even then I feel it should have been openly stated in at least an FAQ section on their site. iRivers engineers for example recently admitted the same on the 6Moons review of the Astell & Kern AK100 DAP. 
 
Being silent about the whole impedance topic and not including even the most basic measurements like crosstalk, SNR etc on their official spec sheet is still puzzling to me, even if they were caught off guard. It´s Meridian´s first headphone product, sure, but I´d expect more from such a well established company. Anyone who´s followed the scene even remotely would know that sensitive low-ohm headphones are a current trend because of popular battery powered mobile electronics. My guess is that the Explorer was built as a DAC first (might even be pretty good) and foremost, then had a hastily put together (compared to the DAC section) headphone amp added.