IPB

Welcome Guest ( Log In | Register )

1/8 Source Impedance Rule of Thumb, Split from "Audible Differences in DAC's?"
Arnold B. Kruege...
post Feb 25 2013, 15:51
Post #1





Group: Members
Posts: 4254
Joined: 29-October 08
From: USA, 48236
Member No.: 61311



QUOTE (mzil @ Feb 24 2013, 16:10) *
QUOTE (Arnold B. Krueger @ Feb 24 2013, 05:58) *
Agreed. However a FIIO E3 plugged into a UCA 202 gets you there for less than half of that.

If I am understanding you correctly, you are suggesting bypassing the built-in headphone out already found on the UCA-202 and instead using its line out to the Fiio E3 to drive some headphones?


BTW I made a typgraphic error above. I meant FIIO E5. I had to look at the one on this computer to refresh my memory! ;-)

Yes. The headphone jack on the UCA 202 has a source impedance of about 50 ohms which can lead to audible frequency response changes with some headphones.

The Fiio e5 is said to provide a source impedance of less than 1 ohm:

http://nwavguy.blogspot.com/2011/03/fiio-e...dphone-amp.html
Go to the top of the page
+Quote Post
 
Start new topic
Replies
mzil
post Feb 25 2013, 18:25
Post #2





Group: Members
Posts: 703
Joined: 5-August 07
Member No.: 45913



QUOTE (Arnold B. Krueger @ Feb 25 2013, 07:51) *
QUOTE (mzil @ Feb 24 2013, 16:10) *
QUOTE (Arnold B. Krueger @ Feb 24 2013, 05:58) *
Agreed. However a FIIO E3 plugged into a UCA 202 gets you there for less than half of that.

If I am understanding you correctly, you are suggesting bypassing the built-in headphone out already found on the UCA-202 and instead using its line out to the Fiio E3 to drive some headphones?


BTW I made a typgraphic error above. I meant FIIO E5. I had to look at the one on this computer to refresh my memory! ;-)

Yes. The headphone jack on the UCA 202 has a source impedance of about 50 ohms which can lead to audible frequency response changes with some headphones.

The Fiio e5 is said to provide a source impedance of less than 1 ohm:

http://nwavguy.blogspot.com/2011/03/fiio-e...dphone-amp.html

^There is (or was) an E3, but it lacks a volume control and is not well thought of by nwavguy, so I wasn't sure what exactly you were suggesting. Thanks for the clarification.

Regarding the Behringer UCA202's output impedance spec of 50 ohm for the UCA202 and driving low impedance headphones, I suspect the importance of strictly adhering to the "1/8th rule" is a bit exaggerated. He only shows a worst case scenario, his Ultimate Ears SuperFi 5 Pro, and from there scares everyone into accepting this rule as gospel. I really wish I could see more curves than just that. For all we know the amount of deviation plummets with a conventional, non-balanced armature design with a similarly low impedance, or if one accepts deviations of say +/- 1 dB as being relatively benign (considering the much larger, comparatively rollercoaster curves of different headphones in general, one model to the next), his "rule" becomes more like "1/2" or "1/4" , for all we know. Your thoughts?

This post has been edited by greynol: Mar 14 2013, 01:53
Reason for edit: Added quote which links to the original discussion for context
Go to the top of the page
+Quote Post
mzil
post Feb 26 2013, 19:05
Post #3





Group: Members
Posts: 703
Joined: 5-August 07
Member No.: 45913



Perhaps it is useful to you since you have the output impedances of these various devices commited to memory, I don't, so I have no idea by how much they break the 1/8th rule of thumb. Remember, I never questioned if impedance can have consequences on the frequency response. That's not the topic.

QUOTE
The purple line on this graph looks pretty audible to me. I'll leave evaluation of the rest of the parameters to you.


I'm not interested in what you deem audible, I'm interested in what nwavguy deems audible. EEs aren't always the best psychoacousticians, I've found.

I'd ideally like to see (the curves of) an example of a combination of devices (headphone and amp) which just barely breaks his 1/8 rule (say for example 1/5th, 1/6th, or 1/7th). I would like to know why he goes with 1/8th as his rule of thumb and not, say for example, 1/6th, 1/7th or 1/9th.

It all comes down to the fact that I once saw him comment on the deviation of some curve, possibly completely unrelated to impedance, I can't recall, which he deemed "an audible problem". I, on the other hand, looked at the greatly expanded dB scale on the left edge and noted that this "problem" amounted to an overall frequency response deviation of just +/-1 dB (or so, IIRC) from 20-20kHz, with relatively smooth transitions from octave to octave, nothing abrupt, and thinking to myself "He calls that an audible problem?".

Sorry, I don't have the time to re-examine everything he has ever written to find it again, but it established in my mind, at the time, that what he deems audible and what I deem audible might not align.

If I happen to stumble upon it in the future, I will report back.

This post has been edited by mzil: Feb 26 2013, 19:07
Go to the top of the page
+Quote Post
Arnold B. Kruege...
post Feb 26 2013, 23:24
Post #4





Group: Members
Posts: 4254
Joined: 29-October 08
From: USA, 48236
Member No.: 61311



QUOTE (mzil @ Feb 26 2013, 13:05) *
Perhaps it is useful to you since you have the output impedances of these various devices commited to memory, I don't, so I have no idea by how much they break the 1/8th rule of thumb. Remember, I never questioned if impedance can have consequences on the frequency response. That's not the topic.

QUOTE
The purple line on this graph looks pretty audible to me. I'll leave evaluation of the rest of the parameters to you.


I'm not interested in what you deem audible, I'm interested in what nwavguy deems audible. EEs aren't always the best psychoacousticians, I've found.


I'll excuse the slur as you obviously have no idea who I am or what I've studied or done.

Given that NWAVguy is spinning his wheels with an overkill headphone amplifier your prejudices seem odd to me.

This post has been edited by Arnold B. Krueger: Feb 26 2013, 23:24
Go to the top of the page
+Quote Post

Posts in this topic


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 24th November 2014 - 10:43