Headphones have a number of benefits. If they're well made they sound fantastic for the price, and you can listen at the volume you want without disturbing the family or the neightbours. The HD650 were the top of the Sennheiser consumer range at $899 before the HD800 came along at $1999. At $899 they were a good buy, now at $599 they are a sensational buy and are our best selling headphone.
To do better, you have to go to the HD700 or HD800, although at a much higher price. Team the HD650s up with a headphone amp like the Musical Fidelity HPA and you have a seriously good hifi experience while not causing friction, particularly late at night or in apartments where noise travels and neighbours might get tetchy. The HD650 are an open-back design of studio monitor standard, and while we do recommend a separate headphone amplifier they can be connected directly to any amplifier or player with a headphone socket. They are supplied with both large and small jacks to suit the different equipments you might use them with.
Like all things, this special will not last forever, so get them while you can!