Sennheiser HD 650's thin sounding?

IMHO....Sounds like either a loose connection or a bad set of phones. I don't believe that they should sound "thin".

I've never owned the 650s but my 600s developed more fullness in the bass over time. Perhaps it is too early to definitively say the 650s are bass-light.

Regards,

They will break in. However, I just replaced my 570's with AKG 701s and the difference is like moving from bose mini cubes to Thiels.

580 is way better than 570. It is pretty much the same thing as HD-600 with the same drivers. HD-600 is tuned a little bit better (position of the drivers).

HD650s deliver more bass than HD580 but needs 250-500hrs break-in time according to one review I read. HD-580 was one of the best bargains when Sennheiser discontinued it - I bought mine for $140.

Even new the 650 will not sound thin, and will produce more bass energy than the 580 or 600.