I’ve had my HD650s for about a little over a year now. Have not used them very much as I listen mostly at night with my closed backed Shure 1540s so I don’t disturb my wife. Plus they need a lot more power then my Macbook/DFCobalt can cleanly supply. I need to hook them up to my Benchmark DAC3 to get the best out of them. Still I find them too warm and dark for me. The deep bass is missing. The mids are smooth and warm and pleasant. This is their strongest area. The upper mids and treble are too recessed and the higher treble a little grainy especially on massed strings.
I usually do audio comparisons with short one or two minute sections of large orchestral works so I can remember what each sounds like. Using the Benchmark DAC3/Macbook as a source I compared the HD650 to the 1540. Both offer a smooth laid back presentation. However when I switch from the 650 to 1540 it’s like someone turned a sonic light on in the concert hall. The soundstage expands; Instrument separation and detail emerge. The whole audio picture in my head becomes alive. Like listening to good quality speakers and not headphones. I’ve done this comparison a few times now and the result is the same. for me the Shure 1540 is just superior in all respects. It’s even much more comfortable as well… So I decided to sell my HD650s and just listed them on Amazon. I know there are many advocates of this model but for me they just don’t match my preferences.