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Sennheiser HD660 S vs HD650 - Which side are you on?

Sennheiser HD 660 S

SENNHEISER PXC 550-II Wireless NoiseGard Adaptive Noise Cancelling, Bluetooth Headphone with Touch Sensitive Control and 30-Hour Battery Life, Black

PXC 550-II

Sennheiser PXC 550 II Over-Ear Headphones

The Very Important Sennheiser HD 580, HD 600, and HD 650

Sennheiser HD 660s Open-Back Headphones

Sennheiser HD 660S2 review: Legendary reference cans at a high price