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.
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.
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:
Headroom graphs show that DT990 and DT880 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.
First, 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.
Here are the most recent measurements performed by Headroom and Donald North comparing various DT880 impedance options (yellow dotted line is 250ohm, solid green is 600ohm:
And finally, here are some other measurements illustrating similar (non-differences) between different impedance options for the DT880
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 blind 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. A recent "level matched and sighted" ABX among head-fiers who didn't seem to care which impedence version sounded best found that there was no audible difference between the 250ohm and 600ohm. Refer to posts by wavoman on page 16 of this thread.
Hypothesis #2 – Beyerdynamic DT880 250ohm and 600ohm are audibly different when connected to a source/amp with Zout of zero.
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? EDIT (This has been confired NOT to be true, by concurent observations - see page 16)
600ohm Drivers are lighter when held in hands (leeperry) – any evidence to confirm this?
Edited by Catharsis - 11/1/10 at 4:42am