My eq settings for DT 990 pro 250 Ohm(bought in ~2008). EqualizerAPO(free) or similar software/hardware needed. PK=Parametric EQ:
Filter 1: ON PK Fc 403 Hz Gain -6,7 dB Q 1,00
Filter 2: OFF PK Fc 4.654 Hz Gain 18,0 dB Q 3,04
Filter 3: ON PK Fc 1.527 Hz Gain 5,9 dB Q 1,03
Filter 4: ON PK Fc 7.025 Hz Gain -6,7 dB Q 1,79
Filter 5: ON PK Fc 730 Hz Gain 9,4 dB Q 3,06
Filter 6: ON PK Fc 2.302 Hz Gain -3,8 dB Q 2,34
Filter 7: ON PK Fc 102 Hz Gain -3,1 dB Q 2,00
Filter 8: ON PK Fc 164 Hz Gain -3,0 dB Q 2,00
Filter 9: ON PK Fc 66,0 Hz Gain -2,9 dB Q 2,00
Filter 10: ON PK Fc 43,6 Hz Gain -2,7 dB Q 2,00
Filter 11: ON PK Fc 5.159 Hz Gain -8,2 dB Q 6,39
Filter 12: ON PK Fc 953 Hz Gain 4,1 dB Q 3,45
Filter 13: ON PK Fc 456 Hz Gain 4,5 dB Q 4,97
Filter 14: ON PK Fc 5.695 Hz Gain -4,4 dB Q 4,89
Filter 15: ON PK Fc 3.959 Hz Gain -4,9 dB Q 5,45
Filter 16: ON PK Fc 31,2 Hz Gain -2,1 dB Q 2,48
Filter 17: ON PK Fc 648 Hz Gain 3,3 dB Q 4,69
Filter 18: ON PK Fc 4.307 Hz Gain -4,3 dB Q 12,57
Filter 19: ON PK Fc 578 Hz Gain -1,8 dB Q 13,25
Filter 20: ON PK Fc 557 Hz Gain 0,5 dB Q 4,95
Filter 21: ON HS Fc 6.000 Hz Gain 3,0 dB
Automatically generated settings(REW) except for filter 21.
I consider this (seemingly weird)result as more accurate than stock HD650.
At first I thought it was placebo. But after many hours of listening to almost anything(including dolby headphone material) I still prefer this sound tonally(although there seems to be a little sibilance around 10Khz, because the correction was limited up to 8Khz). Main improvements include clearer/more present mids, less boomy midbass and very low fatigue(an indicator of good sound in my books).
I would like to hear other owners' opinions.