[scottzg]

Alright, i've been reading about output impedance, and i understand that with a relatively low output impedance there is more electrical damping and the headphone offers up a more accurate sound.  
 
So as i understand it with the etymotic er-4 series the drivers are the same; the difference between the er-4s and er4-p is an impedance is added in line, which is essentially duplicating an output impedance.  How is it that increasing the output impedance improves the advertised accuracy?
 
 
Here's the linkie i'm referring to
http://www.etymotic.com/ephp/epcomp.html
 
Thanks for deconfusing me!

 

[xnor]

Ok, there's quite a bit of background knowledge you need to understand what's going on.
 
The quick explanation:
1) Etymotic uses some form of diffuse field equalization to measure accuracy of the frequency response of their earphones.
 
2) According to that curve, ER-4P would need a bit more treble to be more accurate.
 
3) ER-4P has rising impedance in the treble range.
 
4) High output impedance will change the frequency response according to the impedance curve.
So 3) and high output impedance will result in a slight treble boost.
 
5) => Higher accuracy* score.
 
*) Olive/Welti have developed a new target/equalization curve that suggest that Ety's curve is not very accurate itself. ER-4B for example lacks around 7 dB bass relative to 5 kHz. The ER-4S about 4 dB.

 

[scottzg]

  Ok, there's quite a bit of background knowledge you need to understand what's going on.
 
The quick explanation:
1) Etymotic uses some form of diffuse field equalization to measure accuracy of the frequency response of their earphones.
 
2) According to that curve, ER-4P would need a bit more treble to be more accurate.
 
3) ER-4P has rising impedance in the treble range.
 
4) High output impedance will change the frequency response according to the impedance curve.
So 3) and high output impedance will result in a slight treble boost.
 
5) => Higher accuracy* score.
 
*) Olive/Welti have developed a new target/equalization curve that suggest that Ety's curve is not very accurate itself. ER-4B for example lacks around 7 dB bass relative to 5 kHz. The ER-4S about 4 dB.

 
So to put what you're saying in moron's (scottzg's) terms, etymotic research has picked a target for accuracy, and are using the source's output impedance as a tool to tune the sound and hit their accuracy goals.  On the other hand, the standard for accuracy is not a simple objective measurement and ety's standard may be out of date.
 
This makes intuitive sense to me; hooking my Q701s up to my o2 amp was an epiphany, and so connecting my hf3s to it was a real disappointment; i liked them out of my receiver more.
 
Thank you for the response!!

 

[xnor]

Yeah, that's a very nice and simple summary.
 
 
The problem with the target curve are not objective measurements as such though, but that they chose the diffuse field equalization. Diffuse field means sound arriving from all directions equally, unlike speakers in a real room where direct sound is coming from the front (left/right speaker) plus reflections arriving a bit later from the walls, floor, ceiling etc.
 
Luckily they have noticed that an unmodified diffuse field equalization would have been too bright, so they modified it slightly: http://www.etymotic.com/technology/hwmra.html
They basically added a 5 dB roll-off at 10 kHz. Some manufacturers really could learn something from them in that aspect (I'm thinking of those nasty treble peaks).
 
 
The good thing is: if you know that your headphones are accurate according to that target curve you can add a slight downwards tilt with an EQ and arrive at even better sound.