abstract:Beyerdynamic GmbH & Co. KG is a German audio equipment manufacturer, which produces microphones, headphones, wireless audio systems and conference systems.
To explore this, I switched to using Beyerdynamic DT 990 Pro over-ears with a high impedance of 250 ohms and found that the difference was obvious: the iPhone 4 and 4S were the only devices to provide sufficient volume in quiet recordings using these headphones.