[supersleuth]

Quote:

Where's Headroom dammit! They said there were going to have the DT880 600ohm measurement but nothing yet!

You can make that comparison for the DT990, though. FR of the 250 and 600 versions is identical within experimental error. The conclusion is left as an exercise for the reader.

 

[maverickronin]

FR ain't everything.  The harmonic distortion is way different.
 

 

[maverickronin]

Actually I just thought of another reason why the 600s would sound better.  FWIR most of the people on here who recommend the 600s over the 250s seem to listen to them on OTL tube amps.  Since such amps typically have quite high output impedance, a higher impedance driver will provide a higher damping factor.
 
That difference should be quite audible.  It's probably wouldn't be audible on an SS amp since their output impedance is typically so low that the damping factor on the 250s is already beyond the threshold of audibility.

 

[supersleuth]

 
Quote:

The harmonic distortion is way different.

Quite the contrary. There is only one peak that has the remotest chance of being audible, and that peak is exactly superimposable between the two graphs.
 
Update: it's even worse than that: that first big peak is present in every one of Headroom's graphs for every can- it's clearly an artifact of their measuring equipment. The very small distortion products that might be real in the DT990 graphs are nowhere near audibility so the slightly different frequencies and amplitudes of those products between the 250 and 600, even if you believe the measurements, are completely meaningless.

 

[Armaegis]

Quote:

Actually I just thought of another reason why the 600s would sound better.  FWIR most of the people on here who recommend the 600s over the 250s seem to listen to them on OTL tube amps.  Since such amps typically have quite high output impedance, a higher impedance driver will provide a higher damping factor.
 
That difference should be quite audible.  It's probably wouldn't be audible on an SS amp since their output impedance is typically so low that the damping factor on the 250s is already beyond the threshold of audibility.

While I haven't done a direct comparison with the Beyers, I can attest to the fact that damping factor (and thus impedance matching) is quite important. I built myself a Bottlehead Crack amp recently, which has an output rating of 100 ohm (or maybe it was 120, I don't remember). Anything below that like the typical 32 ohm can and it sounds awful. The drivers lose all control and everything sounds flabby and distorted. Moving up the resistance increases the damping factor and improves control, most noticeably in the lower end. It also tends to slope the frequency response slightly downwards.

 

[maverickronin]

Quote:

 
Quite the contrary. There is only one peak that has the remotest chance of being audible, and that peak is exactly superimposable between the two graphs.
 
Update: it's even worse than that: that first big peak is present in every one of Headroom's graphs for every can- it's clearly an artifact of their measuring equipment. The very small distortion products that might be real in the DT990 graphs are nowhere near audibility so the slightly different frequencies and amplitudes of those products between the 250 and 600, even if you believe the measurements, are completely meaningless.

That one big peak is the 500hz tone being fed to the headphone!  Of course it shows up on every graph!

 

[xnor]

Haha, that's funny. A harmonic distortion product @ 0 dB that shows up on every headphone measurement...  of course the measurements must be flawed! Heh.
 
How'd you come up with that one? At least read the description of headroom's measurements before trying to interpret the graphs!

 

[supersleuth]

Yeah, without even looking there, of course it's the test tone. D'oh!
 
It remains true that the results show no audible distortion difference between DT990 250 / 600.

 

[maverickronin]

I think those harmonics are far enough apart that masking shouldn't be an issue so they should be audible.  Anyone know what the thresholds for that kind of thing are?

 

[supersleuth]

 
Quote:

Anyone know what the thresholds for that kind of thing are?

About 1% or -40dB. Way above what you see in those plots. For transducers with audible THD you have to shop at your nearest Wal-Mart.

 

[maverickronin]

Is that really all?  I'm gonna have to do some tests or something.

 

[Shike]

Quote:

FR ain't everything.  The harmonic distortion is way different.
 

-50dB is less than .05% . . . that's at -60dB

 

[Catharsis]

Hello faithful sound science head-fiers.  I have edited post #1 to reflect a summary of the first 7 pages of evidence / discussion of the proposed hypothesis. Thank you for your contributions.
 
Quote:

Hi everybody,
 
I see that everyone is on a DT880 (600ohm) kick these days, and head-fier's feel that it's important to put the emphasis on the "600ohm" just so everybody knows that you clearly have the best DT880.
 
My question is: does anybody have any objective (that's right I said objective) proof that the DT880 600ohm is any different than the other impedance options in terms of sound quality.  I have redone this first post, with a summary of the first 7 pages of responses that have been submitted by faithful members of the head-fi sound science forum.  You will find evidence in both support and rejection of my hypothesis, using evidence obtained from various sources (what constitutes "evidence" is in the eye of the beholder).
 
Hypothesis #1 – Beyerdynamic DT880 250ohm and 600ohm are audibly identical when connected to a source/amp with a Zout of zero.
 
Evidence
 
The Beyerdynamic DT880 600ohm has identical housing, identical drivers / diaphragm (voice coil has thinner wire / more windings), and identical model # to the DT880 250ohm / 32ohm. It would be unreasonable to expect massive differences (as many head-fiers suggest) when comparing different impedance options of a single model #.  Furthremore there is no evidence to suggest that the drivers (including voicecoil) in the various Beyerdynamic headphones of different impedances are of different mass.  This isn’t a K701 / DT880 / HD650 comparison where you would expect to hear or measure real differences.
 
There is no evidence to show higher impedance loads are consistent with better / specific sound qualities.  Headphones ranging from 25ohm (Denons), to 32ohm (Grado), to 70ohm (Sony) to 300ohm (Sennheiser) exhibit excellent transient response, decay, impulse response etc and there is no positive or negative correlation between impedance, mass (perhaps largely because mass is always undetermined) and impulse response.  There is evidence however, that lower impedance headphones draw more current which has a very negligible negative impact on measures such as THD, SNR, and crosstalk.
 
http://rmaa.elektrokrishna.com/Comparisons/Comparison%20-%20Cowon%20D2%20-%2012%20-%2048%20Ohm.htm
 
 
The following measurements demonstrate that lighter diaphragms are not necessarily “faster” (as measured by impulse response graphs / spectral decay graphs).  I’ve contrasted the Stax 4040 (considered a “light” electrostatic diaphragm), and the Denon AH-D5000 (considered a “heavy” dynamic diaphragm).  These graphs illustrate that such oversimplifications are faulty.  Shike has posted further comparisons between electrostatic "light" transducers, and dynamic "heavy" transducers on page 6 to further challenge this simple generalization.
 
First, the Stax 4040: 

 
Denon AH-D5000
 

 
 
Headroom graphs show that DT990 (250ohm / 600ohm) and DT880 (32ohm / 250ohm) show no noticeable difference in any objective measurement (other than impedance curves).  Though some posters insisted that the higher inductance of the high impedance voice coils attenuate high frequency SPL, headroom graphs suggest otherwise.  Unfortunately data is not available to compare 600ohm / 250ohm versions of DT880.
To illustrate that there are slight variations when measuring identical headphones (experimental variance), I’ve used the MDR-V6 / MDR-7506 and the K701/K702 charts to act as controls.
 

 
And finally, here are some measurements illustrating similar (non-differences) between different impedance options for the DT880 and DT990.
 

 
As illustrated on page 7, THD measurements between different impedance options yield minimal results, well below the threshold of audibility.  THD differences cannot account for perceived differences in sound quality.
 
No proper ABX tests have been performed with more than 1 subject comparing the DT880 250ohm and the DT880 600ohm.  ABX tests that have been performed without proper methodologies have led to conflicting results. Some people have found little to no difference, others have found huge differences resulting in inconclusiveness. 
 
Hypothesis #2 – Beyerdynamic DT880 250ohm and 600ohm are audibly different when connected to a source/amp with Zout of zero.
 
Evidence
 
Higher gain settings might introduce more distortion when driving 600ohm version though this is a reflection of the amp and not the headphone and is likely achieved with amplifiers with Zout >0ohm.
 
600ohm DT880 likely has flatter response when plugged into a high impedance output (>250ohms for example).  The difference is likely to be subtle (+/- 1dB)
 
600ohm Drivers are smaller (nikongod) – any evidence to confirm this?
 
[size=12pt]600ohm Drivers are lighter when held in hands (leeperry) – any evidence to confi[/size]rm this?

 

[chinesekiwi]

Counter point one:
 
Higher gain settings might introduce more distortion when driving 600ohm version though this is a reflection of the amp and not the headphone and is likely achieved with amplifiers with Zout >0ohm.
 
RMAA M3 amp stats:
 

 
The THD was actually higher at 8 ohms than it was for the others .0011 to .0009 but this is a null point as it's inaudible and within margin or error.
 
Anyone measured the sensitivity of both the DT880/250 and DT880/600 in dB/mW or dB/V? 

 

[xnor]

Quote:

Counter point one:
 
Higher gain settings might introduce more distortion when driving 600ohm version though this is a reflection of the amp and not the headphone and is likely achieved with amplifiers with Zout >0ohm.
 
RMAA M3 amp stats:
 

 
The THD was actually higher at 8 ohms than it was for the others .0011 to .0009 but this is a null point as it's inaudible and within margin or error.

He was talking about higher gain. You're talking about load impedance.
 
---
 
I'd add that with higher impedance you need higher voltages, which some devices might struggle to provide without clipping (at high levels).